Ampacity/Ca Ampacity/Capacity pacity Page Page - Cable Editor Editor Refer to Chapter 45 – Cable Ampacity Ampacity and Sizing for detailed information. information.
Calculation Methods and Standards Dependent on the cable installation type, different methods can be used to calculate cable ampacity.
IEEE 399 This calculation method is according to the IEEE Std 399, IEEE Recommended Practice for Industrial and Commercial Power Systems Analysis. It covers installation types of underground duct and directly buried. The calculation is based on ampacity at a base condition and and adjustment factors factors derived from detailed detailed calculations calculations using the Neher-McGrath Neher-McGrath method. method. These factors established a maximum feasible load capacity, which results in no reduction of the cable’s expected lifetime. The overall derating factor is composed of several components as listed on the following page. Fta = Derating factor for ambient temperature Ftc = Derating factor for maximum allowable conductor temperature Fth = Derating factor for underground soil thermal resistance Fg = Derating factor for cable grouping Fc = Derating factor for A/G tray covers Fm = Derating Derating factor for A/G tray maintained spacing spacing Fce = Cumulative effect factor for A/G t rays Fm = Derating factor factor for A/G conduit (NEC and diversity diversity factor) Ffc = Derating factor factor for A/G fire coating coating Ffs = Derating factor for A/G fire stop Ffw = Derating factor for A/G fire wrap
ICEA P-54-440 The method based on ICEA P-54-440 applies to cables in above ground trays using calculated derating factors based on tray size, cable fill, and environment conditions. The actual values of tray depth, width, and % fill entries will be taken into account, which 1 gives more accurate results and is based on the method described in the Stolpe paper (Paper 70 TP 557-PWR) . However, the
2 Stolpe method may provide a smaller ampacity for large cables (for example, 750 mm ) compared to those from ICEA P-54-440. 0 In addition, if both the ambient temperature temperature and conductor temperature temperature differ from those shown in the ICEA standard (40 C 0 ambient temperature temperature and and 90 C conductor temperature temperature), ), the resulting ampacity values may be smaller because be cause the standard used the product of both correction factors as the temperature temperature correction. In ETAP calculations, the ambient temperature temperature and conductor temperature values temperature values are used directly in the calculation and, therefore, yield more accurate results. In the used method, the following AC resistance resistance equations equations for temperature temperature corrections corrections are employed: R’ = R(234.5 + Tc) / (234.5 + Tb) Copper Conductors R’ = R(228.1 + Tc) / (228.1 + Tb) Aluminum Conductors Conductors Where: R = Resistance Resistance at at the base temperature temperature Tb Tb R’ = Resistance Resistance at at the operating temperature temperature Tc Tc O Tb = Conductor base temperature temperature in in C O Tc = Conductor temperature temperature limit limit in C NEC does not cover 1/C cables in A/G A /G Trays that have a size < 1/0 AWG. Therefore, 1/C cable installed in i n A/G Trays shall be size 1/0 AWG or larger. Same limitation is applied to ICEA P-54-440. NEC (NFPA 70)
This method calculates derating factors according to National Eclectic Code (NEC). It applies to cables in above ground trays, above ground conduits, air drop, and underground direct buried and underground conduits. NEC does not provide ampacity derating due to bottom cover or correction of the ampacity multiplying factors due to the cumulative effects of combinations of tray covers and fireproofing. In general, cable sizes of 2/0 AWG and smaller are installed in cable trays in a randomly filled manner, with a maximum of two cables high. Base ampacity of randomly filled trays are based on installations at a uniform depth up to the maximum of 30% fill for 3 or 4-inch tray depths. The method applied here corresponds to a maximum fill condition and does not consider fill conditions exceeding the nominal depths. For NEC standard, the selected cable Base ampacity must be in accordance with the ampacities listed in the tables from NEC Article 310 and Appendix B. Users have the option to select to read the cable Base ampacity from either the Library or directly from the NEC tables. . Please contact the support team of ETAP in order to enable the Library Data option as this option is hidden in the standard release. The default is set to use the NEC ampacity Tables. The NEC method is only applicable to a cable insulation voltage rating of 35 kV or less. Ambient temperature temperature correction correction factor should be calculated based on the equation below, as required by NEC standard.
where: I = ampacity from tables at ambient TA 1 1 I = ampacity at desired ambient TA 2 2 o TC = conductor temperature temperature in in degree Celsius ( C) o TA = surrounding ambient from tables in degree de gree Celsius ( C) 1 o TA = desired ambient in degree Celsius ( C) ÄTD = dielectric loss temperature temperature rise. rise. ETAP currently uses the following equations:
These formulae come from AIEE-IPCEA – “Power Cable Ampacities – Copper Conductors”, p. III. B and IEEE Std. 242-1986, section 8.5.2.4. In case the Ta ambient temperature checkbox is checked under the Ampacity/Capacity page of the cable editor, these two equations will be applied for the operating conductor temperatures that are outside the range provided by the NEC tables for both A/G and U/G installations. The Ta adjustment will come from the NEC tables if the checkbox is checked. If the checkbox is unchecked, these equations will apply to both the Ta and Tc temperature correction factors.
If the Base Tc of the selected cable from the Library does not match any of the NEC tables, the Base ampacity will be set to 0. If the Base Ta of the selected cable from the Library does not match any of the NEC tables, ETAP will automatically convert the ambient temperature to the one of the NEC tables, retrieve the ampacity, and convert back to display the ampacity at the Base ambient temperature. The conversion factor will depend on whether the Ta adjustment per NEC Table is checked or not. For U/G Duct and U/G Buried installations, if the Operating RHO is different than the Base RHO, then the following derating rules are applied: Using ETAP Library Data
IEEE 399 Tables 13-5 through 13-7 are applied. In case a different RHO than the ones specified in these tables is entered, interpolation between the two closest RHO values will be used.
Using NEC Tables
For LV cables installed in U/G Ducts, at 50% Load Diversity, only Base RHO = 60 C.cm/W is allowed. If the header of the selected cable from the library does not match this condition, 0 ampacity shall be provided. At No Load Diversity, Base RHO of 90 and 120 C.cm/W are allowed. If the operating RHO is different than these two values, interpolation or extrapolation between and outside these two given points is applied. Table 310.16 is specified for U/G Buried installation but does not provide a RHO. Therefore, changing the Operating RHO will have no effect as this table is RHO-independent.
Tables B.310.8 through B.310.10 are provided at RHO of 90 C.cm/W. If the Operating RHO is different than the Base RHO, then the IEEE 399 Tables 13-5 through 13-7 shall apply. In case an insulation type is not listed in any of the NEC tables, e.g. XLPE, SBR, Neoprene, etc, no ampacity shall be provided by the NEC ampacity calculation method. It is also important to know that both insulation type and conductor base temperature (Base Tc) must match the header of the said NEC table. An exception shall be made for Rubber and Rubber 2 insulation types as they are general types of insulation and were present since the earliest version of ETAP and, therefore, were mapped to any of the columns o that supported rubber-based insulation types at 75 C. For instance, the under-ground ampacity tables in Appendix B are all listed at o o o 75 C. If the header of the selected cable mentions 90 C instead of 75 C, then the method will read the base ampacity from NEC tables 310.16 and 310.17 based on the number of conductors per cable and installation type. Grouping factor is applied based on the number of conductors per cable and the number of cables per location or conduit controlled by # C/Loc field under the Grouping section. Rows and Columns can be defined for cables installed underground per NEC Figure 310.60 for high voltage cables and Figure B.310.2 for low voltage cables. Load diversity can be applied at 50 % and at 100 % (Without Load Diversity option). The entire grouping factor can be bypassed by checking the Without Grouping Effect option under the Amp Adjustment section of the Ampacity/Capacity page of the cable editor. For more than 4 conductors in cable or location, NEC tables 310.15(B)(2)(a) and B.310.11 shall apply. For above ground (A/G) installation in trays, NEC sections 392.11 for low voltage cables and 392.13 for high voltage cables shall apply. These two sections also handle the Top Cover and Maintained Spacing options for A/G Trays installations as displayed in the figure below. NEC does not cover 1/C cables in A/G Trays that have a size < 1/0 AWG. Therefore, 1/C cable installed in A/G Trays shall be size 1/0 AWG or larger. In case the “Without Grouping” option is checked, even if the cable is a 4/C through 10/C, the grouping factor will be equal to 1 and the ampacity of that cable will be obtained from the NEC tables, which are designed for 1/C, 2/C, and 3/C only. Therefore only 1 through 3 conductors of the cable will be considered for current-carrying. The footnote (*) in NEC Tables 310.16 and 310.17 for cable sizes 14, 12 and 10 AWG in these tables refers to 240.4.D. The overcurrent protection shall not be exceeded after any correction factor is applied: 14 AWG Copper: 15 amperes 12 AWG Aluminum and Copper-Clad Aluminum: 15 amperes 12 AWG Copper: 20 amperes 10 AWG Aluminum and Copper-Clad Aluminum: 25 amperes 10 AWG Copper: 30 amperes On the Cable Editor: Protection page, check the Overload Protection nominal current In. It must be filled out as Protective Device or User-Defined. If violation is found, ETAP posts a message: "Protective device’s In exceeds the limit of XX amperes as specified in NEC 240.4(D)". If this limitation is violated but there is no protective device defined, then the message will not be posted.
BS 7671 Standard This method is based on BS 7671 - 2008 (17th Edition): Requirements for Electrical Installation. It applies to a number of types of installation, including above ground and underground configurations. This method can be used for cables at nominal voltages up to and including 1000V a.c. and 1500V d.c. o o The displayed cable Base ambient temperature (Ta) is fixed at 30 C for cables in Air and 20 C for buried cables directly in soil or in ducts in the ground per BS 7671. The actual cable operating ambient temperature can be specified in the Operating Ta field. The cable’s Base and Operating conductor temperature (Tc) is determined based on cable conductor type and insulation type corresponding to Tables 4D1A and onwards of BS 7671. Cable Base Ampacity (Current-Carrying Capability) is from Tables 4D1A and onwards of BS 7671. Under certain conditions, the base ampacity may not be available from these tables and the “Base” Ampacity field will show zero or/ and a message will be posted. In this case you may refer to ETAP log pane for more information. Cable Ampacity/Capacity calculation result is displayed in the “Derated” Ampacity field. The following correction factors are considered for cable Capacity calculation: Ca – Correction factor for ambient temperature. This factor is from Table 4B1 or Table 4B2 of BS 7671 Appendix 4. Cg – Correction factor for grouping. This factor is from Tables 4C1, 4C2, 4C3, 4C4 or 4C5 of BS 7671 Appendix 4. Ci – Correction factor for conductors embedded in thermal insulation. Refer to Section 523.7 of BS 7671 for detailed information. Cc – Correction factor for the type of protective device or installation condition, such as a BS 3036 Fuse. A factor of 0.725 is applied for cables protected by a Fuse to BS 3036. Refer to Section 5 of BS 7671 Appendix 4 for detailed information. A BS 3036 Fuse is specified on the Protection page of cable editor by selecting Device ID or User-Defined Overload Protection device. Cr – Correction Factor for Soil Thermal Resistivity. Refer to Section 2.2 and Table 4B3 of BS 7671 for detailed information. Note: Interpolation or extrapolation may be used if a factor cannot be found directly from the tables. If a correction factor cannot be determined, the “Derated” Ampacity field on the Ampacity page will show zero. In this case you may refer to ETAP log pane for more information.
Sheath/Armor and Jacket Layer According to BS 7671, sheath layer is an important factor in current-carrying capacity calculation and the sheath layer can be either metallic or non-metallic. Determination of the Base Ampacity for a cable for a particular installation method may require the cable to be Armored and/or Sheathed. Such setup can be performed in the Physical page of the Cable Editor. In some cases a message will be posted providing information of such requirement. In other cases Base and Derated Ampacity will be displayed as zero. You may also refer to ETAP log pane for more information. In the current version of ETAP, a sheath layer is only metallic: lead, aluminum or copper. For 1/C cables, Steel Armor is considered as non-magnetic. A Jacket in ETAP is treated as non-metallic sheath for BS 7671 based calculation. Therefore, for current- carrying
capacity calculations based on BS 7671, a cable is considered to have a sheath layer if the cable has either a sheath type or a jacket type specified. It is required to enter a nonzero thickness value if a Sheath/Amor or Jacket Type is selected. Note that Paper type Jacket is not treated as a sheath for BS 7671 based calculation.
Note: Flexible cable is not handled in this ETAP release. IEC 60364 Standard
This method is based on IEC 60364-5-52: Selection and erection of electrical equipment - Wiring systems. It applies to a number of types of installation, including above ground and underground configurations. This method can be used for cables with nominal voltages up to and including 1000V a.c. and 1500V d.c. The displayed cable Base ambient temperature (Ta) is fixed at 30° C for in air installation and 20° C for in ground per IEC 603645-52. The actual cable operating ambient temperature can be specified in the Operating Ta field. The cable’s Base and Operating conductor temperature (Tc) is determined based on cable conductor type and insulation type corresponding to Tables A.52-1 to A.52-13 of Annex A, IEC 60364-5-52. Cable Base Ampacity (Current-Carrying Capability) is from Tables A.52-2 to A.52-13 of Annex A, IEC 60364-5-52. Under certain conditions, the base ampacity may not be available from these tables and the “Base” Ampacity field will show zero. In this case you may refer to ETAP log pane for more information. Cable Current Carrying Capacity Calculation result is displayed in the “Derated” Ampacity field. The following correcting factors are considered for cable Current Carrying Capacity calculation:
Ca – Correction factor for ambient temperature. This factor is from Table A.52-14 or Table A.52- 15 of IEC 60364-5-52 Annex A. Cg – Correction factor for grouping. This factor is from Tables A.52-17 to A.51-21 of IEC 60364-5-52 Annex A. For a group containing different sizes of insulated conductors or cables are not considered for this ETAP release. Cr – Correction Factor for Soil Thermal Resistivity. Correction is considered based on Table A.52-16 for soil thermal resistivities other than 2.5 K-m/W (250 C-cm/W). Note: Interpolation or extrapolation may be used if a factor cannot be found directly from the tables.
If a correction factor cannot be determined, the “Derated” Ampacity field on the Ampacity page will show zero. In this case you may refer to ETAP log pane for more information. Sheath and Jacket Layer
According to IEC 60364-5-52, sheath layer is an important factor in Current Carrying Capacity calculation and it can be either metallic or non-metallic. In the current version of ETAP, a sheath layer is only metallic: lead or aluminum. A Jacket in ETAP is treated as non-metallic sheath for 60364-5-52 based calculation. Therefore, for Current Carrying Capacity calculation based on 60364-5-52, a cable is considered to have a sheath layer if the cable has either a sheath type or a jacket type specified. It is required to enter a nonzero thickness value if a Sheath/Amor or Jacket Type is selected. Note that Paper type Jacket is not treated as a sheath for 60364-5-52 based calculation.
Type If the option of Installation Type is selected, the Installation Type list field contains all the installation types currently available in ETAP. When one of these installation types is selected, the Standard list field will contain only the standards applicable to the selected installation type. The table below gives all the installation types and applicable standards.
Sub-Type
When the BS 7671 or IEC 60364 standard appears in the Standard field, the installation sub-type and installation method will also show up along with the installation type. You can select a different installation sub-type from the list.
Method This field displays the installation method for the selected sub-type per Table 4A2 of BS 7671:2008, Requirements for Electrical Installations as shown below.
This field displays the installation method for the selected sub-type per Table 52-3, IEC 60364-5-52, Selection and erection of electrical equipment - Wiring systems as shown below.
Note: Magnetic/Non-magnetic Installation Magnetically installed cables imply that there is a continuous raceway (conduit) around the cables with circulating current due to the magnetic field of the cables. This circulating current will cause the cable reactance (X1 and X0) to increase by up to 15% for smaller size cables, and 5 to 10% for larger size cables. The following table shows when to use cable libraries designated as Magnetically and Non-magnetically Installed cables: Cable Library Header Magnetically Installed
X
U/G Duct – PVC Conduits U/G Duct – Mag. Conduits
Non- Magnetically Installed
X
U/G Buried
X
A/G Tray – No Cover
X
A/G Tray – Solid & Mag. Material A/G Conduit - PVC
X X
A/G Conduit – Mag. Conduit Air Drop
X
Results
Operating/FLA This field displays the required load current for the cable. For a branch cable, the required current will be the Average or Phase Max operating current entered by user or updated by load flow calculations in the Loading page of the cable editor. For an equipment
cable user can select to display either the operating or full load current (FLA) of the load.
Base The full rated current value in amperes for the chosen cable before any correction occurs. Depending on the selected standard, this value is the base Ampacity in ETAP cable library or is from NEC tables or is the current-carrying capability from tables of IEC 60364-5-52 or BS 7671. This is the ampacity stated or specified by the manufacturer or other authoritative sources, such as NEC, IEC or BS . Note that if the calculation standard is ICEA P-54-440, this field is hidden, since the base ampacity is not required for the calculation by the standard.
Derated The calculated maximum allowed current carrying Capacity (Ampacity) for the chosen cable after all the correction factors have been applied to the Base Ampacity based on the specified installation conditions.
Allowable Ampacity (Alert) This is the maximum allowable ampacity of the cable. It is used in the load flow output reports to indicate the percent of cable overloading. This value is also used as a base for the cable flow constraint in the optimal power flow studies.
ETAP provides options for selecting the maximum allowable current: Derated User-Defined UGS Calculated
Select this option to make the derated ampacity the maximum allowable current for this cable. Select this option to enter the maximum allowable current for this cable Select this option to use the ampacity calculated by the Underground Raceways Systems module.
Temperature /RHO This section includes information about cable temperature and earth thermal resistivity if the installation type is U/G Duct or U/G Buried.
Base Ta This is the ambient temperature in degrees Celsius centimeter obtained from the library for the base ampacity. The ambient temperature is the temperature at a cable installation location when the cable installation is absent. Base ampacity for U/G cables are usually given at 20 degrees Celsius.
Tc
Conductor temperature in degrees Celsius obtained from the library for the base ampacity. This order is usually given at 90 degrees Celsius. RHO The thermal resistivity of the soil in degrees Celsius centimeters per Watt obtained from the library for the base ampacity. The fields for RHO will be hidden if the installation type is not U/G Duct or U/G Buried.
Operating Ta
Ambient temperature for actual underground installations in degrees Celsius. The ambient temperature is the temperature at the cable installation location when the installation is absent. Tc
Maximum allowable conductor temperature for actual underground installations in degrees Celsius. RHO
The thermal resistivity of the soil for actual underground installations in degrees Celsius centimeters per Watt. Ta Adjustment per NEC Table This Check Box only appears when NEC standard is selected. Please refer to NEC standard section.
Note: This checkbox is only available when Tools | Options (Preferences) set to “FALSE” and for cable insulation voltages below 2 kV.
Ampacity (Capacity) Ampacity (Capacity) ratings are displayed for comparison of base, derated and, required ampacities. The method used here is based on a concept of a derating factor that is applied against a base ampacity (capacity) to calculate the derated ampacity (capacity). Id = F x Ib, where Id is the derated ampacity (capacity), F is the total derating factor and Ib is the base ampacity (capacity).
Tray This section is enabled when the installation type is A/G Trays and the Standard is either ICEA P-54-440 or NEC.
Top Cover Select Top Cover if there is a removable top cover on the cable tray. Bottom Cover Select bottom cover if there is a bottom cover on the cable tray, whether it is removable or solid, of more than 6 feet. Cumulative Effect Cumulative effect applies correction factors for combinations of barriers, fire coatings, and covers on cable trays. The following table summarizes the factors ETAP uses: Fire Coating
X X X X
Fire Stop
Fire Wrap
Top Cover
Bottom Cover
PS Uses…
X X
Fire Wrap Smaller Smaller Top & Bottom
X X X
X
X
X X
X
Wrap X
Wrap
X
Wrap
Maintained Spacing Check this box to indicate that cables are kept in the tray with maintained spacing.
Ampacity Adjustment The Ampacity Adjustment section is enabled when the cable installation type is A/G conduit and the Standard is NEC. From this section, you can select options to consider grouping effect.
Without Grouping Effect NEC standards do not allow for grouping effects (that is, the number of rows and columns) of cables. If the check box is not selected, grouping effects of number of rows and columns will be considered. Note that when this box is checked, the Rows and Columns fields and the Fire Protection section will be hidden.
With 50% Load Diversity and Without Load Diversity The level of load diversity used in calculating correction factors can be either 50% or none.
Layout This section is enabled when the standard is BS 7671 and the installation type is one of the above ground types.
This section or part of this section is enabled when the standard is IEC 60364.
Horizontal Select Horizontal layout with Touching or Spaced if applicable. Note that this field is hidden if it is not applicable for the selected installation type.
Vertical Select Vertical layout with Touching or Spaced if applicable. Note that this field is hidden if it is not applicable for the selected installation type.
Spaced Select this option if the cables are placed with required spacing (spaced by a clearance between adjacent surfaces of at least one cable diameter (De)) between them. Note that this field is hidden if it is not applicable for the selected installation type.
Touching Select this option if the cables are placed touching each other in the installation. Note that this field is hidden if it is not applicable for the selected installation type. Please refer to BS 7671 and IEC 60364 for the definitions of Spaced and Touching.
Trefoil This field is hidden if it is not applicable for the selected installation type and mirrors the corresponding selection in the Configuration page.
Flat This field is hidden if it is not applicable for the selected installation type and mirros the corresponding selection in the Configuration page.
No of Trays Select No of Trays for determining correction factor for grouping based on Tables A.52-20 or A.52-21 of IEC 60364-5-52. If BS 7671 Standard is used, the correction factor is based on Tables 4C4 or 4C5 of BS 7671 - 2008 (17th Edition)
<= 0.3*Cable OD or > 0.3*Cable OD Switch between these two selections for different Installation Methods. Refer to Table 52-3 of IEC 60364-5-52. If BS 7671 Standard is used, refer to Table 4A2 of BS 7671 - 2008 ( 17th Edition)
<= 0.3*Cable OD or > 0.3*Cable OD Switch between these two selections with different Installation Methods. Refer to Table 52-3 of IEC 60364-5-52.
1.5 De <= V < 20 De or V > 20 De Switch between these two selections with different Installation Methods. Refer to Table 52-3 of IEC 60364-5-52. If BS 7671 Standard is used, refer to Table 4A2 of BS 7671 - 2008 ( 17th Edition)
Circuit Clearance This field is enabled when in ground (UG Duct or U/G Buried) installation is selected. Refer to Tables A.52-18 and A.52-19 of IEC 60364-5-52. If BS 7671 Standard is used, refer to Tables 4C2 and 4C3 of BS 7671 - 2008 (17th Edition)
Grouping In this section, user can specify the installation information related to the calculation of cable grouping factors. The fields in this section are dependent on the installation type and standard selected.
Note: For BS 7671 and IEC 60364 standards, this section is unavailable if a cable is a Copper conductor, Mineral insulated and the Conductor Temperature (Tc) is set to 105 ° C based on the standard. For more information refer to Tables A.52-7 and A.52-9 of IEC 60364-5-52 and Table 4G2A of BS 7171 BS 7671 - 2008 (17th Edition)
Parameters in Grouping Section for IEEE 399 Standard, U/G Raceway Grouped cables operate at higher temperatures than isolated cables. To derate the ampacity, the number of rows and columns of the duct bank must be specified to determine a cable grouping adjustment factor. The cable ampacity adjustment factors are based on 7.5 inches center-to-center spacing. For more details see the IEEE Brown Book.
Parameters in Grouping Section for NEC Standard Grouped cables operate at higher temperatures than isolated cables. To derate the cable ampacity, the number of r ows and columns of conduit installed next to each other, as well as the total number of conductors per location or conduit can be specified to determine a cable grouping adjustment factor.
The number of Rows and Columns affects the grouping factor as followed: Using ETAP Library Data
For A/G Conduit installation, up to 6 by 6 Rows by 6 Columns can be defined per IPCEA P-46-426 Table IX. For U/G Buried and U/G Duct installations, the grouping derating factor is calculated based on IEEE 399 Tables 13-8 through 13-11 for the Rows and Columns entered.
Using NEC Tables
For A/G Conduit installation, Rows and Columns are fixed to 1 as NEC does not provide any grouping factor for this installation. For U/G Buried and U/G Duct installations, Rows and Columns fields are limited t o the combinations allowed by NEC Figure 310.60. This applies to MV and HV cables only (2 < kV ≤ 35).
NEC does not support grouping factors based on more than 4 current-carrying conductors per location or conduit for MV and HV cables (2 < kV ≤ 35), therefore, the #C/Loc is fixed to 1 if such cable is selected. The number of current-carrying conductors per location or conduit needs to be calculated as followed: # of conductors per location = (# of current-carrying conductors per cable) x (# of cables per location or conduit) NEC Table B.310.11 Number of Conductors 4 through 6 7 through 9 10 through 24 25 through 42 43 through 85
Ampacity Correction Factor 50 % Load Diversity 80 % 70 % 70 % 60 % 50 %
NEC Table 310.15(B)(2) (a)
Ampacity Correction Factor No Load Diversity
Number of Conductors 4 through 6 7 through 9 10 through 20 21 through 30 31 through 40 41 and above
80 % 70 % 50 % 45 % 40 % 35 %
Parameters in Grouping Section for ICEA P-54-440 Standard, A/G Trays The following items are displayed only when ICEA is selected.
Height Height of cable tray specified in inches or centimeters
Width Width of cable tray specified in inches or centimeters
% Fill The total amount of cable tray cross-sectional area used by cables placed in the tray, including gap between cables.
Where ni is the number of cables in the tray with di ameter di and l is the number of different sizes of cables in the tray.
Depth Depth of cable mass calculated in inches or centimeters using Height*%Fill/100. If the calculated depth is smaller than the cable diameter, an * sign will be displayed on the right of Depth and above Derated, and the cable diameter will be treated as the depth for derating calculation.
Fire Protection for ICEA or NEC Standards, A/G Installation The fire protection area provides optional libraries from which to choose various fire protection devices. Each of the three libraries may be selected individually to best describe the fire protection associated with the cable tray. The fire protection data is used to further derate cables based on the fire protection material specifications selected from ETAP library. The ampacity correction factors applied for fire protection is based on 10 CFR 50, Appendix R for Fire Wrap, Fire Stop, and Fire Coating.
Fire Coating The Fire Coating Library provides a selection of configurations. Each configuration has an ampacity correction factor (ACF)
associated with it, which is applied against the base ampacity. For maintained spacing trays, if the fire retardant coating results in a reduction of the spacing between adjacent cables or groups to less than the required values, the cable shall be considered to be non-maintained spacing. On the other hand, if remaining space in a randomly filled tray is used up by cable coating and no other cable can be installed in the tray; credit may be taken for a reduction in cable % fill below nominal value. Fire retardant coating is not a standard procedure for A/G conduits.
Fire Stop The Fire Stop Library provides a selection of configurations with ampacity correction factors for cables in tray routed through fire stops. Note: for A/G conduits, there may not be any reason to derate the cable for fire stops since typical fire stops are constructed with expanded foam depth of 4 inches or less. This is considered to be insufficient to cause an increase in cable temperature.
Fire Wrap The Fire Wrap Library provides a selection of configurations. Each fire barrier configuration has an ampacity correction factor (ACF) associated with it. This ACF must be applied whenever the raceway is wrapped for a length exceeding 6 feet and whenever the raceway has multiple, wrapped segments whose combined length exceeds 6 feet and which are spaced less than 10 feet apart.
Fire Protection for BS 7671 Standard, A/G Installation This section is about thermal insulation. Refer to Section 523, BS 7671 for detailed information th According to BS 7671-16 Edition, thermal insulation for fire protection may be considered for all installation types, except Installation Methods 4 and 6. For Installation Method 4 or 6, cables are in conduits which are in thermally insulated walls or above thermally insulated ceilings, and the effect of thermal insulation is already considered in the current-carrying capacity tables.
BS 7671 - 17th Edition th Refer to Section 523.7, BS 7671–17 Edition for detailed information. th According to BS 7671-17 Edition, thermal insulation for fire protection may be considered for all installation types, except Installation Methods 1, 2, and 3. For Installation Methods 1, 2 and 3 the cables are in conduits which are in thermally insulated walls or above thermally insulated ceilings, and the effect of thermal insulation is already considered in the current-carrying capacity tables.
Thermal Insulation Applied Check this box if the cable has thermal insulation.
Insulation Length Enter the length of able thermal insulation in mm. # of Circuit This field is enabled when BS 7671 - 16th Edition or IEC 60364-5-52 is selected. This is used for reduction factor of grouping. The maximum allowable # of circuit is limited based on the standards. Back to the top
U/G Duct Underground duct banks encased in concrete.
Base Ta
Ambient soil temperature in degrees Celsius centimeter per Watt obtained from the library for the base ampacity. Base ampacity for U/G cables are usually given at 20 degrees Celsius. Tc
Conductor temperature in degrees Celsius obtained from the library for the base ampacity. This order is usually given at 90 degrees Celsius. RHO The thermal resistivity of the soil in degrees Celsius centimeters per Watt obtained from the library for the base ampacity.
Operating Ta
Ambient temperature (temperature of the surrounding soil) for actual underground installations in degrees Celsius. Tc Maximum allowable conductor temperature for actual underground installations in degrees Celsius. RHO
The thermal resistivity of the soil for actual underground installations in degrees Celsius centimeters per Watt.
Grouping Grouped cables operate at higher temperatures than isolated cables. To derate the ampacity, the number of rows and columns of the duct bank must be specified to determine a cable grouping adjustment factor. The cable ampacity adjustment factors are based on 7.5 inches center-to-center spacing. For more details see the IEEE Brown Book. Back to the top
U/G Buried Directly buried underground ducts.
Base Ta Ambient soil temperature in degrees Celsius centimeter per Watt obtained from the library for the base ampacity. Base ampacity for U/G cables are usually given at 20 degrees Celsius. Tc
Conductor temperature in degrees Celsius obtained from the library for the base ampacity. This order is usually given at 90 degrees Celsius. RHO
The thermal resistivity of the soil in degrees Celsius centimeters per Watt obtained from the library for the base ampacity.
Operating Ta
Ambient temperature (that is, the temperature of the surrounding soil) in degrees Celsius for underground installations. Tc
Maximum allowable conductor temperature is in degrees Celsius.
Grouping Grouped cables operate at higher temperatures than isolated cables. To derate the cable ampacity, the number of r ows and columns of the cable locations must be specified to determine a cable grouping adjustment factor. The cable ampacity adjustment factors are based on a 7.5-inch center-to-center spacing. For more details see the IEEE Brown Book. Back to the top
A/G Trays Above ground cable trays. The free air base ampacity from the libraries are used for cables installed in trays.
Base Ta
Ambient air temperature in degrees Celsius obtained from the library for the base ampacity. The value is usually specified at 40 degrees Celsius Tc Maximum allowable conductor temperature in degrees Celsius obtained from the library. Conductor temperature for the base ampacity is typically 90 degrees Celsius.
Operating Ta
Ambient air (atmospheric) temperature (that is, the temperature of the air surrounding the area where the tray is installed) is in degrees Celsius. Tc
Maximum allowable conductor temperature in degrees Celsius. Conductor temperature for the base ampacity is typically 90 degrees Celsius.
Tray NEC If chosen, NEC methods of calculating derating factors for cable trays will be used. NEC does not provide ampacity derating due to bottom cover or correction of the ampacity multiplying factors due to the cumulative effects of combinations of tray covers and fireproofing. In general, cable sizes of 2/0 AWG and smaller are installed in cable trays in a randomly filled manner, with a maximum of two cables high. Base ampacity of randomly filled trays are based on installations at a uniform depth up to the maximum of 30% fill for 3 or 4-inch tray depths. The method applied here corresponds to a maximum fill condition and does not consider fill conditions exceeding the nominal depths.
ICEA Select this option to choose an ICEA P-54-440 method of calculating derating factors for cable trays. The actual values of tray depth, width, and % fill entries will be taken into account, which gives more accurate results and is based on the method described 1 in the Stolpe paper (Paper 70 TP 557-PWR) . However, the Stolpe method may provide a smaller ampacity for large cables (for 2 example, 750 mm ) compared to those from ICEA P-54-440. 0
In addition, if both the ambient temperature and conductor temperature differ from those shown in the ICEA standard (40 C 0 ambient temperature and 90 C conductor temperature), the resulting ampacity values may be smaller because the standard used the product of both correction factors as the temperature correction. In ETAP calculations, the ambient temperature and conductor temperature values are used directly in the calculation and, therefore, yield more accurate results.
In the used method, the following AC resistance equations for temperature corrections are employed: R’ = R(234.5 + Tc) / (234.5 + Tb) Copper Conductors R’ = R(228.1 + Tc) / (228.1 + Tb) Aluminum Conductors Where: R = Resistance at the base temperature Tb R’ = Resistance at the operating temperature Tc Tb = Conductor base temperature in OC Tc = Conductor temperature limit in OC
Top Cover Select Top Cover if there is a removable top cover on the cable tray.
Bottom Cover Select bottom cover if there is a bottom cover on the cable tray, whether it is removable or solid, of more than 6 feet.
Maintained Spacing If cable spacing is maintained within the tray, then the effects of top cover, bottom cover, and fire wrap are ignored. For 3-phase cables larger than 2/0 AWG in a single layer, the arrangement requires spacing of 1/4 of overall effective diameter of the grouped circuit.
Cumulative Effect Cumulative effect applies correction factors for combinations of barriers, fire coatings, and covers on cable trays. The following table summarizes the factors ETAP uses: Fire Coating
X
Fire Stop
Fire Wrap
Top Cover
Bottom Cover
X
X
Fire Wrap X
X X
X X
Smaller
X
Smaller
X
Top & Bottom
X
X X
PS Uses .
X
Wrap X
Wrap
X
Wrap
Grouping The following items are displayed only when ICEA is selected.
Height Height of cable tray specified in inches or centimeters
Width Width of cable tray specified in inches or centimeters % Fill The total amount of cable tray cross-sectional area used by cables placed in the tray, including gap between cables.
Where ni is the number of cables in the tray with di ameter di and l is the number of different sizes of cables in the tray. Depth Depth of cable mass calculated in inches or centimeters using Height*%Fill/100. If the calculated depth is smaller than the cable diameter, an “*” sign will show up on the right of Depth and above Derated, and the cable diameter will be treated as the depth for derating calculation.
Fire Protection The fire protection area provides optional libraries from which to choose various fire protection devices. Each of the three libraries may be selected individually to best describe the fire protection associated with the cable tray. The fire protection data is used to further derate cables based on the fire protection material specifications selected from ETAP library. The ampacity correction factors applied for fire protection is based on 10 CFR 50, Appendix R for Fire Wrap, Fire Stop, and Fire Coating.
Fire Coating The Fire Coating Library provides a selection of configurations. Each configuration has an ampacity correction factor (ACF) associated with it, which is applied against the base ampacity. For maintained spacing trays, if the fire retardant coating results in a reduction of the spacing between adjacent cables or groups to less than the required values, the cable shall be considered to be nonmaintained spacing. On the other hand, if remaining space in a randomly filled tray is used up by cable coating and no other cable can be installed in the tray; credit may be taken for reduction in cable % fill below nominal value.
Fire Stop The Fire Stop Library provides a selection of configurations with ampacity correction factors for cables in tray routed through fire stops.
Fire Wrap The Fire Wrap Library provides a selection of configurations. Each fire barrier configuration has an ampacity correction factor (ACF) associated with it. This ACF must be applied whenever the raceway is wrapped for a length exceeding 6 feet and whenever the raceway has multiple, wrapped segments whose combined length exceeds 6 feet and which are spaced less than 10 feet apart. Back to the top
A/G Conduit Above ground cable conduit
Base Ta This is the ambient air (atmospheric) temperature is in degrees Celsius obtained from the library. Tc
This is the maximum allowable conductor temperature is in degrees Celsius obtained from the library.
Operating Ta
This is the ambient air (atmospheric) temperature is in degrees Celsius. It is the temperature of the air surrounding the area where the tray is to be installed. The value is usually specified at 40 degrees Celsius. Tc
This is the maximum allowable conductor temperature is in degrees Celsius. The value is usually specified at 90 degrees Celsius.
Ampacity Adjustment NEC w/o Grouping Effect NEC standards do not allow for grouping effects (that is, the number of rows and columns) of cables. If the check box is not selected, grouping effects of number of rows and columns will be considered.
NEC w/ 50% Load Diversity & NEC w/o Load Diversity The level of load diversity used in calculating correction factors can be either 50% or none.
Grouping Grouped cables operate at higher temperatures than isolated cables. To derate the cable ampacity, the number of r ows and columns of conduit installed next to each other, as well as the total number of conductors per location (this conduit), can be specified to determine a cable grouping adjustment factor. # of conductors per location = (# of conductors per cable) x (# of cables per location)
Number of Conductors 4 through 6 7 through 9 10 through 24 25 through 42 43 and above Number of Conductors 4 through 6 7 through 9 10 through 20 21 through 30 31 through 40 41 through 60
Ampacity Correction Factor 50 % Load Diversity 80 % 70 % 70 % 60 % 50 % Ampacity Correction Factor No Load Diversity 80 % 70 % 50 % 45 % 40 % 35 %
Fire Protection Fire protection provides optional libraries to choose various fire protection method. Each of the three libraries may be selected individually to best describe the fire protection associated with the conduit. The fire protection data is used to further derate the cable ampacities based on the fire protection material specifications selected from ETAP library. The ampacity correction factors applied for fire protection is based on 10 CFR 50, Appendix R for Fire Wrap, Fire Stop, and Fire Coating.
Fire Coating The Fire Coating Library provides a selection of configurations from which to choose. Each configuration has an ampacity correction factor (ACF) associated with it, which is applied against the base ampacity. Fire retardant coating is not a standard procedure for A/G conduits.
Fire Stop The Fire Stop Library provides a selection of configurations with ampacity correction factors for conduits routed through fire stops. Note: there may not be any reason to derate the cable for fire stops since typical fire stops are constructed with expanded foam depth of 4 inches or less. This is considered to be insufficient to cause an increase in cable temperature.
Fire Wrap The Fire Wrap Library provides a selection of configurations. Each fire barrier configuration has an ampacity correction factor (ACF) associated with it which must be applied whenever the raceway is wrapped for a length exceeding 6 feet and whenever the
raceway has multiple, wrapped segments whose combined length exceeds 6 feet and which are spaced less than 10 feet apart.
Air Drop Air drop consists of cables suspended without the use of trays or conduits. No cable grouping for air drop cables are considered.
Base Ta
This is the ambient air (atmospheric) temperature from the library in degrees Celsius. Tc This is the maximum allowable conductor temperature is in degrees Celsius obtained from the library.
Operating Ta
This is the ambient air (atmospheric) temperature. The temperature of the air surrounding the area where the tray is to be installed is in degrees Celsius. Ambient air temperature for the base ampacity is 40 degrees Celsius. For cables in direct sunlight, the air temperature may be increased by a typical value of 15 degrees Celsius.
Operating Tc This is the maximum allowable conductor temperature is in degrees Celsius. Conductor temperature for the base ampacity is 90 degrees Celsius.
Fire Protection Fire Protection provides optional libraries to choose various fire protection devices. Each of the three libraries may be selected individually to best describe the fire protection associated with the airdrop cables. The fire protection data is used to further derate the cable based on the fire protection specifications selected from ETAP library is based on 10 CFR 50, Appendix R for Fire Wrap, Fire Stop, and Fire Coating.
Fire Coating The Fire Coating Library provides a selection of configurations. Each configuration has an ampacity correction factor (ACF) associated with it, which is applied against the base ampacity.
Fire Stop The Fire Stop Library provides a selection of configurations with ampacity correction factors for cables routed through fire stops.
Fire Wrap The Fire Wrap Library provides a selection of configurations. Each fire barrier configuration has an ampacity correction factor (ACF) associated with it. The ACF must be applied whenever the cable is wrapped for a length exceeding 6 feet and whenever the raceway has multiple, wrapped segments whose combined length exceeds 6 feet and which are spaced less than 10 feet apart.
Correction Factors The correction Factors tool is only available when BS-7671 or IEC 60364 standard is selected.
Correction Factor Button Click on the Correction Factors button to display the Correction Factors Editor
Correction Factors Editor The editor displays the correction factor value that is being applied when the installation conditions differ from those for which the base capacity (ampacity) value was specified.
Ambient Temperature Ca – Correction factor for Ambient Temperature
Grouping Cg – Correction factor for Grouping.
Thermal Insulation Ci – Correction factor for conductors embedded in thermal insulation.
Protective Device or Installation Condition Cc – Correction factor for the type of protective device or installation condition.
Note: Only applies for BS 7671 while the BS 3036 Fuse option is checked in Overload Protection device section of the Cable Protection Page or for installation method is "in a duct in the ground" or "buried direct".
Soil Thermal Resistivity Cr – Correction Factor for Soil Thermal Resistivity
Cable Report Selection List This list contains all the output files from the cable calculations in the current project folder. Select a file to view the report or to create a new report. Note: in the latter case, the existing file will be overwritten. When Prompt is selected, a new file will be created.
Cable Report Manager Button The Cable Report Manager button is used t o access the various output reports.
References: 1. J. Stolpe, "Ampacities for Cables in Ramcomly Filled Trays," IEEE Summer Power Meeting and EHV Conference, LA, Calif., July 12-17, 1970. Static Load Overview Induction Machine Overview Synchronous Motor Editor Overview Capacitor Overview Motor Operated Valve Overview
Cable Editor Overview Info Page Physical Page Impedance Page Configuration Page Loading Page Ampacity Page Protection Page
Sizing Phase Page Sizing Gnd/PE Page Reliability Page Routing Page Remarks Page Comment Page AC Elements Editor Overview
