Cable in Duct Bank De-rating
Cable in Duct Bank De-rating
(OP)
Dear all,
I am aware that this topic has been discussed in many previous threads however none of the threads I saw has indication for de-rating of cables with SI cross-sections i.e. mm.sq.
Any reference? or is it valid to directly transform from AWG\kcmil to mm.sq.
Thank you
I am aware that this topic has been discussed in many previous threads however none of the threads I saw has indication for de-rating of cables with SI cross-sections i.e. mm.sq.
Any reference? or is it valid to directly transform from AWG\kcmil to mm.sq.
Thank you






RE: Cable in Duct Bank De-rating
Regards,
Miki
RE: Cable in Duct Bank De-rating
More info here: http://www.calcware.com/cwnmcalc2.htm or see Wikipedia. Note - I have no affiliation with Calcware and have never used it.
dpc
RE: Cable in Duct Bank De-rating
Sizing conductors and selecting protection devices - Legrand www.legrand.com/files/fck/File/pdf/Power_guide/EX2...
RE: Cable in Duct Bank De-rating
I notice that underground cables in concrete duct-bank are only mentioned in NEC. Is there any reference that considers this method as well. IEC mainly considers ducts in ground or directly buried while from NEC it is concluded that having different configurations of duct banks such as with 6 or 9 ducts leads to different permissible loading level which is not addressed in the IEC or did I miss it somewhere.
P.S: my question is related to MV cables 13.8 kV and 34.5 kV single-core.
Thank you.
RE: Cable in Duct Bank De-rating
RE: Cable in Duct Bank De-rating
I didnt mean that the NEC is limited to concrete encased ductbanks however the de-rating factors for such laying method are only shown in the NEC. Concrete encased ductbank is not shown in IEC unless i missed seeing it.
Thanks.
RE: Cable in Duct Bank De-rating
Second, Reference D it is destined for buried conduits. NEC [Neher &McGrath] consider concrete RHO=85 [dgr.C*cm/W].In this case if Earth RHO>concrete RHO then the ampacity acc.to IEC will be less. If the shield is grounded only at one end, the difference will be negligible even up to 45 kV cable.
RE: Cable in Duct Bank De-rating
So how to calculate the ampacity of cables if we have the input from the manufacturer for directly buried if we are going to have a concrete encased duct bank up to 3 x 3 configuration?
I presume now that NEC is the only available reference apart from using specific programs such as ETAP or CYME.
Thanks
RE: Cable in Duct Bank De-rating