Primary duct bank - Utility

[fshah]

Is there any possibility of the circulating current due to use of the steel reinforcing bars in concrete encased duct structures (Concrete encased duct banks - 4" Dia. PVC Ducts, 3/4" rebars ) ?

Any assistance will be greately appreciated.

 

[davidbeach]

All three phases in each conduit or single phase per conduit?

 

[fshah]

For 500 MCM cable we use only single phase per duct but in case of smaller cable we do run three phase in one duct.
Thanks.

 

[davidbeach]

If you allow a closed re-bar loop to enclose anything other a whole number of complete three-phase circuits you will have severe heating due to circulating currents. If re-bar loops see no net current through the loop, then no, you will not have significant heating.

 

[7anoter4]

I agree with davidbeach .The ducts- PVC or Steel – will be free of re-bar between but only at the duct bank periphery- around- may be a closed loop of re-bar. A re-bar along the duct-beside the duct- may be provided. In order to hold the ducts only 2-3" concrete will be poured between two adjacent duct without any rebar.