PARALLEL CIRCUITS? CHECK GROUND SIZE
Parallel current-carrying conductors may need bigger grounds.
- Published in Southwire's Power Cable Update newsletter in February 1998
- Reprint permission granted
Need more ampacity for a large feeder? It's easy. Just hook two conductors in parallel. But be sure to check the National Electrical Code (NEC). There are some requirements. One of them affects the size of grounding conductors.
"Section 310-4 of the NEC sets limits on paralleling conductors in multiple raceways or cables," says Dave Mercier, applications engineering manager. You can parallel aluminum or copper conductors 1/0 or larger if they're the same length, the same size and material, with the same insulation type and have the same type terminations.
Grounding Conductors Have To Be Bigger
Here's the part about grounding conductors: When you run conductors in parallel, you have to parallel the grounding conductors, too, and each grounding conductor must be capable of handling the maximum expected fault current.
NEC Section 250-95 says, "... the equipment grounding conductor, where used, shall be run in parallel. Each parallel grounding conductor shall be sized on the basis of the ampere rating of the overcurrent protecting the circuit conductors in the raceway or cable, in accordance with Table 250-95."
Table 250-95 spells out minimum grounding conductor sizes for overcurrent devices from 15 to 6,000 amps.
"Paralleling conductors is a useful technique," says Mercier, "but you have to be aware of the grounding requirements when you use it." |
