If busduct is being run as the service entrance conductors on a 480V 3P/3W system (No L-N loads served from service entrance switchgear) does the busduct need to be a 3W busduct with the (3) phases and an integral ground or does it have a be a 4W busduct with the dedicated neutral bus. For service entrance neutral with no L-N loads the neural conductor only needs to comply with 250.24(C) but I'm not sure how this relates to busduct and the physical construction? Would the ground bus integral to busduct comply with 250.24(C) or do you need a dedicated neutral bus?
Service Entrance with Busduct
- Thread starter mull982
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beanland
Senior Member
- Location
- Vancouver, WA
Bus Dust is a Wiring Method
Bus Dust is a Wiring Method
Bus duct is just a wiring method. If you use cable-duct, conduits and cables, or something else, all the NEC requirements exist. If the supply is a grounded wye source, you have to run the neutral from the transformer into the service.
Bus Dust is a Wiring Method
Bus duct is just a wiring method. If you use cable-duct, conduits and cables, or something else, all the NEC requirements exist. If the supply is a grounded wye source, you have to run the neutral from the transformer into the service.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Why can't the 3 wire + EGC busduct be used with the EGC being used as the neutral?
beanland
Senior Member
- Location
- Vancouver, WA
EGC is a wire
EGC is a wire
As long as the EGC is a conductor that can be designated the grounded conductor, not an raceway/enclosure like a conduit, then the EGC wire/bus is just a name applied to a conductor. I could just as well name the bus the grounded conductor rather than the equipment grounding conductor.
This grounded conductor must meet the sizing requirements for that rather than an EGC. If you have four equal bus conductors, then this conductor has the required rating.
The other concern is that this grounded conductor cannot be bonded to the bus duct enclosure except where permitted, at the service.
EGC is a wire
As long as the EGC is a conductor that can be designated the grounded conductor, not an raceway/enclosure like a conduit, then the EGC wire/bus is just a name applied to a conductor. I could just as well name the bus the grounded conductor rather than the equipment grounding conductor.
This grounded conductor must meet the sizing requirements for that rather than an EGC. If you have four equal bus conductors, then this conductor has the required rating.
The other concern is that this grounded conductor cannot be bonded to the bus duct enclosure except where permitted, at the service.
Usually the ground bus (EGC) in busduct is much smaller than the phase bus. How are you able to tell if this bus will meet the size requirements of 250.102 since that table is based on cable sizes?
That is a good point. I'm not sure if the bus is intermittently bonded throughout busduct or if it is isolated from busduct housing. I know some busduct's have an option to either use busduct enclosure as ground or have a separate bus inside of busduct for ground. The use of the busduct case as a neutral/grounded conductor for service entrance would be prohibited.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
IMO that's the issue as long as the EGC is 12.5% of the phase conductor size it should be sufficient as a neutral.
I'm curious where you get the 12.5% criteria from?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I was thinking 250.24(C)(1) but after perusing that section it only applies to a raceway. I've done a brief search and it seems like busduct for SEC's has fallen through the cracks.
Fnewman
Senior Member
- Location
- Dublin, GA
- Occupation
- Sr. Electrical Engineering Manager at Larson Engineering
If using a High Resistance Ground system per 250.36, no neutral conductor in the bus duct is required.
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