Sub Feed quick Question

[doug glasscock]

Quick question.
1600amp-277Y/480VAC service with a main distribution panelboard (MDP) in the main Building. 277Y/480VAC.
There is a 400AMP breaker in MDP feeding the aux building.
The aux building has a 400amp main breaker in a MCC construction. All loads in the aux building are 3 phase.
Do I have to carry the neutral to the building?

 

[sjaniga]

Re: Sub Feed quick Question

I believe it would depend on if your MCC has a slash rating of 480/277, If so, you would be required to provide the voltages listed, if it is a straight voltage of 480, it would not require the neutral.

 

[vanwalker]

Re: Sub Feed quick Question

all i can find is to the service equipment.agree with the post above also. it would be no different than a 3 phase motor load in another building? GEO

 

[james wuebker]

Re: Sub Feed quick Question

Doug, just remember if some time down the road you have 277v lighting then the neutral is needed. If only using it for 3 phase motors, no neutral is needed. Remember that it isn't that much more money to pull a neutral if you should ever need it in the future. Pulling it later could be both costly and difficult.
Bye

 

[tom baker]

Re: Sub Feed quick Question

The second building requires an equipment grounding conductor (always). The netural can sometimes be used as an equipment grounding conductor, but it is recommended that the neutral not be regrounded at the second building. See Section 250.32
If the neutral is not pulled, then an equipment grounding conductor is installed sized per 250.122
Please review section 250.32(B)(2) as well.
You didn't state in your post if you are pulling an equipment ground or not. Also the second building will require a grounding electrode system

 

[doug glasscock]

Re: Sub Feed quick Question

Thank you all for your responses.
They were, as always, very helpful.
Doug

 

[tpwd]

Re: Sub Feed quick Question

answer is no....and about the equipment grounding conductor, if he run nonmetllic conduit [pvc] he wouldn't even be required to pull one...just re-establish the ground system at the aux. building, as required anyway....

 

[brad troxel]

Re: Sub Feed quick Question

I concur with the above, if you need 277v later on, put in a 480/277v transformer, or seperately derived system.

 

[don_resqcapt19]

Re: Sub Feed quick Question

tpwd,
You have to have either the grounded conductor of the EGC at the second building. See 250.32(B). There is no way to clear a ground fault at the second building if you don't have one of these two conductors. You would also have a violation of 250.4(A)(5) if you leave out both the grounded conductor and the EGC.
Don

 

[tom baker]

Re: Sub Feed quick Question

TWPD: re-establishing the ground system at the second building is done for a different reason than running a grounded conductor or equipment ground to the second building. One is for stablizing the voltage to ground, the other is to provide a low impedance path to the source for clearing line to case faults.
Mike Holts 2002 Grounding and Bonding text is an excellent resource on this important topic.

 

[tpwd]

Re: Sub Feed quick Question

don_resqcapt19,
keep reading...250.32 A, B-1,B-2, C....

First:
?02 NEC Article 250.32.[A] requires both the main building and the aux. building have a ?grounding electrode system? [250.50 tells that a grounding electrode system is comprised of IF AVIAILABLE ON PREMISES each item in 250.52 A1 to A6 shall be bonded together to form such system] you don?t have to install them if they are not there already. But if none are available then you must install one or more of A1 to A7.
1. metal ug water pipe if 10? or more is in the ground
2. metal frame of building
3. concrete-encased electrode
4. ground ring
5. rod or pipe
6. plate

Second:
how to ground the aux. building
Article 250.32 says IF THE aux. building has a GROUNDED SYSTEM [neutral], you must use:
250.32.B.(1) if you pull an EGC with the hots and neutral you must isolate the grounds and neutrals at the aux. building?OR?
250.32.B.(2) if you do not pull an EGC with the hots and neutral and there are no metal conduit between buildings, you must ground the neutral at the aux. building and connect the EGC just like a service is required to do?.OR?

250.32.C UNGROUNDED SYSTEM, as we have with this question, you must connect the required grounding electrode system at the aux. building to the disconnecting means.

so, no..there are excetions that says you are not required to run an EGC to an aux. building....

 

[hornetd]

Re: Sub Feed quick Question

tpwd
Sorry, I don't buy it. Just as in a service if the circuit originates in a grounded system it is part of a grounded system. Failing to run an EGC or the grounded conductor together with an EGC does not make it an ungrounded system. If that building has lights and/or convenience receptacle outlets a metallic pathway exist between the two buildings in the form of the circuit that supplies those loads. That being true you must run an EGC with the circuit because if you ran a grounded conductor with the circuit in the presence of a metallic pathway between the two buildings 250.32 requires that a separate EGC be run.
--
Tom