Neutral not required

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edavis2293

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The secondary of a 480/277v transformer will supply power to a motor control center without neutral loads. Am I required to pull a neutral to the MCC and what Section of the NEC describes this installation? Grounding electrode system is located at the transformer outside the building.
 
Re: Neutral not required

You don?t need to pull a neutral. The NEC talks about when you need a GEC and when you need an EGC and what to do to connect them. But I don?t think it ever says that you need a grounded conductor (i.e., neutral) to be run to any panel. Besides, if you pulled a neutral to the MCC, would there even be a place to land it?
 
Re: Neutral not required

Thank You. I also think it is not required by omission. Several sections deal with the absence of the neutral but I haven't found one that pins it down for seperately derived systems.

Space is normally provided for connection of grounding conductors and I suppose for the neutral. However, there will be nothing connected to it. Fault current is carried by the equipment grounding conductors and the neutral, in this case, requires a seperate, isolated bus to prevent a parallel connection with the grounding conductors.
 
Re: Neutral not required

The NEC is not crystal clear (on anything) yet it gives clear guidlines on this subject in Article 250. In section 250.30 the grounding of a separately derived system is explained. Keep in mind that the requirements of 250.4 must always be met also. in 250.30(A)(8)gives the rules for where a grounded conductor is installed and system bonding jumper is not installed at the source. In simple terms, an effective ground fault current path must be established, and if the system bonding jumper is installed at the disconnect then the grounded conductor must be at the disconnect because it is the return path for fault current to the source. If the system bonding jumper is installed at the source, then the equipment grounding conductor run with the circuit from the source to the disconnect is the return path for fault current to the souce, and therefore if no load is present for the grounded conductor there is no need for it to be installed.
In conclusion, if you ground and bond at the source(bonding and grounding must be done at the same place) then an equipment grounding conductor must be run with the conductors from that point, and if you ground and bond at any other point as allowed by 250.30(A)(1) then the grounded conductor must be run with the conductors to the point of bonding. Hope this helps, and read it slowly!
Fred Bender
 
Re: Neutral not required

IF THE TRANSFOMERS OUTSIDE THE BUILDING AND THE mcc is inside is there a disconnect outside by the transformeR?? YOU must ground at the iST DISCONNECT SWITCH or the transformer .I took it it was a Utility owned transformer in your ist post. Sounds like a Outside feeder tap if the transformers customer owned.
 
Re: Neutral not required

Actually, if the neutral is not taken as a circuit conductor, it is not required to be grounded. You are permitted to use a wye secondary as a three wire delta if you choose to do that. If fact, you can even corner ground this delta. :D
 
Re: Neutral not required

BUT if the Neutral is Grounded at the transformer it must be brought to the ist disconnect switch or Grounded at the transformer IF in the building! If not in the building and No disconnect Switch at the transformer where do you hook the grounding electroide at the Building?? He said this was a 277 /480 thus neutral was grounded so either a Neutral OR a Equipment Ground(if disconnect at the transformer ) must be brought in to Tie to the grounding Electrode conductors that Are we required in the building. If a Ungrounded Delta you still Ground the same but no neutral is present, If a conor grounded delta you ground the same BUT the grounded leg becomes your Grounded conductor.
 
Re: Neutral not required

He said this was a 277 /480 thus neutral was grounded so . . .

Oops, my bad. Sometimes you have to read the opening statement before putting your foot in your mouth. :eek:
 
Re: Neutral not required

I was on a job where we fed two seperate MCCs from a main switch.
the switchgear had one main disconnect and two 2000 amp switches - one for each MCC

each MCC was fed with five parallell runs of 500 kcmil - 3 phases, and a 'neutral'

both of these MCCs fed ONLY 480 volt loads, thus needing no 'neutral'

but we pulled them anyway... when i terminated the 'neutrals' in those MCCs, i noticed that, although there was in fact a place to terminate them that connected to a bus, that bus didnt go anywhere... it was only as long as the section was wide.. it really didnt do JACK except for use up about 200 feet of 500 kcmil wire.

i felt that it was a real waste of time..

oh, and by the way, the BOND to the case of each MCC was achieved by a 500 kcmil jumper from the 'neutral bus' to the ground bus in each MCC
 
Re: Neutral not required

each MCC was fed with five parallell runs of 500 kcmil
Click to expand...
It would have been better to have used the "neutral" for another phase conductor so you would have had 2000 amperes of capacity instead of 1900 amperes. :D
 
Re: Neutral not required

since we have a 480/277 volt transformer, Section 250.20(B) requires the system to be grounded. section 250.24 tells you where to make the grounding connection. I assume the xformer is pad mounted outdoors, therefore, is will be grounded at the ground grid at the xformer. Since it is a grounded system, a conductor must be installed to the building disconnecting means to provide a low impedance ground fault path back to the source xformer. Section 250.30 requires a bonding jumper to be installed between the xformer and the bldg. disconnect. Section 250.28(D) requires it to be sized in accordance the size of the phase conductors.
 
Re: Neutral not required

since we have a 480/277 volt transformer, Section 250.20(B) requires the system to be grounded.
Click to expand...
John, I hate to disagree with you but which part of 250.20(B) requires the system to be grounded?

(1) doesn't apply since the ? to neutral voltage exceeds 150 volts.

(2) doesn't apply if the neutral is not used as a circuit conductor.

(3) doesn't apply since this is not a high leg delta.

Sorry John, I stand by my original statements. :D
 
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