250.32(B) curiousity

Open Neutral

Senior Member
While waiting for PSE, I got asked about about an existing case. Outbuilding fed with 3 #6's but no fourth wire. Further, it appears the neutral bus is locally grounded...

Now https://iaeimagazine.org/magazine/20...-requirements/ does what I think is a credible job of showing why that's not allowed.

But I got to wondering about alternative solutions. I invite you to tell me how crazy/wrong I am with these.
  1. If he has only 240VAC tools and lighting, use the three #6 for L1, L1, and ground. (i.e: Is a neutral required if not needed?)
  2. He could buy a 240:120-0-120 transformer, declare the CT to be the neutral, ground it to the local & ground to main wires. That could handle hand tools.
  3. Some 240V tools have a 120V control system/DRO, and would have to run off the transformer. Big loads, big transformer, big buck$
  4. When you call the PoCo with the words "open neutral" {....Never heard of HIM..} they may show up with a large autotransformer with a centertap; they install it at your meter until they can fix your damaged feed. Suppose Joe Bridgeport did the same; it would only need to be sized for his 120V loads.
  • So are there reasons each of the above won't work? Will any of them be allowed under the Code?
Let the stoning begin!
 
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Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
The only place the neutral/grounded conductor is required is at the service entrance. If loads don't require a neutral, then you're not required to run a neutral.
 

oldsparky52

Senior Member
At present, it's 60A. But I'm more interested in my left field ideas than the cold hard reality....
The way I understand you, it will work. It may not be the most efficient or cost effective method of doing it and I don't know if you can find a 240V only subpanel. You can always remove the neutral bus but then you have modification issues to deal with. Might do some informative labeling.
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
The way I understand you, it will work. It may not be the most efficient or cost effective method of doing it and I don't know if you can find a 240V only subpanel. You can always remove the neutral bus but then you have modification issues to deal with. Might do some informative labeling.
You don't have to remove the buss, you just don't hook anything up to it.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
What you have proposed (#2, separate small xfmr for loads that need 120V) is done all the time with 3 phase 3 wire delta services. It becomes a local SDS (separately derived system). I don't see an issue with it.
 

romex jockey

Senior Member
Location
Vermont
The old 250.32 B allowed us to run a 3 wire ,MBJ @ outbuildings w/GEC's

Which is basically what the POCO's do

Then they decided that there were too many 'return paths' , pipe, telecon, h20, etc

So they changed 250.32(B) to a 4 wire w/GEC's (remote OCPD's need only apply)

Keep in mind that we could (legally to code) install a dozen SDS's within a structure ,all w/MBJ's & GEC's

so yeah, let the stoning begin.....:lol:

~RJ~
 

kwired

Electron manager
Location
NE Nebraska
What about just leaving it alone. As long as there are no other metallic paths between the buildings and it was installed before the code change it is legal and safe.
I think he must have a true EGC that is green or bare and is sized per 250.122, if so does that change your reply any? Some cases the conductor size may still be sufficient and if so then I agree with you other than technically it can not be green or re-identified unless it os 4 AWG or larger.
 

kwired

Electron manager
Location
NE Nebraska
What you have proposed (#2, separate small xfmr for loads that need 120V) is done all the time with 3 phase 3 wire delta services. It becomes a local SDS (separately derived system). I don't see an issue with it.
Is done with 3 phase 4 wire where voltage change is made as well - 480 volts to 120/240 or even 480 three phase to 208/120 three phase all the time as well. No neutral is brought to the separate building with the 480/277 supply unless there is intent to supply 277 volt loads.
 

jaggedben

Senior Member
I concur with leaving it alone unless there is some good reason not to (e.g. new permitted work being done and can't convince the AHJ it is worthy of grandfathering). But for the sake of discussion...

An auto transformer is not an SDS by definition. But it doesn't have to be to be a solution. The problems I see are...
- it's not allowed to reidentify a 6awg from white to green. For a #4 feeder it would be fine.
- it's my understanding that an autotransformer in this situation can only handle a limited phase imbalance. So you may need a bigger transformer than you think you need, depending on the maximum possible load imbalance.
 

GoldDigger

Moderator
Staff member
So the transformer creates a SDS solving the neutral dilemma.

Will the autotransformer do so as well?
As a non-SDS configuration the autotransformer, uses as a grounding transformer, is not NEC compliant, but is perfectly fine for POCO to use temporarily for their service to you. Not sure where it stands in the NESC as a permanent installation.
 
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