jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Separately derived system (generator) and selection of correct transfer switch
- Thread starter Jennifer K.
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jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Yes, genny noodle need only go as far as genny disco.
Design wise not my favorite, but could be done.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Let’s note that except for LRB’s scenario, this is a terrible idea.
From a theoretical point and NEC wise it could be done, but most likely no one is going to.
OP even mentioned future use and this setup would be a problem waiting to happen.
From a theoretical point and NEC wise it could be done, but most likely no one is going to.
OP even mentioned future use and this setup would be a problem waiting to happen.
- Occupation
- Licensed Electrician
That's my point too.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
OP presenting the question is okay, anyone actually doing it, outside of what LRB presented, gets Gibbs smacked.
James was just presenting a scenario.
LRB
Member
- Location
- Interior Alaska
To all... have had ocation where we had many years later, needed 277 lighting load. in that case we installed 480V delta to 480 volt Y (SDS) tranny to establish noodle. Of course we had 208V delta- y trannys (SDS) for utilitys in which case we do not use a N on primary side.
First the OP has set the requirements for whether the generator will be wired as an SDS or wired as a NON-SDS system. I imagine those are the cards she was dealt.
The OP said the neutral would terminate inside the building with the ungrounded conductors in a new distribution panel board. No one said anything about leaving the neutral conductor outside at the generator.
The OP asked if it would be ok to bond the neutral to ground there, at the new distribution panel board. No one has answered that question as yet. I will say though good chance the generator has a main at the generator.
I believe code says when a neutral of an SDS is grounded it has to bonded to the main grounding system of the electrical service and sized per NEC.
Problems? None. When the customer decides to add a TS that will serve a load that needs/requires a neutral conductor the TS will be required to have a switched neutral. Added cost? Yes.
Given the information provided by the OP does she have any other choice?
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Um, I said I agreed.
Legal yes, I still say bad design-I see nothing but future problems and wasted money, but not my problem.
As the other stuff you just brought up, I gotta check before I answer.
I must have missed where she said that.
No problem as I said, in my previous post, If a TS is installed down the road and a neutral conductor is required. The neutral shall be switched per NEC.
>>>>>>>>>>>
NOTE:
Even though the load being served is 3ph only a neutral may still be required by the manufacture of the TS if it is an ATS. I have seen semi-automatic MTS that required a neutral for their operation.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
James, the more I read the OP the more I am getting a headache rumbling around 240.24-240.30 trying to reconcile what is where.
I understood your scenario well enough.
As far as whatever she is doing or attempting to do, I dunno. Getting too screwy for me.
Edit: I was typing when you posted, did not see it before I posted.
I understood your scenario well enough.
As far as whatever she is doing or attempting to do, I dunno. Getting too screwy for me.
Edit: I was typing when you posted, did not see it before I posted.
david
Senior Member
- Location
- Pennsylvania
Isn't it more correct to say the Gen. Neutral gets bonded at the generator or it gets bonded at both the Gen. and the building
250.30 (A) (1) last sentence when the source is located outside
You can't bond the neutral at both places.
Reread 250.30 (A) (1).
If the generator has a main disconnecting means at the generator then the neutral is bonded there. That's the way I read it.
It would have been nice if the OP would have given more info.
It was not until post #12 the OP mentioned the generator was outside the building. That fact changed the game.
It would have been nice to know,
KW rating of generator as well as the voltage rating?
Type of occupancy?
3ph only load/s the generator will be supplying power to when called upon by a TS and or customer?
MTS? ATS? Both?
Who was responsible for the sizing of the generator and selection of the TS/s? Was an EE involved in the process?
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david
Senior Member
- Location
- Pennsylvania
I don't agree with that 250.30 (A) (1) exception #2
exception 2 you would run a single neutral / bond to the building the neutral would be bonded at both locations.
you are required to bond it at the outside location you are permitted under the conditions of exception #2 to bond it at both locations
Reread exception #2
Note, first disconnecting means. Just a guess it is at the generator. Maybe the OP will chime in and let us know for sure.
shall be permitted if doing so does not establish a parallel path for the grounded conductor.
So say the main disconnecting means is not at the generator.
The feeder could be direct burial, ran in PVC conduit, but it could not be installed in metallic conduit.
And what ever the feeder wiring method is used a wire conductor EGC could not be installed with the grounded feeder conductor either.
If the neutral is bonded outside as well as inside the EGC will be in parallel with the grounded conductor.
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david
Senior Member
- Location
- Pennsylvania
Ill reread it but i don't think i need to, it is a feeder so if you bond the neutral as required at all outside sources of a separately derived system and run an equipment ground from the out side source bonded neutral, you would not bond the neutral at the building ,you would bond the equipment ground to the grounding electrode system at the building but the neutral would be insulated (float)
what the exception permits is a neutral / bond as a single conductor the same as you would see at a typical utility transformer supplying a service. here you have a SDS (GEN) with a feeder supplying a building
you keep saying re-read what am i reading wrong?
Edit: in the exception the neutral serves a duel purpose in addition to the Neutral it serves as a bonding jumper from the source to the equipment grounding system at the building
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david
Senior Member
- Location
- Pennsylvania
under exception 2 you bond at both the outside source and at the building and you only run a (" white Neutral") you do not run a ("green bond") the white conductor serves as a ("white neutral" and also as a "green bond")
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
I agree. But I think it worth adding a couple of points. We are assuming a grounded system. You would need the TS's to be set up for straight 480 volt operation (no neutral for controls). It limits you if the need ever arises that you need to connect line to neutral loads. Of interest also in a set up like this, the generator would be required to be set up as a SDS as otherwise the generator side of the system would be floating and operating ungrounded.
David,
My apologies if I misunderstood what you said in post#31.
"or it gets bonded at both the Gen. and the building"
If the neutral is bonded at the generator it cannot be bonded at the building again.
With exception,
Exception #2
NOTE: Exception #2 is referring to a transformer.
>>>>>>>>>>
My understanding if the generator neutral conductor is bonded at the generator a bonding jumper shall be installed from the generator grounded neutral conductor to the building electrical service grounding system.
Best regards,
Jim
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ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
You can if the ATS switches the neutral and the N-G bond at the building is on the POCO side of the ATS. You have to, I believe.
david
Senior Member
- Location
- Pennsylvania
Here is the problem with exception 2 SDS just being a transformer.
250.30 (A) (1) requires all outside SDS sources to be bonded at the source or at some point outside
So if left as such you could never bond the neutral at the building when the outside source is a SDS Generator. Since the last sentence of 250.30 (A) (1) mandates all SDS sources outside be bonded at the source.
In 2017 ex 2 is changed from a transformer to a separately derived source. So it was never there intention to not allow a feeder from an outside Generator to be bonded at the building and that was corrected in 2017/ 250.30 (A) (1)Exception 2
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