Mutiple Power Source Neutral Bonding.

Status
Not open for further replies.
LISHAJI

LISHAJI

Member
Location
Albany, NY
I have a 3ph 208/120V 225A Utility Supply for a Fish Hatchery Unit & a 30kW 3ph backup Generator for this supply. There is some spare capacity on this generator, which I want to use it as a backup for a 120V residential load. This residence is supplied by a seperate 1 ph 120/240V utility transformer. Now the Utility requires all neutrals to be bonded together. So if I where to bond the neutral of the 3ph-Utility, 1ph-Utility & 3ph-Generator, am I violating any CODE or producing any safety issues or multiple ground paths etc. The maximum distance between any two sources would be 200ft. The 3ph load are 3 ph motors balanced loads while the 1ph residential load may be little unbalanced on each leg. Your input would be much appreciated as to where I stand. :)
 
NEC has no objection i quess

NEC has no objection i quess

Article 230.2(D) States- Different Characteristics. Additional services shall
be permitted for different voltages, frequencies, or phases,
or for different uses, such as for different rate schedules.

And all these services have their Neutral bonded together with the structural steel, I quess ?
 
I would think that the utility primary neutral effectively inter-ties these neutrals already, the TS aside. You'd need to run a parallel neutral with your feeders, which may be a problem.
 
could the groundED conductors off of the transformer be concidered bonded to the main service neutral if they are attached to building steel or the grounding electrode conductor?
edited because i ment grounded instead of grounding
 
Last edited:
electricalperson said:
could the grounding conductors off of the transformer be concidered bonded to the main service neutral if they are attached to building steel or the grounding electrode conductor?
Click to expand...

Yes, the grounding conductor off the pole mounted transformer is bonded to the main service neutral and is attached to grounding electrodes.
 
LarryFine said:
I would think that the utility primary neutral effectively inter-ties these neutrals already, the TS aside. You'd need to run a parallel neutral with your feeders, which may be a problem.
Click to expand...

You have a point. This would create a neutral loop which is effectively grounded at (2) transformer points and (2) service entrance points. What are the major problems we can think of??
 
LISHAJI said:
You have a point. This would create a neutral loop which is effectively grounded at (2) transformer points and (2) service entrance points. What are the major problems we can think of??
Click to expand...

When I first read this thread my 1st thought was that you would have 2 seperate services interconnecting ,even though the ATS would seperate the ungrounded conductors, you'd still be creating the possibility of back feeding to the power company's equipment. If there were to be a short in the system, it would create the need for very costly repairs. A definite No,No .

The areas that I've found, thus far in the '08 code, are as follows :
1) Article 100 Definitions ... Seperately Derived System ,
2) VI Service Equipment Disconnect Means 230.70 ,
3) 230.75 Disconnection of Grounded Conductor ,
4) 230.76 Manually or Power Operable ,
5) 230.204(D) ,
6) 250.20(D) ,
7) 250.24(A),(3) ,
8) 250.30(A) .

These are the sections that I've found thus far relating to your question .
I'll continue to research this matter and post what else I may find .
I hope this helps you to find your answer .

Carl :)
 
LISHAJI said:
Now the Utility requires all neutrals to be bonded together.
Click to expand...
Can you be more specific? What exactly are they wanting to see?

If what I'm picturing is correct (I've mulled over a few different scenarios), then I don't see a code violation myself. But I'm a little confused about the above, and the big picture - what is the nature of the commercial building? Are they all on one lot? Neighborly agreement? :confused:

Given your description of balanced 3? loads in the commercial building, I don't see a real-world safety issue here off-hand, but without seeing the big picture I'm not real comfortable saying that.
 
The Original Question In Relation To Seperate Services

The Original Question In Relation To Seperate Services

LISHAJI said:
I have a 3ph 208/120V 225A Utility Supply for a Fish Hatchery Unit & a 30kW 3ph backup Generator for this supply. There is some spare capacity on this generator, which I want to use it as a backup for a 120V residential load. This residence is supplied by a seperate 1 ph 120/240V utility transformer. Now the Utility requires all neutrals to be bonded together. So if I where to bond the neutral of the 3ph-Utility, 1ph-Utility & 3ph-Generator, am I violating any CODE or producing any safety issues or multiple ground paths etc. The maximum distance between any two sources would be 200ft. The 3ph load are 3 ph motors balanced loads while the 1ph residential load may be little unbalanced on each leg. Your input would be much appreciated as to where I stand. :)
Click to expand...

Getting back to the original post ... I understand or perceive you to be asking if the NEC prohibits the grounded conductor(s), Neutral(s), of seperate individual sources , the power company & an onsite generator, to be connected at the same time of useage (interconnected simutaniously) .
If this is indeed the topic in question than for the reasons brought to attention previously, #7 , Yes ... per reviewing the afforementioned in my understanding & opinion, it is indeed against the NEC code.

Perhaps you should send Mike Holt an email on this for confirmation or even the NFPA
in order to clarify this matter for all of us ... Go directly to the horse (source) .

Carl :)
 
Last edited:
georgestolz said:
Are they all on one lot?
Click to expand...

The owner of both the service is same. There is a commerical account & a residential account and housed in the same property. I couldn't find any voilation of NEC. However it gives rise to multi-point grounding which is pretty controversial in-lieu of single-point grounding.

If I was to model the system, it can be imagine as a square area with the upper left corner to be a pole mounted transfomers supplying 3? 208/120V and the upper right corner to be a pole mounted transformer supplying 1? 240/120V. The lower left is the Commercial service and lower right the residential service. The service entrance is underground. The length is about 150ft each side.
 
Krim said:
you'd still be creating the possibility of back feeding to the power company's equipment. If there were to be a short in the system, it would create the need for very costly repairs. A definite No,No .
Click to expand...


The utility company requires to be notified that there is a generator hooked up, so they are aware that the system is energyized when they undertake routine maintenance. But I am not sure what can be the effect of a short circuit on the system. I am not grounding the generator neutral nor switching the neutral at the ATS, so it is not a seperately derived system. Could you please elaborate the short circuit scenario?
 
Last edited:
LISHAJI said:
The utility company requires to be notified that there is a generator hooked up, so they are aware that the system is energyized when they undertake routine maintenance. But I am not sure what can be the effect of a short circuit on the system. I am not grounding the generator neutral nor switching the neutral at the ATS, so it is not a seperately derived system. Could you please elaborate the short circuit scenario?
Click to expand...

My thinking is based on the fact that if the generator is creating its own power source and the power company is bringing in their power,derived from another source,& if there were a short in the emergency fed system with both systems neutral conductors not being seperated,there is the potential of the on site generated power being fed directly to the power companys equipment through the neutral conductor. The two seperately derived power sources would collide at some point in the lines !

Carl
 
georgestolz said:
What bad things do you foresee from this connection? It doesn't seem any different from other compliant installations.
Click to expand...


What I could think of, is that due to imbalance in load there would be a difference in neutral current in the neutral conductors at different points. This could give rise potential difference between these points in the neutral system & could drive a stray circulating current causing some heating in the conductors.
 
And if a butterfly flaps it's wings in New York it could affect the weather in Chicago. But only slightly. :)

All neutrals are interconnected between the utility and end user's systems, I don't see how throwing a generator in the mix is going to change things all that much.
 
georgestolz said:
And if a butterfly flaps it's wings in New York it could affect the weather in Chicago. But only slightly. :)

All neutrals are interconnected between the utility and end user's systems, I don't see how throwing a generator in the mix is going to change things all that much.
Click to expand...


Thanks for expert comment. I was not sure whether it was a Pterosaur flapping its 25ft wings or the butterfly it 2.5 inch wings. Now I got the drift.:wink:
 
LISHAJI ,
As long as you've checked with your A'sHJ and the local power company,and they are OK with the arrangement , there's nothing to be concerned with.
I would like to know thier final say in the matter though for future personal reference if you wouldn't mind sharing .

Carl :)
 
Krim said:
LISHAJI ,
As long as you've checked with your A'sHJ and the local power company,and they are OK with the arrangement , there's nothing to be concerned with.
I would like to know thier final say in the matter though for future personal reference if you wouldn't mind sharing .

Carl :)
Click to expand...

Yes it was okayed by the PoCo.
 
Krim said:
LISHAJI ,
So the PoCo does not require that the neutrals, although they are from seperately generated sources, be isolated from one another through a disconnect switch. Is this correct ?
Click to expand...


Switched neutral with a seperately derived system is a better option in this case, but I quess the PoCo don't find many transfer switches doing this, the way they want, so they direct connecting neutrals together.
 
Status
Not open for further replies.
Top