Generator Hookup

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Kopper

Member
Location
Lewisburg, Pennsylvania, USA
Occupation
Electrical Contractor
I am doing a generator hookup using one 30 amp inlet to power two 200 amp panels installed for a 400 amp service. I plan to use a junction box to tie the inlet into both panels but doing so creates a situation that could potentially be unsafe. (the neutrals from both panels will be tied together with a 10 AWG wire) the grounds and neutrals are bonded together in both panels so the tie could also happen over the ground. I would like to use a 4 pole breaker mounted between one of the 200 amp panels and the junction box to eliminate the situation. (using two generator inlets and a "y" adapter could work but could also create the same situation if it was forgotten and not removed after use). My question is will a circuit breaker detect the over current on the neutral or ground and open just as it would on the line legs?
 

rlundsrud

Senior Member
Location
chicago, il, USA
Could you make a diagram to show us what you are doing. This doesn't sound correct to me, but I might be misunderstanding what you are doing. Make sure you detail how you intend to do the neutral.

Also, is the ATS a two pole? That is an important aspect in how you plan to install the system. I typically prefer a two pole ATS so I don't need to run a separate GEC.
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
I am doing a generator hookup using one 30 amp inlet to power two 200 amp panels installed for a 400 amp service. I plan to use a junction box to tie the inlet into both panels but doing so creates a situation that could potentially be unsafe. (the neutrals from both panels will be tied together with a 10 AWG wire) the grounds and neutrals are bonded together in both panels so the tie could also happen over the ground. I would like to use a 4 pole breaker mounted between one of the 200 amp panels and the junction box to eliminate the situation. (using two generator inlets and a "y" adapter could work but could also create the same situation if it was forgotten and not removed after use). My question is will a circuit breaker detect the over current on the neutral or ground and open just as it would on the line legs?

I've done what you are doing but I used breaker interlocks to prevent feeding back out to the utility, It doesn't sound like that's what you are planning to do. Please, do use interlocks.
And the neutrals should already be tied together in the meter base or the service disconnect anyway.

Here is a link to interlocks I've used: http://natramelec.com/
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
From your OP it sounds like you are using the breakers to back feed the panels without any type of transfer switch to assure utility power is disconnected when the generator is in use. If that is the case it is both dangerous and a violation
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
what makes you think you can feed two 200A panels with a 30A generator?

have you done a load calculation to see that this works?

i agree with a previous poster that unless you are adding in an actual transfer switch, the danger you are adding by having the extra N-G bond is minimal compared to the danger of having no transfer switch.
 

Kopper

Member
Location
Lewisburg, Pennsylvania, USA
Occupation
Electrical Contractor
I am definitely using interlocks - they are already installed. My plan was to simply use a 4 pole breaker to connect the two line legs, the neutral and the ground from one of the panels to the junction box. This would create a positive disconnect between the panel neutrals when turned off or if an overcurrent situation should occur on any of the legs including the ground or neutral. The entire system would still be grounded but any connection between the boxes via ground or neutral would not be possible with the 4 pole breaker in the off position. I will try to include a diagram soon.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I am definitely using interlocks - they are already installed. My plan was to simply use a 4 pole breaker to connect the two line legs, the neutral and the ground from one of the panels to the junction box. This would create a positive disconnect between the panel neutrals when turned off or if an overcurrent situation should occur on any of the legs including the ground or neutral. The entire system would still be grounded but any connection between the boxes via ground or neutral would not be possible with the 4 pole breaker in the off position. I will try to include a diagram soon.

I don't think you are allowed to open the EGC.

I don't see how this would prevent generator power from backfeeding to the utility.
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
I don't think you are allowed to open the EGC.

I don't see how this would prevent generator power from backfeeding to the utility.

OP stated in post #6 that he is using interlocks. They won't allow you to turn on the generator input breaker unless the main breaker is off so back feeding to the utility is impossible.
I just don't understand the neutral concerns. both 200 amp panels neutrals and hot's should be tied together in the meter socket or service disconnect (if there is one). Now if the neutral is bonded in the generator that will cause a problem for the ground fault receptacles in the generator.
 

Kopper

Member
Location
Lewisburg, Pennsylvania, USA
Occupation
Electrical Contractor
The only time it should be a concern is if one of the parallel neutrals coming to either one of the panels should for some reason fail - in that scenario the 10AWG coming from each panel and connected in the j box would create a path on which 200 amps of current would potentially try to flow causing a dangerous situation. If i am thinking correctly it would only be a problem in a neutral failure situation and the homeowner is concerned about that... My idea is to place the 4 pole breaker in the loop between the panels to provide the protection the homeowner is concerned about. (The homeowner does have engineering credentials of some sort which made him search this out in the first place.)
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
The only time it should be a concern is if one of the parallel neutrals coming to either one of the panels should for some reason fail - in that scenario the 10AWG coming from each panel and connected in the j box would create a path on which 200 amps of current would potentially try to flow causing a dangerous situation. If i am thinking correctly it would only be a problem in a neutral failure situation and the homeowner is concerned about that... My idea is to place the 4 pole breaker in the loop between the panels to provide the protection the homeowner is concerned about. (The homeowner does have engineering credentials of some sort which made him search this out in the first place.)

Well, that is certainly a possibility........ :happysad:
 

Kopper

Member
Location
Lewisburg, Pennsylvania, USA
Occupation
Electrical Contractor
My initial question was and still is: Will the breaker sense the neutral current and open the breaker just as it would for the lines or do i need a particular kind of breaker?
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
My initial question was and still is: Will the breaker sense the neutral current and open the breaker just as it would for the lines or do i need a particular kind of breaker?

I would think current is current and a standard breaker wouldn't care if it was neutral current or line current. But don't quote me on that....
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I just do not see any purpose served by the 4 pole breaker at all.

It does not appear like you could interlock it with anything so it is pointless to have it there.

If PB A and B are currently wired in parallel (which is how they would have to be to get a 400A service out of two 200A PBs, I don't see how this works at all.
 

iwire

Moderator
Staff member
Location
Massachusetts
If PB A and B are currently wired in parallel (which is how they would have to be to get a 400A service out of two 200A PBs, I don't see how this works at all.

Likely not in parallel.

A common and money saving tactic when you need a 300 or 400 amp service is use two 150 or 200 amp main breaker panels side by side supplied from a single 400 amp meter supplied by 300-400 amp conductors.

You end up with many more circuit spaces for much less money than using a single 400 amp main breaker panel.
 

iwire

Moderator
Staff member
Location
Massachusetts
I can't see how the dual interlock kits, independent of each other, could be legal.

Why not, there is no safety issue?

One could backfeed 1 panel and have POCO powering the other.

Yes, that could happen, it is not unsafe.


The neutral issue is a code problem but having multiple panels with multiple interlocks from one generator is not a safety issue.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Likely not in parallel.

A common and money saving tactic when you need a 300 or 400 amp service is use two 150 or 200 amp main breaker panels side by side supplied from a single 400 amp meter supplied by 300-400 amp conductors.

You end up with many more circuit spaces for much less money than using a single 400 amp main breaker panel.
How would that not be in parallel?
 
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