Generator Interlock for 400 amp residential

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Ryancbell121

Ryancbell121

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Pennsylvania
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Master Electrician
I have installed generator interlock kits for 200 amp residential services and portable generators. I want to install 2 interlock kits on each 200 amp main panel of a 400 amp residential service. I will splice the conductors from the generator inlet to each panels interlock breaker.

Is there any issue with this? I read an another forum and people were saying that you have neutrals going to each panel, I dont see the problem with that since the current flows back to the generator and not on the Service neutral.
 
Current will take both paths back to the generator simply because the grounded conductors are bonded together via the GEC and EGC's.

This can't be avoided though unless you switch the neutral during transfer, which obviously isn't happening in your setup.

Any standby system scheme with multiple feeders/branches and a non separately derived system will be the same way. Think hospitals or other applications where different emergency system branches are legally required.
 
kwired said:
Current will take both paths back to the generator simply because the grounded conductors are bonded together via the GEC and EGC's.

This can't be avoided though unless you switch the neutral during transfer, which obviously isn't happening in your setup.

Any standby system scheme with multiple feeders/branches and a non separately derived system will be the same way. Think hospitals or other applications where different emergency system branches are legally required.
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So the neutral and ground have to be separated in the portable generator?
 
You do have a parallel path because of the generator feed neutral is connected to both panels, even when the generator is not in use. You still have the same problem using two 200 amp manual or automatic transfer switches, unless they switch the neutral, but usually not an electrical issue (but is a code issue) because the unbalanced load is very unlikely to overload the larger neutral conductors.
 
Ryancbell121 said:
So the neutral and ground have to be separated in the portable generator?
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Unless you are going to switch the neutral with the transfer switch, yes. This applies even if you only were feeding one transfer switch. The system bonding is done at the service bonding in this situation. That allows an EGC to feed back to the generator and bond the frame of the generator. If you bonded at both the service and the generator then the EGC would be carrying parallel neutral current between the two.
 
This doesnt seem safe. Normally interlock breakers are 30 amps. If I have 2 30 amp breakers (one on each 200 amp panel), one phase on one panel can be pulling 20 amp and the same phase on the other panel can be pulling 20. If the overload on the generator fails then the wire will overheat.
 
kwired said:
Unless you are going to switch the neutral with the transfer switch, yes. This applies even if you only were feeding one transfer switch. The system bonding is done at the service bonding in this situation. That allows an EGC to feed back to the generator and bond the frame of the generator. If you bonded at both the service and the generator then the EGC would be carrying parallel neutral current between the two.
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Makes sense. Since the neutrals aren’t switched then the generator will be a non separately derived system. Only one bonding jumper allowed in this situation, at the main panels. So we need a floating neutral in the portable generator and a label on the portable generator saying neutral unbonded.

What if they take the portable generator off the property, is floating neutrals hazardous since they don’t clear ground faults?
 
Ryancbell121 said:
Makes sense. Since the neutrals aren’t switched then the generator will be a non separately derived system. Only one bonding jumper allowed in this situation, at the main panels. So we need a floating neutral in the portable generator and a label on the portable generator saying neutral unbonded.

What if they take the portable generator off the property, is floating neutrals hazardous since they don’t clear ground faults?
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Floating neutral will still not get you compliant! If you had only one panel or main, you would be fine. But you have two panels, how are you going to take one neutral from the generator, and not connect it to both panels? Are you just connecting it to one panel? Using the neutral from the other panel back thru the service to get to the generator? No code compliant way unless you switch the neutrals in this situation. Electrically, you probably won’t have any problems, but not code wise.
 
hillbilly1 said:
Floating neutral will still not get you compliant! If you had only one panel or main, you would be fine. But you have two panels, how are you going to take one neutral from the generator, and not connect it to both panels? Are you just connecting it to one panel? Using the neutral from the other panel back thru the service to get to the generator? No code compliant way unless you switch the neutrals in this situation. Electrically, you probably won’t have any problems, but not code wise.
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The portable generator has to be floating neutral since the neutral is not switched in the main panels since I’m using interlock kits. I’ll feed both panels with the ungrounded, grounded, and grounding conductors from the portable floating neutral generator.
 
Ryancbell121 said:
The portable generator has to be floating neutral since the neutral is not switched in the main panels since I’m using interlock kits. I’ll feed both panels with the ungrounded, grounded, and grounding conductors from the portable floating neutral generator.
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Draw out what you just said, floating neutral has nothing to do with it. Your neutral is tied together at the generator, floating or not. You are effectively paralleling the panel neutrals with the generator because it has a single point connection. If you had two generators, you would be fine.
 
One of my regrets about my own setup is that I went to 400 cause "I could" and the main reason I wish I didnt,, probably could have made it on 200 and would have made gen power a lot easier.
 
hillbilly1 said:
Draw out what you just said, floating neutral has nothing to do with it. Your neutral is tied together at the generator, floating or not. You are effectively paralleling the panel neutrals with the generator because it has a single point connection. If you had two generators, you would be fine.
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Floating neutral has a lot to do on an unswitched neutral. The neutral is not tied to the ground when you remove the bonding jumper in the generator. If you leaving the bonding jumper in the generator you will have two paths back to the generators source, back through the main house panels and through the generator bonding jumper.

Floating neutral portable generator —> hot,hot,neutral,ground 240v cord —> inlet on side of house —> nm cable hot,hot,neutral,ground —> junction box —> splice—> feed each 200 amp panel with hot,hot,neutral,ground. Interlock kit and breaker
 
hillbilly1 said:
Draw out what you just said, floating neutral has nothing to do with it. Your neutral is tied together at the generator, floating or not. You are effectively paralleling the panel neutrals with the generator because it has a single point connection. If you had two generators, you would be fine.
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IMG_0664.jpeg
 
hillbilly1 said:
Draw out what you just said, floating neutral has nothing to do with it. Your neutral is tied together at the generator, floating or not. You are effectively paralleling the panel neutrals with the generator because it has a single point connection. If you had two generators, you would be fine.
Click to expand...
You’re only allowed one system bonding jumper, that’s why you take it out of the generator when you can’t switch the neutral on transfer switches
 
hillbilly1 said:
Draw out what you just said, floating neutral has nothing to do with it. Your neutral is tied together at the generator, floating or not. You are effectively paralleling the panel neutrals with the generator because it has a single point connection. If you had two generators, you would be fine.
Click to expand...
If you don’t remove the bonding jumper in the generator then you give the electrons a path to take via the bonding jumper in the generator back to the generator source. Remove the bonding jumper so they stay on the neutral. If there is a ground fault in the system (house), The current goes back to the main panels on the ground wire then through the main panels bonding jumper then back to source.

Floating generators require 120v receptacles to be gfci protected in 445.20a
 
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