Two Residential Meters One Generator

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rsilk

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I am connecting two residential meters to one generator. I’m comfortable with sizing the gen set and using one ATS as the Master and the 2d as the slave. I am not comfortable with leaving the neutrals bonded through the generator.
My experience in the trade tells me that the neutrals should be isolated from each meter under non EM conditions? I can not find a code or and answer from a local inspector.
Any thoughts?
 
You should not have more than one neutral to earth/ground conductor bond in any service. Anything else will risk avoidable objectionable current in the ground system.
In addition, if there are GFCI devices mounted at the generator, any downstream bond, including the main system bonding jumper of each service can trip that GFCI.
The most comprehensive way to avoid these problems, including problems involving separate feeders from the generator to the two services, is to use ATSs that also switch the neutral (4-pole). This lets you avoid any connection to the POCO neutral(s) while operating from the generator.
 
hillbilly1 said:
(Three pole, this residential, most likely single phase, though a four pole would be much easier to get, but controls would be tricky)
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Good point. An additional complication where there are single phase to neutral loads is that the switch must interrupt the phase conductors before the neutral on switching away and make the neutral before the phases on switching toward. So a three phase switch with no provision for neutral switching cannot be substituted for a two hot plus neutral switch
 
GoldDigger said:
Good point. An additional complication where there are single phase to neutral loads is that the switch must interrupt the phase conductors before the neutral on switching away and make the neutral before the phases on switching toward. So a three phase switch with no provision for neutral switching cannot be substituted for a two hot plus neutral switch
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Even better point. Have never really thought about that.........
Is that code?
 
qcroanoke said:
Even better point. Have never really thought about that.........
Is that code?
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I do not remember it being code, just good design to avoid burning up connected loads. But it might be in there somewhere.
It doesn't come up when not switching the neutral, and neutral switching got more relevant with the increased use of GFCI protection on generators.
The other situation where it is relevant is when disconnecting an MWBC. (Don't disconnect the neutral unless both breaker poles are open.)
 
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rsilk said:
I am connecting two residential meters to one generator. I’m comfortable with sizing the gen set and using one ATS as the Master and the 2d as the slave. I am not comfortable with leaving the neutrals bonded through the generator.
My experience in the trade tells me that the neutrals should be isolated from each meter under non EM conditions? I can not find a code or and answer from a local inspector.
Any thoughts?
Click to expand...
I assume you are using each ATS for each residential and the ATS is between meter and main panel. Then your ATS (s) become service disconnect mean they shall come with CB on utility side. MBJ and GEC shall be at the ATS. Existing MBJ and GEC at each panel shall be removed. Ensure you have separated ground bus and isolated neutral bus in each panel. EGC/SSBJ and N are required to run from gen to ATS.
1. If your ATS is non-switching N, then additional MBJ and GEC are NOT required at gen.
2. If your ATS is switching N, then additional MBJ and GEC are required at gen.
 
I have been informed by an engineer from Generac that this is done all over the country without a problem. Just use two “standard” single phase switches, one the master and the other the slave. If my inspector approves this, then I plan to install a permit Safety Sign at the generator stating,
Caution connected to TWO services, disconnect both before servicing Generator.
I’ll soon see if there are any GFCI problems!
 
Why can't you set the ATS ahead of the meter- if power company will allow, and then just feed both meters from there. Of, course you would need an ats large enough for both or have load shedding involved.
 
rsilk said:
I have been informed by an engineer from Generac that this is done all over the country without a problem. Just use two “standard” single phase switches, one the master and the other the slave. If my inspector approves this, then I plan to install a permit Safety Sign at the generator stating,
Caution connected to TWO services, disconnect both before servicing Generator.
I’ll soon see if there are any GFCI problems!
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Oh yeah, it’s done a lot, and technically it will work, but if you follow it to the letter of the code……… most inspectors just ignore it.
 
hillbilly1 said:
Oh yeah, it’s done a lot, and technically it will work, but if you follow it to the letter of the code……… most inspectors just ignore it.
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Where in the code does it say the neutral must make before the hots when being transferred?
(I'd just like to know)
 
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