Circuits from 2 different services allowed in same box ?

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avm32

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Electrician
Hello,

Doing a pre-inspection for installing an automatic generator in a residence that currently has 2 separate 200A service panels (both currently directly fed from the same meter).
The issue is that the light switch box of the bathroom has 2 circuits coming into it - one from Panel1, the other from Panel2.
I don't think this is a code violation or a safety concern as both circuits reside on the same service and I don't see any safety issues.

After the auto generator is installed, the meter will feed into 2 separate 200A Auto Transfer Switches (ATS). The 2 separate ATS is the only way I can do this, can't do a single 400A ATS (do to some non-electrically-related circumstances).
After installing the 2 separate ATS the main panels will now become subpanels with separate ground / neutrals.
I think it is possible for one ATS to fail and that can lead to the bathroom having one circuit powered from the generator and the other from the utility - this in the same box.

Of course the neutrals and live wires from the 2 circuits would be separate in this box.

Q1: Is this a code violation - Is it allowed to possibly end up with 2 different services in the same box ?
Q2: Should I separate the grounds from the 2 different circuits in this box ? How would this look like considering that the grounds are just exposed bare wire ?

Thanks!
 
Q1- Its a little misleading to call the circuits in the same box services. you got it right earlier when you said subpanels. No violation but perhaps some labels on the wires
Q2- see 250.144
 
Thanks !
tom baker said:
Q1- Its a little misleading to call the circuits in the same box services. you got it right earlier when you said subpanels. No violation but perhaps some labels on the wires
Click to expand...
Yes, I was just trying to point out that in an ATS fault situation you would end up with 2 separate services in that box since one subpanel would be fed from generator and the other from the utility.

I would think that such scenario would be not allowed by code since someone could mix up the wires in the box and end up backfeeding the generator into the grid. This was actually the situation here - the 2 circuits in the box were wired together at the box by I'm assuming the bathroom remodeling guys. The 2 circuits are on different panels but on same phase so they didn't blow up.

However if someone makes same mistake after ATS install then you might end up feeding the automatic generator into the grid.
 
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avm32 said:
Hello,

Doing a pre-inspection for installing an automatic generator in a residence that currently has 2 separate 200A service panels (both currently directly fed from the same meter).
The issue is that the light switch box of the bathroom has 2 circuits coming into it - one from Panel1, the other from Panel2.
I don't think this is a code violation or a safety concern as both circuits reside on the same service and I don't see any safety issues.

After the auto generator is installed, the meter will feed into 2 separate 200A Auto Transfer Switches (ATS). The 2 separate ATS is the only way I can do this, can't do a single 400A ATS (do to some non-electrically-related circumstances).
After installing the 2 separate ATS the main panels will now become subpanels with separate ground / neutrals.
I think it is possible for one ATS to fail and that can lead to the bathroom having one circuit powered from the generator and the other from the utility - this in the same box.

Of course the neutrals and live wires from the 2 circuits would be separate in this box.

Q1: Is this a code violation - Is it allowed to possibly end up with 2 different services in the same box ?
Q2: Should I separate the grounds from the 2 different circuits in this box ? How would this look like considering that the grounds are just exposed bare wire ?

Thanks!
Click to expand...
If the power goes out and the ATS(s) switch to generator power, how could you have power from both the generator and utility if the utility power is out? Even if one ATS fails, you would still not have power from the utility.
 
Little Bill said:
If the power goes out and the ATS(s) switch to generator power, how could you have power from both the generator and utility if the utility power is out? Even if one ATS fails, you would still not have power from the utility.
Click to expand...
I was thinking more like:

- Power cuts off
- Generator switches on
- 1 ATS switches to Generator mode and faults (locks up)
- Power comes back on
- Generator switches power back to utility - but actually just one ATS, the other ATS remains from generator
- Generator takes another minute to cool down before shutting off - during this 1 minute in the box there would be both generator and service power.

Anyway the above is indeed a corner case - the real concern is remodel guys bridging the circuits from the 2 panels, then you will never notice anything until ATS failure at which point the generator will backfeed into the grid.
 
A generator is a power source (and can be separately derived ot not) but it is not a service.
Services only come from utilities.

Your point about the risk of incorrect update work is well taken, but what-iffs like that should not be part of code enforcement.
Risks of material or equipment failure are recognized. Risks of incompetent work are generally not.
In some cases the Code does not allow a mixture of different circuit types, but because of failure risk.
 
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