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I live in Medina County, Ohio, USA.

This other question discusses a bit about running two load centers from a meter. I am wanting to do exactly that. I currently have service that supports 200amp (confirmed with city). My existing disconnect in garage is 100amp and has a 3 wire cable going to 100amp panel in the house. That cable is routed through difficult places and the electrician tells me it will be expensive to upgrade to the 4-wire cable that would support 200amp.

I really only need 100amp more for the garage, so I did a little research and it appears that I would be able to run another 100amp loadcenter off the meter. The other Stack Exchange question I linked to above discusses that, even going over some code (like you can do this because of an exception if the disconnects are grouped together).

So in order to avoid having to upgrade the whole house to 200amp and replace that cable, which increases the cost drastically, I'd like the electrician to run another loadcenter right off the meter and have it right next to the existing disconnect in the garage. I mentioned this to him and he said we'd still need to replace the cable. Before I go back and forth with him, I'd like to be more informed, which is what I'm trying to do here.

First, is running a second loadcenter code-compliant? The total amps allowed by the two loadcenters would be 200amp, and the meter supports 200amp. The existing disconnect and the new loadcenter would be physically right next to each other.

Second, if that is code-compliant, would the existing 3-wire cable between the existing disconnect and the house panel need to be upgraded? If so, why? It would never have more than 100amp (protected by the disconnect breaker).

Third, is there anything special that would need to be done to run a second loadcenter or is it just run in parallel from the meter?

See my professional diagram below.

Thanks for your help, Mike

enter image description here

  • Interesting question and I am sure Harper or one of the other pros will give a full answer. But one issue that may come up is how many grounds there are. It looks like the 100 Amp is grounded at the house panel. That may be an issue because the 100 Amp in the garage will also need a ground - and by definition they will be two separate grounds unless you ran a new cable (with ground included) and put in a 200 Amp panel in the garage with the 100 Amp in the house becoming a subpanel. The alternative is indeed two separate feeds - and I have no idea if that is permitted or not. – manassehkatz-Reinstate Monica Oct 12 '18 at 1:15
  • Is the disconnect a separate box from the meter socket, or a meter-main with the meter socket and main disconnect as a single unit? – ThreePhaseEel Oct 12 '18 at 1:23
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    Is the "100A" disconnect near the meter, is that merely a switch, or does that have breakers/fuses in it? If you hypothetically pulled 150A through it, would it detect the overcurrent and do a safety trip, or would it just cheerfully carry the current until it overheated? – Harper - Reinstate Monica Oct 12 '18 at 6:17
  • @manassehkatz I'm not sure about the grounding. – MikeJansen Oct 12 '18 at 12:03
  • @ThreePhaseEel - the disconnect is separate from the meter. Meter is outside. Disconnect is inside. – MikeJansen Oct 12 '18 at 12:03
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The issue with 3/4 wires isn't about ampacity. It's about grounding electrode systems and

Where's your main panel?

Electrical service is 3-wire from the pole to the main panel, and it operates under service rules. After the main panel, power must be carried 4-wire and it operates under the feeder rules.

Right now it's arguable (and possibly grandfathered) that the disconnect and your run from garage to house is all part of the service. To follow this logic through, the house has the one main panel and thus the one official neutral-ground bond. The cable run benefits from the 310.16b7 uprate, meaning the wire only needs to be rated for 83% of ampacity, or 83A not 100A.

If you add the garage panel as you mean to, with both disconnects right next to each other, the house run can no longer be a service. It moves the "main panel" point to the garage. Now the house panel is a subpanel. It will need separation of neutral and ground in the panel and all the way back to the garage. The connection is feeder not service, and ground must be present. That means the permissive 83% uprate goes away and the wire must be rated for full 100A, so it may be now too small.

The upside is that ground can be retrofitted separately, it doesn't require total replacement of the cable. Ground does not need to be bundled with the conductors because it does not flow current except in emergencies. It can follow any practical route.

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    Although I agree with your answer the AHJ needs to be consulted. I lived in Dayton Ohio and owned a home there EVERYTHING in this cape cod was wired Wrong , from white being wired hot and black as neutral, all the switches were opening the neutral, not the hot. I called and found out I could change things no big deal. I also found they would even allow me to up size the feeder to my garage, just the opposite of what you are doing but since my service was larger than required I only had to change the meter base so I had 2 separate disconnects (breakers) with no updates required except wire awg – Ed Beal Oct 13 '18 at 2:09
  • @Harper - thanks! You clarified for me what I was missing. The electrician said something similar but you clarified it. – MikeJansen Oct 14 '18 at 21:03

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