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I'd like to add a subpanel to add a couple circuits (Extra inverter Mini Split ACs, well pump, etc.) but my main interior panel is full and recessed in concrete. I added a manual transfer switch from the main breaker next to the electric meter (utility - power generator).

Can I tap the main lines with a polaris style 3 way splice insulated connector into a new sub panel box? If I splice this way, should I splice from the utility line or can I splice from the load line that goes into the interior service panel? Would I need to get a 125 amp sub panel for the new circuits I need and want to have spare for future use? Which would be better and cheaper? BR breakers are the most common here, but I keep hearing about Siemens.

Side note: My home uses 125 amp and noticed that the wire used from the main 125 amp breaker next to electric meter that goes to the interior service panel is 2 AWG. I had purchased 1/0 AWG wire. I'm not sure whether to change to 2 AWG wire or keep the 1/0 AWG for the transfer switch and subpanel.

  • What's the amp rating of the transfer switch, and why did you mount it outside next to the meter-main? – ThreePhaseEel Jul 29 '18 at 14:23
  • The transfer switch is 125 amp. Mounted next to meter main because it was way easier, less messy, and less crowded, than connecting next to the service panel. – Rick Jul 29 '18 at 14:27
  • How many switching poles does your transfer switch have? – ThreePhaseEel Jul 29 '18 at 14:44
  • 2 poles. It is a double pole double throw transfer switch. My ACs are 240 volt as well as the well pump. – Rick Jul 29 '18 at 14:47
  • BR are the cheapest there. – Harper Jul 29 '18 at 19:53
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You can tap this

What you want to do here is replace the existing set of 3-way splice connectors that tap the feeder for the surge protector with 4-ways, and then use the newly opened connector-ports to run a feeder up to the transfer switch.

You're fine on size

The reason why the existing feeder is 2AWG is because it's copper most likely -- 2AWG copper is good for 115A at 75°C, which is fine for a dwelling unit feeder application due to the 83% rule. Your 1/0 aluminum wire will be fine, though -- the ampacity rating's about the same, and CuxAl rated Polaris connectors work fine for copper-to-aluminum connections when torqued to spec (AlumiConns are essentially miniature versions of them, even).

You will need a 125A subpanel for the standby loads given the style of transfer switch (DPDT safety switch) you linked -- I would recommend getting a 30 space main lug unit. (Siemens has the advantage that the PL line of loadcenters comes with some niceties that you don't get with BR, but it seems like most of the supply houses in your area are loyal to Eaton, so a BR loadcenter is fine and dandy here.)

One caveat here

Since you got a two-pole transfer switch (instead of a three-pole), you must consult your generator manual (or generator manufacturer) for the correct procedure for pulling the neutral-to-ground bond on your generator, as your transfer equipment is set up for a non-separately-derived generator source. Otherwise, you'll have issues (such as false GFCI trips on the generator with some generators, and energized boxes due to errant neutral current flowing on grounds) due to the duplicate neutral-to-ground bond on the generator.

  • This is good advice and would be code compliant in the U.S. – Ed Beal Jul 29 '18 at 19:33

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