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[Electrical] Small 200 amp box help!

Hey guys!

I am buying a house with a 200amp service panel, because of the actual space on the wall due to pipes and joists, they put in a small box with 20 breaker spots and of course There are 5 double tapped breakers. I want to put a similar or sub panel right next to it, any suggestions on the breaker size to feed this panel? The house is 1500 sq ft. the usual equipment, nothing crazy, I also plan to get a generator in the future, I would not be doing the wiring for that, but is there anything I could get panel wise that would make it easier to wire a generator? Please be kind, thanks in advance!!

Milford, NH
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Since you are planning on getting backup generator get a panel that supports it and put backed up loads on the new panel and connect non critical loads on the old panel.

The size of the sub panel needs to be based on how much stuff you want to run through it. Given that 100A service is the minimum for residential service that size panel will be readily available and probably the cheapest. Just to be clear the minimum rating does not apply to sub-panels, you are free to use whatever size you want.

I'll leave it to the pros for more specific advice.


LXI 483
O Fallon, MO

1 recommendation

reply to jhf
Sub-panels are a mess. Especially when you start piling them on top of each other. I'd avoid it if possible.
A 200A 20/20 is a rarity (100A 20/20 is common). They do exist - only buffoons use them.
You probably have a 200A 20/40 panel that requires the use of tandem breakers to get the "maximum" circuit count (in the olden days, resi panels were limited to 42 circuits).

You can also get quad breakers (really just 2 tandems) that keep the 240V breakers from hogging 4 circuits (2 spaces). While these are expensive, they are MUCH cheaper than unnecessarily replacing a panel.

I can't tell you how many unscrupulous electricians will go into someones house with a 20/40 panel and tell them they need a new panel.

Adding a generator is a bridge you'll have to cross later. Sub-panels make adding a generator a PITA.

In the off chance your 200A panel really is a 20/20, then you should probably have it replaced rather than dick around with a sub panel. Have a licensed electrician come up with a workable solution on the location.
...or the sheriff will grab ya and the boys will bring you down. The next thing you know, boy - oh you're prison bound...

Chuckey, TN

1 recommendation

reply to jhf
Click for full size
I was in the exact same situation. 20/40 panel and needed a subpanel for a generator. I ended up adding a 150 amp subpanel that supported 30 circuits. My main panel is a Siemens so I went with another Siemens panel. Moved all critical circuits that can be fed by a generator over to the subpanel and left the big stuff like heat pump and stove on the main panel. Hooked everything up to the subpanel with combination arc flash breakers. I feel much better knowing they are there and highly recommend them.

To hook up the generator I ran an underground wire from an external garage that houses the generator to the sub panel. I used a back feed 30 amp breaker and a generator isolation switch. When the power goes out, I go out and turn on the generator. Then I turn off every circuit on the sub panel. Turn off the main breaker on the sub panel and then turn on the back feed breaker so that the sub panel is now energized from the generator. The gen isolation switch is a must and it prevents both the main power and the generator from being on at the same time. I wired in a monitor panel that shows voltage and frequency and amp load. I turn on circuits in the house, making sure that I don't exceed 30 amps and trip the breaker.

Also you will need a way to know when the main power comes back on so that you can turn off your generator. After moving everything over to the subpanel, I wired in a new lighting circuit in the room that houses the panels. The lighting circuit is hooked into the main panel. There is a hard wired alarm hooked up to this light. Whenever the generator is running, I'll turn on the light. It won't come on unless the main power is restored. Then I'll know that the main power has been restored.

Lanett, AL
That's a really cool looking meter. Where did you get the parts for it from? I assume the load runs through the meters to give the amp readings?


Cedar Rapids, IA
Agreed it does look pretty awesome. I imagine it's not running all the load through it, rather using an inductive coil around the supply line to measure the amps, and just the wires from that running to the ammeter. There would be 120V running to it likely, but minuscule current for the voltmeter.

Chuckey, TN

2 recommendations

Exactly. I have two induction coils around the wires feeding the panel. Here is the model: »www.amazon.com/gp/product/B00INS···F8&psc=1

Used a plastic box from Lowes. Cut the openings to mount the meters. Bought a frequency counter off eBay. The whole thing is fed from a 20amp 240v breaker. Ran 1 amp fuses to each 120v leg since the meter will never draw 20 amps. The breaker acts as an on/off switch.

Northport, NY
reply to Sly
So im a bit confused. You do have an interlock or back feed preventer?

Chuckey, TN
It's a mechanical interlock: »www.amazon.com/Siemens-ECSBPK05-···ECSBPK03

Of course depending upon the panel someone has, a different interlock will be required.

reply to jhf
Even if it is a 20/40 - consider larger, rather then a sub-panel...

I've got a 100A service at my house, and with a finished basement and a few other things, I've had to add a few tandems to my 32/64 panel.

I'm not pushing the mains at all; it's just real estate in the panel that's at a premium - dedicated plug for the kegerator, dedicated plug for the bar fridge and wine cooler, basement lights and plugs; basement bath, hot tub, A/C, etc - it adds up fast!

A couple years ago, I saw a guy with an 42/84 panel at his house - while I thought it was overkill (and it is) - I can't disagree with his thought process!