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Bill Park
adding a sub-panel


First post here.

What I think is a simple question, probably not unusual.

House built in the 1950s. Over the years, various owners have added to the electrical system. But the mains are plenty for the home.

My problem is that there are a few breakers which have more than one wire attached to them. I understand that this is a no-no. We have only lived here for two years, but we plan to move in a couple of years and I suspect that this wiring will not pass a home inspection (though it passed just fine when we bought the place!).

I want to correct the probem. Obvious answer seems to me to be a sub-panel. I want to do it correctly and safely.

Can I put a breaker in the main panel to supply the sub-panel, and run a heavy gauge 4 wire feed to that sub-panel, and keep it located close to the main panel?

Do I have to have a splice box, or can I splice the extra circuit feeds inside the mains panel? I am assuming that the wire on the circuits that I need to split out to a sub-panel will not be long enough to reach a sub-panel.

Are there size requirements for such a box, and are the splices required to be a certain type of connection, or may I just use wirenuts?

Do I need to isolate the neutral bar, to avoid 2 paths to ground?

I have a lot of experience with wire and voltage, I've been a stagehand all my life working with movies, theater, and concert power and the various voltages and connectors involved. But I am totally out of my element when it comes to homes and home wiring, beyond adding an outlet or ceiling fan, or changing a light fixture.

Thanks in advance for any help and advice,


Re: adding a sub-panel

My full answer seems to have been delayed by the sites spam filter. I would suggest you consider replacing some of the breakers with double breakers. They take up one slot but provide two separate breakers.

Timothy Miller
Re: adding a sub-panel

Howdy, how big is your main panel? i was faced with a similar question this last summer and we installed a larger service panel as after the wiring and sub panel cost the larger panel was a few dollars cheaper.

Moon Over My Hammy
Re: adding a sub-panel

The usual is to run a four-wire 120/240v feeder circuit to the remote panel two hots one for each 120 phase side, a neutral and insulated grounding conductor.

The distance and size (amps) of the feeder circuit, rating of the remote panel/bus and the OCPD determine the wire guage needed for the feeder.

Then home run the moved circuits to the remote panel. All splices have to be contained. It is important to balance both the main panel and the remote panel so you don't have unbalanced loads (which can cause dim or bright lights, low voltage/excessive current draw for motor load starts, etc.

Check with your local building department or hydro office for specifications and details it is the type of project that almost always requires a permit and inspection (very important to have especially if you're planning to sell in a few years). Most areas will allow a home owner to do the work with a permit and inspection but some will not, it depends. They might require you to do some electrical code updates on the circuits you move to the remote panel.

When we did this our first plan was to move some of the 240 appliances to the remote panel but our building department said if we did we would have to redo the wiring for those circuits and upgrade them to four wire circuits so we left them on the original panel, they would have required us to upgrade the wiring to the A/C outside too if we did that. We moved the receptacle circuits and lighting circuits instead. We were required to rewire some of those circuits that had undersized grounding wire in the BX and make multi-wire circuits regular branch circuits. We were required to upgrade the bedroom circuits to ARC fault protection (we did with a device outside the remote panel box at first but missed the deadline and had to get special breakers instead that was a costly mistake can't return installed used parts) and add GFCI protection (we did with special GFCI breakers) to the 2005 standards, was easy using special breakers instead of expensive receptacles. We also were required to make sure every receptacle and switch had grounding wire on those circuits, it wasn't too dificult and was nicer to replace them all at the same time since so many were old had paint on them and stuff. They also warned us about tamper resistant receptacles due to be required so we went ahead and got those in case we didn't pass the final inspection before the date deadline. We were doing some upgrades in the bathrooms anyway so we rewired each of them to two individual circuits and added an extra one in the master bath for the hopefully future jet tub. Held off on replacing the regular tub due to the economy and budget concerns but we are all set to upgrade in the future because we pre-wired for it. We left the garage and exterior lights and receptacles on the original panel so we didn't have to upgrade them.

We did have to get a kit for the remote panel to isolate the grounding and some kind of bus bar kit. Some of the splices for larger wires not allowed to use wire nuts have to use other devices depends on the size.

After all that work there was a problem with the incoming wires from the power company and there was an event that required us to replace the wires from the meter to the main panel and damage so we ended up replacing the main panel afterall. For whatever reason they did not require us to upgrade the wiring that they would have made us do if we moved those circuits to the remote panel but we did have to put the garage circuit on GFCI and GFCIs on the exterior receptacles and put bubble covers over them. Then we had to have bond wires from the water line to a rod also and another rod had to be put in by the remote panel and a bond to it.

If we had to do it over again I would have just replaced the original panel it would have been more money upfront but much cheaper overall.:mad:

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