Sub-Panel Ease..?


Old 04-30-07, 10:54 AM
Thread Starter
Join Date: Apr 2007
Posts: 31
Sub-Panel Ease..?

I want to add a sub panel specifically for 240 volt appliances in my garage.
There is a 100 amp box in the utility room 15 feet away basically on the same wall I would like the sub, so I assume this would not be too difficult. The box that already exists (in the utility room) the home depot guy says is no longer produced. (It is the type with the longer (longest?) type breakers and two hot poles seperated by about an inch (or a little more). Sorry I do not know a better way to describe this box, but I assume there are not too many discontinued boxes like this one. (It is from 1981 or 1982).
The box looks and works great so I do not want to replace this one but would like to put a 50 amp (dual pole..?) breaker in this (main) box and run two hot wires from it to the newly constructed box to create a 50 amp 240 volt sub panel. Is this possible, the correct way to do it, and as easy as it sounds?
Thanks you.
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Old 04-30-07, 02:22 PM
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Join Date: Sep 2005
Location: USA
Posts: 4,291
What's the brand of the breaker box you're describing. If you provide the manufacturer and model number, I'm sure someone here will be able to provide a lot more details. Also, even though the box may be discontinued, you can probably get replacement breakers for it (maybe not at HD, but at an electrical supply house). If it's that new ('81-'82), you'll have no problems.

Do you have open slots in your current panel? If it's only 15' away, that's your easy answer.

If you do need a subpanel, yes, it's pretty easy, but there are a lot of details. Get yourself a good book, and read around on this site too. You need to properly size your wires, ensure you have a 4-wire feed (2 hots, 1 neutral, 1 ground), separate the neutral bar from ground in the subpanel, etc.

Good luck - and feel free to ask more questions!

Old 04-30-07, 04:29 PM
Join Date: Oct 2006
Location: Wilmington
Posts: 4,219
1. Disregard 90% of the info from big box people!!!!!!!!
2. If you have a 100A service, and you want to add 50A, you likely need a main panel upgrade to at least 150A.
3. If you are asking these questions here, I would recommend you consult a professional.
Old 04-30-07, 04:31 PM
Join Date: Apr 2006
Location: New Bern, NC
Posts: 1,623
just because you have spare spaces in your panel, does not mean that you have the spare capacity for adding extra circuits. The calculations do not work that way.

We need to do a full load calculation on your home, then determine how much is available for expansion. I doubt that you have much left.

BTW asking the clerk at the big box store about how to wire your home is like asking the cash register person at the drug store about how to have your teeth fixed. She sells tooth brushes, she is not a dentist. He sells parts he is not an electrician.
Old 04-30-07, 05:02 PM
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,399
From the description it may be a Zinsco panel. It would be a funny thing if so because HD sells Zinsco-compatible breakers.
Old 05-01-07, 12:45 AM
Thread Starter
Join Date: Apr 2007
Posts: 31
Thanks for all the answers, I do not have a problem getting the breakers,

Just the box is impossible to find. (I dont need the exact same box for the sub as a I have for the main, I just thought it would be good to use the same type for the sub, and I really like this type better; don't ask me why.)
To respond to the question of full house loads, I have done most of the calculating. I have two 100 amp breakers in the outdoor (main) panel at the service disconnect (meter) with two sub panels inside: One upstairs and one down: one with 50 amps worth of breakers and one with 60. The one downstairs (the one I want to use) has 60 amps worth of breakers, but only 30-40 amps worth are ever used (some are for pumps, heaters, trash compactors and empty outlets that are never used).
So I figure I can put in a 50 or 60 amp dual pole breaker into this box (I assume that it is a 100 amp capacity box taking into account all the above information) and run 2 really heavy (I have yet to figure what guage) guaged hot wires from this breaker to create the new 240 volt sub panel. Is this as easy as this? Or am I missing something (besides finding the correct guage of wire to use and following the directions (included with the box?) for installing the neutral and ground wiring.
Old 05-01-07, 11:43 AM
Join Date: Apr 2004
Location: Ontario Canada
Posts: 1,767
You don't do a load calculation by adding breaker labels.
You at most add up the power drawn by all the actual or anticipated loads on each circuit and add that. At least you'd do an ideal by adding the fixed appliances to a per sq ft value (don't know off hand), to account for liginting and general purpose branch circuits.

If you can run a sub panel of that, you would run a 6/3 with Gnd to your new sub panel.

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