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Goldhedge · Jul 14, 2007, 07:51 PM

Got a 3rd car garage. Installing 4 wall plugs - double-gang. That's 4 plugs per box.

Anyway, I'm using 12 ga wire to do the job. Want 20 amps to power tools with. Don't want to 'run out' is what I'm thinking. The 'extra plugs' are for lights to see by, or any thing else that might need power. Got a drill press, band saw, table saw (110vac), a grinder, and a power sander. Not all will be running at the same time.

I have a 200 Amp Cutter Hunter service panel. Just checked the panel and apparently, I can only use so many 20A ckt breakers. Most in use are double breakers too.

I have access to one 20A breaker. Another 20A breaker won't push down because the center terminal being wider there than below. Got lots of room in there, but they are 'reserved' for bigger breakers.

The question is "how many double-gang outlets can one put on a 20A circuit?

I don't think any of the tools draw 20Amps. I'm just looking to do it right. Some day, the 'next owner' might need some power in the garage. It's a 'man cave' you know!

From the national electrical code I just happened upon:

Q. What is the maximum number of duplex receptacles on a two-wire 20 ampere circuit?
Section 220-3(c)(6). The NEC does not have a specific rule that says 10 receptacles on a 15 ampere circuit or 13 receptacles on a 20 ampere circuit. For 15 ampere circuits, the calculation is as follows: 120 volts x 15 amperes = 1800 VA/180 VA = 10 receptacles, and for 20 ampere circuits, 120 volts x 20 amperes = 2400 VA/180 VA = 13 receptacles.

* Many people think that when calculating the number of receptacles the load should be reduced by 80%, but this is not the case! Yes, the NEC limits the load on receptacle circuits to 80% for portable appliances [210-23(a)] and, yes, the maximum continuous load on a branch circuit shall not exceed 80% of the circuit rating (protection device) [220-3(a) and 384-16(c)], but these rules don't apply to the number of receptacles per circuit. I wish the NEC were more specific, but it's not.

National Electrical Code Questions and Answers

Looks like I'm covered with 8, but would the local code be that different than the National?

Also, is this over kill for a garage? :)

tkrussell · Jul 15, 2007, 04:19 AM

The rule you found, one, is for non-residential circuits generla purpose circuits. Outlet circuits in a home follow a square foot rule and is for general purpose lighting.

The 180 VA rule is widely used as a guideline when looking for the maximum outlets on a circuit.

You however, do not have what can be considered as general purpose. The outlets are for a specific purpose in a specific location. If the tools that will be used are small and random, the 180 VA/outlet, and this can be two outlets on one duplex, you should be fine. If there is an outlet for a certain large tool, treat that outlet separately, and give that one outlet a separate circuit.

Good research on the NEC question/answer. It is a bit confusing as it touches upon a few issues, as it is written by and for electricians Think you understand it?

On the load issue , most local codes should be in line with the national code, I have never found any local that was different, but, as I mention in my Read This First post, and my signature, always check with local codes.

Goldhedge · Jul 15, 2007, 11:45 AM

Thanks for the reply.

I happened to run into an electrician friend today and he said it would be easy to put in a 50A subpanel next to the main. Then run 8ga wire between them. I could then add all the breakers needed and be within code.

I'll do that.