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Old 01-26-2010, 09:43 AM   #1
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Garage outlets: 20A or 15A???


I'm getting ready to wire up some outlets in my garage. Should I install them on dedicated 15 amp circuit or 20 amp circuit. What dictates this?

The outlets will be used to power tools while finishing my hotrod (e.g. grinders, drills, bench grinder, drill press, etc)

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Old 01-26-2010, 10:01 AM   #2
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Garage outlets: 20A or 15A???


As best as I can tell from what DIY electrical experience I've had, there isn't anything that dictates when a 15 amp circuit must be used. The only thing I've seen has been where 20 amp circuits are dictated (such as for bathrooms and kitchen counter-top outlets).

So I believe the rule is that you can always wire a circuit for 20 amps if you want to... BUT, all of the wiring must meet the specs for a 20 amp circuit (which generally means #12 wire). So if you do wire the garage for 20 amps, you still have to run #12 wire to light that 13 watt CFL lightbulb by the garage door. You can't use #12 wire for all the outlets, then turn around and use #14 on the same circuit for the lights. Basically, the breaker must be sized for the weakest link of the circuit.

The thing I did was to add a "workshop" circuit to my basement. On this seperate circuit, I ran #10 wire (just for overkill), and installed a 20 amp breaker and 20 amp recepticals (the ones where one of the blades is shaped like a 'T'). The 20 amp outlets allow you to use power tools that require more than 15 amps... but so far I haven't run across any power tools I've needed to get that needed that much power.


Last edited by HooKooDooKu; 01-26-2010 at 10:04 AM. Reason: clarity
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Old 01-26-2010, 10:06 AM   #3
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Garage outlets: 20A or 15A???


Personal preference general use outlets 20 amp circuit. For lighting, calculate the load.
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Old 01-26-2010, 10:07 AM   #4
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Garage outlets: 20A or 15A???


For a garage where you will be using power tools use 12g wire & 20a circuit
Breakers are about the same cost, wire is a little more
I never run any 14g wire to outlets
Garage must be GFCI protected
I woudl do at least 2 outlet circuits, 3 would be better

Lights do a seperate 14g 15a circuit (1800w)
Unless you will have a ton of lights then do 20a & 12g (2400w)

#10 wire does not really buy you anything unless running a longer then maybe 100'
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Old 01-26-2010, 10:12 AM   #5
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Garage outlets: 20A or 15A???


My garage is only wired in a single circuit at 15a, while my dining room is 20a... I'll never understand why they did that. If I have a space-heater plugged in, I can't use power tools or the breaker will pop. It would be no question to me whether to set it up at 15 or 20. I would probably do several 20a circuits, so that you can use multiple high-draw things at once if you need to (space heater, grinder, dust collection system, high-powered lighting, etc).
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Old 01-26-2010, 10:41 AM   #6
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Garage outlets: 20A or 15A???


I wired my workshop 120v outlets with each a dedicated 20a circuit to two outlets in a double gang box. I have one 20a circuit to a few outlets in the ceiling for drop cords and work lights on reels.

Two 15a circuits - one for interior lighting and another for exterior lights.
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Old 01-26-2010, 10:45 AM   #7
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Garage outlets: 20A or 15A???


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Originally Posted by 47_47 View Post
Personal preference general use outlets 20 amp circuit. For lighting, calculate the load.
How do you calculate the load for lighting?

Here's what I mean by way of example:

I want to put X number of lights on a circuit. My plan is to install 40 watt bulbs in these outlets. Now a person COULD install 100 watt bulbs in these outlets if they wanted to. So do I design for 40 watts or 100 watts.
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Old 01-26-2010, 10:47 AM   #8
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Garage outlets: 20A or 15A???


So it sounds like it would be best to run a 20 amp circuit for my outlets. I already have my lighting on a 15 amp circuit, so I think I should be covered.

Thanks guys!
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Old 01-26-2010, 10:50 AM   #9
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Garage outlets: 20A or 15A???


By NEC code you design for the load
I use 13w CFL's & design for that load
But I usually allow enough spare wattage to cover putting a few 75w bulbs in

I like CFL's, but a future homeowner may like reg bulbs
We aren't planning on moving....but you never know
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Old 01-26-2010, 11:03 AM   #10
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Garage outlets: 20A or 15A???


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Originally Posted by HooKooDooKu View Post
How do you calculate the load for lighting?

Here's what I mean by way of example:

I want to put X number of lights on a circuit. My plan is to install 40 watt bulbs in these outlets. Now a person COULD install 100 watt bulbs in these outlets if they wanted to. So do I design for 40 watts or 100 watts.
Always design for the worst case scenario. Use the maximum fixture wattage as stated by the manufacturer when laying out the circuits.
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Old 01-26-2010, 11:10 AM   #11
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Garage outlets: 20A or 15A???


Many recessed housing fixtures can take up to a 150w bulb
All of the ones I use could take a 100w bulb or better
So planning for the Max capacity of a fixture can be a problem
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Old 01-26-2010, 11:17 AM   #12
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Garage outlets: 20A or 15A???


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So planning for the Max capacity of a fixture can be a problem
No, it would just mean you need more circuits - right? If you had 12x 150w lights, you could serve that with a 15a circuit, but nothing else (or 16 on a 20a circuit).

I don't think it would be wise (regardless of whatever code may be) to put in 18 lights on a 15a circuit and say "I'll just use a 100w bulb instead of the 150w max it says on the housing." Your wife/kid/future-owner won't know that it's not right ahead of time, and may go and replace bulbs with the full 150w that the lights say they accept, and then you have a problem.
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Old 01-26-2010, 12:09 PM   #13
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Garage outlets: 20A or 15A???


I'm not about to calculate my circuit on an imaginary load
I calculate based on true load, that's allowed by code
No way I'm putting 12 13w CFL's (156w) on a 15a 1800w circuit
I have more then 18 lights on my circuits
If a future homeowner somehow decides they need 100-150w bulbs they will need to rewire
Each lighting circuit is completely mapped with which lights/fixtures are on each circuit

There isn't a single 100w light bulb in my house
In fact there isn't anything over a 60w bulb, almost the entire house is CFL or LED

My wife hasn't changed a light bulb in over 6 years
In additon residential lighting is not continous, very rare we have more then 500w of lights on spread across the 3 lighting circuits I have
And in the main room the 2 lighst we use most are lamps plugged into an outlet circuit
Same with the bedrooms
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Old 01-26-2010, 12:27 PM   #14
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Garage outlets: 20A or 15A???


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I'm not about to calculate my circuit on an imaginary load
I calculate based on true load, that's allowed by code

I have more then 18 lights on my circuits
I wouldn't call it "imaginary load," I'd call it "potential load."

If it is allowed to do the way you're doing it by code, I suppose that is fine. Even then though, 18 lights on a single circuit seems like a lot.

Quote:
Originally Posted by Scuba_Dave View Post
My wife hasn't changed a light bulb in over 6 years
If you get hit by a bus tomorrow, will she know that she is limited to using 13w fluorescent bulbs only? What if she wants it brighter and decides the 26w screw-bulbs are better?


I'm not nit-picking your situation, but in general I think it is a better idea to over-provide power to the "true load" than to not be able to meet the potential load. This is getting off topic now.

Last edited by hyunelan2; 01-26-2010 at 12:30 PM.
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Old 01-26-2010, 12:35 PM   #15
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Garage outlets: 20A or 15A???


I have over 100 light fixtures/bulbs in my house (counting each bulb as one) - not counting table lamps
Its not practical to wire for what someone may do
Incandescents are required to use 30% less power in the next few years
The current code is outdated with CFL's & LED's becoming used more & more

Someone who has all LED's could actually run an entire house off a single 15a circuit
My most "heavily" loaded circuit, if every light was turned on - would use 1267w out of 1800w available
If I went by Max fixture watts (100 max- not 150 on recessed) that number would be 2840 watts - once the addition is completed & all fixtures installed

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