Garage wiring questions

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  #1  
Old 05-15-05, 10:07 AM
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Question Garage wiring questions

I'm finishing my 3-car garage. I'm an automotive enthusiest, so it will get a bunch of 110V outlets, a couple 220V outlets, and a couple banks of 8' T8 flourescent fixtures.

I'm trying to figure out how many 110V outlets I can run on a circuit, and what size of breakerand wire to run. I figure I'll put in 8 to 10 outlets.

Also, what size of wire/breaker for my lights? I want to put in probably 10 8' lights, two rows of 2 and two rows of 3. Each row will be on their own switch, and the switch boxes will be split up with 2 switches on opposite walls.

Thanks for the help!!
 
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  #2  
Old 05-15-05, 10:37 AM
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You can put as many receptacles on a breaker as you want. That's not the issue. The issue is what you want to plug in and use at one time. A 20 amp circuit can supply 2400 watts. That can be split between one one device, or as many as you can plug in, but you cannot exceed 2400 watts.

If it were my garage, I would run 2 or 3 20 amp circuits for receptacles, alternating every other receptacle (or every third receptacle) on the same circuit. Remember that these receptacles need to be GFCI protected.

As for 240 receptacles, these are better run for the specific device that needs 240 volts. What do you have or anticipate using that needs 240, and what are it's current requirements?

As for lights, I would say to put them on a single 15 or 20 amp circuit. 15 amp because it's easier to work with.


However, there is much more to deal with. Is this garage attached or detached? If detached then you will want a sub panel. If attached, you still might be better off with a sub panel.
 
  #3  
Old 05-15-05, 09:12 PM
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Originally Posted by racraft
You can put as many receptacles on a breaker as you want. That's not the issue. The issue is what you want to plug in and use at one time. A 20 amp circuit can supply 2400 watts. That can be split between one one device, or as many as you can plug in, but you cannot exceed 2400 watts.

If it were my garage, I would run 2 or 3 20 amp circuits for receptacles, alternating every other receptacle (or every third receptacle) on the same circuit. Remember that these receptacles need to be GFCI protected.
Hmm, wasn't aware that GFCI was required. Thanks for that tip. The lights don't require GFCI protection, right?

I have no clue what the current draws from typical automotive and woodworking tools are. Is there a good online referrence that list some standard current draws?

As for 240 receptacles, these are better run for the specific device that needs 240 volts. What do you have or anticipate using that needs 240, and what are it's current requirements?
Right now all I have is a compressor that I will convert to 240. I'll have to check what the current draw is, but I'm sure it's not too high since it's currently running on 120V.

As for lights, I would say to put them on a single 15 or 20 amp circuit. 15 amp because it's easier to work with.
So I can put all 10 lights on one 15A circuit? I wasn't sure how to figure this - I didn't know if I needed to account for startup current spike like you do with electric motors.


However, there is much more to deal with. Is this garage attached or detached? If detached then you will want a sub panel. If attached, you still might be better off with a sub panel.
The garage is attached. The breaker box is set up for 200-amp service. Normally they do 100-amp, but I told the electrician who wired the house what my plans were, so the builder ok'ed him to put in a 200A box.
 
  #4  
Old 05-15-05, 09:21 PM
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To address your question about guages of wire - here is the rule

14 guage wire - 15 amp max
12 guage wire - 20 amp max
10 guage wire - 30 amp max

Anything above 30 amps check with you local Lowes/Home Depot/ Ect.

In a work shop situation I perrsonally would never use less than 12 guange wire. Even thogh something like the lights for example might do just fine on 14 guage wire, you have to think about what if you decide to add more lights later. For the outlets I would have 12 guage wire on 20 amp curcuits.

Also one other VERY important point is DO NOT neglect to look at the raitings of the outlets and switches themselves. If you buy outlets rated at 15 amps you cannot put them on a 20 amp curcuit. It's going to cost a little more, but this way you should be able to plug in any 120 volt tool or device.
 
  #5  
Old 05-15-05, 09:27 PM
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A couple of things have caught my attention.

First of all how can you connect your compressor to 240 volts? You stated that it is right now on 120 volts. You can't just decied to change to higher coltage like that.

Secondly GFCI is not required for the lights.

And thirdly if you look at the box the lights come in it will tell you the ammount of current the lgiht will use. Multiply that ammont by the number of lgihts to tell you how big a breaker you will need. Also you did mention about having the lights in rows. I too would recommend seperate switches and put each on seperate breakers to break it down some. Keep in mind this - I one sting of lights trips the breaker then you will be in the fixing the problem. Yes you can plug in a portable light, but it is much easier just haveing other working lights.
 
  #6  
Old 05-15-05, 09:29 PM
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Sorry - a little too quick on the keyboard -

If one string trips the breaker you will be in the dark.
 
  #7  
Old 05-16-05, 04:47 AM
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In the USA it is perfectly acceptable and within code to place 15 amp receptacles on 20 amp circuits, as long as there is more than one receptacle on the circuit, which includes using one duplex receptacle.

As for the lights tripping the breaker and leaving you in the dark, that is a possibility, but a remote one. So remote that I wouldn't worry about it. The main reason a circuit breaker trips is because of a user induced overload (ie someone tried to pull more current than the breaker allows). A properly run circuit with only lighting on it will not have that problem. GFCI protection is not required for lights.

GFCI protection is also not required for special purpose receptacles that you cannot access for general use. This would include garage door openers where the receptacle is in the rafters (near the opener), refrigerators and freezers where the receptacle is blocked by the appliance. (Note, some inspectors will requires that these receptacles be single instead of duplex, but others argue that the appliance in the way prevents their use for something else.)

If your compressor can be converted to 240, it will draw roughly half the current it now draws at 120. The directions will tell you what that current is. You will need a breaker, receptacle, plug and cord for that current. The wire for that circuit can be larger than it needs to be.

If you want general purpose 240 volt receptacles, I would suggest gearing them toward 30 amp. You can always make the breaker smaller and use a different receptacle. It's not always easy to replace the wire.
 
  #8  
Old 05-16-05, 07:43 AM
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Thanks guys, lot of good info here!!

When I get closer to wiring it up I might draw up a rough schematic and post it up to see if you guys think I'm doing it the best way.

I have some 12/2 wire already, I'll just use that up first then go with whatever else I choose.
 
  #9  
Old 05-16-05, 09:42 AM
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Originally Posted by racraft
In the USA it is perfectly acceptable and within code to place 15 amp receptacles on 20 amp circuits, as long as there is more than one receptacle on the circuit, which includes using one duplex receptacle.
It may be within the code, but it not a very smart thing to do here. Think about the situation - a work shop. By keeping all of the outlets at 20 amps you allow for heavier duty tools to be used.
 
  #10  
Old 05-16-05, 05:41 PM
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tpaairman,
I've been around lots and lots of power tools. A tool with a 20 amp, 120 volt plug is fairly uncommon. I remember one compressor and maybe one table saw. Most tools that require this much power are available in 240 volts. I'd spend my money on a little better quality 15 amp receptacle rather than buying a whole bunch of 20 amp ones.
 
  #11  
Old 05-16-05, 07:51 PM
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Originally Posted by Phil H
tpaairman,
I've been around lots and lots of power tools. A tool with a 20 amp, 120 volt plug is fairly uncommon. I remember one compressor and maybe one table saw. Most tools that require this much power are available in 240 volts. I'd spend my money on a little better quality 15 amp receptacle rather than buying a whole bunch of 20 amp ones.
Ya, I don't have anything like a table saw, I'll just put in 15A receptacles and wire for 20A. If I or the next owner want to run something bigger some day, the receptacle(s) can be replaced.
 
  #12  
Old 05-17-05, 12:56 AM
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Personally I would use 20 amp receptacles on all 20 amp circuits for a couple of reasons.
First, since I would only use pro grade, and not the cheap devices, the price difference is minimal. But mostly because there are many household appliances and tools that are rated at more than 12 amps and the NEC limits a cord and plug connected load to 80% of the receptacle’s rating. Although, the majority of this equipment comes with a 15 amp plug, technically a 1800 watt hair dryer, microwave oven or a 13 amp saw should not be plugged into a 15 amp receptacle.
 
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