220 Wire Guage help

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We recently had a home built and I'm checking on what I think is a mistake on the electricians end. Along with the house, we had an exterior garage built. In this garage a sub panel contains two 60amp 220 breakers (for two 220 60 amp line), also a water heater which they have on a 30 amp breaker, along with this there are three 110 20 amp breakers and one15 amp breaker. First on the main panel of the house this sub panel is only protected with a 100A Breaker...this can't be correct ight? What guage wire should be run out to this exterior garge, it's about 75 ft.. I friend of mine told me it look way under guaged but we couldn't find the guage labeled on it. What should be the proper guage copper wire to run to handle two 60 amp 220, a 30 amp 220, three 20 amp 110, and one 15 amp 110. Thanks
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A 100A breaker is fine. A 15A breaker would be allowed too. Just think about why the breaker is there in the first place.
Many houses have 100A for the whole house. Unless you have some special needs, 100A for just a garage is more than you will ever need.
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Hi This isn't a typical garage, we are running some High Wattage Lights (a bunch of 100 watt lights) which we are running off one of the 220 60amp circuits and two 2 ton AC units running off the other 220 circuit. In most cases , these will all be on at the same time. So not even counting the water heater, We could be pulling over 100 amps with the lights and AC units....The Garage is actually be used as a Photo Studio and is good size (near 1200 sq feet). I should have maybe explain how it was being used be I would have thought they would caculate the FuseWire on the Max that can be used. Thanks
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The real issue is what the wire is that runs to the subpanel. Is it sized to handle 100 amps? If not, you'll need to resize the breaker. Other than that, if it doesn't trip from your loading, and you've calculated all the "constant" load factors correctly, you're OK.
BSmith wrote:

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What guage wire should this run be? I don't understand how a 100 amp breaker will not trip if your pulling over 100 amps at one time?
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What guage wire should this run be? I don't understand how a 100 amp breaker will not trip if your pulling over 100 amps at one time?
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Andrew Duane wrote:

Right, and #3 AWG copper ought to be large enough for a 75 foot run, you'll only drop about 2 volts when drawing near the full current rating of that 100 amp breaker.
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat \'57 EE)
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I'm still unclear as to why only a 100A breaker, it still seems to me if the lights and AC units were on, along with what ever devices, why wouldn't the 100 A breaker trip, specially when the lights/AC units are first kicked on? At times we will be pulling more electric than most homes use.
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Actually, your intended load appears to be under 50A at 240V. Eg: Four tons of A/C will be drawing somewhere in the neighborhood of 20A-40A at 240V (rule of thumb: somewhere around 1300W/10,000 BTU, a ton is 12,000 BTU), and 20 100W lightbulbs will only add another 10A or so.
The 100A breaker is sized to protect the subpanel feed. #4 (or larger) copper is good for 100A. The subpanel breakers may add up to considerably more than 100A, but the 100A breaker limits the _total_ instantaneous usage to 100A.
The fact that you put a device on a 20A breaker doesn't mean that it actually consumes 20A, only that the circuit won't deliver more than 20A.
Check the plate amp ratings on the A/Cs (of actual _usage_, not what it says the circuit should be sized as) and figure out the total of other things will be.
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Chris Lewis, Una confibula non set est
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The wattage lights were running are 1000 Watts each, at time we may be running very close to using the entire 220- 60 amps (this we know for sure). The AC units are running just about 20A a piece, water heater I don't know. The extra 20A left over from the 60 60 amp circuit will later be used to run a 1 ton AC unit in another structure to be built later. The Lights, AC units and other misc equipments (computers and such) will all be running at the same time. This is my concern all this will be running togeather?
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BSmith wrote:

Keep in mind that a 100 amp 240V supply will power 200 amps of 120V load. I suspect that is where your math is getting confused.
You still need to find out how long and what gauge that supply line is.
BTW what are you doing in that garage, growing pot?
--
Joseph Meehan

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I'm not getting a very clear idea of what breakers you have - your original description was quite confusing. How many 1000W lights have you got? (you originally said 100W)
You'd need 14 1Kw lights to "fill" a 240V 60A circuit. Are you _really_ running them directly off a 60A circuit - with #6 wire to each fixture? Unless these are special direct wire fixtures, this is a code violation.
Is it _two_ 60A circuits (total four breakers) or one (2 breakers) etc.
If the water heater circuit was chosen as the absolute legal minimum for the heater, a 30A breaker means that it draws between 16A and 24A. Probably the low side. Most water heaters (unless deliberately upgraded to larger "optional" elements) are in the 2500-3200W range (eg: 10A-15A), but the electricians should be wiring them for the max wattage elements permissible in the equipment (usually 4500-4800W, 20A -> 30A circuit).
I'm going to assume 15A for the heater.
So that's 40A for AC, 15A for water heater, another 10A for a future AC, leaving you 35A/240V for the lights and whatever else. Not knowing how many of these lights you have, can't tell what you really have left.
My garage was wired with 100A @ 240V. The major equipment is two 240V heaters rated at 20A, plus (at most) 30A at 240V or so with maximum simultaneous workshop tools running (saw or planer under heavy load, DC, compressor, and IR spot heaters running), plus maybe 10A for lighting. So, I might be able to make an instantaneous 80A if I worked at it.
You might be somewhat close, depending on how many lights you have.
With that many lights, no wonder you need the AC.
--
Chris Lewis, Una confibula non set est
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We will be running about 12 1000 watt lights, actually some will be 650 watts but in total it will equal 12-13 1000watt lights. Tes that is why we are running the two AC units. The studio is actually a Video Studio and we need to keep it Cooled down to about 68 degrees (Arizona tempatures of over 100 degrees). The lights are wired into special 220 lighting dimmer panels with 18 ACX outlets that control a max of 18 lights, which combined can handle 60 amps at 220. Off the 110 20 amp outlets we'll be running 4 production video camera, computers ,monitors, and more. We may occasionally may need to sttill run an extralight or two off the other 110 20 amp outlets.
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Oh. Yikes. If your garage circuits are all fed off one 100A feed, it's definately undersized, and should probably be closer to 150A or even 200A. Indeed, I'd wonder about your main panel too. It better be at _least_ 200A.
I'd make the assumption that the electrician didn't understand the occupancy ("simultaneous usage") factor in your case and miscomputed.
[If your garage was a house, code would probably automatically have made it 200A]
You have, I think, two choices:
1) Make the assumption that the ACs will be turned off during "lights/camera/action". You do want to avoid the noise, right? If the ACs are off during lights up, you have enough ampacity.
This is awkward and error prone. You'll probably make mistakes occasionally. Directly interlocking the lighting such that turning the lights on kills the AC will probably damage the AC.
2) Reengineer the feed, eg:
- get the electrician back in and get him to redo his calculations and come up with a way of dealing with it.
- One way would be to run the two 60A/240V circuits seperately from the existing subpanel feed.
Indeed, this sounds like it should be designed as "commercial" space, which means lots of 120V circuits with only a receptacle or two apiece (the production lighting being separate from that).
A real lighting engineer may be necessary to redo this properly.
--
Chris Lewis, Una confibula non set est
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Maybe a lighting expert can do something about huge energy waste of incandescent lighting. Win/win.
J
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snipped-for-privacy@sme-online.com wrote:

yes, since most TV studios have switched to electronic ballasted fluorescent tubes for much if not all of their lighting, why shouldn't you do the same. Area lighting with fluorescent, spots with incandescent/halogen.
linear tubes are available with 98% color rendering accuracy, see this one for example
http://www.1000bulbs.com/product.php?productU
Electronic ballasts cuts overall fixture power by about 20%
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Yes your right, it's in our plans. One thing is we own all these lights now, they are moved over from our old studo and all payed for. The lights you are talking about are called KinoFlo, they are great, but very expensive. We are going to move i that direction, but for we need to use what we got. Also Kinoflos are great, but not always the answer, for certain lighting they are too soft and flood the set too much. Within in the next few years we arelooking at opening a bigger studio off my property, this we would utilize mostly Kinoflos.
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On Thu, 18 May 2006 17:24:15 -0000, snipped-for-privacy@nortelnetworks.com (Chris Lewis) wrote:

Not unless thgis is the main feeder for the whgole house. If it is a sub panel you can't use 310.15(B)(6)
#2 is a better choice but you could use #3 if you can find it.
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Slow down there BSmith...
The original question seemed to be "is my wire undersized for my panel, given that the wire size is not known?" to which the answer is "who knows? what's the wire size?".
There was also a side question about if 100A breaker at the main is okay for feeding a panel with more than 100A of cumulative breakers, to which the answer is "yes, it is fine and completely typical." Just take a look in any home's main breaker box. My house, e.g., has 100A feed and 100A main breaker, but about 300A worth of breakers in the main panel.
Two 2-ton AC units on 220 should gobble up about 30A or so. That gives you 70A * 240V = approx 17 kilo-watts worth of illumination, which (to my non-photographer mind) seems like a hell of a lot of light.
Now if you do actually need more than 100A, you really needed to tell your electrician that upfront, and pay extra for a much heavier circuit. At this point nothing can be done but rip the whole thing out and start over. I'm pretty sure you aren't allowed (and for very good reason) to just add a second circuit to get more power.
-Kevin
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BSmith wrote:

High wattage lights? Grow lights for pot?
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