220 Wire Guage help

[BSmith]

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

[kevin]

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.

[BSmith]

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

[Andrew Duane]

[BSmith]

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?

[BSmith]

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?

[Jeff Wisnia]

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

[BSmith]

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.

[bill allemann]

how is the feed circuit run to the outbuilding? e.g. underground conduit, underground NM cable, 3 exposed conductors like a service drop, SE cable, etc bill

[BSmith]

Underground, PVC conduit. The wire is unmarked as to what guage it is.

[Chris Lewis]

According to BSmith :

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.

[BSmith]

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?

[Joseph Meehan]

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?

[Chris Lewis]

According to BSmith :

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.

[gfretwell]

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.

[BSmith]

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.

[John Grabowski]

Did you specify to your electrical contractor what your loads were going to be? From what you describe a 100 amp panel may be marginal at best. A 100 amp panel is only good for 80 amps continuous load (3 hours or more). I have wired a number of TV and photo studios and I would have put in at least a 200 amp panel based on your load schedule. Not every electrician is familiar your type of operation. Your electrician may have sized it like a home, but I know that once the hot lights are on, those A/C units will be running continuously. Also, I would have installed three electrical panels; one for the electronics, one for lighting, and one for the mechanical equipment. It is best to have all of the electronic equipment come out of the same panel to keep ground hum to a minimum. Keep your dimmer racks away from all other equipment and out of the shooting area if possible. It's best if they are in their own air conditioned room or closet.

If the wire is in conduit, it may be possible to pull in a larger size if the pipe is a little oversized. Use copper wire.

I'm wondering if your A/C units will be big enough to handle the heat load.

[Chris Lewis]

According to BSmith :

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.

[Stan]

"BSmith" wrote in message news: [e-mail]...

Up to the point that the original poster said something about running a large lighting load plus AC units it sounded like a pretty standard (and more than adequate) installation for a domestic/home garage. Total capability (provided that wire is heavy enough) for say 15,000 to 16,000 watts, with perhaps some concerns about the starting currents of various motors? In one manner it wouldn't matter if those watts are 110 or 220 volt provided they are distributed within the capabilities of the individual circuits, and the total safe load not exceeded. I would have no trouble, as I do in my own garage running some lighting the occasional couple of kilowatt heater (it's cooler here!) and a few tools; in such an installation! probably including a 5 HP (220 volt) air compressor! But this isn't just a garage it's some kind of (film?) studio? That is; is it a business; which is being sub-fed from the main panel of a residence? Maybe should have had its own service? So I respectfully suggest that whoever made up the original specification erred when specifying a 'garage'? Rather like saying "Need vehicle to take some people to location 'xyz'". And then when a standard taxi capable of say four passengers arrives, exclaiming, "Oh but I've got a hockey team with 12 players and 2 coaches"! And finding it needs at least a stretch limousine or small bus? By the way what are the local municipality rules for operating a commercial enterprise in, or associated with, a residence? We had a problem with someone who was welding in his 'home' work shop. It was later determined he was operating a business and the town council ordered him to desist! Taking a guess at what 'some' home studios are used for; be a pity if the lights go out just when a 'climax' was being reached, because the electrical requirement was incorrectly specified before the start. Haven't seen anything yet that suggest electrician did anything not normal or standard? BTW high electrical consumption (even when people have tried to 'cheat' the meter) has, here given away quite a few 'grow ops'!

[barry]

Maybe a lighting expert can do something about huge energy waste of incandescent lighting. Win/win.

J