A question about A/C combination disconnects.

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jaylectricity

jaylectricity

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Location
Massachusetts
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licensed journeyman electrician
I'm installing two 220V A/C midsplits in a bowling alley on Saturday. He wants me to use combination disconnects for each of the units to to give him some power outside.

The disconnect shown here:
http://www.squared.com/us/products/load_centers.nsf/unid/9359F3D62420A9B985256A630072D297/$file/acdisconnectFrameset.htm

Says the gfi is "factory wired to ground." Do I need 12-2(+Ground) or 12-3(+ground)? I'm using BX in a suspended ceiling The runs are 125 and 200 feet to each side of the alley, so the difference is the cost of the wire is relatively substantial.

Any help would be appreciated. I'm sure this is a no-brainer to somebody.
 
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These disconnects typically require a separate circuit for the GFCI receptacle. If you're looking to run just one cable then I would run a 4 wire cable. Two phase conductors for the single phase, 240 volts and the other phase conductor and neutral fro the GFCI receptacle. The EGC will be provided by the cable armor of the AC cable.
 
Jay, Trevor is correct; from the SqD site: 20A GFI Receptacle mounted to trim for easy wiring (requires separate 120V circuit) You'll only need 2-cond+gr for the receptacle's supply circuit.

If you only need 12ga for the AC units also, the 4-conductor cable idea may work $-wise, but if you need 10ga or larger, it won't be worth it. In that case, run separate cables to a J-box and nipple through the wall.
 
Thanks guys, the manual to the unit says 2 pole 20 amps. The unit wasn't on site to check the nameplate.
I don't do a lot of commercial work so I would hate to get caught with a bunch of MC that I couldn't use.
I think I think I'll be good with the 4 wire MC, my supply house has it for $305 for 250 ft. about $40 more than NM. Does that sound right?
 
Hm... then I got a price of $100 for 250 feet 250 coil and $300 for 1000 ft reel of 12/2 MC with ground. At half the price it sounds like I found a winner.
 
Jay, definitely get the nameplate numbers before buying wire. You need to cover the "minimum circuit ampacity" with the wire size.
 
If your using a 20 amp circuit for the unit why not use 1 phase wire from it for the receptacle? Plus a neutral.

I see the code allows this as long as it is connected to the line side of the disco. 210.63

On the other hand if the instructions for the disco required a separate circuit that would trump the code? Correct?

Then I would consider just adding a receptacle box and not use the combination disco. Depends on the $.
 
Then I could run 12-3 to each unit. Hmm...I'll have to consider that...once I get a definite on the nameplate that is.
 
Dennis Alwon said:
Before you jump the gun on that make sure you read art. 210.23(A((2)
Click to expand...

Thank you Dennis. That states that I would have to upsize the A/C circuit to at least 10 wire which would completely negate the reason for pulling 3 wire. He just accepted my price with me bringing two separate circuits to each disconnect, so I'm not even going to bother with the 3-wire method.
 
jaylectricity said:
Thank you Dennis. That states that I would have to upsize the A/C circuit to at least 10 wire which would completely negate the reason for pulling 3 wire. He just accepted my price with me bringing two separate circuits to each disconnect, so I'm not even going to bother with the 3-wire method.
Click to expand...
You're welcome
 
Circuits distance.

Circuits distance.

Do you need to consider voltage drop? If the runs are 125 and 200 feet that's a long way.
 
I considered it, but only for about 5 seconds. Tell me what the voltage drop is. The NEC doesn't require it, but if my circuit is riding on the brink of having to draw 20 amps because of a lower voltage, I wouldn't want to have to re-run the circuits to it.

I tried googling a way to come up with the answer, but most of the pages were for low voltage lighting.

All I need is a chart that says:

This size wire
@ this length
And this many volts
wiil experience this much voltage drop

From school I remember something about how much voltage drop over 1000' but I can't remember that either.
 
Thanks Trevor,

I used very liberal measures, (220 ft) for the longer one and the drop is less than 5% as noted in art. 210-19A Fpn 4 so it looks like I'm good.
 
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