Forum Thread

running 2 220 volt outlets in series

dealgate 6,368 1,085 January 27, 2016 at 07:09 AM
I want to put a 220 volt air compressor into a room that has a 220 volt line that passes through the room to power a clothes dryer. The dryer is not in this room but the cable is very accessible since the room is unfinished. Is it within code for me add a junction box to splice into this 220 volt line and wire in my 220 volt compressor? So in essence I want to run 2 devices off of 1 220 volt circuit.

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#2
I'd say yes so long as the breaker and wiring are sized for at least the FLA of both devices. Now the wire was installed intending to only run a dryer but now you are adding something else. I realize that you probably wouldn't run the 2 co-currently, but I think the code will be a stickler on that.
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#3
Quote from Dr. J View Post :
I'd say yes so long as the breaker and wiring are sized for at least the FLA of both devices. Now the wire was installed intending to only run a dryer but now you are adding something else. I realize that you probably wouldn't run the 2 co-currently, but I think the code will be a stickler on that.
If this was 110, it would not be an issue, you can have as many outlets as you want (for residential) on one circuit. I am just not sure of the code for 220 if it is the same. The wire is sized to the breaker to protect the wire. BTW: Both could be on at the same time. And the wire and circuit is proper for either device. If they over-taxed the circuit, it would blow, but not hurt the wire.
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#4
Quote from dealgate View Post :
If this was 110, it would not be an issue, you can have as many outlets as you want (for residential) on one circuit.
Not quite. They don't define a hard limit like they do in the commercial code, but the load calculations basically stipulate the same limit the exception being when an "outlet" (includes ceiling lights, etc.) is going to use less wattage than the standard load calc.

Generally circuits for specific equipment aren't supposed to supply anything else. It's a bad idea to over load a circuit and count on the breaker tripping, they don't always react as fast as you'd like. What does the nameplate on your dryer list for it's power consumption (given in watts or VA)
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#5
Quote from dealgate View Post :
If this was 110, it would not be an issue, you can have as many outlets as you want (for residential) on one circuit. I am just not sure of the code for 220 if it is the same. The wire is sized to the breaker to protect the wire. BTW: Both could be on at the same time. And the wire and circuit is proper for either device. If they over-taxed the circuit, it would blow, but not hurt the wire.
no you can't have as many as you want! 10 max by code.
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#6
Quote from lancerstunning View Post :
no you can't have as many as you want! 10 max by code.
I'm pretty sure the NEC does not limit the number of outlets on a residential branch circuit. Can you post a cite?
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#7
Quote from dealgate View Post :
I'm pretty sure the NEC does not limit the number of outlets on a residential branch circuit. Can you post a cite?
Residential code does contain a max number of lights and outlets per circuit -- code is set and enforced by area so it can and does differ slightly in some areas but there is indeed a limit in all code-enforced areas. NEC would have nothing to do with local code as it varies. But I guarantee your locale has a limit should you ask. It is also common sense to not create too large of a circuit, imagine 25 outlets in a circuit all with devices on it and the draw you could potentially have.
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#8
Quote from eekthecat View Post :
Residential code does contain a max number of lights and outlets per circuit -- code is set and enforced by area so it can and does differ slightly in some areas but there is indeed a limit in all code-enforced areas. NEC would have nothing to do with local code as it varies. But I guarantee your locale has a limit should you ask. It is also common sense to not create too large of a circuit, imagine 25 outlets in a circuit all with devices on it and the draw you could potentially have.
The point of this post was not to see how many outlets could be crammed on a circuit. But since it came up, I would still like to see a cite that there is a limit on number of outlets on a residential circuit. My search of the NEC code says there is no limit.

Whether you have 1 outlet or 100 outlets on a circuit does not make it any safer or any more dangerous.
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#9
Quote from dealgate View Post :
My search of the NEC code says there is no limit.
It's in the load calculations, somewhere in section 220 iirc. It isn't a hard numeric limit like you find in elsewhere. In practice, most people still follow the same rules as commercial most of the time (15A*120*.8/180W = 8 receptacles / 15A 120 V circuit).

For your specific question regarding the dryer the most relevant section is 220.54
In a typical residence with 1 dryer, you can't apply a demand factor to the power consumption of the dryer. The code specifies a minimum 5KW circuit (20.8 A @ 240V) or the nameplate rating of the dryer (which pretty much always specifies 30A / ~8KVA) whichever is higher.

If you do put a compressor on the same circuit as the dryer you can be pretty confident it's a code violation.
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Last edited by jkee January 28, 2016 at 12:08 PM
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#10
Quote from jkee View Post :
It's in the load calculations, somewhere in section 220 iirc. It isn't a hard numeric limit like you find in elsewhere. In practice, most people still follow the same rules as commercial most of the time (15A*120*.8/180W = 8 receptacles / 15A 120 V circuit).

For your specific question regarding the dryer the most relevant section is 220.54
In a typical residence with 1 dryer, you can't apply a demand factor to the power consumption of the dryer. The code specifies a minimum 5KW circuit (20.8 A @ 240V) or the nameplate rating of the dryer (which pretty much always specifies 30A / ~8KVA) whichever is higher.

If you do put a compressor on the same circuit as the dryer you can be pretty confident it's a code violation.
OK this helps. I'll probably just run a new 220 volt line just for the compressor.
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#11
Quote from dealgate View Post :
OK this helps. I'll probably just run a new 220 volt line just for the compressor.
Just for clarity, building wiring is all parallel not series. Think of it as 2 parallel lines with outlets in between tapped into both. If it were series, you'd have 1 wire between each outlet instead of 2 (+ground) and the voltage at every outlet would be different and dependent on the other series loads.
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#12
Quote from dealgate View Post :
The point of this post was not to see how many outlets could be crammed on a circuit. But since it came up, I would still like to see a cite that there is a limit on number of outlets on a residential circuit. My search of the NEC code says there is no limit.

Whether you have 1 outlet or 100 outlets on a circuit does not make it any safer or any more dangerous.
NEC doesn't offer local code enforcement for that. Just because the NEC doesn't list it doesn't mean it isn't code in your locale.

Some locales have 8 has a hard set rule, some 10, and some 12. I don't believe I've seen more than 12 anywhere but it could and probably has been a possibility. But there is definitely a code limit for a series and NEC is not the source of that limit -- at least I'm not aware of any listing in the NEC as this is a local code enforcement option. Hopefully that clears up the confusion.
Quote :
Whether you have 1 outlet or 100 outlets on a circuit does not make it any safer or any more dangerous.
Yes it does by load and real-world application of load. There isn't a scenario that is applicable to the real-world where you could run 100 circuits and then say with certainty that the load distributed across those would not be extraordinary for the circuit.

Code enforcement takes into account the location and types of loads that apply to that location. IE: you are going to tie a refrigerator with a bathroom circuit, an electric stove circuit, and a living room circuit -- even if that is only 5 outlets.

Heavier load locations almost always get a dedicated circuit, which is what I'd do for your setup. You wouldn't want your dryer and compressor to send peak loads at the same time -- whatever that calculation is could be too high.
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#13
Quote from dealgate View Post :
OK this helps. I'll probably just run a new 220 volt line just for the compressor.
That is probably the best way to go. It's easier than running thicker Romex to the dryer; the really thick Romex is a bear to work with. And I don't know if your city would even let you run the two outlets in series anyway.
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#14
yes you can, do it
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