Is it kosher to gang 240v

MTboatguy

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I am just wondering, is it kosher to gang wire 2 240v plugs? I am running a 50 amp breaker through 10/2 wire to my plug on my compressor that is rated at 15 amps on start up and would like to gang another plug on the circuit for my heater that will pull about 21 amps, which comes out to 36 amps total load on a 50 amp circuit, looking at the math as long as I have secure connections I can't see where it would be a problem, with the 80% factor, it would still have 40 amps available to power both items and both plugs are wired with 10/2 wire which is the correct size for heat and such.

This sub panel is wired to home at the power box on the power pole and has a 100 amp breaker in the main on the pole, running through 2 gauge buried wire with a neutral and a ground. The compressor and the heater would rarely be running at the same time, but with 40 amps available, I can't see it tripping the breaker unless something odd happened.

Thanks
 

sam am I

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Hmmmm, I don't think they make 30A 240V receptacles that are made to "daisy chain" off of like 15/20A 240V duplex types are.

I could be wrong (I'm not a licensed electrician) but, going by the make of the hardware out there, I'd say no it's NOT ok, an addition run from the sub panel has to be made for an additional 30A 240V receptacle.


As mentioned, unless you're using 15/20A 240V duplex types.........

See 15R types (120V here) and how they're are wired off the main bus but can be duplex 15/20A and wired for 240V as per manu's 240V duplex type allow BUT, as seen the 30R and 50R types also tap the main but, manu's don't make/allow duplex in those amperes.

Just guessing though MT............
 
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Scott Danforth

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From my quick search....pulled from another site

There is nothing in the NEC that precludes multiple outlets off a 220 branch circuit.
I believe that the reason that you read "there can only be one" is that typically 220 supplies motors in the shop. Placing multiple motors on a single 220 circuit requires that the branch, and breaker be sized accordingly to run multiple 220 loads simultaneously.
The motors section of the NEC has covers this. There is a little flowchart at the beginning of the motors sections that guides you through it.
In a small shop though, it may be easier, and more cost effective to run seperate circuits depending on the layout, machinery involved and the local inspectors interpertation and application of the code requirements.

Long story short, start with your local AHJ
 

MTboatguy

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Sam, there is a 50 amp breaker, with a 15 amp 240 volt load and a 21 amp 240 load on a 50 amp circuit with the correct wiring for amps and 50 amp is fed by a 100 amp main power pole circuit, max amp draw from the compressor is just a bit over 15 amps on start up and the heater at full load is 20.83 amps, the total of the circuit is 35.83 amps and the 80% factor gives me 40 amps max so with my math and it is not new math, the gives us 4.17 amps headroom. The reason I asked, I want to make sure I am figuring this correctly.

Thanks.
 

MTboatguy

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I just measured it with my amp meter, drew the tank down to 20 psi and then turned it on, 16.56 amps when the motor kicks in and then it stabilizes at 15.13 amps while it is filling the tank.
 

jakedaawg

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Not sure what kind of compressor rig you have...mine comes on at 90 psi. You can tell a difference when it starts at 90 versus at 0 like when I drain the water out of the tank.

my shop, not inspected, has a 100 amp 240v line that feeds both my compressor motor and a receptacle for whichever welder I happen to plug into it. Never had an issue.
 

bigdee

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Nothing wrong with multiple outlets BUT there is in this case. 10/2 on a 50 amp breaker is OK on DEDICATED motor loads. However it is NOT OK to oversize breaker on resistive loads. If you were using 6/2 instead of 10/2 you would be fine.
 

sam am I

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Sam, there is a 50 amp breaker, with a 15 amp 240 volt load and a 21 amp 240 load on a 50 amp circuit with the correct wiring for amps and 50 amp is fed by a 100 amp main power pole circuit, max amp draw from the compressor is just a bit over 15 amps on start up and the heater at full load is 20.83 amps, the total of the circuit is 35.83 amps and the 80% factor gives me 40 amps max so with my math and it is not new math, the gives us 4.17 amps headroom. The reason I asked, I want to make sure I am figuring this correctly.

Thanks.

Ahhh, ok MT sry bout that, I read it wrong. Thought you were wanting to daisy chain directly off the back of a 240V 30A receptacle somehow for feed to another 240V 30A receptacle.:sleeping: long day........
 

MTboatguy

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Nothing wrong with multiple outlets BUT there is in this case. 10/2 on a 50 amp breaker is OK on DEDICATED motor loads. However it is NOT OK to oversize breaker on resistive loads. If you were using 6/2 instead of 10/2 you would be fine.

Hi Bigdee,

Could you expand a bit on this, I understand Resistive load and Motor load, the company that made the heater told me that putting the heater on a breaker between 30 and 50 amps would be fine using 10/2 wire, did I miss something?, does the resistive load actually generate more heat in the line or cause a larger draw than what is stated on the label of the heater. I am just trying to figure out what the ramifications would be on the 50 amp breaker.

Thanks, learning every single day on this, I am very comfortable with 120v wiring but have not done much in the 240v arena.
 

bigdee

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Hi Bigdee,

Could you expand a bit on this, I understand Resistive load and Motor load, the company that made the heater told me that putting the heater on a breaker between 30 and 50 amps would be fine using 10/2 wire, did I miss something?, does the resistive load actually generate more heat in the line or cause a larger draw than what is stated on the label of the heater. I am just trying to figure out what the ramifications would be on the 50 amp breaker.

Thanks, learning every single day on this, I am very comfortable with 120v wiring but have not done much in the 240v arena.

They told you wrong NEC does not allow a 50 amp breaker on a #10 branch circuit....period. Dedicated motor loads are the only exception as long as motor is equipped with overcurrent protection. The motor's overcurrent device protects the branch circuit conductors and the over sized breaker is for the starting current and short circuit protection. Heaters are considered continuous load, so branch circuit conductors are to be sized at least 125% of heater current. The breaker has to be sized for the conductor(30 amp for 10/2). NEC article 310.15.
 
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bigdee

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Really don't see an alternative other than running another 10/2 circuit from panel to heater.
 
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MTboatguy

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Really don't see an alternative other than running another 10/2 circuit from panel to heater.

Okay, thank you, I can run another breaker that is not a big deal or I can run a sub panel for the compressor, either way, I want to be safe, just trying to understand things and figured you guys would give me the straight scoop.

Thanks again.
 

poconojoe

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They told you wrong NEC does not allow a 50 amp breaker on a #10 branch circuit....period. Dedicated motor loads are the only exception as long as motor is equipped with overcurrent protection. The motor's overcurrent device protects the branch circuit conductors and the over sized breaker is for the starting current and short circuit protection. Heaters are considered continuous load, so branch circuit conductors are to be sized at least 125% of heater current. The breaker has to be sized for the conductor(30 amp for 10/2). NEC article 310.15.

BIGDEE is spot on. No larger than 30 amp breaker to protect 10 gauge wire.
 

bwkre

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As an electrician, in Canada, there is nothing wrong with installing more than one 240 outlet on a circuit. As long as the breaker is not larger than the outlet rating, in amps, and the cable is large enough to handle the amps, then it would be acceptable. Of course this does not take into account distance, actual load being drawn, duty cycle, etc. You could feed a 50 A outlet with #10, with a 30A breaker and be legal! But not with a 50 A breaker.

If I were wiring the compressor it would be 12/2 cable and a 20A breaker. More than enough to satisfy the start requirements as the breaker can handle it without tripping. As well the cable is suitable for 20A and the actual draw is below the 80%. Only other factor would be the distance.
As for the heater, 10/2 cable as 12/2 is too small. Heating loads must not exceed 80 % of the wire rating so 24A.10/2 is good for 30A. As for the breaker, a 25 A if available for the panel, but a 30 would also be legal as he next standard size.

If you already have enough 10/2 for both runs, nothing says you cant run the compressor with 10/2, but with a 20A breaker! Still legal
 

MTboatguy

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My neighbor who is a Mater Electrician ended up doing it for me in exchange for a couple of beers, he is also a county inspector and approved it, so everything is good to go.

Thanks for the reply's guys!
 

bigdee

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My neighbor who is a Mater Electrician ended up doing it for me in exchange for a couple of beers, he is also a county inspector and approved it, so everything is good to go.

Thanks for the reply's guys!

Sounds like a good neighbor to have. Congratulations!
 
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