Can I add a lighting circuit to one side of a 2 pole 240v breaker ?

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Aclub

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Hello ! I am new to the forums but have found many answers here in the past. Just want to thank you all for the assistance.
I have an exterior storage shed heated with a 500w 240v baseboard heater on a 2 pole breaker (20A). Is it possible to tap one side of that circuit for a light ? Lets say 120w. I have been unable to find anything clear about it in the NEC. It would only be drawing 1-2 amps max but when the heat and lights are on at the same time one side would have 6amps and the other only 4. Would this cause problems or is the current differential small enough to be overlooked ?
 
How do you plan to give the current from the 120 volt load a chance to return to the source (i.e., on what should be a grounded - or neutral - conductor)? Does the heater circuit already have a neutral wire?

You may think that adding 1-2 amps from a 120 volt load is a small thing. That, at least, is right. But the heater, rated 500 watts at 240 volts, is drawing only just over 2 amps of its own. So you would be running 2 amps on one leg and 4 amps on another. Still, this is not a big deal. You are still well below the circuit's 20 amp limit. But I do recommend that you complete the math, before getting too far into a design.

To answer your basic question, I don't see an NEC violation, unless there is no neutral (grounded) wire already in the heater circuit. And if you are thinking of using the equipment grounding conductor (i.e., the green or bare copper wire) to serve as the neutral return path, that would be a serious violation and a definite safety hazard.
 
charlie b said:
How do you plan to give the current from the 120 volt load a chance to return to the source (i.e., on what should be a grounded - or neutral - conductor)? Does the heater circuit already have a neutral wire?

You may think that adding 1-2 amps from a 120 volt load is a small thing. That, at least, is right. But the heater, rated 500 watts at 240 volts, is drawing only just over 2 amps of its own. So you would be running 2 amps on one leg and 4 amps on another. Still, this is not a big deal. You are still well below the circuit's 20 amp limit. But I do recommend that you complete the math, before getting too far into a design.

To answer your basic question, I don't see an NEC violation, unless there is no neutral (grounded) wire already in the heater circuit. And if you are thinking of using the equipment grounding conductor (i.e., the green or bare copper wire) to serve as the neutral return path, that would be a serious violation and a definite safety hazard.
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There are some LED lights (Drivers) that accept 240V(L-L); you would need to check the manufacturer's data sheet to ensure 2 phase conductors and not 1 phase/neutral for 240V. This would be the easiest work around.
 
charlie b said:
By the way, how did you come up with 6 amps and 4 amps here:
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Used 120v instead of 240 when i divided the heater wattage:happyno:. there is an insulated neutral wire available. Heater is installed with 12/3 romex using the 2 conductors and no neutral leaving the neutral free to be used.
 
It is common for appliances like electric dryers to connect the heating element line to line for 240 and the drum motor line to neutral for 120V, but the dryer circuit includes a neutral. (There may or may not be a separate EGC in legacy installations, but the neutral is always there!)

As stated, as long as the neutral is present it is not a big deal in terms of safety to have a separate load attached to one side of a 240 circuit.
Note that your receptacle installation must meet the NEC requirements for receptacle(s) on a 20A circuit, and you may have converted a straight 240V circuit to an MWBC with additional requirements.
 
Aclub said:
Used 120v instead of 240 when i divided the heater wattage:happyno:. there is an insulated neutral wire available. Heater is installed with 12/3 romex using the 2 conductors and no neutral leaving the neutral free to be used.
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What is the disconnecting means in the shed?

Is this essentially a wire running into the shed and directly into the heater?
 
I believe I have my solution. I'm going to replace the heater with a 120v model (needs replacing anyway) and use the other conductor for the lighting circuit and single outlet. GFCI of course. There is currently a 2 pole toggle switch in an outdoor box above the door as a disconnect to the shed I'm gong to move to a proper height just inside the door.
 
Aclub said:
I believe I have my solution. I'm going to replace the heater with a 120v model (needs replacing anyway) and use the other conductor for the lighting circuit and single outlet. GFCI of course. There is currently a 2 pole toggle switch in an outdoor box above the door as a disconnect to the shed I'm gong to move to a proper height just inside the door.
Click to expand...


There's no need to change the heater voltage. You have a single branch circuit with a neutral and EGC, and a disconnect that opens both ungrounded conductors. That meets the requirements for a single branch circuit supply to a structure.

There is absolutely nothing wrong with a 120v load on an 120/240v branch circuit. The total load is nowhere near the 20a OCPD. There is no danger of an overloaded neutral. Think of this terms of a feeder instead of a branch circuit...if you installed a small main lug or main breaker panel to that 12/3 NM cable, installed a GES and a pair of breakers, your load on the now feeder cable is the same.
 
Is this shed a dwelling accessory building? If so that opens a bigger can of worms in recent codes than it used to.
 
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