240v a/c line


Old 09-19-05, 09:05 PM
Thread Starter
Join Date: Sep 2005
Posts: 8
240v a/c line

i have a 240v line going to a window a/c unit which draws 8 amps. now this line has a neutral in it which is not used by the a/c unit. could i tap off of the line before it gets to the a/c for a light. this would only be somethin like a 100w at the most. i understand that the 240v is a balanced load which needs no neutral, so im wondering if the light on one side would unbalance the load.

thanks in advance , cajun
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Old 09-20-05, 04:15 AM
Join Date: Jan 2004
Location: Oregon
Posts: 1,219
In general, the answer is 'no'.

In your case, if you actually have x-3 cable running to the AC (meaning two hots, a neutral, and a ground), and if the circuit is a 12 ga, 20A circuit, and if the air conditioner specifications do not require a dedicated circuit, then I believe that the answer is 'yes'.

1) This AC is 'equipment fastened in place' by many interpretations. As such, if the load is > 50% of the circuit, it must be a dedicated circuit. But if this is a 20A circuit, then the load is < 50% of the circuit.

2) If you actually have a neutral, then you will have 120V available. You are permitted to use 'multi-wire' circuits to supply 120V loads, and if you actually have a neutral wire then this is a multi-wire circuit.

3) You cannot violate the listing requirements in the AC manual.

Even if code would permit you to do this, it is probably a bad design choice. The light will probably flicker considerably every time the AC compressor cycles on.

Also, please wait for confirmation on this from others. Because this is an 'unorthodox' installation, there is a significant chance that I've missed some additional code detail that would prohibit this installation.

Note that doing this _will_ unbalance the load; but that is fine as long as the load is less than the allowable limits for the circuit and you have a connected neutral.

Old 09-20-05, 07:24 AM
Join Date: Sep 2000
Location: United States
Posts: 18,497
I agree with Jon on both counts--it's legal and possible, but a bad idea. Probably not the worse idea in the world, granted, but bad anyway. Most of the time, people only consider such a goofy solution because they don't have enough experience to find a better one. Try to get an electrician or electrically knowledgeable friend to help you find a better solution.

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