Wire size for 240 volt heater


Old 11-13-18, 07:42 PM
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Wire size for 240 volt heater

I thought I was finished with questions about my heater installation project but heater instructions confused me yet again. I ran 12/2 wire and put in 20 amp double pole breakers for 240 volt heaters The heaters I bought are 2000 watt 240 volt. They would draw 8.3 amps according to manufacturer. Here's the problem. The manufacturer instructions say that the required wire size is 14 and the breaker size is 15amp. I'm clear in my understanding that a 15 amp breaker would be enough to handle the heater and that 14 gauge wire is the size usually used with 15 amp breakers. However, everything I've read on installing a 240 volt heater says to use 12/2 and 20 amp double pole. I can't change the wire size at this point. So, do I hook them up and change the breaker to 15amp double pole? I will have one heater on each circuit.
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Old 11-13-18, 09:24 PM
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No problem using the #12 on a 15 amp circuit.
Old 11-14-18, 07:01 AM
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There is no God given rule linking 20 amps and 240 volts. Now, common tools, appliances, lights, and other devices intended for 15 amp circuits may be connected to 20 amp circuits.

The following are allowed for this heater:

Fourteen or larger gauge branch circuit with 15 amp breaker,

Twelve or larger gauge branch circuit with 20 amp breaker.

You mentioned heaters plural. Two will operate on one (12 gauge) 20 amp circuit but there is one obscure technicality that the layman would not know about unless told. Heaters are categorized as "continuous loads" in which case up to 80% of the branch circuit rating may be used. In this case the 16.6 amps drawn by two heaters would be excessive. The other category, "intermittent loads," may use the full rated amperage, say, 15 amps of a 14 gauge circuit.

You may not substitute one 30 amp circuit for, say, two or three 15 or 20 amp circuits .

Not applicable here is that for very long distances from panel to load, it may be necessary to upsize the wiring e.g. 12 or even larger for 14 amp circuit. This lessens energy waste due to voltage drop which in turn is dependent on amperes drawn (and independent of circuit voltage).
Old 11-14-18, 11:46 AM
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Thanks, I will use 20amp breaker. They are dedicated circuits so only one heater to each.

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