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It is my understanding that if I need to draw, for instance, 30 Amps from a 240 V circuit (Live-Live) then there will be 30 Amps running from both wires, not half and half. So, the AWG sizes for the wires should be something accord to that.

The question arose from the installation manual of an electrical oven I am buying for a my home. It is a 240 V oven, with 4 wires (L, L, N and ground), and it says it needs a 40 Amp breaker. The specs says it draws at most ~31 Amps. So far so good. But then we get to the wiring size recommended and it says "12 AWG". I would expect at least 8 AWG for that load. But as I'm not quite sure if my understanding of currents/loads in a L-L circuit are correct, I rather ask.

In any case, I'm going to use 8 AWG wire, but this got me curious about this subject.

The manual with the recommendations is this, the oven model is WOS92EC0AS. https://www.whirlpool.mx/content/dam/global/documents/201506/installation-instructions-W10351242-RevC.pdf

Rodrigo Gómez
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  • It may be wise to include a link to the spec sheet so we can be certain the device is drawing 31A at 240v, but this does appear to be an exceedingly odd recommendation. – K H Oct 12 '18 at 22:04
  • Thanks! I'm updating the question with the link to the installation manual of the oven. The model number is WOS92EC0AS, which says the max wattage is 7400W at 240V – Rodrigo Gómez Oct 12 '18 at 23:16
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    So to be clear, 7400W is for a 240VAC double convection oven. If yours is a single convection oven, you'd be looking at 3720W. What does the wattage marking on the actual oven say? The document appears to correctly spec that models rated from 7.3 to 9kW at 240V should receive a dedicated 40 amp branch circuit and a dedicated 20 amp branch circuit for 4.8kw and below. Ads on a few websites for the model you mention appear to show a single oven. – K H Oct 13 '18 at 01:22
  • I could not find a power rating specific to the model in the manual, however, there is a table from which you are asked to select the correct wattage based on the voltage and type of oven. Is this where you obtained your power rating? Also are you certain you have 240VAC and not 208? – K H Oct 13 '18 at 01:26
  • You are right! Mine is a single oven. I haven't received it yet and, as you say, there are not much in a way of information regarding specific power ratings. For some reason I understood the "double" as in double heating elements (which I believe it has) not the "double size". So I guess the manual is indeed correct -- I do have 240v. – Rodrigo Gómez Oct 13 '18 at 03:09
  • Everywhere I can see now says the total draw is 3,600W, which is inline for the 3,720W mentioned in the manual. I hate the "1 manual for 10 different models" in general, specially with so many possibilities. – Rodrigo Gómez Oct 13 '18 at 03:15
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    Make sure to take line drop into account if it's a really long wire run. – K H Oct 13 '18 at 03:33
  • Thanks. The wire run will be really small. Maybe 6-7 m at most. I will keep the 8 AWG anyway, in case I ever want to put something bigger there. Here in Mexico we usually have brick walls everywhere so doing changes afterwards is very complicated/expensive. – Rodrigo Gómez Oct 16 '18 at 18:22
  • You would be amazed at what you can fish into cinderblock/brickwork after the fact, although it does take skill and a concealed work permit. – K H Oct 16 '18 at 18:26

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The high currents do pass from L to L, so each of those will see the full current. There may be some small current flowing from one of the lines to neutral for the controls/clock, but that's not important. I'd say that you need at least 10AWG - depending on the wire type and temperature rating - to handle that. FOr 60C rated NM wire that'd need 8AWG.

Phil G
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