Electrical – Re: 240V electric furnance – what is Dual Supply Circuit Vs. Single Supply

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I am having a Intertherm 012H 240v electric furnace installed. The installer asked me which wiring system would i prefer. The manual offers a choice:

A.) Single @ 51.2 total amperes with a max over-current rating of 70 (which i believe requires #4 wire

B.) Dual "A"/Dual "B" Single A is 27.1, max over is 40, Single B is 24.2, max over is 30.

My questions are:

  1. Which is best Single or Dual? One big 70 amp breaker with big fat, hard to bend wire, or Dual, with separate breakers and easy to use wire?

  2. If dual, if one circuit pops (either a or b) will the furnace continue to operate.

  3. Would i be correct to assume that either method would need 4 wire? Sinfle being #4/4 wire. And Dual A #8/4 wire. Dual B #10/4 wire

Thanks to all those who reply. Bruce

Best Answer

Use the dual breaker method -- whoever wrote the manual needs a Code-slap with 424.22(B), as the single breaker method doesn't comply with it.

(B) Resistance Elements. Resistance-type heating elements in electric space-heating equipment shall be protected at not more than 60 amperes. Equipment rated more than 48 amperes and employing such elements shall have the heating elements subdivided, and each subdivided load shall not exceed 48 amperes. Where a subdivided load is less than 48 amperes, the rating of the supplementary over-current protective device shall comply with 424.3(B).

If you're short slots -- use a double-stuff (quadruplex) breaker.

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