Can a #12awg be protected by 25A CB for Elec Spc Heat Eq

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jschultz

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I am reviewing a job that another engineering firm did. 1999 NEC is code for project.
The electric wall heater is a 4kw at 208v/1 phase.

So i get 4000/208= 19.2 amps x 1.25=24 amps for branch overcurrent and branch conductor.

So normally I would use a #10awg. But they selected a #12awg. table 310.16 has asterick next to #12 which the note says see 240-3. 240-3(d) small conductors states that a #12 can be protected by 20 amperes unless allowed in e thru g.
g. does not have fixed electric space heating listed.
So I assume the #12 has to be protected by 20A CB max for this application. And a #10 should be used for the conductors.

What is your opinion?
 

jschultz

Member
Re: Can a #12awg be protected by 25A CB for Elec Spc Heat Eq

Why a 30A CB?
It is only one piece of equipment on the branch circuit.
and 25A does not exceed 30A.
 

charlie b

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Location
Lockport, IL
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Retired Electrical Engineer
Re: Can a #12awg be protected by 25A CB for Elec Spc Heat Eq

You need a #10 wire (minimum), and it can be protected by a 30 amp breaker (maximum). You could also use a 25 amp breaker, but I wouldn?t. I have no better reason than that the cost is probably the same, and that the extra 5 amps might prove useful on some future date.

Did ?the other engineering firm? provide a reason for selecting a #12?
 

jschultz

Member
Re: Can a #12awg be protected by 25A CB for Elec Spc Heat Eq

Did ?the other engineering firm? provide a reason for selecting a #12?

I have not finished my peer review yet. So they don't know it is an issue yet. I wanted to make sure I was not missing something before I included it as a comment.

The other engineering firm is designing my church. I have been less then happy with the work they have done so far. They did site lighting design. They had upsized the current carrying conductors from #12 to #8 but still had a #12 ground. I asked about it and they stated that a #12 is the correct size for a 20A overcurrent device. I sent them the section of the code that states you have to upsize the ground if you upsize current carrying conductors for voltage drop.

They originally did not have panelboard schedules or a demand load calculation on the drawings. Only a schedule of panelboards. So I asked that panelboard schedules and demand load calculations be provided. The demand load came out to be 999.49 amps. The service was then changed from a 1000 amps to 1200 amps. If I would not have asked, then we would not have been able to add a few lighting fixtures. So now I am doing a more thorough review.
 
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