simple but dumb question

g-and-h_electric · Jul 13, 2022

Mitsubishi ductless "mini split" installation....... Nameplate rating of 15 amp for compressor, .3 amp fan. They specify max OCP of 30, so a 25 would be fine. Based on the load any reason I cant feed it with #12? Article 440 ( I think) says I can. , but there is discussion with the HVAC guys saying it should be #10 . It is a short run of 25 feet or less, so voltage drop isnt an issue.

What do we all think

Howard

mtnelect · Jul 13, 2022

Just follow the nameplate ... it's done for you.

wwhitney · Jul 13, 2022

So what's the nameplate MCA? That's what you need to follow for wire sizing.

Cheers, Wayne

g-and-h_electric · Jul 13, 2022

MCA on nameplate is 30..... I was interpreting 440 to say I can size conductors for load and mcp for reliable starting... BUT I have been wrong before....

howard

retirede · Jul 13, 2022

g-and-h_electric said:
MCA on nameplate is 30..... I was interpreting 440 to say I can size conductors for load and mcp for reliable starting... BUT I have been wrong before....

howard

In post 1, MOCP is 30. So MCA = MOCP? Sounds fishy.

wwhitney · Jul 13, 2022

g-and-h_electric said:
MCA on nameplate is 30.....

If that's correct, you'll need 30A ampacity, so #10 AWG Cu, since you can't practically use the 90C ampacity of #12 Cu.

Cheers, Wayne

g-and-h_electric · Jul 13, 2022

"D'OH" I was thinking Max over current.... Minimum circuit size is 21 Therefore #10 it is!

Looks Like I am buying lunch tomorrow.....

howard

infinity · Jul 13, 2022

g-and-h_electric said:
"D'OH" I was thinking Max over current.... Minimum circuit size is 21 Therefore #10 it is!

Looks Like I am buying lunch tomorrow.....

howard

If you're using something other than NM cable #12 AWG can have an ampacity of 25 amps.

Strathead · Jul 13, 2022

g-and-h_electric said:
"D'OH" I was thinking Max over current.... Minimum circuit size is 21 Therefore #10 it is!

Looks Like I am buying lunch tomorrow.....

howard

No, #12 is perfectly legal

wwhitney · Jul 13, 2022

Strathead said:
No, #12 is perfectly legal

In a 75C wiring method, which excludes LFNC, NM, and UF.

Cheers, Wayne

LarryFine · Jul 13, 2022

Thus, NM cables require #10, everything else, like THWN in conduit, #12 is okay.

simple but dumb question

g-and-h_electric

Senior Member

mtnelect

HVAC & Electrical Contractor

wwhitney

Senior Member

g-and-h_electric

Senior Member

retirede

Senior Member

wwhitney

Senior Member

g-and-h_electric

Senior Member

infinity

Moderator

Strathead

Senior Member

wwhitney

Senior Member

LarryFine

Master Electrician Electric Contractor Richmond VA