Electrical Question

JUGHNE

ED, if I were to pigtail say #4 AL to #8 CU I use a compression connection such as the Blackburn WR series. Comes with the anti oxi compound built into the connector.

The new AH in question might have it's own CB with lugs that often may handle the old 60amp wire size......so change nothing as the AH is protected by it's own CB of 30amp.

Chris, I put #6 CU on a 60amp CB all the time. Especially if THHN conductors are in a raceway...more cooling. Another grey area perhaps in the NEC.

The old post was revived by one with questions of AC wiring/CB size.

hvacfreak2, motors themselves are not treated as hermetic compressor motors are, different animal.

ChrisJ

> @JUGHNE said:
> ED, if I were to pigtail say #4 AL to #8 CU I use a compression connection such as the Blackburn WR series. Comes with the anti oxi compound built into the connector.
>
> The new AH in question might have it's own CB with lugs that often may handle the old 60amp wire size......so change nothing as the AH is protected by it's own CB of 30amp.
>
> Chris, I put #6 CU on a 60amp CB all the time. Especially if THHN conductors are in a raceway...more cooling. Another grey area perhaps in the NEC.
>
> The old post was revived by one with questions of AC wiring/CB size.
>
> hvacfreak2, motors themselves are not treated as hermetic compressor motors are, different animal.

What about 6-3 NM-B specifically?

JUGHNE

The lowest chart rating for #6 CU is 55 amps.
Now the code allows you to go to the next size of CB or fuse if that 55 is not a standard size. Standard ratings start at 15 thru 6000amps. In the list are.....30,35,40,45,50 60,70 etc. So in the case you need a 55amp CB you are allowed to go up to 60A CB or fuse.

60 amp fuses/CB for #6 CU has been the standard forever.
Also your 60A subfeed or any branch circuit should never be loaded to more than 80% of its rating. If your 60A circuit is running at say a nearly constant 48A then you should up the size to perhaps 100A.

Much of the loading of services is based on diversity of use.
Your electric range, dryer, oven etc. has heating elements that are cycled on and off fairly rapidly and not a constant load.
Residential service wire is allowed to be down sized by 1 size of conductor because of these factors. Commercial service are not allowed that because of the unknown future use.
200a resi service will pass with 2/0 CU
200a commercial service must have the 3/0 CU

Apartments with multiple ranges are allowed to down size the main conductors because of the diversity of use. Formula is in the code.
Restaurants with things like deep fat fryers get this also, because of heater elements cycling.

Koan

@Jamie Hall , @Fred, @hvacfreak2
Since this is an AC condenser, it comes under sect 440 in the NEC. 125% of full load is 29.2 amps. This is the MCA, and the wire is sized to this level, so #10 for a short run is ok. The MCO is 50 amps so this is the breaker size. As far as I know this ONLY applies for AC condensers. (Single motor compressors). It is not for any other "normal" circuit. See Mike Holt's video earlier. He mentions that sect 440.22 governs the breaker and 440.33 covers the wire sizing.

hvacfreak2

hvacfreak2, motors themselves are not treated as hermetic compressor motors are, different animal.

Feeder sizing was my only point ( 125 % FLA ) .

Jamie Hall

Yes on the 125% etc. However, for the unwary, there's a gotcha: it applies only when the motor load is the only load on the circuit and is hard wired.