A/C Unit wire size.

[nizak]

MCA nameplate rating on a 3 ton unit -18.7 A

Max Breaker Ampacity 30 A

Wire size = 10/2 or 12/2 NMB ??

90' length

 

[infinity]

12/2 NM and a 30 amp OCPD. MC cable 14/2 and a 30 amp OCPD with 75° C terminations.

 

[mbrooke]

12/2 NM and a 30 amp OCPD. MC cable 14/2 and a 30 amp OCPD with 75° C terminations.

If going by earlier code cycles you can even do 14/2 at 60*C :angel:

 

[JFletcher]

I"m drawing blanks on how 14ga wire can be used here. Any help would be appreciated....

 

[peter d]

I"m drawing blanks on how 14ga wire can be used here. Any help would be appreciated....

#14 used to be rated at 20 amps in the 60C column, but not so anymore.

 

[infinity]

If going by earlier code cycles you can even do 14/2 at 60*C :angel:

Yes, that changed in the 2011 NEC. Thanks Canada. :roll:

 

[nizak]

Does the wire need to be rated at 125% of the minimum circuit ampacity?

 

[infinity]

Does the wire need to be rated at 125% of the minimum circuit ampacity?

No, the MCA already has the 125% built into the number. MCA on the nameplate is the minimum conductor size.

 

[kwired]

MCA nameplate rating on a 3 ton unit -18.7 A

Max Breaker Ampacity 30 A

Wire size = 10/2 or 12/2 NMB ??

90' length

As mentioned 12 is minimum, 14 once would have been minimum, but with 90 feet you may want to consider voltage drop and maybe end up running 10 anyhow.

Add: 14 still is minimum if using conductor that can use 75C ampacity column, you are limited to 60C with NM cable.