M C A

[relbas]

I have an Ac unit with the mca rating of 19 Amp
Recomended fuse/breker size is 20 Amp.
Does #12THHN correct wire size? or it needs to be #10?
Thanks

 

[iwire]

12 AWG would be fine.

But are you sure the MCA is 19 amps with Maximum Over Current protection of 20?

Seems pretty odd.

 

[relbas]

Yes I do have a manufacture cut sheet
Thats why I am confused.
Do I have to add 125% to the MCA current?

 

[augie47]

Step one, IMO, would be to double check with the manufacturer. They have been known to make typos. There was once a nameplate posted here with a MOCP less than the MCA.
In all probability your 12 THHN would be good.

can you post a copy of the cut sheet ?

 

[relbas]

Sorry
The MOP is not given
Instead manufacture put on the specks "recomender fuse/breaker size 20 Amp"

 

[relbas]

Electrical Requirements
Power Supply ....................208 / 230V, 1-Phase, 60 Hz
Recommended Fuse/Breaker Size.......................20 A
MCA ..............................................19 A
Voltage
Indoor - Outdoor S1-S2 ......................AC 208 / 230V
Indoor - Outdoor S2-S3 ........................DC 12 - 24V
OPERAtING RANGE
Indoor Intake Air Temp. Outdoor Intake Air Temp.
Cooling Maximum 95?F (35?C) DB, 71?F (22?C) WB 115?F (46?C) DB
Minimum 67?F (19?C) DB, 57?F (14?C) WB 14?F (-10?C) DB
Heating Maximum 80?F (27?C) DB, 67?F (19?C) WB 75?F (24?C) DB, 65?F (18?C) WB
Minimum 70?F (21?C) DB, 60?F (16?C) WB 6?F (-14?C) DB, 5?F (-15?C) WB
Compressor ..................DC Inverter-driven Twin Rotary
Fan Motor....................................0.93 F.L.A.
Sound Pressure Level
Cooling (Non-ducted/Ducted)..................... . . 54 dB(A)
Heating (Non-ducted/Ducted)...................... . 57 dB(A)
DIMENsIONs INcHEs / MM
W 35-7/16 / 900
D 12-5/8 / 321
H 35-7/16 / 900

 

[infinity]

Under the 2008 NEC, #14 conductors with a 20 amp OCPD would be compliant.

 

[acrwc10]

#12 sounds fine, #14 could even work, the big question is, How long is the wire run from the panel to the AC unit ? you may need to account for voltage drop. unless you don't mind motors burning up on a regular basis.

 

[Mgraw]

Technically the mca could be larger than the mocp. The standard requires when the calculated mocp is smaller than the mca the mocp shall be equal to the mca or the next larger common breaker/fuse size.

 

[infinity]

Technically the mca could be larger than the mocp. The standard requires when the calculated mocp is smaller than the mca the mocp shall be equal to the mca or the next larger common breaker/fuse size.

Can you explain how the MCA can be larger than the listed MOCP?

 

[mark32]

What does MCA stand for? Minimum circuit ampacity?

 

[ActionDave]

Yes. Minimum Circuit Ampacity The other is Maximum OverCurrent Protection

 

[acrwc10]

Wire to the minimum.
breaker/fuse to the maximum.
If the MCA is 19 amp in most cases you could run a #14 and if the MOCP is 30 you can put it on a 30 breaker/fuse.
The MOCP is only protecting against a groung fault. The Over Current protection is from in side the Air conditioning compressor motor.

 

[Mgraw]

Can you explain how the MCA can be larger than the listed MOCP?

Generally say you have multiple components of the same size as you largest load. The mca is calculated using rla or fla x 1.25 of all the same size plus the remainder of the loads. The mocp is calculated using only one of the components x 2.25 plus the remainder of the loads. This would be the calculated mocp. However the standard does not allow the mocp to be smaller than the mca so the listed mocp would be equal to or greater than the mca.

 

[cowboyjwc]

Are you guys sure about the #14 on a 20 amp breaker?

240.4(D) says that the over current protection for #14 shall not exceed 15 amps.

 

[iwire]

Are you guys sure about the #14 on a 20 amp breaker?

240.4(D) says that the over current protection for #14 shall not exceed 15 amps.

(D) Small Conductors. Unless specifically permitted in 240.4(E) or (G), .......

IMO 240.4(G) applies here.

 

[cowboyjwc]

(D) Small Conductors. Unless specifically permitted in 240.4(E) or (G), .......

IMO 240.4(G) applies here.

OK, just making sure that's where we were going with that. I know they took off the note and move it, just making sure that no one thought they changed the ampacity tables.

 

[relbas]

Isn't this section for derating calculation?