Wire size needed

[qcroanoke]

Have an HVAC nameplate that calls for 17 amps MCA and Max. overcurrent of 20 amps.
Can I use #12 or does the 17 amp MCA require #10 even though the max. overcurrent is 20 amps?

 

[charlie b]

The "Mnimum Circuit Ampacity" is 17. The ampacity of #12 THHN is 25, and that exceeds the minimum. Yes, you can use #12.

 

[qcroanoke]

The "Mnimum Circuit Ampacity" is 17. The ampacity of #12 THHN is 25, and that exceeds the minimum. Yes, you can use #12.

Thanks Charlie.
The 17 MCA threw me had it been 16 I would have not hesitated to use #12.
16 amps being 80% of 20 amps had me wondering.......

 

[sd4524]

You could use 14 gauge if it falls under 240.4d

 

[Dennis Alwon]

You could use 14 gauge if it falls under 240.4d

I agree you can use 14 gauge

 

[charlie b]

You could use 14 gauge if it falls under 240.4d

I don't follow. Are you suggesting a 15 amp breaker as well?

 

[sd4524]

I am suggesting a 20 amp breaker with 14 gauge wiring.
Table 240.4(G) I wrote d last post. I always size wire off of minimum ckt amps. 14 gauge is rated for 20 amps.

 

[ceb58]

Have an HVAC nameplate that calls for 17 amps MCA and Max. overcurrent of 20 amps.
Can I use #12 or does the 17 amp MCA require #10 even though the max. overcurrent is 20 amps?

If its one of the buildings I will have to work on then use #8 :grin:

 

[Jim W in Tampa]

if its one of the buildings i will have to work on then use #8 :grin:

why ? -------------

 

[Chamuit]

If its one of the buildings I will have to work on then use #8 :grin:

That much voltage drop?

 

[Jim W in Tampa]

That much voltage drop?

We must assume that if the run is long enough to deal with voltage drop that the installer upsized for that reason. Not simply that you like larger wire .

 

[ceb58]

why ? -------------

Easier to pull out after a lightning strike:grin:

Originally Posted by ceb58
if its one of the buildings i will have to work on then use #8 :grin:

Its more of a joke than anything else. Mike works for the company that makes our communication buildings.

 

[Jim W in Tampa]

Easier to pull out after a lightning strike:grin:






Its more of a joke than anything else. Mike works for the company that makes our communication buildings.

Back when i was in TV repair business i loved lightning, keep in mind I live in FL. The snow birds kept us busy till April then we had dry spell till LIGHTNING every crack was $$$$$$$$
Loved the sound as long as not my house

 

[qcroanoke]

If its one of the buildings I will have to work on then use #8 :grin:

Unless the highway patrol has a building in Angola you're safe! :grin:

 

[qcroanoke]

Its more of a joke than anything else. Mike works for the company that makes our communication buildings.

Yep!
See, we always try to size our wire to the breaker on our A/C units. Even though we don't have to by code. Our buildings house communication equipment for police and fire department radios as well as cellular sites and we just don't want to have to explain or justify smaller (yet legal) wire sizes feeding our A/C units if a building goes down because of an A/C unit failure.
Now POCO sub-station switch buildings are a whole nuther story.......

 

[infinity]

Yep!
See, we always try to size our wire to the breaker on our A/C units. Even though we don't have to by code. Our buildings house communication equipment for police and fire department radios as well as cellular sites and we just don't want to have to explain or justify smaller (yet legal) wire sizes feeding our A/C units if a building goes down because of an A/C unit failure.
Now POCO sub-station switch buildings are a whole nuther story.......

Why would the AC unit possibly fail if you sized the conductors for the MCA?

 

[qcroanoke]

Why would the AC unit possibly fail if you sized the conductors for the MCA?

It most likely wouldn't but when the building could be hundreds of mile away from where it was manufactured and people are pointing fingers we don't want them pointing at us. We've actually had customers call us and want to know how we could install an A/C unit with undersized wires from the factory in them!
Example: MCA is 60. We found a wire from the factory that couldn't have been much bigger than a #10! That must be why the compressor failed! We're not paying for this!
Then we have to explain we have no control over what the factory uses and it is all legal because it has a UL label on it.
It just ain't worth it......

 

[Jim W in Tampa]

It most likely wouldn't but when the building could be hundreds of mile away from where it was manufactured and people are pointing fingers we don't want them pointing at us. We've actually had customers call us and want to know how we could install an A/C unit with undersized wires from the factory in them!
Example: MCA is 60. We found a wire from the factory that couldn't have been much bigger than a #10! That must be why the compressor failed! We're not paying for this!
Then we have to explain we have no control over what the factory uses and it is all legal because it has a UL label on it.
It just ain't worth it......

The wiring inside the units are usually 105 degree. Seldom see any melted but often see terminals burned off.

 

[Dennis Alwon]

Yep!
We always try to size our wire to the breaker on our A/C units.....we just don't want to have to explain or justify smaller (yet legal) wire sizes feeding our A/C units if a building goes down because of an A/C unit failure.

That's silly. If you truly understand why it is okay to wire an a/c with a smaller wire than the OCPD, then you wouldn't worry about the building burning down. If that ever happened the NEC would not allow this rule.

 

[nhfire77]

Back when i was in TV repair business i loved lightning, keep in mind I live in FL. The snow birds kept us busy till April then we had dry spell till LIGHTNING every crack was $$$$$$$$
Loved the sound as long as not my house

Same thing applies to poorly installed fire alarms. The lightning crashing sounds like a cash register.

I sell surge protection, but it's value is not seen until too late. Oh well.