unpaulie
Member
I want pre wire for a Mr Cool 36K unit. It looks like I need to run 10/2 wire to a AC disconnect. Am I on the right track?
Pre Wire for 36K Mr Cool
- Thread starter unpaulie
- Start date
handymancanfixit
Well-known member
I am installing the same unit and I will run 10/2 NM and put it on a 30A breaker.
Use the 35A breaker, your better off.
handymancanfixit
Well-known member
10 Gauge NM-A is rated for 30A max load per the NEC. A 35A breaker on 10 Gauge wire would be a code violation.
No it is not, HVAC is one of a number of types of equipment that is allowed to use wire & overcurrent device combos that are not permitted for normal branch circuits, in fact if the OP wished, & 12 AWG THHN/ THWN & 35A fuse could be used & still be code compliant. You wire for the minimum & use the maximum size fuse or circuit breaker allowed on the label, the 125% has already been calculated also. It's always funny when home inspectors complain about 10 AWG w/ a 40A breaker on A/C equipment.
In most cases it's fine, just depends what the equipment label says.wyliesdiesels
Well-known member
Speedy Petey
Well-known member
This is why you are a handyman and not an electrician.
wyliesdiesels
Well-known member
Speedy Petey
Well-known member
LOL, that's why I'm here.I was gonna say that but held my tongue
handymancanfixit
Well-known member
No it is not, HVAC is one of a number of types of equipment that is allowed to use wire & overcurrent device combos that are not permitted for normal branch circuits, in fact if the OP wished, & 12 AWG THHN/ THWN & 35A fuse could be used & still be code compliant. You wire for the minimum & use the maximum size fuse or circuit breaker allowed on the label, the 125% has already been calculated also. It's always funny when home inspectors complain about 10 AWG w/ a 40A breaker on A/C equipment.
I see, and stand corrected. NEC 430 and 440, HVAC and Motor loads.
MCA - minimum circuit ampacity. This is the calculation of what the minimum size wire is for the particular unit. The MCA is actually calculated out of UL 1995 - the standard for HVAC equipment. It generally follows our 125% of the largest motor plus the other loads rules. This value is taken as is on the nameplate (in other words, you don't multiply it by 125%, etc.). So if the MCA on a unit is 30A, you can use a #10AWG copper wire for the unit.
MOP - maximum overcurrent protection. This is the maximum size fuse or breaker permitted to protect the unit. Again, the manufacturer has already done the calculations to arrive at this value. If it says 50A maximum overcurrent device, then you can use a 50A breaker or fuse.
So, I will use a 35A breaker bacause that is the MOP for the unit in question.
handymancanfixit
Well-known member
What? No windbag response from "Speedy Petey", the fastest "electrician" in the most expensive 100k rig in NY?