Question about breaker/fused disconnect sizing

[Landor]

I'm working on a mini split install and ran into something that I'm not sure about. The unit is a Mr Cool DIY 2 ton mini split. I've used 10ga. wire to supply the unit and the only disconnect I could find seems to require 30A fuses.

The label on the compressor reads as follows:

Outdoor Fan Motor Load 0.6A
Compressor Load 12.0A
Minimum Circuit Ampacity 15.0A
Max Fuse 25.0A

So does this mean that the breaker should be 15A and the fused disconnect should be 25A?

Any help is much appreciated, thanks!

 

[rockwithjason]

fuse ratings on disconnects are the max rating. you can use any fuse up to that size in them.

 

[sberry]

Basically you need a 15 amp wire, a number 14 with a maximum fuse or breaker of 25. Use 14 wire and a 20A breaker in this case.

 

[Landor]

Ok, so 20 amp breaker and 25 amp fuses. That makes sense. Thanks for the help guys.

 

[Norcal]

14 gage wire with either 25 ampere fuses and/ or circuit breaker is code compliant.

 

[Landor]

14 gage wire with either 25 ampere fuses and/ or circuit breaker is code compliant.

Norcal - Thanks for the info but just so I understand, why is 14ga good with a 25A fuse or circuit breaker? I've always heard/read that 14ga/15A, 12ga/20A, etc. Is it because it's an HVAC system?

 

[alfredeneuman]

I'm not Norcal but there is an exception for both A/C equipment and motors.

The nameplate on AC equipment guides the installation.
It is marked with the load the unit draws, computed with all the factors to give a total amps that the wire is required to carry.

The nameplate also lists the Maximum fuse or circuit breaker size to use.

Motors (and AC units) draw more current when starting, and the bigger breaker or fuse will allow for this.

 

[Landor]

Thanks for the clarification. It was the "Minimum Circuit Ampacity" that threw me a bit as this is the first time I'd seen that.

 

[pinkerton]

Ok, so 20 amp breaker and 25 amp fuses. That makes sense. Thanks for the help guys.

when did we/he say breaker? I'm confused. You're going to use a 30A fused disconnect at the load and install 25A fuses in it. Now where are you putting the breaker? Are you referring to the breaker in the panel feeding?

 

[wyliesdiesels]

Norcal - Thanks for the info but just so I understand, why is 14ga good with a 25A fuse or circuit breaker? I've always heard/read that 14ga/15A, 12ga/20A, etc. Is it because it's an HVAC system?

HVAC equipment and motor circuits, as said above, have exceptions to the ampacity table 310.15(b)(16) that limits wire amapcity and thus breaker size such as #14 to 15a, because there is separate overload protection for the motor or HVAC equipment. In this case the breaker or fuses are for ground and line to line fault only.

when did we/he say breaker? I'm confused. You're going to use a 30A fused disconnect at the load and install 25A fuses in it. Now where are you putting the breaker? Are you referring to the breaker in the panel feeding?

The 30a is the max size fuse for the disconnect.

And yes he needs a breaker in the panel but there really is not point in using a fused disconnect. A non fused A/C pullout disconnect will satisfy code as far as requiring a disconnect at the unit for servicing.

OP dont forget a service outlet near the compressor for such things as HVAC vacuum pumps.

 

[Landor]

And yes he needs a breaker in the panel but there really is not point in using a fused disconnect. A non fused A/C pullout disconnect will satisfy code as far as requiring a disconnect at the unit for servicing.

OP dont forget a service outlet near the compressor for such things as HVAC vacuum pumps.

Yes, the breaker I'm referring to is the one in the panel feed. As far as a fused disconnect, that's all that was available locally, so it's what I'm using.

I have included an outlet near the unit! That will probably come in really handy one day.

 

[pinkerton]

Yes, the breaker I'm referring to is the one in the panel feed. As far as a fused disconnect, that's all that was available locally, so it's what I'm using.

I have included an outlet near the unit! That will probably come in really handy one day.

Then i'd put 30a time delay fuses in it, especially if it's class J or CC - this way you'll never have to change them due to nuisance trip. They'll still provide better short circuit protection than the breaker.