Fordean
Senior Member
- Location
- New Jersey
- Occupation
- Electrical Contractor
Proper Labeling
- Thread starter Fordean
- Start date
DBill64
Member
- Location
- Washington, USA
- Occupation
- I&E Technician
Here is an article over your exact question:
www.hvacrschool.com
It seems the way manufacturers calculate the MCA in accordance with UL standard UL 60335-2-40 has changed pretty recently. I would highly recommend giving this a read, as well as referencing the UL standards they talk about. Their example also seems to be a the exact same Mitsubishi mini split that you are installing as well.
Why the Breaker Size May Be Lower than the MCA (and Why That's NOT Necessarily a Code Violation)
If you look at the label, you will see that the breaker size is 25 amps, and the minimum circuit ampacity (MCA or wire size) is 29 amps.
www.hvacrschool.com
It seems the way manufacturers calculate the MCA in accordance with UL standard UL 60335-2-40 has changed pretty recently. I would highly recommend giving this a read, as well as referencing the UL standards they talk about. Their example also seems to be a the exact same Mitsubishi mini split that you are installing as well.
DBill64
Member
- Location
- Washington, USA
- Occupation
- I&E Technician
From my brief skim: Use the breaker size (and matching conductor size) they recommend, but of course do not exceed the MOCP.
jmellc
Senior Member
- Location
- Durham, NC
- Occupation
- Facility Maintenance Tech. Licensed Electrician
No, let's special order a 49.9 amp breaker or fuse.
So to make a long story short, according to the article, the 25A breaker is a recommended size, and not a maximum size. The breaker could be sized anywhere up to 49 amps.
Confusing, because of the way the 25 is listed below the "Max Fuse Size", most people assume its also a max breaker size.
Also, according to the article, the NEC doesn't require the breaker size to be larger than the MCA. That's different than what I always believed - I thought the branch circuit size had to be as large as the MCA, and I thought that included the breaker size.
That explains a lot, because we have seen at least a few other similar posts.
Confusing, because of the way the 25 is listed below the "Max Fuse Size", most people assume its also a max breaker size.
Also, according to the article, the NEC doesn't require the breaker size to be larger than the MCA. That's different than what I always believed - I thought the branch circuit size had to be as large as the MCA, and I thought that included the breaker size.
That explains a lot, because we have seen at least a few other similar posts.