Fuse Sizing for Heat Pump Disconnects

[h1h2h3]

I am on a job where we have a group of existing heat pumps that need to be checked for proper installation. The manufacturers name plate states that the maximum time delay fuse or HACR C/B allowed is 15A, however, upon opening the discos we found that they were fused with 20A time delay fuses. It is my understanding that, ideally, the disco should be fused in accordance with the pumps FLA and should not exceed the maximum fuse allowed by the manufacturer. Our plan was to swap out all the 20A fuses with new 15A fuses, and all the 30A fuses with 25A fuses (there are several heat pumps with max allowable fusing at 25A). Does anyone see where this might be an issue? Are we correct in assuming that they should be changed? Motors and HVAC are not my strong suit and i would appreciate any feed back.
Also, FYI, the branch circuit is sized correctly and is protected up to the disco accordingly, that is 20A C/B for #12 and 30A C/B for #10. Also, the units have no integral fuses or OL protection that we can see.

Thank you again.
God bless.

 

[cadpoint]

Were you truely opening the box for the first time? Or was it a case where your supplier supplies a price for both disconnects and fuses?

I'd call the manufacture back and ask, including checking there own specifications, then ask for a paper trail chase and then / or do the same with your supplier.

Most of my experiences have been the supplier never gets the fuses correct...

 

[dkidd]

Are we correct in assuming that they should be changed? QUOTE]

Yes. in order to meet the UL, the fuses need to be right.

 

[h1h2h3]

Were you truely opening the box for the first time? Or was it a case where your supplier supplies a price for both disconnects and fuses?

I'd call the manufacture back and ask, including checking there own specifications, then ask for a paper trail chase and then / or do the same with your supplier.

Most of my experiences have been the supplier never gets the fuses correct...

This was the very first time that we had opened the disco. The fuses have been existing for quite some time. What causes me to second guess my judgement is that not a single unit had fuses sized @ 15A or lower, or in the case of the 25A max unit, at 25A or lower.

 

[h1h2h3]

Yes. in order to meet the UL, the fuses need to be right.[/QUOTE]


By "right", are you refering to the maximum allowable fuse on the name plate, or is there a code reference that I should be aware of that will lead me to the selection of the proper fuse. I would look that up myself, however, i am currently a distance away from home and i, regretfully, neglected to bring my nec along with me. I know that there is a table somewhere in 430, I believe, that gives % values of the FLA for OCPD selection. I just cant recall from memory where that is, or what it actually states.

 

[stew]

any inspector will catch this obvious error and red tag it if it were a new install. You are definatly correct in assuming that these need to be fused per nameplate,no exceptions.

 

[h1h2h3]

any inspector will catch this obvious error and red tag it if it were a new install. You are definatly correct in assuming that these need to be fused per nameplate,no exceptions.

That is what I thought. Its just that they were all incorrect, and i started to wonder if there was something i was missing. Thank you very much for your feedback (to all posters.)

 

[LarryFine]

Are we correct in assuming that they should be changed?

As stated above, definitely.

Also, FYI, the branch circuit is sized correctly and is protected up to the disco accordingly, that is 20A C/B for #12 and 30A C/B for #10.

FYI, the BC breakers could be sized as the units require (15a and 25a, respectively), allowing non-fused discos.

Plus, those conductors may actually be larger than required; they can be sized per the Minimum Circuit Ampacity, despite being smaller than the usual sizes required on those breakers.

 

[dkidd]

There is a good article at

http://www.iaei.org/magazine/?p=3944

 

[haskindm]

As stated above, definitely.

FYI, the BC breakers could be sized as the units require (15a and 25a, respectively), allowing non-fused discos.

Plus, those conductors may actually be larger than required; they can be sized per the Minimum Circuit Ampacity, despite being smaller than the usual sizes required on those breakers.

I agree with Larry.