HVAC disconnect

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wireday

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New England
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Master electrician
Does a outside chiller need a fused disconnect,I am replacing the feed and a new disconnect, the one that’s there now is not fused.
 
wireday said:
I’ve been told that the hvac guys like to have them, just was wondering about code
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NEC requires a disconnecting means within sight of the unit. Can be integrated into the unit, can be the branch circuit device if it is located "within sight".

Whether a fuse is also necessary depends on the unit and it's instructions.
 
wireday said:
Can the information be found on the name plate
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If fuses are required it should mention this on the nameplate.

The need for a disconnecting means is an NEC requirement, but there is more then one way to have an acceptable disconnecting means
 
The chiller name plate says hvacr breaker which it has, is there any harm to having a disconnect with fuses even though it’s not required?
 
Dennis Alwon said:
Some chillers have their own disconnect built in so no disconnect is needed AFAIK
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an to further complicate things, some of the ones I encounter have a disconnect but it requires a tool (screwdriver) to access thus not readily accessible.
 
augie47 said:
an to further complicate things, some of the ones I encounter have a disconnect but it requires a tool (screwdriver) to access thus not readily accessible.
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I believe in NC we would accept that. What do you do when you have those generator panels that have screws to get to the overcurrent protective device? Some are thumb screws but they get tightened by some with pliers
 
augie47 said:
And to further complicate things, some of the ones I encounter have a disconnect but it requires a tool (screwdriver) to access thus not readily accessible.
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I'd take that rather than what I see all the time: locks. Screwdriver I have. I've had to cut off a few locks when the homeowner can't remember where the key is.
 
wireday said:
The chiller name plate says hvacr breaker which it has, is there any harm to having a disconnect with fuses even though it’s not required?
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The only harm is you might have to run larger wire from the panel to the fused disconnect.
Example: You have an MCA of 19A and a Max OCPD of 35A, so you run a #12 AWG wire on a 35A breaker to a non-fused disconnect. All is legal with this set-up

Now, add a 35A fused disconnect and it changes things. The run from the panel now has to have a #10 wire (depending on the type of wire) because it's now a feeder because of the fused disconnect. You can drop the wire size back down from the disc. to the unit.

If the nameplate doesn't say "fuses" or "fuses only" then a breaker is allowed. I never use a fused disc. unless required.
 
Little Bill said:
The only harm is you might have to run larger wire from the panel to the fused disconnect.
Example: You have an MCA of 19A and a Max OCPD of 35A, so you run a #12 AWG wire on a 35A breaker to a non-fused disconnect. All is legal with this set-up

Now, add a 35A fused disconnect and it changes things. The run from the panel now has to have a #10 wire (depending on the type of wire) because it's now a feeder because of the fused disconnect. You can drop the wire size back down from the disc. to the unit.

If the nameplate doesn't say "fuses" or "fuses only" then a breaker is allowed. I never use a fused disc. unless required.
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I think 430.62(A) would still allow 12 AWG feeder and 35 amp breaker in that situation. If the feeder supplied more than one load, you would have to add that load to minimum ampacity of the conductor and to your selection of an overcurrent device. If you had an additional 10 amp load supplied by said feeder I think you could use 10 AWG and 45 amp breaker - small conductor rule of 240.4(D) gets a little blurrier here though, but for conductors larger then 10 AWG I think there is no question you could do it that way. 240.4(G) however sends us to other sections including 430 and 440 so I think it can apply to small conductors as well.
 
wireday said:
The chiller name plate says hvacr breaker which it has, is there any harm to having a disconnect with fuses even though it’s not required?
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I "think" the reason that fuses are often used on expensive equipment is that fuses are more reliable than breakers.
 
growler said:
I "think" the reason that fuses are often used on expensive equipment is that fuses are more reliable than breakers.
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Maybe. They often have more current limiting ability and/or faster response time to short circuit/ground faults.
 
Little Bill said:
The only harm is you might have to run larger wire from the panel to the fused disconnect.
Example: You have an MCA of 19A and a Max OCPD of 35A, so you run a #12 AWG wire on a 35A breaker to a non-fused disconnect. All is legal with this set-up

Now, add a 35A fused disconnect and it changes things. The run from the panel now has to have a #10 wire (depending on the type of wire) because it's now a feeder because of the fused disconnect. You can drop the wire size back down from the disc. to the unit.

If the nameplate doesn't say "fuses" or "fuses only" then a breaker is allowed. I never use a fused disc. unless required.
Click to expand...

kwired said:
I think 430.62(A) would still allow 12 AWG feeder and 35 amp breaker in that situation. If the feeder supplied more than one load, you would have to add that load to minimum ampacity of the conductor and to your selection of an overcurrent device. If you had an additional 10 amp load supplied by said feeder I think you could use 10 AWG and 45 amp breaker - small conductor rule of 240.4(D) gets a little blurrier here though, but for conductors larger then 10 AWG I think there is no question you could do it that way. 240.4(G) however sends us to other sections including 430 and 440 so I think it can apply to small conductors as well.
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Would you agree that a fused disconnect is an OCPD?
Would you agree that it is the final branch circuit overcurrent device?

Now look at this definition of a feeder.

Feeder. All circuit conductors between the service equipment,
the source of a separately derived system, or other power
supply source and the final branch-circuit overcurrent device.
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HVAC Guys....

HVAC Guys....

wireday said:
I’ve been told that the hvac guys like to have them, just was wondering about code
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No savvy HVACR Tech will endorse FUSED disconnects on any 3 phase motor load. This always invariably leads to Destructive Single Phase faults on older generation gear in general.
 
StarCat said:
No savvy HVACR Tech will endorse FUSED disconnects on any 3 phase motor load. This always invariably leads to Destructive Single Phase faults on older generation gear in general.
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Do they use inferior overload protection, or design compressor motors differently and they can't handle this as well as other motors under same conditions?

Phase loss still happens once in a while whether it be caused at local disconnect or upstream from service equipment.
 
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