HVAC Load Calculation

If the OP wished to use a 300 amp panel to allow for future loads there would be no problem as long as the feeder was sized accordingly
 
augie47 said:
If the OP wished to use a 300 amp panel to allow for future loads there would be no problem as long as the feeder was sized accordingly
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Per 430.62 doesn’t permit the use of the next standard size of protection for the feeder. Per 430.62 the overcurrent protection for the feeder calculates to 265 amps so it would have to be protected by a 250 amp ocpd
 
Jaybone812 said:
Per 430.62 doesn’t permit the use of the next standard size of protection for the feeder. Per 430.62 the overcurrent protection for the feeder calculates to 265 amps so it would have to be protected by a 250 amp ocpd
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That's only if the conductors are sized per 430.24. If you provide 300A conductors, it's fine to use a 300A OCPD, see 430.62(B).

Cheers, Wayne
 
wwhitney said:
That's only if the conductors are sized per 430.24. If you provide 300A conductors, it's fine to use a 300A OCPD, see 430.62(B).

Cheers, Wayne
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I figured that was implied by my previous comment about 430.24 in response to you sizing your feeder conductors per 430.24 and thought the topic of conversation had shifted to using 430.62(a) to size protection for the feeder conductors sized by 430.24
Didn’t think 430.62(b) applied
My apologies for not clarifying. And being vague . Because of course if the ampacity of the feeder conductors is 300 amps then it can be Protected by a 300 amp ocpd
 
Dennis Alwon said:
Does max fuse mean you must use a fuse? I thought it had to say max fuse only but I may be wrong
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If there was change in wording I was not aware of it.

Here is what I always went off From UL.
May be out dated.

If there some new info or I have misunderstood. Please let me know.

Thank you.
 

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If you misunderstand UL then so do I because I see that as meaning a unit with a nameplate that’s marked “max Fuse “ for the maximum size ground fault /short circuit protection device permitted means that a fuse must be installed somewhere in the circuit before the unit , probably at the disconnect , to provide the type of protection specified by the manufacturer . Using a breaker alone to provide the protection violates 110.3(b)
 
Jaybone812 said:
If you misunderstand UL then so do I because I see that as meaning a unit with a nameplate that’s marked “max Fuse “ for the maximum size ground fault /short circuit protection device permitted means that a fuse must be installed somewhere in the circuit before the unit , probably at the disconnect , to provide the type of protection specified by the manufacturer . Using a breaker alone to provide the protection violates 110.3(b)
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Some times when I read things I don't get it correct.
Was thinking maybe an updated version with verbage change adding only.
It would make sense for it to say only. Then there is no confusion.
"Max, fuse only"

In OP case using the in-site rule would cost them to go back and add fused disconnects.
Unless the word only applied.


Now OP has plenty of options. I was thinking of the top of head feeder taps with one to three feeders. This would also help reduce available fault current if that's an issue. Again looking at name plate. The 10 foot and 25 foot tap rule could work to his favor along with the in-site rule.
Rack,wireways,fused disc.

He mentioned single phase feeder with a panel. Now he could use use a three phase feeder(s) with taps. If there was an issue with a 250 or 300 branch in his DP. Now they could run 100 amp feeders with across the buss OCPD. Reducing feeder conductor sizes. This would also place feeders in different places co in siding with the units.

Of course a tag along service receptacle on each rack. Which would mean with in 25'.

Just thinking of options since OP mentioned single phase feeder. I would not do that as it not good practice with three phase available. End up costing more in the long run.

Hope that explains why I mentioned fuse disconnect and why fuse only seamed important to me.

Edit: Would like to add installing a fused disconnect on a mini split sometimes can be a pain. I like to avoid that when ever possible.
 
Tulsa Electrician said:
Some times when I read things I don't get it correct.
Was thinking maybe an updated version with verbage change adding only.
It would make sense for it to say only. Then there is no confusion.
"Max, fuse only"

In OP case using the in-site rule would cost them to go back and add fused disconnects.
Unless the word only applied.


Now OP has plenty of options. I was thinking of the top of head feeder taps with one to three feeders. This would also help reduce available fault current if that's an issue. Again looking at name plate. The 10 foot and 25 foot tap rule could work to his favor along with the in-site rule.
Rack,wireways,fused disc.

He mentioned single phase feeder with a panel. Now he could use use a three phase feeder(s) with taps. If there was an issue with a 250 or 300 branch in his DP. Now they could run 100 amp feeders with across the buss OCPD. Reducing feeder conductor sizes. This would also place feeders in different places co in siding with the units.

Of course a tag along service receptacle on each rack. Which would mean with in 25'.

Just thinking of options since OP mentioned single phase feeder. I would not do that as it not good practice with three phase available. End up costing more in the long run.

Hope that explains why I mentioned fuse disconnect and why fuse only seamed important to me.

Edit: Would like to add installing a fused disconnect on a mini split sometimes can be a pain. I like to avoid that when ever possible.
Click to expand...
I’m in agreement with you if the word “only” was added to the “max fuse” when the unit requires the ground fault /short circuit protection to come from a fuse it would put an end to any all confusion of how that part of the nameplate is supposed to read
 
It was decided to use a subpanel 3 phase which is going to be next to the 12 condenser. The OCP will be 40A, correct? Will I still have to use a disconnector? since the panel will be in the location of the 12 condenser.
 
Jaybone812 said:
I’m in agreement with you if the word “only” was added to the “max fuse” when the unit requires the ground fault /short circuit protection to come from a fuse it would put an end to any all confusion of how that part of the nameplate is supposed to read
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And the
Tulsa Electrician said:
Some times when I read things I don't get it correct.
Was thinking maybe an updated version with verbage change adding only.
It would make sense for it to say only. Then there is no confusion.
"Max, fuse only"

In OP case using the in-site rule would cost them to go back and add fused disconnects.
Unless the word only applied.


Now OP has plenty of options. I was thinking of the top of head feeder taps with one to three feeders. This would also help reduce available fault current if that's an issue. Again looking at name plate. The 10 foot and 25 foot tap rule could work to his favor along with the in-site rule.
Rack,wireways,fused disc.

He mentioned single phase feeder with a panel. Now he could use use a three phase feeder(s) with taps. If there was an issue with a 250 or 300 branch in his DP. Now they could run 100 amp feeders with across the buss OCPD. Reducing feeder conductor sizes. This would also place feeders in different places co in siding with the units.

Of course a tag along service receptacle on each rack. Which would mean with in 25'.

Just thinking of options since OP mentioned single phase feeder. I would not do that as it not good practice with three phase available. End up costing more in the long run.

Hope that explains why I mentioned fuse disconnect and why fuse only seamed important to me.

Edit: Would like to add installing a fused disconnect on a mini split sometimes can be a pain. I like to avoid that when ever possible.
Click to expand...
all of the options you presented are def viable options and are great options when applied the correct way. I’m thinking the path of least resistance here would probably be 150 amp 3 phase feeder to the sub panel and depending on the exact location of the panel and in relation to the units he may have the option to do what he mentioned in an earlier comment and use the the ocpd’s for each of the 12 units as the disconnecting means for the condenser . Personally i think it’s more practical to install a disconnect near or on the unit but the breaker could be an available option depending on the location
 
FWIW, when I recently looked at UL 1995 "Heating and Cooling Equipment", the only significance I could find to the choice of fuse vs circuit breaker was for the calculated SCCR on the unit label. So I believe the only impact of deviating from the type of OCPD shown on the label would be that you can't use the SCCR from the unit label. So if your application requires a specific SCCR, you'd have to recalculate it, if doing so is even an option. Conversely, this would mean that for applications that don't require an SCCR, which IIRC is true for a one or two family dwelling, there would be no problem substituting fuses for circuit breakers or vice versa.

However, UL 1995 is quite long, and it is very possible I overlooked some other reference within it to the choice of fuse vs circuit breaker on the label. What is odd is that most UL standards that provide a choice or optional wording on the label provide a reference in the clause describing that choice or optional wording to a separate clause describing what additional testing or whatever the choice or option signifies. UL 1995's clause on the OCPD type on the label does not.

Cheers, Wayne
 
Tulsa Electrician said:
Some times when I read things I don't get it correct.
Was thinking maybe an updated version with verbage change adding only.
It would make sense for it to say only. Then there is no confusion.
"Max, fuse only"

In OP case using the in-site rule would cost them to go back and add fused disconnects.
Unless the word only applied.


Now OP has plenty of options. I was thinking of the top of head feeder taps with one to three feeders. This would also help reduce available fault current if that's an issue. Again looking at name plate. The 10 foot and 25 foot tap rule could work to his favor along with the in-site rule.
Rack,wireways,fused disc.

He mentioned single phase feeder with a panel. Now he could use use a three phase feeder(s) with taps. If there was an issue with a 250 or 300 branch in his DP. Now they could run 100 amp feeders with across the buss OCPD. Reducing feeder conductor sizes. This would also place feeders in different places co in siding with the units.

Of course a tag along service receptacle on each rack. Which would mean with in 25'.

Just thinking of options since OP mentioned single phase feeder. I would not do that as it not good practice with three phase available. End up costing more in the long run.

Hope that explains why I mentioned fuse disconnect and why fuse only seamed important to me.

Edit: Would like to add installing a fused disconnect on a mini split sometimes can be a pain. I like to avoid that when ever possible.
Click to expand...
You’re def correct about about trying to keep the panel within sight would still require fusible disconnects . I forgot this unit was labeled max fuse . So the panel location is essentially irrelevant. And if it’s me doing this job you’re option of top head feeder taps down to a fused disconnect for an least a few of the units is something id do if practical
 
Jaybone812 said:
Per 430.62 doesn’t permit the use of the next standard size of protection for the feeder. Per 430.62 the overcurrent protection for the feeder calculates to 265 amps so it would have to be protected by a 250 amp ocpd
Click to expand...
True if you choose to use minimum sized conductors which would need to be 250 copper or 350 aluminum.

Should you choose to have extra capacity and go with 300 amp OCPD then you will need at least 300 copper or 400 aluminum for conductors.
 
kwired said:
True if you choose to use minimum sized conductors which would need to be 250 copper or 350 aluminum.

Should you choose to have extra capacity and go with 300 amp OCPD then you will need at least 300 copper or 400 aluminum for conductors.
Click to expand...
You’re correct the comment you’re responding to was vague and I worded it wrong so apologies . My intention was to say:
If you size the conductors in accordance with 430.24 , then 430.62(a) does not permit us to jump to the next standard size breaker to protect the feeder
430.62(b) permits other installs, but like you said if you wanna use a 300 amp breaker you need to use 300 amp conductors
 
So then what would be the conclusion. I would have to use the fuse disconnect or the breaker would do the job? Like I mentioned I’m using a panel 3 phase OCPD 150A that would be in same area as the condensers. I just wanna be sure I wouldn’t be violating code
 
Leonan said:
So then what would be the conclusion. I would have to use the fuse disconnect or the breaker would do the job? Like I mentioned I’m using a panel 3 phase OCPD 150A that would be in same area as the condensers. I just wanna be sure I wouldn’t be violating code
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The units are marked “max fuse” on the nameplate so ground fault /short circuit protection needs to be provided by a fuse . No matter how close you put the panels to the mini split you have to install fuses somewhere in the circuit before the condenser and the easiest most practical way is a fused disconnect
 
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