HVAC conductor and breaker sizing - AGAIN???

GoldDigger

Moderator
Staff member
They didn't leave a 40 amp breaker to be installed - they left a 60 amp breaker. The pullout is not fused, it's just a sliding switch. If it made a snapping noise it would just as well be a big snap switch. Speaking of which, that's what they used on the furnace for a disconnect: a regular ol' light switch.
+1
You will not get any argument from me that what they left him is compliant.

Almost all of this discussion had been about what different scenarios close to what they left might be compliant. And all of them involve work to be done by an electrician.
 

spurlockda

Member
Location
Nevada
Thanks for all the guidance.

Thanks for all the guidance.

I really do appreciate all the words of help. You guys answered (or at least got me started researching in the right direction.

Sorry Peter, didn't mean to annoy ya. I'm not doing a DIY, I just want to monitor the performance of an HVAC contractor that was causing me some concern. I am in a training track so I guess I know just enough to be dangerous. :D

OK, ya'll can close the thread if you want.

Dave
 

peter d

Senior Member
Location
New England
I really do appreciate all the words of help. You guys answered (or at least got me started researching in the right direction.

Sorry Peter, didn't mean to annoy ya. I'm not doing a DIY, I just want to monitor the performance of an HVAC contractor that was causing me some concern. I am in a training track so I guess I know just enough to be dangerous. :D

OK, ya'll can close the thread if you want.

Dave
My apologies, I'm sure you can understand how it looked like a DIY thread.
 

kwired

Electron manager
Location
NE Nebraska
Only thing I have seen that is wrong is the 60 amp breaker being used instead of a 40 amp overcurrent device being applied somewhere in the circuit.

They could have used a 400 amp conductor and 400 amp disconnect if they wanted and it would not have violated any code as long as they found ways to legally terminate that size of conductor at the HVAC equipment that very likely has much smaller terminations.

That 60 amp disconnect or any other similar is about all you will find suitable for the situation, you will not find one rated 40 amps. Too many parts to stock and produce to have one for every possible rating, so there are different levels of standard sizes. For the non fused variety of these inexpensive pull out disconnects there is only one size that is common and it is rated for up to 60 amps. For fusible types - the fuse holder is really the limiting factor otherwise they are built about the same - standard sizes of fuses are 30 amp and less fit one fuse holder and 35 to 60 amp fuses fit another size.
 

spurlockda

Member
Location
Nevada
No worries

No worries

My apologies, I'm sure you can understand how it looked like a DIY thread.
No worries man. Like I said, I'm probably one of those Apprentices who knows enough to be dangerous. I'm away from my normal location contracting things for my Mother's house and when I see things going on by the contractor that don't line up with what I have been taught, I'll whip it out (My Mike Holt manuals, NEC and etc and try to research things before I confront the contractor. I want to be able to show them what I found and how it differs from what they are doing. That way I not coming off to them as a knucklehead. Besides what this post string has been dealing with, I caught him putting two neutrals into the same hole inside the panel bus. And he's splitting neutrals in two different branch circuits. And there is more?

Anyway, thanks again for your patience with this knucklehead Apprentice.

Dave
 

spurlockda

Member
Location
Nevada
Yes sir, snap switch

Yes sir, snap switch

As long as the "regular old" is classified as a snap switch. I do not think an old fashion mercury type silent switch would qualify, for example.
Yes sir, it is a snap switch. In fact, if you read my response about the diy thing, the HVAC guys, split a neutral between the furnace power supply through the snap switch furnace disconnect, and a stand alone steam humidifier.

Thank you.
Dave
 

spurlockda

Member
Location
Nevada
Copy all

Copy all

Only thing I have seen that is wrong is the 60 amp breaker being used instead of a 40 amp overcurrent device being applied somewhere in the circuit.

They could have used a 400 amp conductor and 400 amp disconnect if they wanted and it would not have violated any code as long as they found ways to legally terminate that size of conductor at the HVAC equipment that very likely has much smaller terminations.

That 60 amp disconnect or any other similar is about all you will find suitable for the situation, you will not find one rated 40 amps. Too many parts to stock and produce to have one for every possible rating, so there are different levels of standard sizes. For the non fused variety of these inexpensive pull out disconnects there is only one size that is common and it is rated for up to 60 amps. For fusible types - the fuse holder is really the limiting factor otherwise they are built about the same - standard sizes of fuses are 30 amp and less fit one fuse holder and 35 to 60 amp fuses fit another size.

Yes sir. I intend to point out the flaw in their thinking that the 60 amp breaker in the main breaker panel supplying the circuit for the compressor with nothing to change it down to 40 amps as directed by the manufacturers spec plate on the compressor which says max breaker is 40 amp.
 

Attachments

kwired

Electron manager
Location
NE Nebraska
Yes sir. I intend to point out the flaw in their thinking that the 60 amp breaker in the main breaker panel supplying the circuit for the compressor with nothing to change it down to 40 amps as directed by the manufacturers spec plate on the compressor which says max breaker is 40 amp.

Looking at that nameplate something that may come to a surprise to some is that unit can be fed with 12 AWG 75 or 90 degree conductors and be on a 40 amp breaker and be NEC compliant.

It can not be supplied with NM cable that size though as NM is only permitted to be used per 60 degree ampacity, NM cable would need to be at least 10 AWG.
 

mtfallsmikey

Senior Member
Would rather have a better quality disco myself, like a Square D, disco looks like a QO, but switch only. Seen more than a few of those plug-in units arc and fail. And yes, we used 20 amp. spec grade switches for furnace disco's, used the red emer. sw. plate with them.
 
Would rather have a better quality disco myself, like a Square D, disco looks like a QO, but switch only. Seen more than a few of those plug-in units arc and fail. And yes, we used 20 amp. spec grade switches for furnace disco's, used the red emer. sw. plate with them.
Those SqD discos suck. I hate them. They may look cool but a PIA to land wires in.
 
Looking at that nameplate something that may come to a surprise to some is that unit can be fed with 12 AWG 75 or 90 degree conductors and be on a 40 amp breaker and be NEC compliant.

It can not be supplied with NM cable that size though as NM is only permitted to be used per 60 degree ampacity, NM cable would need to be at least 10 AWG.
Do that and you would cause everybody's head to explode I bet.
 

kwired

Electron manager
Location
NE Nebraska
Those SqD discos suck. I hate them. They may look cool but a PIA to land wires in.
I will second that. The molded case switch is fine, but the enclosure they put it in is what sucks.

Do that and you would cause everybody's head to explode I bet.
I have done that for units with similar rating - had inspectors take a second look a few times then decide it is compliant.

Also throws them off a for a bit when you run 10 AWG NM cable from loadcenter to disconnect then 12 THWN from disconnect to unit.
 

vortac555

Member
Location
deer park ,NY
HVAC Sizing ( Thanks for you Service ) Squid

HVAC Sizing ( Thanks for you Service ) Squid

If I read that correctly With 23.9 min circuit ampacity You only need to size the breaker at 30 amps. The min amperage on nameplate per the code. This number is made up by the compressor plus the fan. Plus 125% All these numbers on on the nameplate on the unit. They can put a 60 amp non fused switch. this is just a safety switch for service. You do require a 110 volt service outlet within 25 feet of the outside unit. And a light and outlet in the attic by the access hatch. if it is a split system.
If the unit is being installed on a force air furnace. You will need power a condensation pump. Normally located by the furnce and you will need a place for the water to drain . So the contractor can run #10 wire rated at 30amp romex is orange color. And depending on voltage to air handler 15 or 20 amp line White or yellow color respectively. Running 20amp is easier to cover both. And the cost is close.
The more I think of this 23.9 next higher breaker is 25. You could probably run 20 amp wire fuse up to 25. However we would install 30 amp to condensor. and 20 to attic and be done.
Hope this helps.
 

kwired

Electron manager
Location
NE Nebraska
If I read that correctly With 23.9 min circuit ampacity You only need to size the breaker at 30 amps. The min amperage on nameplate per the code. This number is made up by the compressor plus the fan. Plus 125% All these numbers on on the nameplate on the unit. They can put a 60 amp non fused switch. this is just a safety switch for service. You do require a 110 volt service outlet within 25 feet of the outside unit. And a light and outlet in the attic by the access hatch. if it is a split system.
If the unit is being installed on a force air furnace. You will need power a condensation pump. Normally located by the furnce and you will need a place for the water to drain . So the contractor can run #10 wire rated at 30amp romex is orange color. And depending on voltage to air handler 15 or 20 amp line White or yellow color respectively. Running 20amp is easier to cover both. And the cost is close.
The more I think of this 23.9 next higher breaker is 25. You could probably run 20 amp wire fuse up to 25. However we would install 30 amp to condensor. and 20 to attic and be done.
Hope this helps.
You can use a 25 or 30 amp breaker if you want, may not hold while compressor is starting, most installers will use the 40 amp max listed on the nameplate to avoid that potential problem.

MCA comes from 125% of the compressor rated load amps plus the FLA of the condenser fan, plus other loads if there are any.

Not an exact formula used that I know of to determine max overcurrent device but is usually around 175 to 200 percent of compressor RLA.
 

spurlockda

Member
Location
Nevada
My jaw dropped a little

My jaw dropped a little

Looking at that nameplate something that may come to a surprise to some is that unit can be fed with 12 AWG 75 or 90 degree conductors and be on a 40 amp breaker and be NEC compliant.

It can not be supplied with NM cable that size though as NM is only permitted to be used per 60 degree ampacity, NM cable would need to be at least 10 AWG.

I was a little surprised when I saw that it could have been fed with 12 gage. Especially when I first looked at the 8 gage whip thinking I would be seeing them run 8 gage all the way to the unit. Remember I had a twinge of doubt even when I went back to check my numbers and came up with 10 gage.
 

spurlockda

Member
Location
Nevada
Confused again

Confused again

I will second that. The molded case switch is fine, but the enclosure they put it in is what sucks.



I have done that for units with similar rating - had inspectors take a second look a few times then decide it is compliant.

Also throws them off a for a bit when you run 10 AWG NM cable from loadcenter to disconnect then 12 THWN from disconnect to unit.
I coulda sworn I read somewhere in my training material that you had to maintain the same gage conductors in the same branch circuit from the loadcenter to the final load of that branch circuit? Some times I feel like my head is going to explode; drinking from the firehose of knowledge.
 

spurlockda

Member
Location
Nevada
Yep

Yep

If I read that correctly With 23.9 min circuit ampacity You only need to size the breaker at 30 amps. The min amperage on nameplate per the code. This number is made up by the compressor plus the fan. Plus 125% All these numbers on on the nameplate on the unit. They can put a 60 amp non fused switch. this is just a safety switch for service. You do require a 110 volt service outlet within 25 feet of the outside unit. And a light and outlet in the attic by the access hatch. if it is a split system.
If the unit is being installed on a force air furnace. You will need power a condensation pump. Normally located by the furnce and you will need a place for the water to drain . So the contractor can run #10 wire rated at 30amp romex is orange color. And depending on voltage to air handler 15 or 20 amp line White or yellow color respectively. Running 20amp is easier to cover both. And the cost is close.
The more I think of this 23.9 next higher breaker is 25. You could probably run 20 amp wire fuse up to 25. However we would install 30 amp to condenser. and 20 to attic and be done.
Hope this helps.
Yup, that's how I calculated it too. Plus, it's supposed to be a pretty efficient system so I think it's miserly in the power used.

Didn't need a condensate pump cause it gravity drains into a floor drain. It's in the basement.

Also, they said I would have to provide the tech service outlet. The compressor is only about 15' line of sight from the corner of the house where the disconnect will be located and the d/c box has a lock-out setup. That corner of the house is also where the service drop/meter box is and with the main panel down in the basement in that same corner. I needed an outdoor outlet setup for the back of the house anyway for code. I installed it using 10 gage THHN-2 running through nonmetallic liquid tite to an outdoor outlet box with the cover that can close even with something plugged in. And I used a 20amp Weather Resistant/Tamper Resistant GFCI. 20 amp breaker in the main panel.

I was planning on extending the branch circuit on up the corner of the house for an LED security light.

You confused me with this:
"You could probably run 20 amp wire fuse up to 25. However we would install 30 amp to condenser."
"20 amp wire - fuse up to 25 - install 30 amp ...

Not sure where the attic thing came into it?
 
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