Max Breaker

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Little Bill

Little Bill

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Semi-Retired Electrician
I know the allowances for HVAC equipment as far as larger breaker, smaller conductors. If the breaker/fuse is just for short circuits, why is there a max size?

I'm trying to finish a house and the HVAC installer told me I needed a 60A breaker for the air handler. When they got it installed, turns out it needs a 45A Max breaker. I can't find an Eaton 2-pole 45A breaker locally but I can find plenty of 50A & 60A. Just wondered why a 50A wouldn't work in place of a 45A is its just for a short circuit?
 
hillbilly1 said:
You can actually go smaller, you don’t have to go with the max. So a 40 may be sufficient. Or you can use a fusible disconnect, and fuse it at 45.
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I was thinking of using a 40A but didn't know if it would cause tripping on in-rush. Don't want to have to go back if I don't have to.

What really irks me is I'm pretty sure HVAC (some anyway) installers are charging the customer for wiring and breakers, but we end up having to run the wire and furnish the breaker. Of course I charge extra for doing it but the customer is the one paying twice. Looks like they could at least furnish the breaker and I would install it.
 
Little Bill said:
I was thinking of using a 40A but didn't know if it would cause tripping on in-rush. Don't want to have to go back if I don't have to.

What really irks me is I'm pretty sure HVAC (some anyway) installers are charging the customer for wiring and breakers, but we end up having to run the wire and furnish the breaker. Of course I charge extra for doing it but the customer is the one paying twice. Looks like they could at least furnish the breaker and I would install it.
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A lot of the new units use inverter drives, especially the air handler, besides, the majority of the load is probably heat strips.
 
hillbilly1 said:
A lot of the new units use inverter drives, especially the air handler, besides, the majority of the load is probably heat strips.
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I have a couple of weeks before I call for final. If I don't come up with a 45A, I will give the 40A a shot. And yes, the heat strips are what drives the OCP size. They changed to smaller KW strips is the reason I'm having to change from the 60A.
 
Do heat strip circuits have a min/max breaker spec? I thought they only used MCA for the strips. Or is this a combo circuit for a mini sit? The strip circuit should be easy to calculate unless the main control board is on the same circuit. Should be (watts of strip * 1.25 + control watts) / volts. Then breaker round up to next standard should be allowed.

Most air handlers come with a huge set of ampacity labels to handle all the heat strip permutations. Did they use the right labels? Did you do a sanity check?
 
suemarkp said:
Do heat strip circuits have a min/max breaker spec? I thought they only used MCA for the strips. Or is this a combo circuit for a mini sit? The strip circuit should be easy to calculate unless the main control board is on the same circuit. Should be (watts of strip * 1.25 + control watts) / volts. Then breaker round up to next standard should be allowed.

Most air handlers come with a huge set of ampacity labels to handle all the heat strip permutations. Did they use the right labels? Did you do a sanity check?
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There is a list of ampacities and the installers mark which they used on the label.
It is not a mini split, just an air handler for a heat pump.
 
Ductless (Mini Split) heat pumps don't have auxiliary heat, forced air heat pumps can. On forced air heat pumps auxiliary heat requires a separate dedicated circuit. So, three possible dedicated circuits. (1) for the Air Handler, (1) for the Condensing Unit and (1) for the auxiliary heat if needed. The Mini Split heat pump air handler(s) each get their power from the Condensing Unit.
 
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hillbilly1 said:
A lot of the new units use inverter drives, especially the air handler, besides, the majority of the load is probably heat strips.
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Which makes no sense the way many are assembled. AHU unit with no strips, 15 amp OCPD is what is marked on the nameplate.

Same unit with 9.6 kW heat strip added - 60 amp OCPD that same motor that had to be on 15 amp device before is now on a 60 amp device.

Add second 9.6 kW strip, that one says 50 amp max OCPD - everything about it is the same as the first one other than there is no blower on same circuit.

Add a 4.8 kW strip it is just one instead of two elements but otherwise the same thing as the 9.6 kW - and it will call for 25 amp max it somehow can't handle the same level of fault as it's identical counter parts on the 9.6 kW units? I understand if you ran only 10 AWG conductor you still need proper protection on it.

Used to see a particular unit several years ago that had two breakers installed, usually both 60 amp whether it was the 9.6 or the 4.8 heater unit connected, and the blower also connected to one of them. Had an optional common lug kit that could be installed if you wanted to run a single circuit to the whole thing. Those did leave the 4.8 bank of heat when present with a 60 amp OCPD as the protection.

I see this whole thing to be somewhat of a game especially for the inspectors when reality is those exact same heat strips apparently are fine on a 60 amp OCPD when also connected with enough other load on the same device.
 
I still have not seen where anyone answered as to why a certain size max breaker should be used if the breaker is just for short circuit. I would hope a 60A breaker would trip as fast as a 40A if a short should occur.
 
Little Bill said:
I still have not seen where anyone answered as to why a certain size max breaker should be used if the breaker is just for short circuit. I would hope a 60A breaker would trip as fast as a 40A if a short should occur.
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It’s that little tag on the unit that says Max ocp, anything else doesn’t matter. If the unit fails, and catches on fire, you know who the lawyers will come after, right or wrong. LOL!
 
Little Bill said:
I still have not seen where anyone answered as to why a certain size max breaker should be used if the breaker is just for short circuit. I would hope a 60A breaker would trip as fast as a 40A if a short should occur.
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That sort of depends on how much current the fault actually carries and the instantaneous trip level of each breaker involved, which from same product line should be higher for a 60 than a 40. But that speed is likely going to take special equipment to measure, to the naked eye it will likely appear about the same with either in most cases.

Now take that same 40 or 60 amp breaker and place it in a situation where the available fault current is significantly less, (weak source, long conductor runs, etc.) you might be able to tell it takes longer to trip in that situation without any special measuring equipment.
 
mtnelect said:
Ductless (Mini Split) heat pumps don't have auxiliary heat, forced air heat pumps can. On forced air heat pumps auxiliary heat requires a separate dedicated circuit. So, three possible dedicated circuits. (1) for the Air Handler, (1) for the Condensing Unit and (1) for the auxiliary heat if needed. The Mini Split heat pump air handler(s) each get their power from the Condensing Unit.
Click to expand...

I distinctly remember hooking up mini splits many many years ago that came with 5kw heat strips if you wanted it. We always ran a 10/2 to the indoor unit and 12/2 nm to the outdoor unit. T-stat wires in between.

I don't know how old you are so this may be before your time and this was not uncommon years ago. I suppose they may not have them with strips anymore because I have not seen one in recent years either.
 
Dennis Alwon said:
I distinctly remember hooking up mini splits many many years ago that came with 5kw heat strips if you wanted it. We always ran a 10/2 to the indoor unit and 12/2 nm to the outdoor unit. T-stat wires in between.

I don't know how old you are so this may be before your time and this was not uncommon years ago. I suppose they may not have them with strips anymore because I have not seen one in recent years either.
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The new ductless (Mini Split) can now work down to 20 degrees. The only drawback is when they go into the defrost mode, to melt the ice build-up. This can take up to 5 minutes.

They are a great HVAC systems, you only service the room you are in, not the whole house.
 
mtnelect said:
The new ductless (Mini Split) can now work down to 20 degrees. The only drawback is when they go into the defrost mode, to melt the ice build-up. This can take up to 5 minutes.

They are a great HVAC systems, you only service the room you are in, not the whole house.
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So what happens when you get a week or so below 20? I guess they don't use them too far up North of NC
 
mtnelect said:
The new ductless (Mini Split) can now work down to 20 degrees. The only drawback is when they go into the defrost mode, to melt the ice build-up. This can take up to 5 minutes.

They are a great HVAC systems, you only service the room you are in, not the whole house.
Click to expand...
mtnelect said:
Yes, they do have units that work down to 0 degrees, but they are more expensive.
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Seeing more and more of them around here all the time. It gets below zero and sometimes for a few days in a row. Haven't seen one yet with any kind of backup heat. Don't know how well they work out for those that have them when extreme cold has set in for a few days though.

Defrost mode is simply a necessity I wouldn't call it a drawback. A drawback would to not have a defrost mode, then the thing would essentially stop functioning simply because you can't get air over the iced over coil anymore.
 
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