Condensing Unit Overcurrent Protection

[kbsparky]

...It's usually #10 for 30amp #8 for 40 amp and so on.

Based on WHAT? 240.4(D)? Why would one apply the requirements of 240.4(D) when the Code plainly states that 240.4(G) should be used?

 

[jap]

Based on WHAT? 240.4(D)? Why would one apply the requirements of 240.4(D) when the Code plainly states that 240.4(G) should be used?

Not taking into consideration the sizing of conductors allowed for a motor circuit,Simply based on almost 99% of all residential loadcenters you take the panel cover off and look at.

 

[kwired]

Not taking into consideration the sizing of conductors allowed for a motor circuit,Simply based on almost 99% of all residential loadcenters you take the panel cover off and look at.

There is usually only one breaker, maybe two if a larger house that feed the AC. The rest of the circuits do have breakers that match conductor ampacity. Large motors (other than AC units) are not that common in dwellings.

Go to a place that has a lot of motors - especially with a large diversity of motor sizes rated over 1 hp single phase or 3- 5 hp three phase and you will see lots of breakers that may look suspicious to someone not used to seeing higher device settings for these type of circuits.

 

[jap]

There is usually only one breaker, maybe two if a larger house that feed the AC. The rest of the circuits do have breakers that match conductor ampacity. Large motors (other than AC units) are not that common in dwellings.

Go to a place that has a lot of motors - especially with a large diversity of motor sizes rated over 1 hp single phase or 3- 5 hp three phase and you will see lots of breakers that may look suspicious to someone not used to seeing higher device settings for these type of circuits.

I've worked in industrial settings my whole career and am very used to seeing breakers oversized for the short circuit protection, I utilize the option myself. but back to our 240v single phase condensor compressor motor that the OP was talking about.
I very seldom see in a residential loadcenter where the electrician utilized using small guage wire protected by a larger than normal
breaker. Its just a fact that its not that common in a house hold. Usually a 30 amp breaker feeding an AC unit has 10/2 wg run to
the outside pullout, a 40 amp breaker usually has 8/2 wg run to the outside pullout and so on. Very seldom do you see a 12/2 wg
run to the outside pullout with a 35 amp breaker in the panel, although they could. I dont downsize the wire from the loadcenter breaker to the outside pullout in residential or commercial for that matter to an A/C compressor. Never have. However, on motors (which I've built controls for on about every size) I do utilize the option. I don't feel like an Internal Thermal Overload that you see on the simple single phase residential compressor units are as sensitive as field adjustable overloads like i install in the starters for my 5 to 200 hp motors that I build the controls for but thats just my opinion not that it matters, since it the manufacturers problem not
mine. There's no use beating my opinion to death, I'm not saying it's wrong i'm just saying I'm used to installing my own protective devices and dialing them in so they suit me that's all.

 

[kwired]

I've worked in industrial settings my whole career and am very used to seeing breakers oversized for the short circuit protection, I utilize the option myself. but back to our 240v single phase condensor compressor motor that the OP was talking about.
I very seldom see in a residential loadcenter where the electrician utilized using small guage wire protected by a larger than normal
breaker. Its just a fact that its not that common in a house hold. Usually a 30 amp breaker feeding an AC unit has 10/2 wg run to
the outside pullout, a 40 amp breaker usually has 8/2 wg run to the outside pullout and so on. Very seldom do you see a 12/2 wg
run to the outside pullout with a 35 amp breaker in the panel, although they could. I dont downsize the wire from the loadcenter breaker to the outside pullout in residential or commercial for that matter to an A/C compressor. Never have. However, on motors (which I've built controls for on about every size) I do utilize the option. I don't feel like an Internal Thermal Overload that you see on the simple single phase residential compressor units are as sensitive as field adjustable overloads like i install in the starters for my 5 to 200 hp motors that I build the controls for but thats just my opinion not that it matters, since it the manufacturers problem not
mine. There's no use beating my opinion to death, I'm not saying it's wrong i'm just saying I'm used to installing my own protective devices and dialing them in so they suit me that's all.

OK, at same time I am saying more care than you maybe give credit for was put into selecting the overload setting for these compressors. They are not a "one size fits all" device. Most are Klixon devices and if you look at the spec number on each unit - they have a pretty long number that does have spec meanings for each digit of the number.

 

[jap]

OK, at same time I am saying more care than you maybe give credit for was put into selecting the overload setting for these compressors. They are not a "one size fits all" device. Most are Klixon devices and if you look at the spec number on each unit - they have a pretty long number that does have spec meanings for each digit of the number.

I'll give them the benefit of the doubt but the simple design of a Klickson makes me feel its not as accurate
as a set of solid state or electronic overloads, although they may be, and that was my whole point.

If the Overload doesnt open at an accurate selected current, then the possibility of overloading the smaller
wire size you've chosen because of it may not be as protected as one might think.

 

[kwired]

I'll give them the benefit of the doubt but the simple design of a Klickson makes me feel its not as accurate
as a set of solid state or electronic overloads, although they may be, and that was my whole point.

If the Overload doesnt open at an accurate selected current, then the possibility of overloading the smaller
wire size you've chosen because of it may not be as protected as one might think.

But I have said it before, it's primary intent is protecting the motor, conductor protection is more inherent. Chances are if it is sized a little too high the motor fails long before the conductor does because of overloading conditions.

 

[Cavie]

I've worked in industrial settings my whole career and am very used to seeing breakers oversized for the short circuit protection, I utilize the option myself. but back to our 240v single phase condensor compressor motor that the OP was talking about.
I very seldom see in a residential loadcenter where the electrician utilized using small guage wire protected by a larger than normal
breaker. Its just a fact that its not that common in a house hold. Usually a 30 amp breaker feeding an AC unit has 10/2 wg run to
the outside pullout, a 40 amp breaker usually has 8/2 wg run to the outside pullout and so on. Very seldom do you see a 12/2 wg
run to the outside pullout with a 35 amp breaker in the panel, although they could. I dont downsize the wire from the loadcenter breaker to the outside pullout in residential or commercial for that matter to an A/C compressor. Never have. However, on motors (which I've built controls for on about every size) I do utilize the option. I don't feel like an Internal Thermal Overload that you see on the simple single phase residential compressor units are as sensitive as field adjustable overloads like i install in the starters for my 5 to 200 hp motors that I build the controls for but thats just my opinion not that it matters, since it the manufacturers problem not
mine. There's no use beating my opinion to death, I'm not saying it's wrong i'm just saying I'm used to installing my own protective devices and dialing them in so they suit me that's all.

Jap, Don't know where you work. I've been a license holder for 40 years in Florida. Currently have an Unlimited Electric license in Florida along with a Standard Inspectors license. Quailified 3 different business, did a two year stint as an Electric inspector. Not tooting my horn here but listen to Kwired, he knows what he is talking about. Oversized fuses and breakers are common place on A/C Heating loads. Especially in residential but also allowed in commercial. There are 10's of thousands of homes wired that way in Florida and other states. Read the nameplate for Max and mim sizes, install it and go to sleep. Search Mike Holts web site and you'll find 8 x 10 color glossy photographs I'm sure.

 

[jap]

Jap, Don't know where you work. I've been a license holder for 40 years in Florida. Currently have an Unlimited Electric license in Florida along with a Standard Inspectors license. Quailified 3 different business, did a two year stint as an Electric inspector. Not tooting my horn here but listen to Kwired, he knows what he is talking about. Oversized fuses and breakers are common place on A/C Heating loads. Especially in residential but also allowed in commercial. There are 10's of thousands of homes wired that way in Florida and other states. Read the nameplate for Max and mim sizes, install it and go to sleep. Search Mike Holts web site and you'll find 8 x 10 color glossy photographs I'm sure.

So your saying if you open most small a/c pullouts in your area that you'll find #12 wire in the disconnect
and a 25a or larger breaker in the loadcenter feeding it?

 

[jap]

Although perfectly fine, that's not the case around here most times. Especially not in 10's of thousands of
installations.

 

[jap]

This topic has gotten way off base from comparing the sensitivity of an integral thermal overload to a field installed Electronic or Solid State overload.

 

[Cavie]

So your saying if you open most small a/c pullouts in your area that you'll find #12 wire in the disconnect
and a 25a or larger breaker in the loadcenter feeding it?

That is correct. 40 amp on #10 is common also.

 

[jap]

Good deal.

 

[jap]

I hope the Air Conditioning guys have thier overload sized properly,since you dont have any evidence of
what it's set at. But then again,if your conductors are sized per the minimum circuit amps which is worst
case scenario plus 25%, which is not indicated on the nameplate either, everything should be ok.

 

[kwired]

..if your conductors are sized per the minimum circuit amps which is worst
case scenario plus 25%, which is not indicated on the nameplate either, everything should be ok.

That is what I have been trying to tell you.

You do have to remember that NM cable must be selected from 60 deg C column. If MCA were 21 amps you could run 12 AWG (before any adjustment factors) but it would have to be 10 AWG if NM cable.

And there are a lot of 18 or 19 MCA units that have 10 AWG run to them that could be 12 AWG. My guess is many installers just don't realize they could run 12 AWG.

 

[jap]

That is what I have been trying to tell you.

You do have to remember that NM cable must be selected from 60 deg C column. If MCA were 21 amps you could run 12 AWG (before any adjustment factors) but it would have to be 10 AWG if NM cable.

And there are a lot of 18 or 19 MCA units that have 10 AWG run to them that could be 12 AWG. My guess is many installers just don't realize they could run 12 AWG.

I heard you all along I just didnt want to cave in that easily.
I also agree the reason most dont install it as such is because they dont realize that they can.

 

[mdpolan]

Inspectors who don't know the code

Inspectors who don't know the code

The NEC is designed in a specific fashion. ALL codes in Chapters 4 on MODIFY the codes in the previous chapters. Simply remind the AHJ that 440 REQUIRES that you use the manufacturers name plate. The Manufacturer has built into the MCA the additional 125% requirement. It does not matter if the Max fuse/ CB is larger then the 310-15 limits for a conductor. Those numbers DO NOT APPLY to breaker size. THINK MOTORS!!