A/C disconnect

[eddieK]

Dude- are you f'ing blind?

You must have 10 electricians on here, some of whom are masters as well as engineers, telling you youre wrong and youre continuing to argue with us? And youre an HVAC tech?

Give me a f'ing break.

Have some humility and admit you dont know what the hell youre talking about which is blatantly obvious by the verbal diarrhea youve left as comments on here...

In regards to your BS about the melted bus stab. I did service work for years and saw melted bus stabs for breakers that fed general use circuits. You have absolutely no clue what youre talking about...

Have a good one. You sure did a damn good job trolling this thread... smh wned: wned2:

It's wrong and unsafe every single time anyone says you can run #10 copper wire on a HVAC condensing unit circuit that has a 50 amp breaker installed for over current protection.

This is serious business and highly dangerous to keep insisting otherwise. In fact, reduced fuse size (5 amps lower than breaker - so that becomes the weakest link - higher amp protection than the minimum circuit ampacity and lower than the breaker installed) at unit disconnects is a common way to protect the system and one of these experts on here actually said that was dangerous - so much for "expert" opinion.

 

[wyliesdiesels]

Still not seen anything posted about a HVAC system, a motor is not a compressor.

AND again - Breakers protect the wire.

No tools huh...well, in the real world the people that service this stuff and fully understand the dynamics do use tools and the follow the codes and the manufacturers requirements (which supersede the code)

Lmao.

I never said i dont have tools.

Not that it matters to you, im a union electrician and of course i have tools. Probably have way more tools than you.

But seeing as how youve turned this into nothing more than a ******* match that i could care less about and im exhausted from working all day, you have a good night troll

 

[AntonLargiader]

Still not seen anything posted about a HVAC system specifically, a motor is not a compressor.

Then you missed my post.

Table 240.4G lists the overcurrent protection exception for HVAC and points you to 440, which is specifically about hermetic electric compressors.

440 Part III describes that overcurrent exception, allowing it to go as high as 225% of the standard value. This is short-circuit protection, not overload protection. Overload is handled at the compressor.

Now, it seems that your position is that you then take that value and backtrack to get the new, larger conductor size and THAT seems to be the issue here. It's not required; that is what the exception is about. 440.6A specifically says that conductors are sized to the RLC.

You don't trust the compressor overload protection and prefer to upsize the wire so that the breaker provides overload as well as short circuit protection. Fine, but the NFPA does not think it's necessary. Do those two sentences sum up this whole disagreement?

 

[alfredeneuman]

First off they are not miss matched...they are the proper breakers made by differing companies....Most likely was a Challenger panel.

The Challenger brand was bought from ZINSCO by Westinghouse, that became later Eaton/Cutler Hammer.
The only breakers that should be in the panel should be either a Challenger or a Cutler Hammer BR (which Norcal calls Zinsco II with good reason).

Not Siemens, Murray or ANY other brand.

 

[wyliesdiesels]

The Challenger brand was bought from ZINSCO by Westinghouse, that became later Eaton/Cutler Hammer.
The only breakers that should be in the panel should be either a Challenger or a Cutler Hammer BR (which Norcal calls Zinsco II with good reason).

Not Siemens, Murray or ANY other brand.

Dang missed his comment about mismatched breakers.

This guy doesnt know squat.

Doesnt know thr code permitted conductor sizing for AC and he doesnt know that using unlisted breakers in a panel is a code violation.

This guy should retire... wned:

 

[wyliesdiesels]

First off they are not miss matched...they are the proper breakers made by differing companies...in the real world you see much worse than this AND you see HVAC systems operating into 30 years and longer, which is where doing it right in the first place and using the proper wire is so critical.

Most likely was a Challenger panel.

What you seldom see in the real world is brand new crisp installs, you see installs old enough where the ground WAS the weather sealed conduit. You see the wrong breakers in particular panels, you see where people double up on breakers. And worse.

Most definitely they are mismatched.

You cant put an unlisted breaker in a panel.

With the exception of classified breakers, only breakers that are the same brand (and listed model) as the panel can be used.

And just because you see it in the real world doesnt make it ok.

Hopefully you only practice mismatching of breakers on residential panels where the AIC is low.

God help you if you do this on a 480v panel...

So to sum up, its clear you dont understand conductor sizing for AC compressors and you dont understand that you cant mismatch breakers in a panel...anything else we should add here?

 

[mm08822]

Dang missed his comment about mismatched breakers.

Easy on yourself.............there was so much bs in this thread it is hard to take your eyes off the ground.

 

[Bert_]

You don't trust the compressor overload protection and prefer to upsize the wire so that the breaker provides overload as well as short circuit protection. Fine, but the NFPA does not think it's necessary. Do those two sentences sum up this whole disagreement?

Sums it up perfectly.

 

[kaffine]

The problem is you were not there. I was. The failure at the bus bar was because the compressor failed, common and run winding shorted.

I am in line completely with what the manufacturers authorize.

It is not safer to under size wiring. The only examples I have been shown is for motors...A condensing unit contains a motor and a compressor, when compressors have liquid refrigerant introduced to them amperage and the associated heat ramp up rapidly, that is why it is important to properly size the wiring.

I not only follow the code I exceed the recommendations.

You can use larger breakers (max over current protection) BUT if you do, you must size the wire accordingly or that breaker is not protecting the wire.

So you are saying the the bus bar stab which is rated for what at least 100 amp per breaker is the weakest link? Really?

And what is a compressor to the electrical system? It is a motor granted it is a specialty motor but the electrons don't care they see it as a motor.

 

[kaffine]

The problem is you were not there. I was. The failure at the bus bar was because the compressor failed, common and run winding shorted.

I am in line completely with what the manufacturers authorize.

It is not safer to under size wiring. The only examples I have been shown is for motors...A condensing unit contains a motor and a compressor, when compressors have liquid refrigerant introduced to them amperage and the associated heat ramp up rapidly, that is why it is important to properly size the wiring.

I not only follow the code I exceed the recommendations.

You can use larger breakers (max over current protection) BUT if you do, you must size the wire accordingly or that breaker is not protecting the wire.

Did you consider that you might have the failures backwards? It isn't the compressor shorting that caused the bus bar failure but the bus bar failure caused the compressor to fail. Having high resistance at the breaker/bus bar connection means that the compressor was operating under brownout conditions constantly.

 

[wyliesdiesels]

Someone pass the popcorn please.

Im all out.

Oh and if you have some Reese's pieces Id appreciate it...

 

[ddawg16]

Someone pass the popcorn please.

Im all out.

Oh and if you have some Reese's pieces Id appreciate it...

How about Reese's peanut butter cups?

And some Jack and Coke.....

 

[ddawg16]

I had to go to the beginning and read the whole thread.

This one deserves to be a sticky.

I won't comment about the contents of this thread.....but I will say this

"You're never too old to learn something news."

 

[anothertor]

Edit: I had to read again in full awake mode I am more interested in content now than sarcasm.

 

[eddieK]

Lmao.

I never said i dont have tools.

Not that it matters to you, im a union electrician and of course i have tools. Probably have way more tools than you.

But seeing as how youve turned this into nothing more than a ******* match that i could care less about and im exhausted from working all day, you have a good night troll

I've turned it into a ******* match? Really?

I noted early in this thread that when it come to HVAC equipment, that the purpose of a circuit breaker is to protect circuit wiring and as such wiring must be sized appropriately.

I have not moved from my position and many here keep wanting to argue against this well established practice.

 

[eddieK]

Did you consider that you might have the failures backwards? It isn't the compressor shorting that caused the bus bar failure but the bus bar failure caused the compressor to fail. Having high resistance at the breaker/bus bar connection means that the compressor was operating under brownout conditions constantly.

Blocked evap coil - clogged condenser coil - high ambient temp and age of equipment...The compressor was being over taxed and when a thermostat is set at a temperature, if the system is not cooling and the structures heat load just keeps climbing, the only thing that will shut the compressor down is the internal overload (unit did not have high pressure switch as most lower tier brands do not)...meaning it was "riding the high limit - overload" essentially short cycling until it either shorted the winding's or the overload stuck and shorted the winding's. This evap coil had almost no air passing over it and the latent heat transfer did not exist, that ends up causing liquid refrigerant to go to compressor (slugging).

This was a hermetic reciprocating compressor, the winding's are wound around each other, similar to how older auto generator winding's were wound, a winding wrapped in bare wire and coated, another wrapped and coated and the last winding wrapped and then coated...excessive heat for extended periods will destroy this protective varnish between winding's.

More importantly to the "theme" on this thread, in any instance of over over current... the entire purpose I brought this up is the appropriate wire in the circuit did not fail, the "consumable" did.

Breakers protect the wiring in a circuit. Under sizing the wire is dangerous in HVAC.

 

[eddieK]

I disagree.... this unit can be wired with #10 & a 50 amp breaker safely and legally, residential or commercial, in the US.

https://www.garagejournal.com/forum/attachment.php?attachmentid=765510&d=1525750382

From page 1 -

This is absolutely dangerous.

The minimum ampacity - 28.8 and max HVAC breaker - 50 means you can install a 30, a 40 or a 50 amp circuit for this unit. I would install a 40 amp circuit, typically wired with #8 copper and at the unit disconnect install 35 amp fuses.

Whatever circuit you install MUST have the appropriate wire for the overload protection you choose. This circuit is for a unit operating a compressor and a fan motor, plus a few minor controls.

 

[eddieK]

I had to go to the beginning and read the whole thread.

This one deserves to be a sticky.

I won't comment about the contents of this thread.....but I will say this

"You're never too old to learn something news."

From page 2 -

Big56

I disagree.... this unit can be wired with #10 & a 50 amp breaker safely and legally, residential or commercial, in the US.

https://www.garagejournal.com/forum/...0&d=1525750382



This is absolutely dangerous.

The minimum ampacity - 28.8 and max HVAC breaker - 50 means you can install a 30, a 40 or a 50 amp circuit for this unit. I would install a 40 amp circuit, typically wired with #8 copper and at the unit disconnect install 35 amp fuses.

Whatever circuit you install MUST have the appropriate wire for the overload protection you choose. This circuit is for a unit operating a compressor and a fan motor, plus a few minor controls. The isolated incidence where the NEC notes you can use #10 wire and a 50 amp breaker does not apply to HVAC equipment.

You should never be too proud to admit you are wrong...If I was I would admit it. This here is a serious safety issue and yes I am still hammering it.

 

[Norcal]

And your still wrong.

 

[alfredeneuman]

And your still wrong.

 

[anothertor]

This is really interesting. Through the years and several projects, I have never heard a professional say anything other than Eddie's basic stance (breakers protect the wire).

Are you guys staying that this is no longer a generalized rule, or that it isn't relevant for an AC install specifically because of the power usage characteristics of compressors/motors?

Sent from my LGLS992 using Tapatalk

 

[alfredeneuman]

or that it isn't relevant for an AC install specifically because of the power usage characteristics of compressors/motors?

That's what this ALL about, the motor and compressor surge at startup.

 

[anothertor]

Ahh. I briefly wondered if (hoped) I was underutilizing my workshop wiring.

That's what this ALL about, the motor and compressor surge at startup.

Sent from my LGLS992 using Tapatalk

 

[wyliesdiesels]

and your still wrong.

 

[wyliesdiesels]

From page 2 -[/B]



https://www.garagejournal.com/forum/...0&d=1525750382



This is absolutely dangerous.

The minimum ampacity - 28.8 and max HVAC breaker - 50 means you can install a 30, a 40 or a 50 amp circuit for this unit. I would install a 40 amp circuit, typically wired with #8 copper and at the unit disconnect install 35 amp fuses.

Whatever circuit you install MUST have the appropriate wire for the overload protection you choose. This circuit is for a unit operating a compressor and a fan motor, plus a few minor controls. The isolated incidence where the NEC notes you can use #10 wire and a 50 amp breaker does not apply to HVAC equipment.

You should never be too proud to admit you are wrong...If I was I would admit it. This here is a serious safety issue and yes I am still hammering it.

The first bolded comment of yours clearly without a doubt shows you dont know the NEC.

Where did you get your training?

Also You need to follow your own advice here.

10+ electricians on here, Mike holt AND the NEC NFPA 70 ALL say youre wrong!!

 

[pattenp]

And your still wrong.

Make it from the east coast.

Read this.... https://www.mikeholt.com/mojonewsar...ning-and-Refrigerating-Equipment~20040102.htm


*

 

[eddieK]

And your still wrong.

Nope - What is wrong is wiring an HVAC circuit with under sized wire.

 

[sz0k30]

Electrically speaking I barely know which end of a hammer to use, but that was FUN!

 

[eddieK]

That's what this ALL about, the motor and compressor surge at startup.

The nomenclature on page 2...the LRA Locked Rotor Amps are 99...Not 50. Maximum breaker size is 50 and minimum ampacity is 28.8. You do not wire an HVAC circuit based upon LRA...you look at the minimum ampacity and the max fuse size and determine it there. You certainly do NOT size the wire by the minimum ampacity and the breaker by the max over current protection,

You can wire a circuit for this unit for 30 amp, 40 amp or 50 amp, and in each instance you must use the appropriate wire. You could use #8 THNN if it is completely ran in conduit (and not excessive in length)with a 50 amp breaker, but you can not use #10.

Locked rotor amps are not part of the RLA equation, breakers and time delay fuses are designed to handle this MOMENTARY surge. All of today's equipment come with delay at break protection, preventing re-starts in less than 1 - 5 minutes, allowing breakers and fuses time to cool down and accept surge again...thermostats have this delay on start or break as well as an option. Locked Rotor happens so fast you can barely read it on your meter.

Once called for if the unit is attempting to start with liquid in compressor the internal overload is the protection (and high press switches). If the unit short cycles (riding the overload - short cycling)...wiring and external protection devices see high amperage.

A Compressor in HVAC is NOT a motor, but there is also an additional motor that circuit controls at the same time.

 

[alfredeneuman]

 

[pattenp]

…..
A Compressor in HVAC is NOT a motor, but there is also an additional motor that circuit controls at the same time.

A hermetically sealed compressor includes the motor to run the compressor. So wiring a typical HVAC unit with a hermetically sealed compressor is basically the same as wiring a motor operated piece of equipment per the NEC.

 

[eddieK]

Make it from the east coast.

Read this.... https://www.mikeholt.com/mojonewsar...ning-and-Refrigerating-Equipment~20040102.htm


*

From your link -

TA DA !!!

"If a 40A protection device is not capable of carrying the starting current, you can size the protection device up to 225 percent of the equipment load current rating (24A x 2.25 = 54A, next size down 50A)."

It is ALWAYS safer to up size and NEVER safer to down size electrical circuit wiring for HVAC equipment.

 

[eddieK]

A hermetically sealed compressor includes the motor to run the compressor. So wiring a typical HVAC unit with a hermetically sealed compressor is basically the same as wiring a motor operated piece of equipment per the NEC.

Wiring it is similar. The difference is the compressor is ONE load and the Condenser fan is an additional motor...AND Motors do not operate the same as Compressors. Compressors are designed to compress VAPOR, when they slug liquid refrigerant they are attempting to compress a liquid, that's hydraulics and causes excessive AND extended amp draw.

I've been doing this since 1978. I have never once encountered a HVAC unit with #10 copper wire circuit protected by a 50 amp breaker because electricians and HVAC contractors know that the rule is the appropriate wire size for the particular breaker.

Hermetically sealed simply means it is not serviceable. The compressor is a motor of sorts but not a true motor, especially, reciprocating (pistons). The Condenser fan does not run the compressor, it moves air across the condenser coil. Two very different components that do two very different things at the same time.

 

[eddieK]

Try this -

https://www.electricaltechnology.org/2014/04/electrical-wire-cable-size-calculator.html

Show me where you should use a 50 amp breaker to protect this wire

https://www.bing.com/images/search?...608022420639976956&selectedIndex=1&ajaxhist=0

https://www.bing.com/images/search?...08043006408265281&selectedindex=44&ajaxhist=0

https://www.bing.com/images/search?...08048735910495445&selectedindex=35&ajaxhist=0

You know what you will not find on these charts? A 208v/240v circuit with a 50 amp breaker protecting #10 wire, especially in HVAC. On that last chart, you may note that the dual element fuses are 5 amps lower than the breaker. That is to be sure the weakest link is OUTSIDE and not in the structure walls.

 

[mm08822]

PattenP, Remember the wise saying from Mark Twain that George Carlin repeated for us.

 

[pattenp]

I've been doing this since 1978. I have never once encountered a HVAC unit with #10 copper wire circuit protected by a 50 amp breaker because electricians and HVAC contractors know that the rule is the appropriate wire size for the particular breaker.

I'm just saying the NEC will allow #10 copper to be protected by a 50A breaker on a HVAC condenser unit when needed even though you never see it done or would do it yourself. It seems you are stuck on determining breaker sizes base on conductor size for general purpose circuits. If I was running a 30A circuit for a resistive heating load then the breaker would be 30A because the rule is different.

 

[pattenp]

PattenP, Remember the wise saying from Mark Twain that George Carlin repeated for us.

Sorry to say, but I had to look it up.

 

[Norcal]

Water heaters are not part of the discussion, A/C equipment is. The rules for A/C equipment allow for different wire / breaker combos then what is required for other circuits.

 

[wyliesdiesels]

Seeing as how this guy is basically saying the NEC is wrong, this has gotten to troll level status.

Wheres a ban hammer when you need one?

 

[pattenp]

I was doing good by staying out of this one, but I got sucked in. Resistance was futile.