The manufacturer said

[david]

If the electric furnace has breakers installed in the unit this usually comes as a kit from the factory. The breakers supplied with the heater kit are sized to the heaters installed and any other load in the unit.

Then perhaps the supplier is installing the 60 amp fuses or 60 amp two pole breakers or they are getting installed at the HVAC guys shop,

All we are asking is for the electrician wiring the home and the HVAC guys to coordinate between the two and at the final either the overcurrent in the panel supplying the units or the overcurrent at the units be in compliance with the name plate max overcurrent protection.

 

[augie47]

Sadly I have to say in this area, there is a high probability of there being a Code problem with the HVAC install whereas there is no Code problem with the rest of the entire house.
Romex installed using ratings higher than 60? ("the HVAC provider told me to run #6); improperly sized OCP ("the supply house does not carry 25 amp breakers"), romex in a wet location ( "say what?)", the nameplate showing MCA/MOCP supplied with the heat kit not displayed (look for the discarded shipping container), the disconnect mounted over the duct work, etc.
.
Even more sad, the those same violations are reoccurring with the same installation companies.

 

[Mgraw]

Then perhaps the supplier is installing the 60 amp fuses or 60 amp two pole breakers or they are getting installed at the HVAC guys shop,

All we are asking is for the electrician wiring the home and the HVAC guys to coordinate between the two and at the final either the overcurrent in the panel supplying the units or the overcurrent at the units be in compliance with the name plate max overcurrent protection.

When I buy a heater kit it is a listed component that I add to the system. I am not going to change the breakers. This is a typical heater kit from the factory.

 

[Mgraw]

Sadly I have to say in this area, there is a high probability of there being a Code problem with the HVAC install whereas there is no Code problem with the rest of the entire house.
Romex installed using ratings higher than 60? ("the HVAC provider told me to run #6); improperly sized OCP ("the supply house does not carry 25 amp breakers"), romex in a wet location ( "say what?)", the nameplate showing MCA/MOCP supplied with the heat kit not displayed (look for the discarded shipping container), the disconnect mounted over the duct work, etc.
.
Even more sad, the those same violations are reoccurring with the same installation companies.

That's everywhere. Working on both sides of the "fence" I see it all. As an electrician I am not going to take a HVAC guy's recommendation on wire size and as a HVAC guy I am not going to tell an electrician what size wire to run.

 

[david]

When I buy a heater kit it is a listed component that I add to the system. I am not going to change the breakers. This is a typical heater kit from the factory.

It is not my intention to indicate what the HVAC guy is going to do.

Anytime I have seen furnaces with field installed kits they come with a sticker that is to be field installed or more commonly these days the furnace has a sticker with a long list of kit model numbers that indicates for the field installed kit one on the list is to be marked.

We do not care if the HVAC guys or the electrician providing the overcurrent at the distribution panel make the change but once we call out the max overcurrent for the heater kit exceeds the kits max overcurrent on the data plate, we are not giving a final approval until the max overcurrent is not exceeded.

 

[jap]

Motors 1 hp and up you are allowed to put smaller wire on a bigger breaker. A/C manufactures just do all the maths for you, the principal are the same.

It's not about putting smaller wire on a larger breakers, all but a small few know you can do that in certain cases.

Do you take the full load amperage of the Air Conditioning Unit and then apply the 250% rule to that to size your Max. Overcurrent protection ?
Or
Do you size the Max Overcurrent protection per the label on the Air Conditioning Unit?

Once you answer that question You'll see why I disagreed with the comparison to wiring a motor that's not part of a packaged unit.

Petrasonra was asking me to answer his question about sizing the wire to the max overcurrent protection at the end so he could say it was not needed.

2 different scenarios.

The max Circuit Breaker suggested on an Air Conditioning unit is rarely 250% more than the Min. Circuit amps.
Generally I find that the difference may be just one wire size between the Min Circuit amps and Max overcurrent protection on AC Units so I bite the bullet and pull the larger size.
It's not like it breaks the bank.

You cant use a question that doesn't apply to the topic to somehow get an answer that your going to turn around and disagree with.

2 different scenarios.


JAP>

 

[Mgraw]

It is not my intention to indicate what the HVAC guy is going to do.

Anytime I have seen furnaces with field installed kits they come with a sticker that is to be field installed or more commonly these days the furnace has a sticker with a long list of kit model numbers that indicates for the field installed kit one on the list is to be marked.

We do not care if the HVAC guys or the electrician providing the overcurrent at the distribution panel make the change but once we call out the max overcurrent for the heater kit exceeds the kits max overcurrent on the data plate, we are not giving a final approval until the max overcurrent is not exceeded.

Yes this is generally a problem on 208 volt services. Heater kits are rated 208/240 but the breakers supplied are sized for 240. But I would never change the breaker on the heater kit, always at the panel.

 

[Mgraw]

It's not about putting smaller wire on a larger breakers, all but a small few know you can do that in certain cases.

Do you take the full load amperage of the Air Conditioning Unit and then apply the 250% rule to that to size your Max. Overcurrent protection ?
Or
Do you size the Max Overcurrent protection per the label on the Air Conditioning Unit?

Once you answer that question You'll see why I disagreed with the comparison to wiring a motor that's not part of a packaged unit.

Petrasonra was asking me to answer his question about sizing the wire to the max overcurrent protection at the end so he could say it was not needed.

2 different scenarios.

The max Circuit Breaker suggested on an Air Conditioning unit is rarely 250% more than the Min. Circuit amps.
Generally I find that the difference may be just one wire size between the Min Circuit amps and Max overcurrent protection on AC Units so I bite the bullet and pull the larger size.
It's not like it breaks the bank.

You cant use a question that doesn't apply to the topic to somehow get an answer that your going to turn around and disagree with.

2 different scenarios.


JAP>

You can absolutely run a larger wire if you want. The point is you don't have to. Just don't tell someone else they can not run the smaller wire if they want to.

 

[kwired]

Motors 1 hp and up you are allowed to put smaller wire on a bigger breaker. A/C manufactures just do all the maths for you, the principal are the same.

Art 440 does tell us how to determine conductor size and overcurrent protection settings, but mostly applies to other then the factory assembled units we commonly find in the wild. If you were to look at each component and figure these values out yourself you almost always come up with what is on the nameplate though or very very close, so you are right - the manufacturer did the math for you.

If the electric furnace has breakers installed in the unit this usually comes as a heater kit from the factory. The breakers supplied with the heater kit are sized to the heaters installed and any other load in the unit.

When I buy a heater kit it is a listed component that I add to the system. I am not going to change the breakers. This is a typical heater kit from the factory.

Correct, it is a listed component, all you need to do is follow instructions and provide minimum conductor size and overcurrent protection according to what is on the nameplate - even if the internal breaker is a 60 but the nameplate calls for a 25 - then 25 is the required protection for your supply circuit.


One thing code doesn't mention when it comes to how much starting current a compressor may draw is the reality of impedance in the supply circuit. If POCO has a small transformer, you have long service conductors, long feeders, long branch circuit conductors or any combinations of those - LRA marked on the unit may never be reached.

I kind of assume the LRA value marked on the unit doesn't figure on any voltage drop when in a LRA condition. Max OCPD may factor in possible drop in voltage IDK, I know many breaker manufacturers would recommend a higher trip setting for a motor with same rating as many of those compressor units, but reality in most instances is that the LRA is limited by circuit and or source impedance and the devices usually will hold at the levels mentioned on the nameplates.

 

[jap]

You can absolutely run a larger wire if you want. The point is you don't have to. Just don't tell someone else they can not run the smaller wire if they want to.

I never did.


Jap>

 

[Mgraw]

Art 440 does tell us how to determine conductor size and overcurrent protection settings, but mostly applies to other then the factory assembled units we commonly find in the wild. If you were to look at each component and figure these values out yourself you almost always come up with what is on the nameplate though or very very close, so you are right - the manufacturer did the math for you.



Correct, it is a listed component, all you need to do is follow instructions and provide minimum conductor size and overcurrent protection according to what is on the nameplate - even if the internal breaker is a 60 but the nameplate calls for a 25 - then 25 is the required protection for your supply circuit.


One thing code doesn't mention when it comes to how much starting current a compressor may draw is the reality of impedance in the supply circuit. If POCO has a small transformer, you have long service conductors, long feeders, long branch circuit conductors or any combinations of those - LRA marked on the unit may never be reached.

I kind of assume the LRA value marked on the unit doesn't figure on any voltage drop when in a LRA condition. Max OCPD may factor in possible drop in voltage IDK, I know many breaker manufacturers would recommend a higher trip setting for a motor with same rating as many of those compressor units, but reality in most instances is that the LRA is limited by circuit and or source impedance and the devices usually will hold at the levels mentioned on the nameplates.

They do consider voltage drop etc. in their calculations. For example, a 200/230v Copeland scroll will start and operate at 180-253v. Copeland knows these compressors will stay in a LR condition for 100-300 milliseconds in this voltage range.

 

[iwire]

They do consider voltage drop etc. in their calculations. For example, a 200/230v Copeland scroll will start and operate at 180-253v.

That voltage range is pretty much the ANSI standard.

 

[Mgraw]

That voltage range is pretty much the ANSI standard.

Yes I was just pointing out that in that range they estimate a LR range as well.

 

[kwired]

They do consider voltage drop etc. in their calculations. For example, a 200/230v Copeland scroll will start and operate at 180-253v. Copeland knows these compressors will stay in a LR condition for 100-300 milliseconds in this voltage range.

And I assume that is for determining what size overcurrent protection is needed to allow for starting.

Actual Nameplate LRC is likely maximum expected if 253 can be maintained or at least if a nominal 240 can be maintained during starting.

I do know better that the instantaneous starting current of any motor or compressor can vary greatly depending on conditions where it is installed. Duration of starting period varies as well, the higher current available the faster the rotor can accelerate the faster the starting duration. Current and time together are important to trip point of the device.

 

[jap]

let me ask you this.

if you are using a CB for the short circuit protection on a motor circuit, the code allows you to size it at 250% of the motor FLC.

lets say you had a 15Hp/480V motor (21 FLA). Code would allow you to use a CB of 52.5 amps (or whatever the next std size is).

The code only requires conductor ampacity of 125% of FLC (in this case #10).

would you size the conductors to the rating of the CB being used (if you went with 250%)? or to the FLC as the code permits.

I'll go ahead and answer this.

Neither.
Seeing as how for (1) the topic is about a packaged air conditioning unit and not simply protection for a motor circuit so I'm not considering the need to use the 250% rule at all
and
(2) You already mentioned the conductor ampacity needed to be 125% of the FLC and you only gave an option for FLC.

JAP>

 

[david]

I'll go ahead and answer this.

Neither.
Seeing as how for (1) the topic is about a packaged air conditioning unit and not simply protection for a motor circuit so I'm not considering the need to use the 250% rule at all
and
(2) You already mentioned the conductor ampacity needed to be 125% of the FLC and you only gave an option for FLC.

JAP>

Everyone knows where the question being asked is leading to.

Ok you can install the installation of AC equipment to meet compliance with the NEC.

And you are aware of that. In your case you state you always increase the circuit to meet the ampacity of the max. over current rating called out on the manufactures data.

You are allowed to do it your way, you have not implied others have to do it that way.

You may be implying that it is good practice, you may take further and imply that is a better practice. What is being ask is it also then implied that it is good practice or perhaps better practice to apply the same standard to a motor circuit that has a max over current in the 250% range of the motors full load amp rating.

The simple answer would be your not implying it is a better practice or even a good practice it?s just your design choice.

 

[jap]

Everyone knows where the question being asked is leading to.

Ok you can install the installation of AC equipment to meet compliance with the NEC.

And you are aware of that. In your case you state you always increase the circuit to meet the ampacity of the max. over current rating called out on the manufactures data.

You are allowed to do it your way, you have not implied others have to do it that way.

You may be implying that it is good practice, you may take further and imply that is a better practice. What is being ask is it also then implied that it is good practice or perhaps better practice to apply the same standard to a motor circuit that has a max over current in the 250% range of the motors full load amp rating.

The simple answer would be your not implying it is a better practice or even a good practice it?s just your design choice.

Other than implying that the way I do it is a good practice or even a better practice for that matter, that is exactly what I thought I said in post #7.

Then Petersonra came along immediately after that in post #8 with a question that somehow "Implied" that sizing the conductors to the Max Overcurrent device would somehow be a waste. I don't care how he does his, I just let it be known that other than the passionate responses from the OP,,,, he's not alone. To each his own.

Especially seeing as how the response he gave in post #3 "Implied" that some posts just weren't even worth responding to.

That's his choice, but, don't start asking me setup questions if I decide to chime in.

JAP>

 

[augie47]

As can by noted by my "thumbs up" in Post #4, I took peteraonra's comment to indicate the earlier thread had reached to point of "immovable object-unstoppable force".
The topic is well worth discussing as it has been here, but as you correctly noted there is a difference in doing something because you think it is good practice and doing something because you feel it is Code required even when a majority of informed folks try to show you otherwise.

FWIW I see the subtle (to me) difference in Art 440 and 430 but, again to me, his analogy between the two made sense in that 240.4(G) relates to both.

 

[david luchini]

FWIW I see the subtle (to me) difference in Art 440 and 430 but, again to me, his analogy between the two made sense in that 240.4(G) relates to both.

I agree. In addition, Art 430 applies to Air Conditioning and Refrigeration Equipment installations, except as modified in Art 440.

 

[jap]

let me ask you this.

if you are using a CB for the short circuit protection on a motor circuit, the code allows you to size it at 250% of the motor FLC.

lets say you had a 15Hp/480V motor (21 FLA). Code would allow you to use a CB of 52.5 amps (or whatever the next std size is).

The code only requires conductor ampacity of 125% of FLC (in this case #10).

would you size the conductors to the rating of the CB being used (if you went with 250%)? or to the FLC as the code permits.

Ok then. Forget about an Air Conditioning unit for a minute.
I'll respond directly to the motor question above just to see where he wanted to go with it.

My Answer: I would size the conductors at 125% of the FLA and install and Overcurrent/Short circuit device up to 250% if need be.

Now,,,,,, what would his reply have been?


JAP>