Article 440 - Air Conditioning Equipment

[mtnelect]

Using the 75 degree column vs 60 is not "derating"

Doesn't that result in a smaller wire size ?

 

[mtnelect]

Ok but what does that change? If u calculate the ampacity required for a package unit, it's the same as a "regular" motor load.

This why they put refrigeration in a separate section of the NEC.

 

[Eddie702]

AC equipment wire size is based on the equipment nameplate MCA Period. And the breaker size is based on the MOCP on the unit's nameplate as well. No calculations needed as the MCA already includes the required 125% included.

Then I rate the required wire size based on the temperature requirements of the lowest temp rated equipment in the circuit Breaker, disconnect and equipment and derate for temp rating and #of conductors etc.

It could well be that all AC equipment is rated for 75C as @don_resqcapt19 mentioned. No one is installing 60 C wire any longer although some may exist in a replacement.

Usually under 100 amps the assumption is 60C and 100 and up 75C

 

[mtnelect]

AC equipment wire size is based on the equipment nameplate MCA Period. And the breaker size is based on the MOCP on the unit's nameplate as well. No calculations needed as the MCA already includes the required 125% included.

Then I rate the required wire size based on the temperature requirements of the lowest temp rated equipment in the circuit Breaker, disconnect and equipment and derate for temp rating and #of conductors etc.

It could well be that all AC equipment is rated for 75C as @don_resqcapt19 mentioned. No one is installing 60 C wire any longer although some may exist in a replacement.

Usually under 100 amps the assumption is 60C and 100 and up 75C

Correct ... You don't see 60-degree wiring being sold anymore.

Section 440.35 states:
The ampacity of the conductors supplying multirotor and combination-load equipment shall not be less than the minimum circuit ampacity marked on the equipment in accordance with 440.4(B).

 

[mtnelect]

I see nothing stating a wire size. It appears to me that the footnote is related to a table that actually specifies a conductor size.
EDIT: I found the rest of the page.
There is a table of wire sizes at the bottom of the page you showed us. The note applies to that table, but there in no language limiting you to the use of conductors at the 60°C ampacity.

COPPER WIRE SIZE — AWG (1% Voltage Drop)
Supply Wire Length-Feet​	Supply Circuit Ampacity​
200	150	100	50​
6	8	10	14​	15
4	6	8	12​	20
4	6	8	10​	25
4	4	6	10​	30
3	4	6	8​	35
3	4	6	8​	40
2	3	4	6​	45
2	3	4	6​	50

Wire Size based on N.E.C. for 60° type copper conductors.

Section 440.35 states:
The ampacity of the conductors supplying multirotor and combination-load equipment shall not be less than the minimum circuit ampacity marked on the equipment in accordance with 440.4(B).

 

[roger]

Section 440.35 states:
The ampacity of the conductors supplying multirotor and combination-load equipment shall not be less than the minimum circuit ampacity marked on the equipment in accordance with 440.4(B).

And who is saying anything to the contrary?

 

[mtnelect]

And who is saying anything to the contrary?

All the HVAC manufacturers state in their engineering data that the minimum circuit capacity is based on 60-degree wire sizes. As an example, a unit is rated for 45 amps at 60-degrees, a wire size of No. 6 would be needed. If a 75-degree wire was used a No. 8 at 50 amps would be used. That results in a smaller wire size for the HVAC unit. For general electrical work that would be great, but for HVAC work that would be a mistake. It's the manufacturer that determines the correct size, and Section 440.4(B) supports it.

If you would like more engineering data from other manufacturers, I can supply them for you.

 

[roger]

I would just like you to answer my question

 

[shortcircuit2]

440.6 gives direction on size of conductors. If I use a 75° rated conductor on equipment with 75° rated terminals, I am installing per Code.

 

[electrofelon]

All the HVAC manufacturers state in their engineering data that the minimum circuit capacity is based on 60-degree wire sizes.

They do?

 

[mtnelect]

And who is saying anything to the contrary?

I would just like you to answer my question

Just have some patience ... They will magically appear !

 

[don_resqcapt19]

Section 440.35 states:
The ampacity of the conductors supplying multirotor and combination-load equipment shall not be less than the minimum circuit ampacity marked on the equipment in accordance with 440.4(B).

And nothing requires the use of 60°C conductor ampacities for the minimum circuit ampacity. Use of a 75°C conductor with a 75°C ampacity equal to or greater then the minimum circuit ampacity shown on the nameplate is compliant with all of the requirements of the NEC.

 

[mtnelect]

I rest my case ... I will let this forum of prestigious and well qualified members to decide the outcome of my future reputation on this post.

 

[Little Bill]

I rest my case ... I will let this forum of prestigious and well qualified members to decide the outcome of my future reputation on this post.

You said yourself that all the info we need is on the nameplate of the equipment, and that all the figuring has been done for us.
So, using the MCA on the nameplate is the compliant way to handle this.

Nothing else period!

 

[tbassler_99]

I am an electrical design engineer. PE since 2001.

I know that UL permits terminals of electrical equipment 100A or less to be 60°C rated. Not knowing what equipment will be provided, I always use 60°C rating conductor amapacities for equipment 100A or less. It doesn't matter if it is 90°C conductor insulation, the terminals govern.

Of course, if there is a nameplate, the higher terminal temperature ampacity rating of conductor insulation can be used. But it is a no-no for design because you never know.

This has probably already been clearly stated by others, but I didn't exactly see it in quick perusal.

 

[kwired]

Of course, if there is a nameplate, the higher terminal temperature ampacity rating of conductor insulation can be used. But it is a no-no for design because you never know.

Except for the fact that for like 30 plus years there has been almost no equipment that doesn't have a 75C terminal rating, particularly if over 30 amp rating to begin with. Your 15 to 30 amp devices- the small conductor rule of 240.4(D) kind of makes you use same size conductor that would be used for 60C rating in most cases, 430 and 440 applications being maybe the most common places you could possibly use actual 75C conductor ratings.