wire ampacities 310.16 90degree c chart

[mike mcswain]

I reccently had a customer complain that the wire we used was not rated for 60 amps it was #6 seu al. I understand you have to go by the lug rating for correct fuse size but that doesn't change what the ampacity of the conducter is rated for does it ? This is on an a/c compressor that has a min. cir. amp. of 37.4 and a max fuse size of 60 amps so shouldn't # 6 al. be sufficiant enough with a 60 amp breaker ?

 

[skeshesh]

wire ampacity

wire ampacity

I may be wrong about this but I think the rating of the terminals you're connecting the wire to are rated at a certain temperature. Your evaluation of the correct wire ampacity should be based on the terminal insulation type and temperature. So basically if the terminal is indeed rated below 75deg. for a #6AWG wire, then the applied ampacity from the NEC 310 tables would be 55A not 65A. SquareD has a decent paper about this issue, check the link below:

http://ecatalog.squared.com/pubs/Electrical Distribution/0110DB9901R2-02.pdf

 

[raider1]

I reccently had a customer complain that the wire we used was not rated for 60 amps it was #6 seu al. I understand you have to go by the lug rating for correct fuse size but that doesn't change what the ampacity of the conducter is rated for does it ? This is on an a/c compressor that has a min. cir. amp. of 37.4 and a max fuse size of 60 amps so shouldn't # 6 al. be sufficiant enough with a 60 amp breaker ?

When sizing circuit conductors for an A/C compressor you size the circuit conductor using the minimum circuit ampacity and the breaker from the maximum breaker size marked on the A/C nameplate.

So in the example you provided, the circuit conductors for the A/C unit must be sized to carry 37.4 amps. #6 Aluminum SEU cable at 60 degrees has an ampacity of 40 amps (310.16) so you are OK. 240.4(G) permits the overcurrent protective device for an A/C compressor to be sized in accordance with Article 440 Parts III, VI. So the breaker protecting the A/C unit can be sized from the maximum breaker size listed on the nameplate.

Chris

 

[infinity]

I may be wrong about this but I think the rating of the terminals you're connecting the wire to are rated at a certain temperature. Your evaluation of the correct wire ampacity should be based on the terminal insulation type and temperature. So basically if the terminal is indeed rated below 75deg. for a #6AWG wire, then the applied ampacity from the NEC 310 tables would be 55A not 65A. SquareD has a decent paper about this issue, check the link below:

http://ecatalog.squared.com/pubs/Electrical Distribution/0110DB9901R2-02.pdf

SE cable is required to be sized at the 60 degree C ampacity regardless of the terminal rating.

 

[skeshesh]

wire ampacity

wire ampacity

SE cable is required to be sized at the 60 degree C ampacity regardless of the terminal rating.

I don't seen any mention of service entrance in this post. Also, and again I may be wrong due to inexperience, but I thought service entrance rated cable is characterized by being rated at 60deg. C so applying other ampacity variations is meaningless.

 

[roger]

I don't seen any mention of service entrance in this post. .

You missed this.

it was #6 seu al.

Roger

 

[skeshesh]

Ooops! You're absolutely right.

 

[LarryFine]

This is on an a/c compressor that has a min. cir. amp. of 37.4 and a max fuse size of 60 amps so shouldn't # 6 al. be sufficiant enough with a 60 amp breaker ?

What matters is that it's sufficient for the MCA.

 

[gndrod]

SE

SE

I don't seen any mention of service entrance in this post. Also, and again I may be wrong due to inexperience, but I thought service entrance rated cable is characterized by being rated at 60deg. C so applying other ampacity variations is meaningless.

SE Type cable uses permitted [338.10] for interior installation of BC and Feeders provisions must comply to 334 part II limitation of conductor. (NM-B 60deg C)

 

[weressl]

I reccently had a customer complain that the wire we used was not rated for 60 amps it was #6 seu al. I understand you have to go by the lug rating for correct fuse size but that doesn't change what the ampacity of the conducter is rated for does it ? This is on an a/c compressor that has a min. cir. amp. of 37.4 and a max fuse size of 60 amps so shouldn't # 6 al. be sufficiant enough with a 60 amp breaker ?

You have to go by the temperature rating PRINTED on the jacket of the cable.

 

[charlie]

. . . and a max fuse size of 60 amps . . . with a 60 amp breaker?

Everyone has missed the fact that a circuit breaker, even a HACR circuit breaker, is not permitted to be used. A fuse is required to be used if the nameplate says, "Max Fuse Size".

 

[iwire]

You have to go by the temperature rating PRINTED on the jacket of the cable.

There is more to it than that, the jacket may say 90C but the terminals may hold it to 60 or 75 C.

 

[weressl]

There is more to it than that, the jacket may say 90C but the terminals may hold it to 60 or 75 C.

And vice-versa, the terminals may be rated to 75C rise, but the wire is stamped 60C, the later prevails.

My statement was refering to the fact that you can't use the table - alone - to match the wire type to what rise column you decide to use, you must look at the wire's approval rating that is printed on the jacket.

Connection, terminal and protective deveices selection and ratings are of course all needs to be addressed.

 

[weressl]

Everyone has missed the fact that a circuit breaker, even a HACR circuit breaker, is not permitted to be used. A fuse is required to be used if the nameplate says, "Max Fuse Size".

That would NOT be an NEC restriction, but a manufacturers recommendation that may void the warranty but not the legality of the installation. (Often the 'fuse' term used because the literature is put together by non-technical people for non-technical people and OCPD would be a meaningless term for the majority "out there".)

The only device I am aware of having that restriction is some ASD drives, but we are routinely using CB's on them.

 

[iwire]

And vice-versa, the terminals may be rated to 75C rise, but the wire is stamped 60C, the later prevails.

I agree.

My statement was refering to the fact that you can't use the table - alone - to match the wire type to what rise column you decide to use, you must look at the wire's approval rating that is printed on the jacket.

The jacket marking had better match the NEC or we have some other issues.

Connection, terminal and protective deveices selection and ratings are of course all needs to be addressed.

I agree, and I knew you that you knew that, it just did not come across that way (at least to me) in your earlier post.

 

[iwire]

That would NOT be an NEC restriction,

Actually it is well established violation of 110.3(B).

If the HVAC units labeling only indicates a fuse size we must in fact provide a fuse.

 

[gndrod]

Actually it is well established violation of 110.3(B).

If the HVAC units labeling only indicates a fuse size we must in fact provide a fuse.

That would not apply if the unit has internal fusing, would it. (i.e. HVAC split system heat pumps.)? rbj

 

[iwire]

That would not apply if the unit has internal fusing, would it. (i.e. HVAC split system heat pumps.)? rbj

If the labeling only indicates a max fuse size the EC must provide a fuse in line regardless of fusses that may or may not be in the unit.

From the IAEI Magazine

http://www.iaei.org/magazine/?p=3944

Sometimes the manufacturer of the combination-load equipment will specify fuses as the overcurrent protective device. This is important information and must be followed. If the nameplate says fuse only, the equipment has been evaluated and tested only with a fuse. The manufacturer has determined that only a fuse provides the proper overcurrent protection for the hermetic refrigerant motor-compressor and the other internal components. Use of a circuit breaker would be in violation of the Code Section 440-4(b) and 440-22(c). This would also be in violation of Section 110-3(b). This is the equivalent of not following the manufacturer?s instructions provided with the equipment. Not following the instructions is the same as not following the Code.

 

[weressl]

The jacket marking had better match the NEC or we have some other issues.

That was my point. There are cables that do not match the NEC criteria or not listed in the NEC, yet UL approved.

 

[weressl]

Actually it is well established violation of 110.3(B)

I disagree. The Code requires overload protection. It oversteps its authority when tries to enforce other requirements. That is between the AHJ, the User and the listing Authority. There is case law precedent for that.