Conductor Temperature

[Volta]

So if the conductor is connected to a 60 deg C circuit breaker, how can the circuit be arranged through splices, sizes, or insulation types to allow the 'dowstream' components to be used at, say, a 75 deg C ampacity?

Consider:
OCPD with 60 deg termination > 75 deg wire calculated at 60 deg > splicing device rated at 75 deg > 75 degree wire > 75 deg termination, then is the splice a violation?

 

[Dennis Alwon]

Not sure I understand you. The entire circuit would have to be rated 60C but you know that so what are you asking.

 

[jim dungar]

So if the conductor is connected to a 60 deg C circuit breaker, how can the circuit be arranged through splices, sizes, or insulation types to allow the 'dowstream' components to be used at, say, a 75 deg C ampacity?

Consider:
OCPD with 60 deg termination > 75 deg wire calculated at 60 deg > splicing device rated at 75 deg > 75 degree wire > 75 deg termination, then is the splice a violation?

In general, no violation.
Many people feel that 4' of conductor is a sufficient distance to say that you have moved away from the protective device termination limitation.

 

[cadpoint]

If U load the circuit to 75?C then you load the whole circuit and breaker to that temperature.

 

[Volta]

In general, no violation.
Many people feel that 4' of conductor is a sufficient distance to say that you have moved away from the protective device termination limitation.

That was my first impulse, but when revisited didn't seem quite right. This is a real application, and the 60 deg conductor is probably ten feet long.

It seems that the splicing device subjected to 75 degrees is going to conduct that heat to the 60 deg side of the connection. Even in a butt splice, where the wires do not touch, the temperature might be passed through.

 

[Volta]

The same layout with the THHN sizes:

60 amp OCPD with 60 deg C termination > #4 wire calculated at 60 deg ~10 feet > splicing device rated at 75 deg > #6 wire calculated at 75 degrees > 75 deg termination in main breaker of sub-panel.

Is this a 55 amp or 60 amp circuit?

 

[SG-1]

At 30 degreesC I would say you are good for 48 Ampere continuous load.

At 45 degreesC I have an issue with that much load.

 

[Volta]

I think that I recall a (Holt?) illustration of a circuit leaving a panel, splicing to a higher temperature (smaller) wire to run a long distance, then splicing to another lower temp (larger) wire, and then serving the load. Does anyone have access to that?

 

[Smart $]

I think that I recall a (Holt?) illustration of a circuit leaving a panel, splicing to a higher temperature (smaller) wire to run a long distance, then splicing to another lower temp (larger) wire, and then serving the load. Does anyone have access to that?

Square D?

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

 

[wawireguy]

If I'm understanding correctly you look at the temperature ratings of the terminals from one junction to another and derate accordingly for temperature and bundling on that section of wiring.

60deg to 75deg with #4: 70 amps based off 60deg column
75deg to 75deg with #6: 65 amps based off 75deg column

The way I see it you have a 60 amp circuit.

 

[Volta]

Square D?

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

Nice page. I'll have to reread it as it poses another point I want to consider separately.

I think that is it, thanks for posting it. Do you agree with the premise? If the conductor used at a higher temp. is connected to a splicing device, can the second wire on the device truly be calculated at the lower temperature? Can we discount heat transfer through conduction?

 

[Volta]

If I'm understanding correctly you look at the temperature ratings of the terminals from one junction to another and derate accordingly for temperature and bundling on that section of wiring.

60deg to 75deg with #4: 70 amps based off 60deg column
75deg to 75deg with #6: 65 amps based off 75deg column

The way I see it you have a 60 amp circuit.

That's how I saw it to start, and installed it, but when asked to justify it I had difficulty. I think it is right, but I'd like to be sure.

 

[Smart $]

.... Do you agree with the premise?

Yes.

If the conductor used at a higher temp. is connected to a splicing device, can the second wire on the device truly be calculated at the lower temperature? Can we discount heat transfer through conduction?

Yes... but subject to the distance from higher-temperature-rated splice to lower-temperature-rated termination.

 

[Volta]

Yes.



Yes... but subject to the distance from higher-temperature-rated splice to lower-temperature-rated termination.

Well, I wondered what minimum distance could have been used. A short jumper of 18" or so in the supply panelboard would have been very easy, but seemed to be poor design, so it was set up to be at a natural transition point, about ten feet away.

Thanks for your input .

 

[wawireguy]

As a electrician I don't try to re-engineer the code or UL listings. Somebody who gets paid a lot more than I do has already figured it out. If Mike Holt in that diagram figured that is what the code says then that's how I'm going to apply it. Reality in this case is that the the NEC has us over engineer the installs any ways. I wouldn't even worry about "heat" at the 75/60 degree termination point. Install to code with good craftsmanship and keep trucking.