60/75 degC terminals

[KentAT]

When terminals are identified as 60/75degC, which number do you use? Why mention the 60 if they are rated at 75?

 

[jumper]

When terminals are identified as 60/75degC, which number do you use? Why mention the 60 if they are rated at 75?

AFAICT, dual rated so that you can use either 60C or 75C conductors. I imagine that you can use 90C conductors, as long as you do not exceed the load factor at 75C after derating and other corrections.

 

[hardworkingstiff]

If a lug is rated 75C, when would it not be OK to wire it at 60C ?










My thought is it is always OK. Then why dual rate a lug?

 

[jumper]

If a lug is rated 75C, when would it not be OK to wire it at 60C ?

My thought is it is always OK. Then why dual rate a lug?

Cause if says 60C only that what it is, and if it says 75C only people get confused and think that a 60C conductor cannot be used. AFIAK that is the reason for dual rating. Could be a wet/dry thing also like conductors. I dunno.

 

[Hameedulla-Ekhlas]

When terminals are identified as 60/75degC, which number do you use? Why mention the 60 if they are rated at 75?

When selecting the components for a circuit remeber that no circuit is better than its terminations. NEC 110.14(C) ensure that the consideration of termination is included in the selection of the circuit components.
Terminations, like other components is a circuit have teperature rating. The terminations on breakers, switchs or panelboards with a rating of 100 ampere or less may be rated for 60 degree or 75 degree. NEC 110.14(C) stipulates that unless equipment is marked with a 75 degree terperature rating (for Example: 60/75 degree) the circuit ampacity shall not exceed the value given in the 60 degree column of NEC table-310.16. The reason for this is that the heat generated by the current in a conductor is dependent on the conductor size. The consequence of NEC 110(C) is that it establishes a conductor size that is compatible with the termperatur rating of the terminations.

example: the minimum conductor size for a noncontinuous load of 60 ampere would be a 4 AWG conductor unless the terminations are marked 75 degree in which case a 6 AWG would satisfy the requirements. The resistance of the 4 AWG is less than the 6 AWG thus the heat generated would be less and subsequently, the terination rating may be less.

 

[Hameedulla-Ekhlas]

as long as you do not exceed the load factor at 75C after derating and other corrections.,

Jumper: I am a little confused here in load factor and temperature relation. Can you make it a little bit clear please.

 

[Dennis Alwon]

I found this on Wiki Answers. I have never heard this. Has anyone else?

There is a special circumstance with breakers marked "60/75c"...

If you have circuit breakers marked "60/75c", and they are installed together (such as in a 42 circuit panel), you must use the breaker at the 60c rating, and thus size your wire using the 60c column.
If the breaker in question is in an enclosure by itself, again marked "60/75c", you may use the breaker at its 75c rating. Check the ratings of the enclosure, breaker, conductor, and terminals, and you may be able to use a higher rating than 60c.

 

[jumper]

Jumper: I am a little confused here in load factor and temperature relation. Can you make it a little bit clear please.

I can try, if you derate a #12 NM/Romex conductor from 90C (30 amps) to 25 amps and are using it a regular application, than even though the lug/terminations and wire is good for 25 amps at 75C, you must use the 60C column max of 20 amps for the load and breaker. If your wire, calcs and terminations are good for 75C than you can use that as a limit.

 

[david luchini]

I found this on Wiki Answers. I have never heard this. Has anyone else?

I've never heard of that. My understanding is that if you had an entire panel with breakers rated for 60/75, then you could use the 75 deg rating.

But if you added a 60/75 deg breaker to a panel that already had 60 deg only breakers, you would have to use the 60 deg rating.

That seems to make more sense than what wiki said (at least to me.)

 

[RB1]

Dennis,

What you found on WIKI is right out of the UL Whitebook. With the dual rating a breaker installed in a separate enclosure is suitable for 75 degree terminations. In a panelboard you are permitted to use the 75 degree rating only if the panelboard itself is identified for 75 degree terminations.

 

[Dennis Alwon]

Here is what I found in the UL 2010 book.

CIRCUIT BREAKERS (DHJR)

USE

This category covers circuit breakers which, unless otherwise noted, are of the manually operable, air break type, providing automatic overcurrent protection.

PRODUCT MARKINGS AND RATINGS

These circuit breakers and circuit breaker enclosures are intended for use with copper conductors unless marked to indicate which terminals are suitable for use with aluminum conductors. Such markings are independent of any marking on terminal connectors and are located on a wiring diagram or another readily visible location.
1. Circuit breaker enclosures are marked to indicate the temperature rating of all field installed conductors.
2. Circuit breakers with a current rating of 125 A or less are marked as being suitable for 60?C, 75?C only or 60/75?C rated conductors. It is acceptable to use conductors with a higher insulation rating, if the ampacity is based on the conductor temperature rating marked on the breaker.
3. Circuit breakers rated 125 A or less and marked suitable for use with 75?C rated conductors are intended for field use with 75?C rated conductors at full 75?C ampacity only when the circuit breaker is installed in a circuit breaker enclosure or individually mounted in an industrial control panel with no other component next to it, unless the end-use equipment (panelboard, switchboard, service equipment, power outlet, etc.) is also marked suitable for use with conductors rated 75?C.
4. A circuit breaker with a current rating of more than 125 A is suitable for use with conductors rated 75?C.
5. Circuit breakers intended for continuous operation at 100 percent of rated current may be marked to be connected with 90?C rated wire with the size based on 75?C ampacity. A suitable marking is required in a circuit breaker enclosure, whether or not terminals are mounted therein, if it is intended that the breaker to be mounted therein is to be used with aluminum wire.

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