I dont know where he got this

[joeyww12000]

I was having a discussion about derating the other day at work with a fellow electrician. I was telling him as far as derating goes I start at the 90 deg C column depending on insulation, but he says you use the 75 deg C column for 100a and less 60 deg C column for 100 or more. Where did he get that from? He says its in the code book.

 

[chris kennedy]

Here......

(1) Equipment Provisions. The determination of termination provisions of equipment shall be based on 110.14(C)(1)(a) or (C)(1)(b). Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment termination provisions shall be based on Table 310.16 as appropriately modified by 310.15(B)(6).
(a) Termination provisions of equipment for circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, shall be used only for one of the following:
(1) Conductors rated 60?C (140?F).
(2) Conductors with higher temperature ratings, provided the ampacity of such conductors is determined based on the 60?C (140?F) ampacity of the conductor size used.
(3) Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors.
(4) For motors marked with design letters B, C, or D, conductors having an insulation rating of 75?C (167?F) or higher shall be permitted to be used, provided the ampacity of such conductors does not exceed the 75?C (167?F) ampacity.
(b) Termination provisions of equipment for circuits rated over 100 amperes, or marked for conductors larger than 1 AWG, shall be used only for one of the following:
(1) Conductors rated 75?C (167?F)
(2) Conductors with higher temperature ratings, provided the ampacity of such conductors does not exceed the 75?C (167?F) ampacity of the conductor size used, or up to their ampacity if the equipment is listed and identified for use with such conductors

 

[iwire]

I was having a discussion about derating the other day at work with a fellow electrician. I was telling him as far as derating goes I start at the 90 deg C column depending on insulation, but he says you use the 75 deg C column for 100a and less 60 deg C column for 100 or more. Where did he get that from? He says its in the code book.

As Chris posted it comes from 110.14 but do not overlook a key part.

Unless the equipment is listed and marked otherwise,

A lot of equipment is marked otherwise.

Regardless if your insulation is 90 C you can still start at 90 C as long as the finished result does not exceed the rating at 75 or 60 C depending on the terminals rating.

 

[joeyww12000]

I guess Im confused.....why dont we just use the 60 degree C column for everything and not have to worry about it? Also another thing Im getting confused on is this, in the 90 degree C column #12 is rated at 30 allowable amps and 25a in the 60 degree C column, Ive never seen a #12 on a 30a breaker I dont think...?

 

[iwire]

I guess Im confused....

It is a confusing subject.

.why dont we just use the 60 degree C column for everything and not have to worry about it?

Copper is expensive.

Also another thing Im getting confused on is this, in the 90 degree C column #12 is rated at 30 allowable amps

We can use that 30 amp rating for derating but no equipment comes with 90 C terminals so after derating the ampacity can not be higher then the terminal rating.

and 25a in the 60 degree C column, Ive never seen a #12 on a 30a breaker I dont think...?

There are times where we can use 12 AWG at 25 amps and even 14 AWG at 20 amps.

But in most cases 240.4(D) prevents that.

 

[don_resqcapt19]

, Ive never seen a #12 on a 30a breaker I dont think...?

If the load is a motor or AC unit you might see a #12 on a 50 amp breaker and still be in compliance with the code. This is because the breaker is only providing short circuit and ground fault protection and another device is providing the overload protection.

 

[hillbilly]

I was having a discussion about derating the other day at work with a fellow electrician. I was telling him as far as derating goes I start at the 90 deg C column depending on insulation, but he says you use the 75 deg C column for 100a and less 60 deg C column for 100 or more. Where did he get that from? He says its in the code book.

BY the way...

Your fellow electrician got it wrong too.:smile:

steve