Using 90 degree column

[Bmxer883]

I know this has been posted a lot and I've tried to read and understand. I'm having a argument with another electrician. We are industrial not journeyman so nothing gets inspected( I think is crazy cause shops have some scary stuff since it's not inspected).

So we are pulling a circuit to three disconnects 60 and two 30amp so figured 120amp is what we need to size wire. He wants to go off 90 degree column since we use thhn and use number 2 I say we need 1 cause the lugs are only rated 75 I think.

They want to go from a 200amp disconnect to a distribution block then smaller wire to three disconnects. My understanding is only use 90 for de rating. Am I right or wrong? Is there any codes to refer to to show them?

 

[augie47]

As a general rule, you are correct. For "everyday" applications the 75° rating is what you need to go by.
As you stated, the 90° rating is normally used for derating purposes due to ambient and fill.


There are instances where the 60° or 90° ampacities are used (other than derating) but in 99% of the cases you are safe using th3 75°

 

[Bmxer883]

As a general rule, you are correct. For "everyday" applications the 75° rating is what you need to go by.
As you stated, the 90° rating is normally used for derating purposes due to ambient and fill.

Could you point out a code or codes to show that to them?

 

[augie47]

110.14(C) is the most relevant.

 

[tom baker]

If you use the 90 C rating it will be a smaller wire, being smaller it can overheat at the terminal connection, esp on continuous loads

 

[Dennis Alwon]

I know this has been posted a lot and I've tried to read and understand. I'm having a argument with another electrician. We are industrial not journeyman so nothing gets inspected( I think is crazy cause shops have some scary stuff since it's not inspected).

So we are pulling a circuit to three disconnects 60 and two 30amp so figured 120amp is what we need to size wire. He wants to go off 90 degree column since we use thhn and use number 2 I say we need 1 cause the lugs are only rated 75 I think.

They want to go from a 200amp disconnect to a distribution block then smaller wire to three disconnects. My understanding is only use 90 for de rating. Am I right or wrong? Is there any codes to refer to to show them?

If these are motor loads that is not how you would size the feeder

430.62 Rating or Setting — Motor Load.(A) Specific Load.
A feeder supplying a specific fixed motor load(s) and consisting of conductor sizes in accordance with 430.24 shall be provided with a protective device having a rating or setting not greater than the largest rating or setting of the branch-circuit short-circuit and ground-fault protective device for any motor supplied by the feeder [based on the maximum permitted value for the specific type of protective device in accordance with 430.52, or 440.22(A) for hermetic refrigerant motor-compressors], plus the sum of the full-load currents of the other motors of the group.
Where the same rating or setting of the branch-circuit short-circuit and ground-fault protective device is used on two or more of the branch circuits supplied by the feeder, one of the protective devices shall be considered the largest for the above calculations.

 

[Bmxer883]

If these are motor loads that is not how you would size the feeder

These 3 disconnects are for a heat treating electric furnace

 

[augie47]

You are correct. For a 120 amp non-continuous load, a #1 would be the correct size based on 75degree terminations.
There may, however, be an "elephant in the room" based on your OP. What size fuses are in your 200 amp disconnect ?

 

[Bmxer883]

You are correct. For a 120 amp non-continuous load, a #1 would be the correct size based on 75degree terminations.
There may, however, be an "elephant in the room" based on your OP. What size fuses are in your 200 amp disconnect ?

I think we are going to put 125s in 200amp disconnect. The three disconnects will have fuses sized to what they are running we are well under 120 amps just want things sized for full potential cause some other guy down the road could tie into it or something.

 

[kwired]

You are correct. For a 120 amp non-continuous load, a #1 would be the correct size based on 75degree terminations.
There may, however, be an "elephant in the room" based on your OP. What size fuses are in your 200 amp disconnect ?

The other elephant is what is the actual connected loads?

60 amp fused disconnect would be needed even if the actual fuse needed is only 35 amps. And a 30 amp disconnect could only have 5 amp fuses in it.

Common feeder conductor to those only needs to be 125% of continuous plus 100% of non continuous load.

And as described there is likely tap rule violations in what is proposed as well.

A single 120 amp conductor tapped from a 200 amp conductor then tapped again to 60 and 30 amp overcurrent devices is not acceptable for any the tap rules.

 

[electrofelon]

Keep in mind you CAN use the 90 degree column for the conductors themselves, but would need to splice back to 75 degree conductors at each end for the terminations in the equipment.

 

[ggunn]

Keep in mind you CAN use the 90 degree column for the conductors themselves, but would need to splice back to 75 degree conductors at each end for the terminations in the equipment.

Are you saying that he needs to splice to larger conductors at the ends to keep them from getting as hot under load? Obviously, the type of insulation (75 degree or 90 degree) does not matter for this consideration. Also obviously, the temperature rating of whatever he would use to make the splice would have to be 90 degrees or higher.

Metal conducts heat as well as current; how far from the 75 degree terminals would the splice have to be?

 

[jim dungar]

Are you saying that he needs to splice to larger conductors at the ends to keep them from getting as hot under load? Obviously, the type of insulation (75 degree or 90 degree) does not matter for this consideration. Also obviously, the temperature rating of whatever he would use to make the splice would have to be 90 degrees or higher.

Metal conducts heat as well as current; how far from the 75 degree terminals would the splice have to be?

Devices, like fusible switches and breakers, are tested with 4 feet of conductor, it would make sense that this should be the minimum distance.