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Discussion Starter · #1 · (Edited)
IF you have say 90 C and 60 C rated wires in the same conduit in an area with an ambiet air temperature of 40C, how do you derate them for temperature?

IGNORING THE EQUIPMENT TEMPERATURE RATING

4-004 says you have to take the curreent rating from Table 2 using the lowest temperature rated wire, so these amapcitied from this case would come from the 60C column.

The correction factor for the 40C ambient comes from Table 5A. Heres the question, do you derate BOTH conductors using the 60C column or do you take the derating for the 90C using the derating factor from the 90C column and the 60C wire with the derating factor from the 60C column.

In a nut shell do you derate the 90C wires TWICE?
 

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Discussion Starter · #3 · (Edited)
Ya basically. Your 90' will be rated as a 60' and then you would use 5c on both if you have more than three conductors

But what about the temperature rating from 5A, that's the question? You have already derated the 90C cable to 60C by having to use the 60C column in Table 2.

Why should the better 90C cable be derated twice to 60C?
 

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But what about the temperature rating from 5A, that's the question? You have already derated the 90C cable to 60C by having to use the 60C column in Table 2.

Why should the better 90C cable be derated twice to 60C?
If wires of a different temp rating are in the same conduit, all the wires are only good as the lowest one. Think about it, if the temperature was more than 60 and the 60 degree wire was compromised (melted insulation, a short, burning whatever), every wire in that conduit would also get damaged regardless of their rating.

Basically, that 90 degree wire is now a 60 so any derating for too many wires or ambient temp must be done using the 60 degree column
 

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Discussion Starter · #5 ·
I agree, but that is not what I am asking. The debating factors for 60C and 90C wire for a given temperature in table 5A are different.

You have already derailed the 90C cable to a 60C current rating in table 2. If the ambient temperature is above 30C but less than 60C, say 40C, the debating factor for the 60C cable in table 5A is .82 but the detracting factor for the better 90C cable is .93 or do you use the .82 and further debate the already serrated 90C cable by another 11%L
 

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You use the 60 degree derating factor on the 90 degree wire.
That 90 degree wire is no longer rated for 90 degrees if you put it in a conduit with a 60 degree wire
 

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Discussion Starter · #8 ·
Your 90degree wire gets derated twice
Yes it gets derated twice, but does it get derated to 60C twice? Why? It is a better insulation and the higher ambient temp does not have as great an effect on it and you have already derated it to a 60C current value once.

About 6 years ago I took a CSA code course and they said you would use the 90C rating for the 90 C wire from table 5A. I want to know if that has changed?
 

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Discussion Starter · #10 · (Edited)
Because its in a conduit with wires of a lower rating. :blink:

You want to derate using the 90 degree column, use only 90 degree wires
Why? Like I said, table 5A used to be column for column based upon the rating of the wires. Has that changed? When?

It doesn't make sense to apply a punitive derating factor that is lower than necessary for a wire.

Can you quote a rule or example that says 5A has to be applied your way?

I checked the handbook and appendix B and nothing.
 

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2012 code 4-004 (14) "ampacity of conductors of different temp ratings installed in the same raceway shall be determined by the conductor having the lowest temp rating" Table 5a is for when conductors are installed in a Ambient temp over 30' 4-004 ( 8 ) so that would be done after you get your base ampacity
 

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Discussion Starter · #12 · (Edited)
2012 code 4-004 (14) "ampacity of conductors of different temp ratings installed in the same raceway shall be determined by the conductor having the lowest temp rating" Table 5a is for when conductors are installed in a Ambient temp over 30' 4-004 ( 8 ) so that would be done after you get your base ampacity
We have already agreed on that. The discussion is about how do you apply table 5A.

The code is not clear. I was taught at at 2 day CSA code seminar about 5 years ago that 5A is applied column for column. In other words the correction factor for the 90C wire comes from the 90C column and the correction factor for the 60C wire comes from the 60C column. EVEN IF THEY ARE IN THE SAME CONDUIT.

What I want to know is IS THIS THE COMMON PRACTICE STILL OR HAS IT CHANGED? AND can you show me something from a provincial or federal entity that has an example that shows your way of calculating it.
 

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Discussion Starter · #14 ·
This is how I was taught to do it and as far as I'm concerned that's what those two rules tell you
Actually I was taught that was the way to do it too, about 30 years ago, but I was taught by the people at CSA that it was wrong.

The problem is those rules are vague and open to interpretation. And C9.6 says that rules must be interpreted on the literal text and not the intent.
 

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I was taught that when looking at 5A use the column for the insulation rating regardless of any other factors. The key is that 4-004(14) does not change the insulation rating of the conductor. It merely tells you how to determine the ampacity of conductors with mixed temperature ratings. And 4-004(4) tells you how to de-rate conductors due to high ambients based on the insulation temperature ratings.
 

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Discussion Starter · #16 ·
I was taught that when looking at 5A use the column for the insulation rating regardless of any other factors. The key is that 4-004(14) does not change the insulation rating of the conductor. It merely tells you how to determine the ampacity of conductors with mixed temperature ratings. And 4-004(4) tells you how to de-rate conductors due to high ambients based on the insulation temperature ratings.
Exactly, that is what I am trying to confirm here.

It is like you are connecting a 90C conductor to a 75C breaker, you have to use the 75C column from table 2 or 4, but you can use the 90C column from 5A for ambient temperature correction not the 75C column.

What I would like to see if anyone has something from AHJ or CSA showing that. I have lost the notes from the course I took all those years ago and I have to prove to my students that my memory is intact.
 

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troubleshooting said:
Why? Like I said, table 5A used to be column for column based upon the rating of the wires. Has that changed? When?

It doesn't make sense to apply a punitive derating factor that is lower than necessary for a wire.

Can you quote a rule or example that says 5A has to be applied your way?

I checked the handbook and appendix B and nothing.
Yes it does because THE OTHER WIRES in your EMT are rated for 60 degrees. I would fire you if you did this on the job. Section 4 tells you that if you have 2 different rated conductors in a pipe that all of them MUST be treated as the LOWEST temp rating, therefore, your 90degree conductors are now 60 degree conductors, now you run them through a room with an ambient temp of 40 degrees, now you derate BOTH conductors (which are now only rated for 60 degrees) again. It's pretty clear IMO
 

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Discussion Starter · #18 ·
Yes it does because THE OTHER WIRES in your EMT are rated for 60 degrees. I would fire you if you did this on the job. Section 4 tells you that if you have 2 different rated conductors in a pipe that all of them MUST be treated as the LOWEST temp rating, therefore, your 90degree conductors are now 60 degree conductors, now you run them through a room with an ambient temp of 40 degrees, now you derate BOTH conductors (which are now only rated for 60 degrees) again. It's pretty clear IMO
By taking the current from the 60C column for the 90C conductor you have satisfied the rule for 4-004 (14). Read the rule again, 4-004 (8) does NOT say anything about how to use the table 5A or that it is in conjunction with 4-004 (14).

Just because you don't understand it doesn't make it wrong.
 

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Rochsolid said:
Yes it does because THE OTHER WIRES in your EMT are rated for 60 degrees. I would fire you if you did this on the job. Section 4 tells you that if you have 2 different rated conductors in a pipe that all of them MUST be treated as the LOWEST temp rating, therefore, your 90degree conductors are now 60 degree conductors, now you run them through a room with an ambient temp of 40 degrees, now you derate BOTH conductors (which are now only rated for 60 degrees) again. It's pretty clear IMO
BC curriculum teaches it this way.
 

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Discussion Starter · #20 ·
BC curriculum teaches it this way.
One of the other guys here from BC says it is taught the way I was shown by CSA. I don't know when you went through, but things change. Just wait till you see what's coming in the next code book.

If I had my notes from the CSA seminar I attended I would post them. I was hoping someone here would have them.

Do you have anything from an AHJ showing your way is right?
 
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