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Old 05-27-2019, 09:48 PM   #1
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Default Confused about derate or am i just stupid

Hey guys, been a long time lurker. got a quick question regarding derating a conductor. I just got the CEPE2015 to practice for my exam and came across this question. I've seen a couple threads where bulletin 4-12-3 was posted regarding correction factors and 4-006 and i answered the question per se but got it wrong.



ive posted a pic but not sure if you'll see it. but here is the question

350kcmil RW90 @ 45C amb temp run in rigid conduit what is maximum ampacity

This is what i got

350kcmil = 350A from 90deg T2

350A x . 87(T5A 90deg column) = 304.5A still less than 310A from 75deg T2

answer is 254.2A
they use 310A from 75deg T2 and multiply .82 T5A 75deg column.

any clarification would be appreciated.

Thanks yall.
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Old 05-27-2019, 09:55 PM   #2
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Canadian code and Ontario code derate wires differently.

The bulletin you mentioned is only for Ontario. If your studying for the red seal you need to follow Canadian code
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Old 05-28-2019, 08:34 AM   #3
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Default CEC and OESC, difference when derating conductors

Say your wire is 350 RW90 and the termination temp is 75 degree rated.

CEC.
Find the lowest temperature between the wire temp and the termination temp. That is the column you use with the ampacity tables and the deration tables.

Eg;
350 kcmil from table 2 @75 degrees x number from table 5A in the 75 degree column.
(310 x 0.82 = 254.2 amps)

OESC.
Start with the temperature rating of the wire and derate from there. Compare your derated ampacity to the ampacity given in the 75 degree column. You go with whichever one is lower.

Eg;
350 kcmil from table 2 @ 90 degrees x number from table 5A in the 90 degree column.
(350 x 0.87 = 304.5 amps)
Compare that number with the value from table 2 @ 75 degrees(310 amps), use the lower one. (304.5 amps)

4-006 and Ontario bulletin 4-12-4
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Old 05-28-2019, 06:56 PM   #4
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Quote:
Originally Posted by bizzoshaker View Post
Hey guys, been a long time lurker. got a quick question regarding derating a conductor. I just got the CEPE2015 to practice for my exam and came across this question. I've seen a couple threads where bulletin 4-12-3 was posted regarding correction factors and 4-006 and i answered the question per se but got it wrong.



ive posted a pic but not sure if you'll see it. but here is the question

350kcmil RW90 @ 45C amb temp run in rigid conduit what is maximum ampacity

This is what i got

350kcmil = 350A from 90deg T2

350A x . 87(T5A 90deg column) = 304.5A still less than 310A from 75deg T2

answer is 254.2A
they use 310A from 75deg T2 and multiply .82 T5A 75deg column.

any clarification would be appreciated.

Thanks yall.
Just a heads up there are numerous mistakes in the CEPE Program. But based on your answer of 304.5A, this would be the correct number to go by.

Now if the question had just asked you 350kcmil @ 45C amb temp you would then use the 75°C column from Table 2 as there is no temperature indication of the cable as it is clearly larger than No.1 AWG{ Rule 4-006(2)(b)(ii) }
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Old 05-28-2019, 08:56 PM   #5
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Quote:
Originally Posted by Azachi View Post
Just a heads up there are numerous mistakes in the CEPE Program. But based on your answer of 304.5A, this would be the correct number to go by.

Now if the question had just asked you 350kcmil @ 45C amb temp you would then use the 75°C column from Table 2 as there is no temperature indication of the cable as it is clearly larger than No.1 AWG{ Rule 4-006(2)(b)(ii) }
4-006 is for the temperature of the termination of the equipment, not the temperature rating of the cable. So if there is no equipment termination temperature, you use 4-006(2)

If the question is asking about wire rating and there is no equipment mentioned, like wire in a raceway between two junction boxes, then you can use the temperature rating of the wire. So a RW90 you would use the 90 degree column. 4-006 only applies to the first 1.2 meters of wire connected to equipment. 4-006(4)
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Old 05-28-2019, 09:28 PM   #6
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Thank you so much for clearing the air for me. You guys are awesome!
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Old 05-30-2019, 06:45 PM   #7
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We have installed RMUs (safe ring ABB).

It has temperature range from -20 to +40 , but where it used the actual temperature goes to 50 deg . How could i calculate the de rating for this equipment.
Rated current of this unit is 600 amp.

Please find the attached nameplate.

Sent from my SM-J700F using Tapatalk
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Old 05-30-2019, 08:06 PM   #8
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Originally Posted by mohsan514 View Post
We have installed RMUs (safe ring ABB).

It has temperature range from -20 to +40 , but where it used the actual temperature goes to 50 deg . How could i calculate the de rating for this equipment.
Rated current of this unit is 600 amp.

Please find the attached nameplate.

Sent from my SM-J700F using Tapatalk
That is the ambient temp, not the termination temp. that means you can not use that equipment in a room hotter than +40.

If there is no termination temp listed then you would use 75 degrees as per 4-006(2)(b). You would then derate using table 5A for 50 degrees.

But I don’t think the Canadian electrical code is used in Saudi Arabia
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