csa 22.1-2015 rule 4-006 - clarification

[Al-Pa]

Goodmorning,

i'm new in that forum and i'm writing this post to have your feedback about the interpretation of the CSA 22.1 - rule 4-006 regarding the design of power cables.

According to that rules 4-006 point 1) the allowable ampacity of a cables depends on the temperature rating of the terminals in which it's connected, and in the point 4) of the same rule is clarified that the requirement of point 1) is relevant only to the first 1.2 m of the cables from the terminals connection.

Now, i've to design a cables (90°C type) that is routed from and electrical building to a motors in field. I've individuate n°3 different section of the cable routing path:
1) the first one is the routing inside the electrical building, in which the cable laid with few cables in a cable trays and is connected to the MCC terminals (75°rated) and is subject to the indoor temperature
2) the second part is the outdoor path of the routing in which the cable laid with other cables in a cable trays and is subject to the ambient temperature and cables at 90°C
3) the third one is the terminal path in which the cable run alone in order to reach the motor terminals (still at the outdoor temperature)- terminals (75°rated)

For all path i've calculate the right ampacity, according to the CSA 22.1 tables.

Now according to my interpretation of the rule 4-006 the right design of the cables id the lowest ampacity value between the three values calculated for the path above described.

.
My colleague instead claims that the right design of the cable is defined by the ampacity table relevant to 75°C (due to terminals ratings) and the installation method of outdoor path.

in my opinion is not correct, because it not consider point 4) of subrule 4-006.

Since we are not familiar with CSA standards, could you please clarify which approach is correct?



thank you,
Alessandro.

 

[waross]

In order to take advantage of the higher ampacity of 90 degree rated cable, you must terminate the 90 degree cable in a junction box or accepted splice method and use larger, 75 degree rated cables for the first and last 1.2 meters to the starter and to the motor.
Don't forget to check the voltage drop.
Use Table D3 in Appendix D for voltage drops.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Al-Pa]

thank you Waross,

I don't understand the logic and the technical reason of that rule. Could you help me to understand?
in the 4-006 subrule 4) is written
" Subrules 1) and 2) shall apply only to the first 1.2 m of conductor length measured from the point of termination on the equipment."

So in my opinion have a sense to use a 90° Cables for the whole routing and verify if in the ends (from more than 1.2m) the derating of the cable due to 75° table value, the ambient temperature (that can be different form the main routing that have an outdoor path) and the laying method (single cable instead of bunched cables, is greater that the derating of the same cable in the outdoor path (due to different laying method and temperature).

technically speaking it's fit, see also this article "

https://iaeimagazine.org/magazine/features/cec-rule-4-006-and-ontarios-perspective/

"

If not so, what is the meaning of subrule 4) that i've written above?

thank you in advance for any helps,
Alessandro.

 

[LionelHutz]

Nothing saying 75*C cable means you must use cable with 75*C printed on it. It means you must use cable sized as if it were 75*C cable and rated 75*C or higher. 90*C cable is just fine to use in a 75*C sized application.

 

[waross]

EXAMPLE:
Table 2
Allowable ampacities for not more than three copper conductors,
rated not more than 5000 V and unshielded, in raceway or cable
(based on an ambient temperature of 30 °C*)

AWG #6 75C - 65 Amps, 90C - 75 Amps
AWG #4 75C - 85 Amps, 90C - 95 Amps

Required ampacity = 70 Amps.
Case #1, AWG #6 is used at the 90C rating, with JBs and AWG #4 used for the first and last 1.2 meters.
Case #2, Voltage drop is an issue so the cable is up sized to #4 AWG. The 75C rating is greater than the required 70 Amps so the cable may be directly connected at both ends.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

Ambient is assumed to be 30C unless greater.
I had a challenge where the last 7 feet of ambient was 110C, 230F.
We used MI (Mineral Insulated, or PyroTenax) for the last 7 feet.

Bill
--------------------
"Why not the best?"
Jimmy Carter