Tray cable upsized for VD. Quick calculation check.

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Dsg319

Dsg319

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Wv Master “lectrician”
Is this correct? I’m out of town and don’t have my code book with me with my notes pertaining to this.

Situation-pulling (tray cable) branch circuit conductors to a splice box for lighting and receps. Raceway is mostly cable tray, so using TC and engineers have upsized conductors to number #8 for voltage drop. (208v) 20amp OCPD.

Are my calculations correct? We have a 3c #8 cable with #10egc. From my math is seems we need to use the 3rd spare conductor as the EGC since the original is not upsized proportionally to the-ungrounded and grounded conductors.

#12-6,530cm
#8-16,510cm

16,510/6,530=2.52

Original egc size #12 per OCPD multiplied using 2.52 shows the EGC would also need to be a #8.

#12-6,530 x 2.53= 16,455cm. Next size up is #8awg.

Conclusion-spare original green #10wire in cable and use the available 3rd #8as the proportionally sized EGC.
 
Since the required EGC for #14,#12 and #10 is the same size as the phase conductor, when you increase the size of those conductiors the EGC would still be the same as the phase conductor so you are correct, the EGC would need to be a #8.
 
augie47 said:
Since the required EGC for #14,#12 and #10 is the same size as the phase conductor, when you increase the size of those conductiors the EGC would still be the same as the phase conductor so you are correct, the EGC would need to be a #8.
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Guess I could have done it without all the math lol. Thank you.
 
augie47 said:
I did the math a time or two before it dawned on me that m 1 x 1 still equals 1 :)
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Talked to the electrical inspector on job site and tried to talk to him about VD and EGC on tray cable. He said just terminate it how it is on the print.....Have yet to see any notes on prints concerning VD and EGC on prints.

One of two things.
1. Engineers have done calculations to show EGC is sufficient on 20amp ckt with with upsized phase conductors to #8 and #10EGC.

2. They leave it up to the electricians to know wether or not to use the green wire (#10) in the cable or to use the spare #8 conductor as EGC.

🤷‍♂️
 
I would vote on #2.
If there happened to be a problem in the future I would use the #8 since you have that opinion readily available.
 
augie47 said:
I would vote on #2.
If there happened to be a problem in the future I would use the #8 since you have that opinion readily available.
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I’ll bring it to my supervisors attention one more time before starting on terminations. But I just know how it’s going to be, people will look at me like I’m silly (full of poo) for sparing off the undersized #10awg green conductor and using the 3rd #8awg and phasing it green for the proportionally sized EGC.

Plus if I’m terminating in the cabinet, and someone else is terminating in the field or vise versa, I’d say 9/10 they will use the original #10awg green, as I’m plenty of guilty of doing before as well.

So it would really need to be told to each and every person terminating the increased conductors to use the 3rd spare conductor (#8awg) as the increased EGC.

side note- on the bright side in most the instances if there was a ground fault on equipment, it and the steel it’s mounted on or setting on is connected to the station grounding system. Which in turn is bonded to the MCC,cable tray, and nipples going into distribution panels.
 
Easy solution: use the green as the egc and up the OCPD to 40A . :) :)

IMHO you are correct, you need the #8 egc and everyone else associated with the job will give you grief for using it.

Jon
 
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