Table 250.102 (C)

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Danial

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Hi,

I have watched Mike Holt's YouTube video on table 250.102(C) but I was still looking for some clarification.

I have a 2500 KVA transformer with 34.5 KV- 480/277, and #3/0 grounding electrode conductor. On the secondary side of the transformer (Load side) I have 250 feet of feeder and the feeder information is as follow:

8 sets of 4 wire (3 phase, 1 neutral) #600 KCMIL, with 1 #600 kCMIL GND in 4" conduit.
Therefore, in each of the 8 set conduits, I have 5 wires total, 3 phase, 1 neutral, and 1 ground.

I was wondering if that #600 KCMIL ground conductor in each set is accurate? According to note 1 of table 250.102 (C) I have"
8 x 600 = 4800 KCMIL
4800 KCMIL x .125 = 600 KCMIL

Is that the ground wire that needs to be routed in each conduit (set), or is that what the overall size should be and I need to split that up into 8 smaller wires?
 
Is there an OCPD on the secondary side adjacent to the transformer? From the transformer to the OCPD you would need a SSBJ in each raceway based on the size of the conductors in each raceway. After the OCPD you would use T250.122 for the EGC sizing.
 
There is not OCPD immediately before or in adjacent to the secondary side of the transformer. The feeder does terminate in a switchboard, however I understand that table 250.122 indicated that if there is a current limiting OCPD immediately before the feeder, the ground conductor must be sized according to the current limit of that OCPD. This is not the case here, we have a feeder set being separately derived from a transformer. The feeder feeding the transformer on the primary side, had a OCPD before so I used table 250.122 but not on the secondary side.
 
The primary doesn't really matter with regard to your question about 250.102(C) so on the secondary side are these conductors all outside?
 
Yes correct, they are located outside. I was reading more in depth and I got this from NEC.
"and an individual supply-side bonding jumper is used for bonding these raceways or cables, the size of the supply-side bonding jumper for each raceway or cable shall be selected from Table 2 50.102(C)(1) based on the size of the ungrounded supply conductors in each raceway or cable. A single supply-side bonding jumper installed for bonding two or more raceways or cables shall be sized in accordance with 250.102(C)(1)."
So I'm assuming if we have 8 sets, we have to split up the 600 KCmil ground conductor to 8 sets.
600 / 8 = 75 KCmil, which would be a number 1 since #1 is 83.69 Kcmil.
therefor 8 sets of #1, 1 in each conduit for a total equivalent size of 669.5 Kcmil.
Is that correct?
 
I am a bit confused. If this transformer is an separately derived system then wouldn't the conductors be service conductors and not feeders?

Someone smarter than I am needs to handle this. lol
 
Dennis Alwon said:
I am a bit confused. If this transformer is an separately derived system then wouldn't the conductors be service conductors and not feeders?
Click to expand...

Service conductors only come from the utility.
Customer owned transformer secondaries are feeders.
 
The supply side bonding jumper is sized based on the conductors in each raceway, not the total cross sectional area of the conductors in all of the raceways. You need a 1/0 supply side bonding jumper in each raceway.
 
Yes sir, I believe they are feeders.
Oh wonderful, that is perfect. @don_resqcapt19 how did you get the 1/0 if I may ask? I think one of the supers also suggested a 1/0 in each raceway, but how did you get to that number?
 
Danial said:
Yes sir, I believe they are feeders.
Oh wonderful, that is perfect. @don_resqcapt19 how did you get the 1/0 if I may ask? I think one of the supers also suggested a 1/0 in each raceway, but how did you get to that number?
Click to expand...
Section 250.102(C)(2) and Table 250.102(C)(1).

Note 1 to the table would apply were you are using a single supply side bonding jumper for the system. You could do this where you have all of the feeder conductors in cable tray.

You have multiple conduits and you are required to have a supply side bonding jumper in each raceway and section 250.102(C)(2) applies.
 
That makes perfect sense. As it says in the Table 250.102 (C) 350-600 KCMIL would use a #1/0 like you said.

I just really want to appreciate all of you for all your quick and helpful responses. I'd been loosing some sleep over this for a little while but I can finally get some rest now! Thank you so much for the help!
 
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