Grounding and bonding for 480v 3ph 400a service & 75kva transformer

[ctaylo360860]

Here is the plant that I'm working on, the systems, equipment, and work I'm inquiring about is all existing. I work in house for the company and am trying to get the GEC system right. I have not been able to find a bonding jumper to the structural metal you see in the picture below.... Im sure it is needed according to 250.104 (C) structural metal, but wanted to confirm.. see pictures 6 & 7

This picture below is the 400a service disconnect, 75kva transformer, and the 208/120v panel. The 400-amp service is fed with (2) parallel runs of 3/0 copper service conductors, and (2) paralleled #2copper for the grounded conductor. the only GEC i have found is #2 that goes to a single ground rod outside see picture #4, and another #2 that goes to a water pipe. The plumbers got a hold of the water pipe since the main line broke outside. They ended up cutting it off outside and then inside and shoved a piece of 3/4 pex through the 1-1/4 copper line. since they have done this it is no longer part of my grounding electrode system... see pictures 6 and 7

75 kva transformer fed from 100 a cb with (4) # 2 copper conductors. 3 phases and a EGC

Only ground rod found for the Grounding electrode sytem.

I'm wondering if this structural metal needs to be bonded to the grounding electrode system? I would use 250.102(C)(1) to size the bonding jumper from the grounded conductor at the service to the structural metal... the other way i thought about handling this was setting a copper bus bar connector running 3/0 copper from the service disconnect to the bus bar connector. Then i believe i would need to run a 1/0 copper conductor from the busbar connector to the steel. I thought about doing it this way so that i could land the GEC from the 208/120 panel to the busbar connector as well. it should be sized according to 250.66 and because the 208/120 panel is fed with 3/0 copper i would need to run a #4cu from where my sbj is to the busbar connector

any reason #2 would be needed to the water pipe? i thought #4 was the largest size needed.

Plumbers in the wild...

this is the 75 kva transformer fed from a 100a circuit breaker. the ran (3) 3/0 copper conductors for phases. (1) #2 copper for the grounded conductor, and (1) #8 as the EGC. the had the separately derived system bonded at transformer and the 208/120 panel... i unbonded the grounded and grounding conductors at the 75kva transformer. looks the the egc going to the 208/120 panel needs to be atlease a #6 or larger... i say this because the egc is going to a panel that has a 200amp ocpd. looks like they sized it based on the primary 100a ocpd...

208/120v panel fed from 75kva transformer. panel is bonded and the egc is undersized. because i have my grounding and grounded conductors bonded in this panel using the system bonding jumper strap i need to run my GEC from the neutral bar where strap is located to either the service disconnect grounded conductor bar. or if i go the other route and use a copper bus bar connector. the size of my gec will be based on 250.66 the 208/120 panel is fed with 3/0 copper and my gec should be a size #4 or largerl

#8 egc from 75kva transfromer to 208/120 panel



Thanks in advance for any and all help its always appreciated!

 

[augie47]

The only thing that looks correct is the #2 GEC to the building steel which you question. That would be the normal minimum size for a 400m amp service (250.66)
The grounded conductor and SSBJ on the secondary side are undersized.
The transformer does need an grounding electrode connection.

 

[ctaylo360860]

The only thing that looks correct is the #2 GEC to the building steel which you question. That would be the normal minimum size for a 400m amp service (250.66)
The grounded conductor and SSBJ on the secondary side are undersized.
The transformer does need an grounding electrode connection.

I’m not sure you read my post correctly… there is no gec or bonding jumper that I have found to any structural metal… the 2 gec I did find. One was #2 that went to a single ground rod. I thought 250.66a states it doesn’t need be bigger than #6…. The other #2 went to a water pipe main. Which I believe only needs to be sized #4. Plumbers got rid of that so it’s not really part of the system… I agree the #8 that runs from transformer ground lug to the secondary panel needs to be sized using 250.102(c)(1) it is actually a ssbj and not a egc… and the secondary panel needs the egc because I have bonded the grounded and grounding inside the panel and isolated in t her transformer… gec for secondary panel needs to go where the system bonding jumper is…

 

[augie47]

The 400 amp service needs a GEC.
I assumed that was the #2 to building steel but in hindsight that would need to be a 1/0
The transformer would also need a GEC. At the time of this install that would have likely have been to steel (If it had another GEC then the steel would have needed to have a #4 bond jumper_)

 

[Tulsa Electrician]

"The 400-amp service is fed with (2) parallel runs of 3/0 copper service conductors, and (2) paralleled #2copper for the grounded conductor. "
Inst 1/0 minimum for parallel.
310.10 (H). Don't know if exception #2 applies.
Service voltage 480/277?

Then you have options on SDS.
Take GEC to trans and rework panle or run the GEC to panle and rework termination locations.
Either way install proper sized SSBJ. 3/0 conductors to the panle would require a #4 cu SSBJ

Now as far as the underground metal water pipe that was cut off. As long as there 10' in direct contact with earth. Your fine, it serves as an electrode. If not than no. Code does not say water line it says water pipe. 250.52 (A) (1).
If the water pipe does serve as an electrode than a supplemental electrode is required, 1-rod.
If it does not serve than an additional rod is required or you need to prove the single rod meet code.
See 250.53 (A) (2). And exception.

The netural from the SDS should be full size. A lot on line to netural loads. Maybe a load calc to be sure or take some reading.
#2 CU is good for 115 amps at 75c.
Maybe read thru 220.61


Your service conductors are (2) 3/0, 2*167800 for a total area of 335.600 CM. #2 GEC.

Rod , yes #6 cu minimum 250.66 (A)
GEC
Does the structure steel meet the verbage of 250.53 (2), 250.104(C) and 250.104 D (2)

As far as using a buss bar. From the service disc to buss bar does not need to be larger than #2 GEC based on size of service conductors. 250.64 (F)

It appears you have a good handle on what is required.

Hope I read all correctly.

I have seen worse.
Also is that #8 or 6 NM on a 2-p 70, hard to read.

 

[ctaylo360860]

"The 400-amp service is fed with (2) parallel runs of 3/0 copper service conductors, and (2) paralleled #2copper for the grounded conductor. "
Inst 1/0 minimum for parallel.
310.10 (H). Don't know if exception #2 applies.
Service voltage 480/277?

I'm almost certain there was no engineering involved in this install. This is a very small rural town. I have done multiple projects here and have yet to see a set of stamped or sealed prints.... service voltage is 480/277volts.

Then you have options on SDS.
Take GEC to trans and rework panle or run the GEC to panle and rework termination locations.
Either way install proper sized SSBJ. 3/0 conductors to the panel would require a #4 cu SSBJ

correct. they had the sds and the secondary panel grounding and grounded conductors bonded at both locations.... I removed the bonding in the sds because I could just use the bonding strap inside the secondary panel as the system bonding jumper and didnt have enough lugs to do it inside the sds.... As i understand my GEC must go to the panel now because thats where i have my sbj(sytem bonding jumper) is. I should be using 250.102(c)(1) to size my Supply side bonding jumper. which is #4cu or #2alulminum. I didn't have materials when discovering all the goodies so i left it as good as i could for time being....

Now as far as the underground metal water pipe that was cut off. As long as there 10' in direct contact with earth. Your fine, it serves as an electrode. If not than no. Code does not say water line it says water pipe. 250.52 (A) (1).

I'm guessing there is still 10ft in contact with ground for some reason i was thinking that it was 20ft, but that is for 250.52(a)(3) concrete encased electrode... I left it hooked up so it should be part of the grounding electrode system. I meant water pipe somehow auto correct got me...

Also, I learned today that metal underground water pipe grounding electrode conductor is sized based on 250.66 using largest conductor size. i was always under the assumption that it was like a concrete encased electrode and only needed to be sized larger than #4.

If the water pipe does serve as an electrode than a supplemental electrode is required, 1-rod.
If it does not serve than an additional rod is required, or you need to prove the single rod meet code.
See 250.53 (A) (2). And exception.

so since my metal underground water pipe serves as an electrode then i can get a away with one rod as long as it proves it has a resistance of 25ohms or less?
did they have to run #2 from the service disconnect to the ground rod? or could they have gotten away with #6cu?

if i understand correctly they could of ran #6 from the underground metal water pipe to the ground rod?

I ended up running #6 from the service disconnect to two ground rods outside because i thought metal water pipe had to be 20ft in contact and couldnt find another type of GEC. looks like I won't need my #6 and two ground rods now since they actually do have an underground water pipe and rod as there grounding electrode system...

The netural from the SDS should be full size. A lot on line to netural loads. Maybe a load calc to be sure or take some reading.
#2 CU is good for 115 amps at 75c.
Maybe read thru 220.61

Yeah I've seen them downsized maybe once or twice but not 4x. i planned on replacing with neutral from sds with 2/0 copper and running a #4copper for my ssbj (supply side bonding jumper)

Your service conductors are (2) 3/0, 2*167800 for a total area of 335.600 CM. #2 GEC.

i see you used table 8 to find the cm for paralleled conductors. then used 250.66 3/0-350 which gives a #2

Rod , yes #6 cu minimum 250.66 (A)
GEC

so does that mean they could of got away with #6 to the single rod? or would they have had to run #2

Does the structure steel meet the verbage of 250.53 (2), 250.104(C) and 250.104 D (2)

250.53(2)- I don't Belive the metal is in contact with the direct earth or concrete for 10ft or more, but ill have to take a closer look. this plant was built 30 years.
250.104(c) i would say yes and this means the steel needs to be bonded
250.144 d (2)

As far as using a buss bar. From the service disc to buss bar does not need to be larger than #2 GEC based on size of service conductors. 250.64 (F)

so i would use 250.64 if i just had one service and sds? and I could run a #2 gec bases on 250.66 and then from there i can run bonding jumpers of adequate size using 250.102(c)(1) to size conductors to metal structural frame, metal water piping, including sprinkler piping, and if gas is hard pipes from meter to manifold it would also need bonding because of 250.104(a) & (b)

i was wondering if I would need to follow 250.30(6) (a)grounding electrode conductor, multiple separately derived systems. because multiple "two" sds systems on site? i can run 3/0 to the bus bar then jump to each sds with adequate size conductor based on 250.66

It appears you have a good handle on what is required.

Hope I read all correctly.

Thank you for the great response and code references I really appreciate it!

I have seen worse.
Also is that #8 or 6 NM on a 2-p 70, hard to read.

Yes, it needs to be replaced it feeds an air compressor motor that runs constantly. this site is a nightmare...

 

[ctaylo360860]

The 400 amp service needs a GEC.

so looks like there GEC was #2 to underground metal water pipe. I thought this wouldn't work as a gec anymore because of the plumbers cutting it, but i was confusing the concrete encased rod literature with water pipe and it only has to be in contact with direct earth for 10ft not 20ft so it should still be good. they also have #2 from service disconnect grounds to ground rod outside as supplement grounding electrode.

I assumed that was the #2 to building steel but in hindsight that would need to be a 1/0

So the stele is not actually in direct contact with earth for 10ft so i believe it just needs to be bonded using 250.104(C) using 250.102(c)(1)
and chapter 8 2-3/0 conductors have a circulare mll size of 335.600 so i should be able to use a #2cu in bonding the metal frame

The transformer would also need a GEC. At the time of this install that would have likely have been to steel (If it had another GEC then the steel would have needed to have a #4 bond jumper_)

does that sds need the GEC? i have my SBJ (sytem bonding jumper) in the secondary panel? 250.30(a)(2) exception no. 1
Also wondering if i need to use grounding electrode conductor, multiple separately derived systems because i have two transformers on site?

thanks for the replies! really appreicate it!

 

[ctaylo360860]

250.30(a)(5) & 250.30A(6)
i made code references to the book but looks like they have misprinted in 2020nec. 250.30(a)(5) is numbered as @250.30(a)(2)