remote Transformer grounding

S

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
Something that has always challenged me. The scenario is:
An isolation transformer located away from the electrical grounding electrode system. Meaning I have main electric room and then a feed to a separate electric room on a different floor, etc. I am wondering what are the economical ways of installing the GEC. I know we often install a GEC and put a ground bar in each electric room , but barring that. If I don't have metal structural frame or supervision to allow water pipe grounding is the only real option to run a ground back to the building GEC?
 
Strathead said:
Something that has always challenged me. The scenario is:
An isolation transformer located away from the electrical grounding electrode system. Meaning I have main electric room and then a feed to a separate electric room on a different floor, etc. I am wondering what are the economical ways of installing the GEC. I know we often install a GEC and put a ground bar in each electric room , but barring that. If I don't have metal structural frame or supervision to allow water pipe grounding is the only real option to run a ground back to the building GEC?
Click to expand...
Isolation transformer in a different floor?
 
If there is no building steel and more than one transformer we would just run a #3/0 common grounding electrode to each closet connected the the building GES.
 
infinity said:
If there is no building steel and more than one transformer we would just run a #3/0 common grounding electrode to each closet connected the the building GES.
Click to expand...

That is typical for us as well, but wondered if there were alternatives. This is not cheap.
 
Based on 250.118(B) Exception {'23} would it not be permissible to use the EGC as a GEC if properly sized and installed keeping 250.64 into account.
 
augie47 said:
Based on 250.118(B) Exception {'23} would it not be permissible to use the EGC as a GEC if properly sized and installed keeping 250.64 into account.
Click to expand...
Yes, but not so easy when the raceway is ferrous metal, as the EGC/GEC must be bonded at each end of the raceways.

There is no technical reason that the EGC sized as required for the primary feeder circuit cannot serve as the GEC....just code rule that has no technical substantiation.
 
augie47 said:
Based on 250.118(B) Exception {'23} would it not be permissible to use the EGC as a GEC if properly sized and installed keeping 250.64 into account.
Click to expand...
Joe Villani said:
In the 2020 NEC see 250.121(A) Exception
Click to expand...
Since it has to comply with parts II, III and IV, how would you interpret the requirement for the GEC to be essentially unspliced? Another challenge I see with this is that, since the transformer EGC is sized on the secondary amperage, the ground to the primaries panel and the ground conductor in the primary conduit would need to be sized to a minimum of the secondary per 250.66. Am I correct?
 
You can splice it. Look at 250.64(C)(1) (Irreversible splice)

EGC is sized based on the OCPD. Transformer rated current and its OCPD can be drastically different (250%)

I agree that the primary conduit equipment ground would have to comply with Table 250.66 based off the derived secondary ungrounded conductors. Also all the bonding requirements in 250.64(E)

There are some cases where the primary size equipment grounding conductor is larger than the grounding electrode conductor (Step up transformer where you max out the primary side)
 
don_resqcapt19 said:
Yes, but not so easy when the raceway is ferrous metal, as the EGC/GEC must be bonded at each end of the raceways.

There is no technical reason that the EGC sized as required for the primary feeder circuit cannot serve as the GEC....just code rule that has no technical substantiation.
Click to expand...
Yes looping the EGC through the lug on a bonding bushing can be a pain, particularly with larger sizes, but couldn't one just run a jumper from the bonding bushing and h-tap it on to the egc?
 
You must log in or register to reply here.
Top