Building steel bond for 75kva transformer?

Status
Not open for further replies.
G

gomezbrotherhood

Member
Location
Moreno Valley
Inspector, in the city of San Jose had me change out my installation I had done. That came out from the side of my 75kva transformer with a flex 90 for about a foot to where. I went flex to emt up to building steel and installed bonding bushing on both ends of the run. Where I thought I was code compliant. I had to change it out to sraight pipe/LB, because he said Its was not code to use flex for any transformer bonds. :happyyes:
 
What code section did they say was violated? He may be citing 250.64(B) if subject to physical damage, FMC is not on the list of suitable raceways. We've been installing GEC's with FMC for decades.
 
I've never encountered the situation but you guys have really made me put my thinking cap on for this one. I tend to approach transformer grounding electrodes differently than service grounding electrodes but as best I can tell the NEC does not, so I assume 250.64(E) would apply to both.
With that in mind I would question using FMC. IF we have having to bond a ferrous metal enclosure at each end to assure our grounding path it seems to me that a section of FMC, with the 250.118 grounding limitations, would be a weak link in the chain. I would lean toward not accepting it.
 
So the GEC in question is the 90, the flex , the pipe and a bonding bushing with a jumper to bldg steel?No wire type GEC? That sounds like something I d try to do.

Sent from my SM-G360P using Tapatalk
 
Am I missing something? the flex is not the grounding electrode conductor. We only bond each end of the raceway containing the GEC to reduce magnetic effects on that raceway. If it is aluminum flex - may not even be a realistic problem, but still is for the steel raceway it adapts to.
 
kwired said:
Am I missing something? the flex is not the grounding electrode conductor. We only bond each end of the raceway containing the GEC to reduce magnetic effects on that raceway. If it is aluminum flex - may not even be a realistic problem, but still is for the steel raceway it adapts to.
Click to expand...

Personally I don't see a problem as I stated before we've been doing it that way for decades. Problem with this thread is that the OP needs to tell us exactly what the violation is. ;)
 
gomezbrotherhood said:
he said Its was not code to use flex for any transformer bonds.
Click to expand...

Flex is not the "transformer bond", assuming that means grounding electrode conductor, the conductor inside is.

Bonding both ends of a steel tube containing the GEC is a different issue and seems to me was still done originally. Worst case I could see asking for a bonding jumper around the flexible portion of this run, but see no reason to prohibit the flexible conduit altogether.
 
DrSparks said:
I use bare #3/0 cu THHN all the time for xfmrs.
Click to expand...

If you are running one GEC for more than one transformer that makes sense, it is required. If it is just for a single 75 kVA it makes no sense, it does not make things safer but it certainly adds cost to the job.
 
What is "cable armor" as provided for in 250.54(B)? A quick check in the UL product spec does not show anything.
 
iwire said:
If you are running one GEC for more than one transformer that makes sense, it is required. If it is just for a single 75 kVA it makes no sense, it does not make things safer but it certainly adds cost to the job.
Click to expand...

Oh no haha. I usually deal with much larger xfmrs. No, you would size it according to the size of the xfrmr's secondary feeders obviously. Also, I always use #3/0 to bond the water main to building steel and usually it's a very short length from the xfrmr to the nearest steel framing member so I just use a piece of the #3/0 regardless of the xfrmr size.
 
This is why I usually bond in the secondary panel. No muss no fuss just a pipe straight out the top of the panel to the steel beam sitting on top of the precast wall. Little paint grinding and a bonding bushing and you're good to go.


Sent from my iPad using Tapatalk
 
Status
Not open for further replies.
Top