Nylon bolts?

[blueboard]

I have come across the use nylon bolts instead of steel bolts for kindorf straps supporting pvc conduit housing the grounding electrode conductor from the transformers secondary.

The question I have is, "Is this in the NEC, or is it just 'industry standards'?

 

[don_resqcapt19]

You should not have any ferrous metal that completely encircles the Grounding Electrode Conductor. The code does not directly say anything about the supports for your installation. The closest rule is 250.64(E), but that applies to GEC enclosures and not to supports.

 

[hillbilly1]

I had an engineer with Verizon say that it acts like a choke, reducing its effectiveness in dissipating a surge. Changed the straps to one holes, problem solved.

 

[renosteinke]

Don, I challenge your statement that ther should be no ferrous metal completely enclosing the GEC.

Running the GEC in steel pipe is a common practice, and I've often seen this specified by local ammendment. A GEC doesn't accomplish much after the lawnmower cuts it or the local copper thief removes it.

It's no issue 'bonding' the GEC at both ends; hardware is readily available for this purpose.

As for the OP's concern ... I admit I never considered the possibility that a strut and strap together might create a 'complete encirclement' of the GEC. I can't say whether that's an issue or not; I've never encountered the situation.

I suppose nylon bolts might help. I'd just as soon use a PVC strap with ordinary bolts into ordinary strut nuts. I'm not too happy clamping plastic with steel, fearing issues with abrasion and stress cracking of the PVC.

 

[Smart $]

You should not have any ferrous metal that completely encircles the Grounding Electrode Conductor. ...

Don, I challenge your statement that ther should be no ferrous metal completely enclosing the GEC.

...

A clarification would be the ferrous metal should not encircle the GEC in relatively close proximity and not be bonded to it.

 

[don_resqcapt19]

Don, I challenge your statement that ther should be no ferrous metal completely enclosing the GEC.

I should have added without bonding the ferrous metal to the GEC.

Running the GEC in steel pipe is a common practice, and I've often seen this specified by local ammendment. A GEC doesn't accomplish much after the lawnmower cuts it or the local copper thief removes it.

It's no issue 'bonding' the GEC at both ends; hardware is readily available for this purpose.

I did cite 250.64(E) which addresses this.

As for the OP's concern ... I admit I never considered the possibility that a strut and strap together might create a 'complete encirclement' of the GEC. I can't say whether that's an issue or not; I've never encountered the situation.

I have seen pictures of the damage where ferrous metal staps that completely encircled conductors of an "isolated phase" installation. The damage does not occur if you don't completely encircle the conductor. Same as when you cut slots in the ferrous enclosure between the entry points of isolated phases. 300.20

I suppose nylon bolts might help. I'd just as soon use a PVC strap with ordinary bolts into ordinary strut nuts. I'm not too happy clamping plastic with steel, fearing issues with abrasion and stress cracking of the PVC.

The nylon bolts would completely prevent the damage or choke effect, assuming that there is no metal to metal contact.

 

[hurk27]

Strapping PVC with metal straps is also not a good idea if the PVC can not slide in the strap, most PVC straps allows the thermo-expansion of the pipe to slide in the strap, of course short runs this might not be a problem.

But yes the high frequency effect of a lightning strike can induce very high current into ferrous metals that encircle a GEC that can cause a fire.