Bonding of metallic hardware on OH 25kV distribution line

[KillBill7]

I hope everyone is keeping safe. Question came up from site contractor about bonding of hardware and got me thinking........

We have 25kV OH line without shield wire protection so it doesn't have any ground downlead and ground rods etc. Contractor is asking if they need to bond any metallic hardware which is within 100mm of each other to avoid any radio interference or induced voltage/arching issues. They said they have done this on all the distribution lines they have build so far. I am trying to make sense of how would bonding help if it's not grounded.Maybe I am missing something?

I looked at local standards (CSA) and couldn't find any such requirement. On Transmission lines where we have downlead running down the pole base and bonded to the ground rod, it makes sense to bond any metallic hardware to that downlead. But without grounding , does it makes sense to bond any metallic hardware in proximity to each other?

Let me know your thoughts?

 

[bacon4life]

In addition to arcing induced issues, unbonded metallic hardware can concentrate leakage current, leading to eventual pole fires. We bond everything within 300 mm at 115 kV. Unfortunately I don't have any guidance for your 25 kV system. Check out

https://pdfs.semanticscholar.org/d723/ed9f59f6adee67c3acd8cf801d8ecd925915.pdf

for discussion of leakage induced pole fires.

I assume you mean a 3 wire distribution system A neutral wire placed below the phase wires and/or any metallic communications wires would need grounding. The NESC rules for communication worker safety also require extensive bonding.

 

[KillBill7]

Thanks bacon4life for the comment (atleast someone commented)..... Certainly anywhere there is a neutral, a transformer, lightning arrestors etc grounding is needed but that’s entirely different from bonding of hardware. Also at transmission voltages (>69kV) spark gap discharge can be a problem but corona discharge can be a much bigger problem. And un-bonded/un-grounded hardware can lead to current flow into the adjacent wood of the pole, leading to pole fires.

I am curious if bonding of metallic hardware within 100mm or so of each other without grounding it serves any purpose, specially at 25kV? I checked RUS 25kV structures manual, none of standard structures have bonding of hardware. For hardware, since the components are relatively small, induction would most likely be electrostatic, and at 25 kV that’s not likely to be significant. Biggest reason of radio interference is usually the loose hardware (more likely the conductor hardware).

Only time I could see that bonding hardware together and not tying it to a ground would have any benefit is if the two pieces of hardware are very close together and not touching. The bonding would prevent spark discharge over the gap, which could cause RI. But at 25 kV the gap would have to be a few mm or less and does it really cause any significant RI?

Any thoughts will be highly appreciated.