Bonding via bolted connection

[KillBill7]

I am reviewing a structure drawing where the designer has a grounding tabs on crossarm to bond the steel crossarm with the steel pole via copper wire. Crossarm is attached to the pole via 1" through bolts at two locations. My thinking......the four bolted connections between crossarm and the pole should be enough for the bonding the crossarm and bonding via copper wire is a overkill. Let me know your thoughts

I have a attached the screen shot of the structure for the reference.

 

[Palletjack]

Ours aren’t bonded like that. Your right, seems like overkill.
All I see is 6 bolts instead of 4 that should work.
Argument. What if the four bolts come loose?
The two bolts holding the bond could come loose also...

 

[che12345]

Dear Mr. KillBill7 (Electrical)(OP)27 Mar 20 20:11

" I am reviewing a structure drawing ......My thinking......the four bolted connections between crossarm and the pole should be enough for the bonding the crossarm and bonding via copper wire is a overkill."
I am of the opinion that:
a) we expect the cross-arm SHALL be properly Earthed,
b) the four bolted connection [may or may NOT] achieve low contact resistance bonding between the cross-arm and the pole, due to painting, surface treatment and corrosion etc., between the contact surfaces. The (structure rigger) would ensure that the four bolts are correctly tightened, but is NOT responsible to ensure [good electrical contact] between the contact surfaces,
c) " bonding via copper wire is " useful to ensure that the contact resistance is maintained to say < 0.01 ohm. The contact resistance should be verified with (four-terminal) measurement method with current NOT lower than 100Adc ,
d) the additional copper wire (very short in length) including the additional connection point on the structure and the cross-arm would cost (nothing) to the project. But it may save life by ensuring the cross-arm is bonded to the structure, which is understood; properly Earthed.
Che Kuan Yau (Singapore)

 

[itsmoked]

Normally connection assembly fasteners are NOT allowed to be used as grounding connections. Likely for the very reason Che describes.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[KillBill7]

@che I understand your reasoning and it makes sense. But when we look at structures like lattice tower (for example) where each small section is bolted together, then ideally all these sections should be bonded together via grounding conductor, which they are not. I am curious if this is the calculated risk that utilities take because of the remote location (in most cases) of towers.