Steel Structure Bonding

[timm333]

At how many points should a large steel structure be bonded to ground? I know in lightning-grounding, the structure is bonded to ground every 60 feet around the outer perimeter. What about regular electrical-grounding? How often should the steel structure be bonded to the ground-grid for regular electrical-grounding system as per NEC? Thanks

 

[Buck Parrish]

Once , along with the entire electrode system. Their could be some variations like expansion joints.

 

[timm333]

Thanks, what is the NEC rule number?

 

[petersonra]

Thanks, what is the NEC rule number?

the nec does not require the structural steel of a building be bonded at all unless certain conditions exist.

take a close look at 250.52 (A) (2).

 

[petersonra]

I know in lightning-grounding, the structure is bonded to ground every 60 feet around the outer perimeter. What about regular electrical-grounding?

This is not in the NEC. It might be a design decision, but it is not required by the NEC.

 

[timm333]

Can the lightning Class I (or lightning Class II) conductor be used for regular electrical-bonding (for example bonding of a motor frame to ground ring) ?

 

[don_resqcapt19]

Can the lightning Class I (or lightning Class II) conductor be used for regular electrical-bonding (for example bonding of a motor frame to ground ring) ?

I don't think that NFPA 780 permits that, and there is no good reason for any additional bonding of a more over the NEC required equipment grounding conductor.
I know that the additional bonding is a common industrial and petro-chemical practice, but there is no good technical reason to install the additional bonding.

 

[timm333]

Internal equipotential binding, for example connecting the cable trays to ground by lightning Class I conductor is required for lightning protection system. I think when the cable trays and other equipment is bonded as part of lightning protection system, then regular electrical-bonding (of NEC) is not required. That's why I though the lightning Class I conductor could be used for electrical-bonding. What do you guys think?

 

[don_resqcapt19]

Internal equipotential binding, for example connecting the cable trays to ground by lightning Class I conductor is required for lightning protection system. I think when the cable trays and other equipment is bonded as part of lightning protection system, then regular electrical-bonding (of NEC) is not required. That's why I though the lightning Class I conductor could be used for electrical-bonding. What do you guys think?

I have not looked at 780 in a long time, but I think the bonding is required for conductive objects within 6' of a lightning protection conductor. That rule is intended to prevent "side flashes". The voltage drop on the lightning conductors can be so high that there would be a side flash to unbonded conductive objects within 6'.

There is nothing that would permit the lightning protection conductor to be used in place of the NEC required equipment grounding conductor. In fact 300.3(B) would prohibit using the lightning protection conductor in place of the EGC.

 

[timm333]

I could not find lightning protection in 300.3(B). I meant to say that we would still follow the EGC rules of NEC. The only difference would be that we use the lightning Class I conductor for equipment grounding (as long as it meets the sizing of Table 250.122) instead of regular #2 AWG conductor. Will it be possible?

 

[timm333]

Just to clarify: the area of lightning Class I conductor is 65.6 kCMIL, and the area of regular 2-AWG conductor is 66.4 kCMIL. The main difference between the two is that each strand of the lightning class I conductor has to be minimum 14-AWG.

 

[don_resqcapt19]

I could not find lightning protection in 300.3(B). I meant to say that we would still follow the EGC rules of NEC. The only difference would be that we use the lightning Class I conductor for equipment grounding (as long as it meets the sizing of Table 250.122) instead of regular #2 AWG conductor. Will it be possible?

Do you intend to install the lightning Class 1 conductor in the raceway with the ungrounded circuit conductors?

 

[timm333]

Yes inside the raceway.

 

[don_resqcapt19]

Yes inside the raceway.

Sorry, I did not correctly understand your question. I don't know of any NEC section that says you can't do that, as long as it is large enough.

 

[timm333]

Thanks. So for equipment grounding of motors (or cable trays): will it be OK that we connect one end of the conductor to motor (or cable tray) and other end to the nearest column of steel structure; and repeat this procedure for each motor (or cable tray). And then connect the steel structure to ground ring once along the entire electrode system?

 

[ActionDave]

Thanks. So for equipment grounding of motors (or cable trays): will it be OK that we connect one end of the conductor to motor (or cable tray) and other end to the nearest column of steel structure; and repeat this procedure for each motor (or cable tray). And then connect the steel structure to ground ring once along the entire electrode system?

While you can bond or jumper to building steel as much as you like I would say you can't use the building steel as an equipment grounding conductor or as a splice for an equipment grounding conductor.

 

[don_resqcapt19]

Thanks. So for equipment grounding of motors (or cable trays): will it be OK that we connect one end of the conductor to motor (or cable tray) and other end to the nearest column of steel structure; and repeat this procedure for each motor (or cable tray). And then connect the steel structure to ground ring once along the entire electrode system?

No it would not be ok. The EGC must be run with(in the same raceway or cable) the ungrounded circuit conductors back to the power source. [see 300.3(B)} You cannot use the steel structure as the code required EGC. [see 250.118]