Is structural steel permitted for use as a grounding conductor for cable tray?

[sephorous]

At our facility there is some cable tray being installed in a pipe rack. The contractor bonded the cable tray to the supporting structural steel, but did not carry the ground down to the ground grid for the cable tray. The structural steel is grounded at the bottom. Can the structural steel be considered as an acceptable grounding conductor per the NEC?

Thanks.

 

[cadpoint]

Cable tray grounding Article 392.60.

They didn't make it...You did...

Welcome to the Forum.

 

[Smart $]

At our facility there is some cable tray being installed in a pipe rack. The contractor bonded the cable tray to the supporting structural steel, but did not carry the ground down to the ground grid for the cable tray. The structural steel is grounded at the bottom. Can the structural steel be considered as an acceptable grounding conductor per the NEC?

Thanks.

Requirements say the tray has to be connected to the equipment grounding conductor. Neither the structural steel nor the ground grid is an EGC....!!!

 

[Smart $]

Cable tray grounding Article 392.60.

They didn't make it...You did...

Welcome to the Forum.

Hmmm.... cable tray grounding is 392.7 in 2008 NEC, and there are only 13 sections to Article 392.

 

[Little Bill]

Requirements say the tray has to be connected to the equipment grounding conductor. Neither the structural steel nor the ground grid is an EGC....!!!

If the tray is the EGC, then the bonding they did would suffice, yes?

 

[cadpoint]

Sorry for the high numbers, I edited out a grounding article number and it seems incorrectly.

I was bouncing in thought between many Code Articles... sorry for the confusion.

 

[don_resqcapt19]

If the tray is the EGC, then the bonding they did would suffice, yes?

It has to have some connection to the EGC of the circuits that are in the tray. The connection to building steel cannot be that connection. If the tray is physically connected to the equipment where the circuits originate and if the tray itself is suitable for use as the EGC for those circuits you are ok.

 

[Smart $]

It has to have some connection to the EGC of the circuits that are in the tray. The connection to building steel cannot be that connection. If the tray is physically connected to the equipment where the circuits originate and if the tray itself is suitable for use as the EGC for those circuits you are ok.

It doesn't matter whether a metallic cable tray is suitable for use as an EGC. It still must be connected to the EGC of wiring it contains (or rather supports).

392.7 Grounding.

(A) Metallic Cable Trays. Metallic cable trays that support
electrical conductors shall be grounded as required for
conductor enclosures in accordance with 250.96 and Part
IV of Article 250.

250.86 Other Conductor Enclosures and Raceways. Except
as permitted by 250.112(I), metal enclosures and raceways
for other than service conductors shall be connected
to the equipment grounding conductor.

Exceptions omitted for brevity

250.86 is in Part IV of Article 250.

IMO, bonding to structural/grounding grid is okay [250.96(A)], as long as the connection to EGC requirement is met.

 

[don_resqcapt19]

It doesn't matter whether a metallic cable tray is suitable for use as an EGC. It still must be connected to the EGC of wiring it contains (or rather supports). ...

That is what I said.

It has to have some connection to the EGC of the circuits that are in the tray.

 

[Smart $]

That is what I said.

I was referring to the following quoted portion of your post...

... and if the tray itself is suitable for use as the EGC for those circuits...

 

[don_resqcapt19]

I was referring to the following quoted portion of your post...

And that part was refering to the case where the tray is physically connected to the equipment where the circuits originate. In that case, I don't see a need for any other EGC to the tray. That is assuming metallic equipment.

 

[IamJonscranium]

^^^

If the tray is physically connected to the equipment where the circuits originate AND if the tray itself is suitable for use as the EGC for those circuits you are ok.

 

[petersonra]

There is no reason he can't make the connection he did, but there still has to be a connection of the cable tray to the EGC of the branch circuits contained in the cable tray.

As a practical matter, it is all but impossible to isolate a metallic cable tray from the building steel anyway. Considering that there are often hundreds of electrical connections between the cable tray and building steel along the way at the attachment points, it would seem somewhat redundant to add a wire along the way.

It is not something uncommon to see though.

 

[Smart $]

... Considering that there are often hundreds of electrical connections between the cable tray and building steel along the way at the attachment points, it would seem somewhat redundant to add a wire along the way.

I agree. And...

It is not something uncommon to see though.

...I also see many cable tray installations that overly bond and/or ground because of misunderstanding the requirements.

For example, one installation had copper wire jumpers across every joint in a tray system that was marked suitable for use as EGC. If for some reason the cross-sectional area was undersized, putting a jumper across each joint would not change anything.