Grounding Conduits

[brian john]

I have a project, where we did an inspection and now have been asked to work with an electrical contractor in making repairs. here is the problem. There are numerous feeders that are run in the deck (on slab) the conduits are 3" and 3-1/2" ridgid and PVC coated ridgid. Mix and match some are all rigid, others are all PVC coated rigid then some are a combination of both. The were installed with out bushings and there are no threads on either end. In addition there is no bonding of the conduits, they stub out of the deck with no metallic connection. Some of the PVC coated rigid conduits have no continuity to ground.

The conduits need bushings, and this is possible with insuliners, but the bonding is going to be a problem; as some of the conduits are tightly grouped, no way no install a ground clamp on the conduits. Have thought about cadwelding a EGC to the conduit but this will chance damaging the conductors. Any help with this would be appreciated..

 

[websparky]

Re: Grounding Conduits

Humm....

Have you considered drilling and tapping the metal conduits? Since there will most likely be no "proper" way of bonding, maybe a mechanical lug would accomplish the task?

 

[brian john]

Re: Grounding Conduits

I have thought of that......but would that be acceptable, to the inspectors on this site?

This will not be inspected but still....

 

[svaurez]

Re: Grounding Conduits

There is only one answer:Jackhammer

 

[bennie]

Re: Grounding Conduits

You might investigate perforated copper straps.

 

[pierre]

Re: Grounding Conduits

Sometimes we are at wits end to find a solution that may not be in the code, any code. So as professionals we seek a different way that will provide the same end results as if it was installed new. If the answer is to rewire have at it, but sometimes commonsense has to prevail, it is not a perfect world.
Dave has what in my opinion is a good resolve, which will provide the measure of safety we are always striving for.

Pierre

 

[tom baker]

Re: Grounding Conduits

Drilling and tapping would be dicey with conductors in the conduits, as would cad weld. Nether would be allowed by the NEC.
I would go with bennies suggestion of perforated copper strap, use SS fastners and some Kopper Kote under the strap. I would look a the cross sectional area of the strap and determine if its large enough to carry the required fault current.

If you can get to an end, T&B and OZ Gendey both make grounding bushings designed for non threaded conduit. Or you may be able to use a grounding wedge by T&B which slips under a locknut as a retrofit ground.

 

[bennie]

Re: Grounding Conduits

After more thought and Tom's mention of Gedney, I would try the Gedney clamps on the end of each conduit. A lug can then be attached to the clamp.

 

[hurk27]

Re: Grounding Conduits

Appleton make threadless connectors for this type of instalation but the PVC would have to be removed to allow contact?

 

[pierre]

Re: Grounding Conduits

The poster has mentioned the conduits are too close for fittings to be installed. I have seen this happen, but before the conductors were pulled. We did as one poster mentions and did the jackhammer routine - not too much fun.
I am not too sure what the copper straps are - are they listed for the purpose?
What supports the conduits to the enclosures?
I am curious how this will get resolved.

Pierre

 

[brian john]

Re: Grounding Conduits

Couple of catches here, this is an online data center we will have a 6-8 hour window to make all repairs (and the conduit grounding is just the tip of the iceberg). I plan on contacting several manufactures for ideas. Was hoping to come up with a solution that would be code compliant. If only because, we are working with another contractor, out of state and the client has 20 other sites they want us to survey. Oh and complying with the code is Well IMPORTANT....But I also understand in some situations.........

 

[bennie]

Re: Grounding Conduits

What is in the conduits? Power or Data cable?

 

[hbiss]

Re: Grounding Conduits

I was going to ask the same question. I assume they are LV because there are no threads and I would assume just stub up out of the floor.
Exactly how much space is there between the stub ups?

 

[hurk27]

Re: Grounding Conduits

If they only have data cable in them, they can be bonded at the other end if accessable? or any where there is an accessable point. The bonding requirment would only be for the largest current carrying conductor that would likly energize it. If any at all. there are UL listed copper straps (thin) that would comply with both UL and the NEC. that could do this job. They look like a plumbers strap but there made out of copper instead of galv.-steel.
Maybe this is what Bennie was refering too?

250.70
(3) For indoor telecommunications purposes only, a listed sheet metal strap-type ground clamp having a rigid metal base that seats on the electrode and having a strap of such material and dimensions that it is not likely to stretch during or after installation

This is the one I'm talking about.

[ January 04, 2004, 02:38 PM: Message edited by: hurk27 ]

 

[hbiss]

Re: Grounding Conduits

Ok, have a look here- I knew I would remember http://www.electricmotioncompany.com/html/clamps/clamps.html

These guys have ground clamps for utilities. Their Universal strap type clamp (EM-5500) should do it for you. You of course will have to remove any PVC coating.

We use their Trailer I Beam clamps (EM-4015) which could also work for you by clamping on the end of each conduit. Might be a little easier too since less PVC coating would have to be removed.