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GRC Underground #30094 10/04/03 02:39 PM
Joined: Apr 2001
Posts: 507
G
golf junkie Offline OP
Member
When using GRC (galvanized ridgid conduit) underground what do you use for a sealant at the threaded couplings?

Is there a listed sealant for this application?

thanks,
GJ

Work Gear for Electricians and the Trades
Re: GRC Underground #30095 10/04/03 03:19 PM
Joined: Jan 2003
Posts: 4,391
I
iwire Offline
Moderator
Maybe I will get slammed for this, but I do not use any sealant.

It is a given that water will get in the conduit or will accumulate inside the conduit from condensation.

It is my belief that this is the reason for 300.5(D)(5)

Quote
300.5(D)(5) Listing. Cables and insulated conductors installed in enclosures or raceways in underground installations shall be listed for use in wet locations.


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Re: GRC Underground #30096 10/04/03 03:44 PM
Joined: May 2002
Posts: 1,716
R
Roger Offline
Member
Got to agree with Bob again. I could count on one hand the jobs I have been involved with that required special treatment at the couplings. With a perfectly sealed conduit system condensation will still exist and will add up to gallons.

I installed one job where the engineer spec a TEE fitting at the lowest part of any underground conduit in a 2'x 2' gravel pit
(french drain if you will)

Roger

Re: GRC Underground #30097 10/04/03 09:35 PM
Joined: Apr 2001
Posts: 507
G
golf junkie Offline OP
Member
That's a good one Roger!

I had a very bad experience one time. The engineer spec'd GRC for the service and would not allow PVC.

A large parking area drained into the service trench, even after backfilling our service counduit made a very nice drain for the parking lot. And of course it drained right into our brand new service equipment.

We dug the trench out twice before we were able to stop the water. First time we tried to seal the couplings with a rubber sealant........that didn't work. Second time we encapsulated the coupling in bentonite (sp?) that did the trick.

Since that time I've avoided using GRC underground, but I'm looking at a job now where it's in the spec again.

GJ

Re: GRC Underground #30098 10/04/03 09:39 PM
Joined: Apr 2002
Posts: 2,527
B
Bjarney Offline
Moderator
Suggest T&B “Kopr-Shield” or Fel-Pro C5A for conduit threads. Don’t expect a perfect watertight seal, but preservation of raceway continuity during faults.

Page 3 of www.tnb-canada.com/catalogues/pdf/en/t_b/fittings_01a_eng.pdf
or www.newmantools.com/felpro/c5a.htm

For hazardous-location installations, Crouse-Hinds HTL compound is useful.

Re: GRC Underground #30099 10/04/03 10:25 PM
Joined: May 2002
Posts: 1,716
R
Roger Offline
Member
GJ and Bjarney, do either of you or anyone know or have an opinion of a reason GRC would be used over PVC in an underground installation in todays world?

I can't personally justify it in my simple mind. [Linked Image]

Roger

Re: GRC Underground #30100 10/04/03 10:57 PM
Joined: Apr 2002
Posts: 2,527
B
Bjarney Offline
Moderator
Some A&E firms and institutional/industrial facilities have GRC standard in their construction specifications. It’s likely some feel that the durability of steel over non-metallic is a better investment at a small additional cost. The criticality if the contained circuits has a big effect on the decision. One concern facility owners have is what telecom guys call “backhoe fade” or the unfortunate effect of dig-ins. Unscheduled power or communications outages can be staggeringly disruptive and exceedingly costly to some operations.

Running subsurface steel conduit is not that much of a task, and becomes far easier when you ‘get in the groove’ for lack of a better term. [A hydraulic bender at the trench edge is de facto for some jobsites and clients.]

It may be possible to offer a substitute proposal of nonmetallic below minimum specified burial depth, with GRC sweeps extending above ground. Concrete encasement of buried nonmetallic raceway—with or without rebar—might be acceptable to the client’s engineer.




[This message has been edited by Bjarney (edited 10-05-2003).]

Re: GRC Underground #30101 10/05/03 06:23 AM
Joined: Jan 2003
Posts: 4,391
I
iwire Offline
Moderator
No matter what is inside the raceway I would rather run PVC.

If what is in the raceway is critical have me concrete in-case it.

The reason for this is PVC will not change, at least in any of our life times, RMC ends up rusting inside and seems to bond with the conductors making it imposable to remove them if needed.

Greater care must be exercised with the back fill material, most times the site guy owns sand for the back fill on the jobs I work.


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Re: GRC Underground #30102 10/05/03 07:30 AM
Joined: Jul 2002
Posts: 680
W
walrus Offline
Member
I use Kopr-sheild on cut threads otherwise nothing. It won't stop leaks into the conduit as conduit couplings seem to be(are) running thread(no taper) so they won't seal anyway.

I can think of a reason for steel over PVC if transistioning out of a deep hole. If compaction of the the dirt isn't done right the PVC will shear off where it hits native soil. I've seen it many times around tank holes. even rigid will shear if their's a coupling at the transistion


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