What Sealant for RiGiD Conduit - Below Grade?

Vic · October 2014

What do you professional installers use, to seal RiGiD Conduit that is below grade.

ASSUME that pipe-joint compound would be OK, and perhaps Silicone I, as well (?).

Have searched the Net, and there are gas-tight compounds, but am in the center of nowhere on a project (am not going to town for this sealant), and am only looking to seal the conduit from incursion of water (below grade).

Thanks for guidance. Vic

BB. · October 2014

Re: What Sealant for RiGiD Conduit - Below Grade?

I would use pipe dope--It is designed to be water proof (under pressure) and something you can take apart later.

Silicon type products do not bond as well to irregular/oily (common on processed metals) or migrate around after hardening (forms a channel for water incursion).

Of course--I don't think you can really plan on a buried conduit to be water free... It will somewhere/somehow (migration of water from the open ends, rain/etc., or condensation/air inflitration) get wet inside unless there is positive pressure/ventilation. So, all underground connections/etc. should be water proof on their own (or do not make any under ground connections that cannot be serviced).

-Bill

Vic · October 2014

Re: What Sealant for RiGiD Conduit - Below Grade?

Hi Bill,

Thanks for the reply. Yes I always expect underground or exposed conduit to be moist, to wet inside -- hopefully, primarily from condensation.

Am just trying to keep the underground portions from accumulating water on their own.

Have used Silicone I on one underground fitting once (some time ago). For this project, have used a Pipe-Joint compound that never completely hardens ... it is just a bit messier than RTV, but felt (as you stated) that it is intended to make tight joints in threaded metal pipe.

There is nothing that will not be serviceable, but it would be a real pain to get to this RGD pipe, after backfilling (mostly with gravel) ... nothing is impossible.

Thanks for your opinions. Vic

SolarPowered · October 2014

Re: What Sealant for RiGiD Conduit - Below Grade?

Teflon tape can be your best friend, and its 4/5 cheaper than pipe dope or silicone.

Pipe dope which is primarily used for gas lines shouldn't be used on electric conduit, only because the dope compound depreciates the insulation of conductor wire.

Silicone isn't good either because as it dries it may clump up within the conduit making it hard to pull the wire.

Most hard nosed inspectors only require Rigid/IMC conduit as low as 12"~16" below grade, then it can all be sch 40 or dB120 grey PVC, which then only requires pvc glue, which I use christies all in one hot glue, or all in one grey glue for grey and white PVC (white PVC obviously for irrigation, not electrical).

pechan · October 2014

Re: What Sealant for RiGiD Conduit - Below Grade?

Most Industrial Electricians around here (Wyoming) do not use any type of compound to seal up rigid conduit threaded connections as it's purpose is to protect the conductors from physical damage. The conductors must be rated for wet locations.

waynefromnscanada · October 2014

Re: What Sealant for RiGiD Conduit - Below Grade?

pechan wrote: »

The conductors must be rated for wet locations.

Agree. Even with no water leaks, condensation will eventually wet the cables.

SolarPowered · October 2014

Re: What Sealant for RiGiD Conduit - Below Grade?

waynefromnscanada wrote: »

Agree. Even with no water leaks, condensation will eventually wet the cables.

Its not that simple.

DC side conduit runs leading up to DC combiner boxes NEMA 3 require water tight fittings, meyers teflon tape, etc. USE-2 is rated for under ground/wet/UV however have you ever seen a 56 string combiner box flood with water? 56 string combiners are band now but were a sunpower favorite, now everything is 32 string and less. You can do whatever you want on the AC side, because its over current protected and sine wave doesn't grab you the way DC current does, there is nothing shutting off DC panels on a mild cloudy day with some cloud cover, even when the breakers are off if the combiner is flooded, current is floating and bleeding every where to ground, you will get electrocuted. 1000 VOLT systems are extremely dangerous. You really have to get in the commercial game of installing mega watts of DC side solar to really figure out why you want your components water tight.

Also if you can't Teflon tape the good quick way is to use plumbers tape that has the UPC stamp on it for use with under ground conduit.

Vic · October 2014

Re: What Sealant for RiGiD Conduit - Below Grade?

OK, Thanks all for the comments.

Am using Rigid conduit, because would like its mechanical strength, and the ultimate RF shielding capabilities, as there are several additional runs of coaxial transmission line running (in PVC conduit), very close to, and in parallel with the Inverter's AC, and the PV DC runs that are in the individual Rigid conduit runs.

Did wind up using pipe dope, for better of worse. YES, the cables will be rated for wet locations.

It is very difficult to imagine that the pipe dope has anything in it that will attack the insulation on cables running inside that Rigid conduit (IMO).
For whatever reason, had not even considered Teflon tape.

The pipe is in the ground, and backfilled at this point, so it will be an experiment.
Thanks to all for comments/ideas. Vic

SolarPowered · October 2014

Re: What Sealant for RiGiD Conduit - Below Grade?

Vic wrote: »

OK, Thanks all for the comments.

Am using Rigid conduit, because would like its mechanical strength, and the ultimate RF shielding capabilities, as there are several additional runs of coaxial transmission line running (in PVC conduit), very close to, and in parallel with the Inverter's AC, and the PV DC runs that are in the individual Rigid conduit runs.

Did wind up using pipe dope, for better of worse. YES, the cables will be rated for wet locations.

It is very difficult to imagine that the pipe dope has anything in it that will attack the insulation on cables running inside that Rigid conduit (IMO).
For whatever reason, had not even considered Teflon tape.

The pipe is in the ground, and backfilled at this point, so it will be an experiment.
Thanks to all for comments/ideas. Vic

Rigid is only required for traffic rated conditions. If it isn't traffic related, IMC (Inter Mediate Conduit) is a 1/3 less in cost, and would offer the same value you were looking to achieve with RMC (Rigid Metal Conduit). IMC also less dense than RMC, over time will not rust or corrode due to its metal anodizing, so IMC if not in a traffic related condition, will technically last longer, at less depriciation, if not in a traffic related condition.

Vic · October 2014

Re: What Sealant for RiGiD Conduit - Below Grade?

Hi S P,

Yes, this run of conduit is across a driveway, but there is also PVC conduit in the same trench. the driveway is occasionally used, although there will be a few ReadyMix trucks using the drive on occasions (if am lucky).

The Rigid conduit runs are short, and had almost all of it in stock, as it is used for some projects. The cost differential twix IMC and RMC is very small, and actually favored RMC in this case.

FWIW. Thanks, Vic

What Sealant for RiGiD Conduit - Below Grade?

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