Conduit Sealing in Hazardous Locations - IEC Style

[rcw retired EE]

We are building a project in the MidEast that has underground PVC raceways stubbing up in areas classified as Class I Division 2 due to the posibility of natural gas leaking from piping and valves. North American codes require the stub ups to be rigid conduit capped with a conduit sealing fitting to prevent passage of gas through the conduit to other areas. (The contractor changed our rigid conduit riser designs to PVC since no conduit will be used above ground.) The conduit is presently open with cables coming out.

The embedded raceways carry power and control cables from electrical equipment rooms or vaults to stub ups in the classified area. Cables run in channel or tray from the stub-up to sealed equipment enclosures.

We have some cocnerns:

In the IEC world, are PVC conduits allowed in Classified Areas?

What are the typcial methods of sealing PVC conduits to minimize transmission of gasses through the open conduits? Or is it not considered a problem since the conduit is in open air?

Thank you,

Bob Wilson

 

[itsmoked]

I believe it would be a concern.

Having PVC coming out of the ground is considered a problem because of its lack of mechanical protection.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[rcw retired EE]

I haven't seen the actual installation. I believe the PVC stops at the top of concrete.

I also just got word that the contractor did use rigid conduit for the stub-ups in the hazardous areas. We could use the usuasl conduit seals after cables are installed.

I think the problem arises from designing for an IEC installation with a North American mindset.

An installation detail from the plant next door shows the UG cable ducts entering a cast-in-place pull box next to the equipment. Cables are threaded through a short piece of rigid conduit or pipe at grade level and then run up to the equipement. The pipe is filled with a "mineral oil-resisting putty." After cables are installed the pull box is filled with compacted sand and coverd with red concrete. Not much of a chance for gas to get through those ducts. This method protects the cables from damage at grade, provides room for pulling the cable without using 90 degree bends, and provides an enviromental seal.

 

[itsmoked]

"[green]I think the problem arises from designing for an IEC installation with a North American mindset.[/green]"

I agree. On the other hand lots of N.A. rules came of hard knocks and make sense anywhere. Like the no-low-to-the-ground plastic-conduit rules.

Glad to hear the metal stubs were used.



"[green]An installation detail from the plant next door[/green]"

Man - that will protect the cable runs from nuclear blast!

I'd say the mineral oil is overkill once a sound cork is utilized. Or if the mineral oil can be guaranteed to be there the corks would be redundant but that would be hard to prove since a leak would drain the oil eventually.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[Bilegan]

hello rcwilson

I do not know if you will still require this information. Oil and gas facilities in the middle east standards allows the installation as follows;

1. The typical methods of sealing PVC conduits to minimize transmission of gases through the open conduits is to sealed with 3M scotch cast brand 4416 cable duct sealing kits".

2. PVC stub-up are only allowed at 150mm above grade level.

Regards,
Bilegan

Murphy's Law - If anything can go wrong..it will.