sealing multi-conductor I/S cables

[rodgere]

Do the individual conductors of an multi-conductor cable (twisted pair or shielded and also thermocouple)used in an intrinsically safe circuit need to be sealed when leaving a xp enclosure in a clas 1 div 1 location? The cables leaving the seal-off are not in conduit. I am referencing 501.15(D)(2) Ex and 501.15 (E)(1) ex2

another application would have the cables in a seal-tire flexible conduit.

 

[rbalex]

Re: sealing multi-conductor I/S cables

For intrinsically safe circuits you need to start in Art 504 before going to 501.

504.20 Wiring Methods. Intrinsically safe apparatus and wiring shall be permitted to be installed using any of the wiring methods suitable for unclassified locations, including Chapter 7 and Chapter 8. Sealing shall be as provided in 504.70, and separation shall be as provided in 504.30.

504.70 Sealing. Conduits and cables that are required to be sealed by 501.15, 502.15 and 506.16 shall be sealed to minimize the passage of gases, vapors, or dusts. Such seals shall not be required to be explosionproof or flameproof.
Exception: Seals shall not be required for enclosures that contain only intrinsically safe apparatus, except as required by 501.15(F)(3).

The basic requirement is "...to minimize the passage of gases, vapors, or dusts." The reason for the various 501.15 exceptions is that typical sealing compounds are conductive and it would ruin the shields or, in the case of twisted pair only, separation could ruin the effectiveness of the installation.

Note that with intrinsically safe systems, seals "...shall not be required to be explosionproof or flameproof." Any reasonably effective method "...to minimize the passage of gases, vapors, or dusts" should be Approved. Also note the sealing method is NOT required to be listed, simply Approved.

 

[rbalex]

Re: sealing multi-conductor I/S cables

I should have noted the exception [the reference to 501.15(F)(3)] to the exception in 504.70 is critical. In this case, process fluids (liquids or gasses) may be directly introduced into the cable and ?hard? sealing may be necessary.

It's rare even in "conventional" HAZLOC wiring, but it needs to be addressed especially since the cable would provide a migration path through a seal. In my opinion it's one of the toughest HAZLOC sealing applications going.

The standard technique for "general" multiconductor cables, double sealing, once at the termination and another somewhere just beyond doesn't quite do the job since not requiring the shield or twisted pairs to be separated would still provide a migration path through BOTH seals. In this case I'd recommend an epoxy based sealant at the termination.

 

[hardworkingstiff]

Re: sealing multi-conductor I/S cables

Bob,

Would you consider ductseal "approved" ?

 

[rbalex]

Re: sealing multi-conductor I/S cables

Originally posted by hardworkingstiff:
Bob,

Would you consider ductseal "approved" ?

For a "general" intrinsically safe application, I personally would approve it - the lone exception being a 501.15(F)(3) application. Virtually any non-shrinking plasticized material should be acceptable.

In fact, a new exception was added to the main text of [2005] 501.15(C) that, IMO, would make it acceptable at Division 2 / unclassified boundaries since the exception wiped out all listing requirements as it applies to 501.15(B)(2). The exception covers the entire Section 501.15(C). I?m just about ready to post a proposal to tighten it up a bit though. My personal belief in this case is if you believe you need a seal at all in those applications it should be explosion proof or at least listed for the application.

I remember talking to the Chief Engineer of the HAZLOC department of the national test lab of a foreign country. His opinion was that ductseal should even be acceptable for any Zone 2 (and by implication Division 2) application. It actually passes the specified number of "shots" required (5) for Groups IIA & IIB (US Groups C & D). The problem is that most IEC applications use cable seals rather than conduit seals and the cable itself provides fairly substantial structural strength to the seal.

 

[hardworkingstiff]

Re: sealing multi-conductor I/S cables

Bob,

I'd like to ask a more specific question. 1st a statement.

I've noticed electricians now (and I've done this too) run PVC at a service station (gas and diesel) for the intrinsically safe circuits (as well as the power but following 514.8) and turning up with PVC for the intrinsically safe circuits. I used to put steel pipe turning up at the building with a steel sealoff and pouring that one, but I've seen others just turn up the PVC.

Now the question. At a gas station, the PVC going to sumps for an intrinsically safe sump sensor (which has just a 2-wire cable coming out of the sensor) and duct seal as the sealing compound in the conduit,.... pass/fail?

 

[rbalex]

Re: sealing multi-conductor I/S cables

Lou,

In my opinion, ultimately it would pass. There are a lot of ?howevers.?

I?m using the 2005 NEC.

First, a careful reading of 501.10(A) does NOT directly permit intrinsically safe wiring methods in Division 1; in fact, there is no reference to Art 504 or intrinsically safe circuits in mandatory text in Art 501 at all. You have to ?fudge? it in by inference from the general ?Scope? statement in 500.1 which says: ?Articles 500 through 504 cover the requirements for electrical and electronic equipment and wiring for all voltages in Class I, Divisions 1 and 2?? [Bold Italics mine]

Art 504 also ?self-declares? its applicability to Division 1 in 504.20, which then re-introduces sealing requirements of 501.15 via 504.70.

Now that I?m comfortable with using IS (with PVC) in Division 1, lets look at the seals.

The FPN No. 1 to 501.15 states: Seals are provided in conduit and cable systems to minimize the passage of gases and vapors and prevent the passage of flames from one portion of the electrical installation to another through the conduit.

If we assert that there will be no flames to prevent (no ignition source), then we only need to deal with minimizing the passage of gases and vapors and ?ductseal? should do just fine.

BTW this is why I don?t like the new 501.15(C) Exception. In an IS application there is no way to ignite vapors that may possibly get into the raceway; however a fault in the conductors of other types of circuits could. The theory the Proposal that the Exception was based on stated the boundary seals were only necessary to prevent gas migrations. My contention is if you think there are gases to migrate at all you also need to be concerned that they may get ignited, in which case the seal should be XP.

 

[hardworkingstiff]

Re: sealing multi-conductor I/S cables

THANKS Bob!