Field Assembled Capillary thru Conduit Seal (Hazardous Locations) 1

[DRWeig]

OK, Hazardous Engineers:

I'm looking for documentation that says it's OK to pass the capillary tube in a bulb-n-capillary temperature switch when assembling in the field. Of course, the switch itself is in an explosionproof enclosure.

I know it's OK to seal a capillary entering a box, because assembled units have been that way for ages:

JCI A19AUC
UE Version
Markel Version

Those are just a few examples, there are many others. I also got the opinion from my instructor at ISA years ago that it was OK to do so in the field. The capillary is metal and it's sealed at both ends, so it would take two failures for the capillary to allow the enclosure to exchange gases with the surrounding air. Plus, in general, the tiny passage through the capillary would serve as a good cooling path for hot gases resulting from an explosion.

I have a good client who is wanting to reject a field installation in which the capillary was passed through a (listed) conduit seal. The argument is that the seal is not listed for use with capillary tubing. However, I can't find any resource that says that capillaries are not allowed through listed seals.

We've had these inspected and accepted by AHJs around the US for 15+ years. I can't, however, find any written justification for using a conduit seal for something that is not a conductor or cable.

The particular arrangement in question is here:

Capillary thru Conduit Seal Pic

Any opinions out there? Even better, any citations? Even a conduit seal manufacturer's data sheet would be good. Obviously, I'm defending my position -- but the client makes a good point.

Many thanks.

Best to you,

Goober Dave

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[itsmoked]

No, I don't think the client is "making good sense". I think he's being ridiculously anal just for anal's sense. He sounds like a government employee with nothing better to do than throw up road blocks.

All your points are sound. History, flame path, hell, about half an inch of cap tube would exceed all EXP box flanges for cooling, two failures required, etc. The fact that you see no literature on the subject is testament to half a century of common sense prevailing.

Asking the stat makers is pointless because they got their products tested as a unit.

You might find a filler/sealant supplier that has something to site. After all, the sealants aren't probably 'tested' with every different species of wire, it's more of a 'type' cert. It seals 'things' in conduit.

Good luck with this.. You need it.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[DRWeig]

Thanks Keith! Don't cry. You're exactly right.

Best to you,

Goober Dave

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[danw2]

I mulled your question over the long weekend, but can not recall a reference to capillary entering an EXP box.

So I took Magison's "Electrical Instruments in Hazardous Locations", 3rd edition (current edition is 4th) home from work today and skimmed it.

If the word capillary is in the volume, I can't find it. The only reference to any non-electrical apparatus was a reference to double sealing and venting as a special case for a thermocouple in a protective thermowell, due to the potential for the thermowell to fail; not similar to your circumstances (capillary is sealed at both ends).

I'm guessing that the availability of capillary temp switches in their own certified EXP enclosures makes a roll-your-own a non-topic for the people who people standards committees.

 

[DRWeig]

Thanks danw2,

You're right -- some UL guy may see this thread or hear about it another way, in which case the standard may be eventually revised to allow or prohibit some list of items to pass thru a conduit seal. For now, they're ignoring it.

This roll-our-own is made because there are no bulb-n-capillary limit switches available with the manual reset feature and setpoint limits. They're used in air handling units in hazardous locations.

For a true freezestat, it should be impossible to set it below 33°F (0.6°C). For a firestat, manual reset is mandatory. There just aren't any ready-made ones out there for a classified area.

I actually finally got into an e-conversation with a reasonable engineer for the client in this case. He's a good guy. After reviewing the UL 1203 standard, we found that there is no reference to anything that passes through a seal. It only specifies the seal's ability to resist passing gas in an explosion test. While the standard does not specifically permit capillary tubing, it does not prohibit anything at all. It does not specifically mention conductors either. So a seal listed for a particular class, div, and group is not restricted by the scope or specification in the standard as to what passes through it with adequate engineering consideration and supervision.

I actually consider the capillary tube to be safer than a jacketed cable, which often is not stripped at the sealing point and is not sealed inside the enclosure either. The capillary is bare and sealed at both ends, so it will seal well.

This one worked out good.



Best to you,

Goober Dave

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[danw2]

FYI, The United Electric 120 series EXP Class 1, Div 1 temp switches have a manual reset option, option 1530:

The E121 and F120 are bulb and capillary temp models. The models excluded are the dual-switch-in-one-enclosure models.