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#119661 - 01/11/05 07:54 PM Interesting Use of Strain Relief
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(submitted via Joe Tedesco)
 Quote:
These photos were taken in a large clear water plant in northern Ohio.

A piece of flexible cable connects a pvc-coated condulet with an explosion-proof junction box. Both boxes are bolted to the concrete wall. Guess on purpose of flex is to positively avoid transmission of toxic fumes and isolate grounds (sic).

Tom Mason



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#119662 - 01/12/05 08:15 PM Re: Interesting Use of Strain Relief
safetygem Offline
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Registered: 01/30/02
Posts: 114
Loc: Ohio, USA
Tom (or Joe since you submitted the photo),

You said this was a "clear water" plant. I assume by that you mean a drinking water filtration plant as opposed to a Wastewater Treatment Plant.

I don't necessarily have a problem with the use of strain relief. That appears to be appropriate, its the use of the flexible cord that potentially bothers me and appears to be a violation of 400.8(1), if not other prohibitions on the use of flex. That of course is making an assumption that this cord is being used for a 110/120 circuit. Frequently flexible cord is used in treatment plants for flow meters and other process control equipment that is operating at low voltages.

I am curious about your hypothesis that the
 Quote:
purpose of flex is to positively avoid transmission of toxic fumes and isolate grounds


Are you saying that using conduit to the upper level would provide a method for the transmission of the "fumes" to the upper level? That is highly unlikely. Virtually all gases and vapors that might be found in a treatment process are heavier than air and would sink to the lower levels rather than rise. As for the grounds... also an unlikely use for a flexible cord.

Several more questions. Why is the box an "explosion proof" box? It looks like it might be explo-proof, but, is that an assumption or was it marked? Also, if it was explosion proof, why was that necessary in the location? What were the flammable vapors?

I frequently inspect treatment plants in Ohio, and I can't really tell from the first picture what equipment is connected to the cord.

I guess I'd like more information... to evaluate the installation.

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