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#119661 - 01/11/05 07:54 PM Interesting Use of Strain Relief
Webmaster Offline


Registered: 10/07/00
Posts: 3142
Loc: NY, USA
(submitted via Joe Tedesco)
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

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
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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