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Let's review the safety of a custom heater

Hi:

It was built by someone who retired. A pair of band heaters go around a metal tank with various plumbing attached. Water and nitrogen/air will flow through it. Water leakage is not expected and pressure is barely above atm. There is also a tube heater on one of the pipes going to the main tank. Heaters run on 208 single phase. 20A circuit for the bands, and 3A for the tube.

The maker wrapped the tank with fiberglass braid fabric thermal insulation. Then layer of metal tape wraps around the whole thing. I have no idea what covers the studs of the band heaters. I suspect only a thick layer of the fiberglass fabric.

The tank was grounded with a heavy wire tying back to the power source ground. The high temp leads from the band and tube heaters were run about 6-12" in open air into a metal junction box where they tied to power. The tank sits unbolted and the junction box bolted to a heavy metal shelf plate.

Our electrical inspection guy recommended only one absolutely necessary improvement before it can pass an electrical safety inspection (must meet OSHA and NPFA electrical safety requirements): The open air wires have to be protected with conduit or some mechanical shroud.

I plan to put BX flex-armor conduit around the tube heater wires, which will involve devising a custom fitting to fasten the BX to the tube heater.

Second, I plan to run 1/2" EMT conduit from the junction box to the heater. The inspection guy thought it would be OK that there is no way to fasten the conduit to the heater tank, so it would just butt against the outer layer of tape.

I think he assumed that the tank was fastened to the shelf. I discovered it isn't. Now I think the heater needs to be bolted to the shelf so that it can't move relative to the conduit and shear or tug on the wires.

But what else bugs me is the unknown protection for the band heater electrical input studs.

What do you think is required/recommended to protect those studs? Must a junction box be fastened over the band heaters' studs, and the conduit fastened to that box? This would entail a major rework of the insulating tape and fabric, plus substantial additional mechanical engineering.

Or is it reasonable to just bolt the tank to the shelf and run the conduit to butt against the outer tape covering? I don't feel satisfied by this. The problem is there is no way to ensure grounding of the metal tape, which could go live if the band heater bolts punch through the fabric.

I'm inclining toward the more thorough re-work, though that will not make the end user happy. But I'll have to put my name on that inspection form.

Thanks for input.

--
Good day!

________________________________________
Christopher R. Carlen
Principal Laser&Electronics Technologist
Sandia National Laboratories CA USA
crcarleRemoveThis@BOGUSsandia.gov
NOTE, delete texts: "RemoveThis" and
"BOGUS" from email address to reply.
Reply to
Chris Carlen
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Last time I worked in critical stuff 'after the fact' (it was already broken) I, ultimately, left the place.

In my time at the place I did a couple of fmea's and fcmea's (or whatever) on the basis of me not signing for them (I said so coz it was silly)...... and that was not a problem.

I don't fly in big planes or (fundamentalists ignore this, or buy your shit elsewhere) military stuff and I still don't.

You appear to be Chris Carlen.

Problem solved.

DNA

Reply to
Genome

can you help me build a rocket car.

Reply to
surajraj9

you are weird it dosen't make sense

Reply to
surajraj9

Earth leakage trips on all the heater circuits might not be a bad idea.

-- Bill Sloman, Nijmegen

Reply to
bill.sloman

Can you post a pic on a.b.s.e or on a webpage somewhere? I'm kinda partial to the shroud; it sounds like it's to protect people from getting electrocuted. I'd get some perforated metal, like:

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(scroll down) and bend it into some shape around the flying leads and bolt it to the junction box, and form the tank end so that it's close enough that fingers can't get between the gap, but far enough so that it doesn't chafe - maybe protect the tank end of the shroud with some grommet strip like this:
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or similar.

Advantages: You don't have to disconnect anything; you don't have to drill holes to mount BX or conduit, and what would happen at the tank end of the conduit? You say butting up against the metal tape - I wouldn't trust that. It sounds to me like by mentioning "shroud" that your inspector guy is doing you a favor.

And, of course, bolt the tank down. :-)

Good Luck! Rich

Reply to
Rich Grise

By the omnivore, i hate getting into situations like this. That company is in trouble, their "one time" jury rig has been pressed into normal service and is severely non-compliant. For OHSA requirements, bolt the tank down properly. For the heater connections, they must be protected against accidental contact and have a well grounded protective layer in between (the NEC requirements have gotten a lot tougher in the past ten years)any exposed conductor and possible human contact. Make the connection with some form of (flexible) conduit with a separate equipment grounding conductor.

--
 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
  --Schiller
Reply to
joseph2k

here's an idea:

Attach a couple of strips of flat bar to the back of a junction box and cut a suitable hole in the back then strap it in place with one of those banding machines that are used for lumber etc (you can hire them, and a roll of strap at many places (usage is charged by weight))

The same bands could possibly be used to keep it on the shelf.

Don't get the bands too tight or you may crush the tank.

Bye. Jasen

Reply to
jasen

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