C
Chris Carlen
- Jan 1, 1970
- 0
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
[email protected]
NOTE, delete texts: "RemoveThis" and
"BOGUS" from email address to reply.
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
[email protected]
NOTE, delete texts: "RemoveThis" and
"BOGUS" from email address to reply.