thermocouple wire

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rickl

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hi
i have 2 quick questions,
i went on a service call yesterday, customer had a small fire in a peace of equipment. Equipment is a press (it transfers drawings and photos on to canvas ). There is a thermocouple wire that was damaged by the fire about 2"of the insulation was burned off, it's 24 gauge maybe smaller, don't know what type it is. There is plenty of slack in the cable,Question 1 can i splice this cable? if so what is the best way to reconnect ( wirenut, solder, butt splice)
Question 2
is it possible to be shocked while pressure washing a roof of a house, no overhead wires on the property ( 6 acres) 3 tab comp shingles, vent pipes are plastic, Here is the story HO hires a company to pressure wash the roof of there house its about 8/12 pitch. while pressure washing the worker fall breaks his leg and arm, his story was, he was shocked while standing on the roof witch caused him to fall. To me it sounds like he's trying to collect from the HO insurance co.
how would you check something like this ( check each roofing nail to ground)
thanks for any insight you might have
 
Re: thermocouple wire

In the true sense you should not splice thermocouple conductors unless you can make a splice using the same metal as each wire. Each of the two wires are of different metals which is the theory for how they work. You say that there is some insulation left on the wire. If the colors are red and white this is a type "J" thermocouple. It is the most common until you get into very high tempuratues. Also to check to see if it really was true thermocouple wires I seem to recall that one of the conductors will be magnetic and the other will not be.
As to the roof I can only guess that he might have gotten a static shock from the friction of his shoes against the shingles. Wouldn't be much of a shock, probably scared him into jumping.
 
Re: thermocouple wire

Originally posted by rickl:
irenut, solder, butt splice)
Question 2
is it possible to be shocked while pressure washing a roof of a house, no overhead wires on the property ( 6 acres) 3 tab comp shingles, vent pipes are plastic, Here is the story HO hires a company to pressure wash the roof of there house its about 8/12 pitch. while pressure washing the worker fall breaks his leg and arm, his story was, he was shocked while standing on the roof witch caused him to fall. To me it sounds like he's trying to collect from the HO insurance co.
how would you check something like this ( check each roofing nail to ground)
thanks for any insight you might have
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An independent investigation would have to be performed by a consultant to determine if electric shock was the cause of the workers fall.
 
Re: thermocouple wire

I'm guessing the thermocouple wire is just that, wire. If that's the case then I would solder and shrink tube it.

As far as testing the roof ( :D ) I guess you could get it all wet and stick meter probes in a whole bunch of different places and see if you find any significant voltage any where.

But the pressure washer story sounds awful hokie to me. And wouldn't their be manufacturer liability up the yin yang from people using these things if you could get shocked by spraying even hot conductors.

I don't know, the whole thing just doesn't seem to wash. :D

[ July 30, 2005, 07:45 PM: Message edited by: physis ]
 
Re: thermocouple wire

Thermocouples depend on dissimilar metals like iron and constantan. Likely to be difficult in making a good connection. If the wire is still intact, I would tape it up and let it go.

Better still, replace the entire TC wire with the right one.

[ July 30, 2005, 09:34 PM: Message edited by: rattus ]
 
Re: thermocouple wire

Out of curiousity, would there be any difference in the voltage developed at the junction if the thermocouples lead lengths are changed. I would guess no, but I don't actually know that to be true.
 
Re: thermocouple wire

Sam, I believe the length to be relatively unimportant since one would use a hi-Z instrument to measure the thermal emf which is a function of the temperature.

[ July 30, 2005, 09:37 PM: Message edited by: rattus ]
 
Re: thermocouple wire

yeah i would like to replace it, but it would be 4-5 hour job to replace it. how about if i cut the bad part out and use those cheap wirenuts that are all plastic(no metal). or should i just tape it the best i can, or use some of that liquid tape.
 
Re: thermocouple wire

I don't have first hand experience in this, but I think you could cut out the bad part, strip and polish the ends, and make a neat twisted splice. Then cover the twist with silicon grease or similar goop to prevent oxidation and finish it off with shrink tubing. Be sure you maintain polarity!

Anyone else have any ideas?
 
Re: thermocouple wire

rickl, I work on machines that have the j type t/c. Don't splice them with a butt connector. Either pull new wire the same length (approx) or you can by a 2 pin plug ( female & male ) that are made for T/C wire. Price is maybe $2 each. Cut were it's bad and add the plugs there. Myself it's always better pulling new wire but this will work. Now if the insulation in a small area is bad and the wire seems not to be damage at all, just tape them up there. If you do run a new wire make sure you check on each end and see what color of wire goes on them. Sometime you have a red & white T/C wire.White is + Red -. It could be Red & Blue. Red is + Blue -. A lot of ways they hook these up and it depends on the machine.
bye now,
Jim
 
Re: thermocouple wire

thanks for all the help
some more???? i should be able to ring out the wire to make sure there not broken or damaged some where else.
 
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