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Old 12-09-2019, 11:12 PM   #21
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Tetrafluoroetheylene had to find the spelling lol, I keep a roll of black red white green number 10 on my van, I use it for like kitchen equipment that gets extremely hot, my street lights that are HPS get super hot, the insulation can handle up to like 260C, it does cost a lot but ive found it lasts and never burns up in a situation like there where there might be constant high current- high heat being applied to the wire, the insulation can handle it,
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Old 12-09-2019, 11:21 PM   #22
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Tetrafluoroetheylene had to find the spelling lol, I keep a roll of black red white green number 10 on my van, I use it for like kitchen equipment that gets extremely hot, my street lights that are HPS get super hot, the insulation can handle up to like 260C, it does cost a lot but ive found it lasts and never burns up in a situation like there where there might be constant high current- high heat being applied to the wire, the insulation can handle it,
That would be overkill. Would also need special terminations. Also known as hi temp wire, nichrome(?).
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Old 12-09-2019, 11:39 PM   #23
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Ive never used special terminations for it, it comes in all sized my street lighting I use those black high temperature wire nuts, ( the ones that come with the ballast kit that every one throws away to use their own because they think they are the "cheap kind") lol they're designed to be used in a high temperature environment, when I do like steam tables, I use it there also, you will notice when they come from the factory, they have these wires coming off the knobs and for all the heating elements because it holds up and lasts, im a huge fan of the stuff, its kind of expensive yes, but if the environment calls for it, use it. it almost looks like that good ole, cloth wiring were all used to seeing y'all probably have seen it countless times, I just get city electric to order me a few rolls of it, it comes in handy, you can charge a premium for it, and it ends up quality and lasts forever,
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Old 12-09-2019, 11:39 PM   #24
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If the operator doesn't like his job, he may very well have applied some sort of torch to the conduit.........
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Old 12-09-2019, 11:59 PM   #25
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I know, I know, Teacher please let me answer this one......



It was from harmonics.....................
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Old 12-10-2019, 12:09 AM   #26
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If the operator doesn't like his job, he may very well have applied some sort of torch to the conduit.........
Nah, He's a nice guy, Maybe the graveyeard shift lays on the pressure.

This was liquidtight from the enclosure to the motor. Not a blister in that
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Old 12-10-2019, 12:34 AM   #27
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Nah, He's a nice guy, Maybe the graveyeard shift lays on the pressure.

This was liquidtight from the enclosure to the motor. Not a blister in that
Rats......another perfectly good theory shot pieces.........

I think 8s are too small for a 40HP, you did the right thing; 6s will hold just fine.
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Old 12-10-2019, 04:50 AM   #28
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If this is a grinding machine to refinish rolls for mills or something such, a chart recorder logging current might be a good idea. You may be shocked to find an operator is doing a too heavy hogging pass and a light cleanup. If he is smart he may have figured out how to jumper the overloads or jam the reset button in so it cannot trip.
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Old 12-10-2019, 05:56 AM   #29
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You can rule out it wasn't melted from some past incident that nobody checked?
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Old 12-10-2019, 07:09 AM   #30
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This is really weird. I have seen insulation melt but that was on short circuit with a breaker. By the time the breaker reacted, the insulation had bubbled and burned. You would think that a fuse element would have a lower melting point than nylon insulation.

If the wire is undersized, I could see the insulation weakening and discolouring over time but melting is something different.

Those are just my thoughts but, then again, I’m just a dumb pipe kinker and wire yanker .
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Old 12-10-2019, 07:18 AM   #31
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How many amps would cause the insulation on #8 thhn to melt ? I figured it would make it to about 70A.
There is no set temperature. 70A sounds awfully low to melt the insulation off of #8, however, if that 70A was allowed to flow for hours it just might.

In connector tests that I have seen it take some time for 100A to melt the insulations off of #12 wire.
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Old 12-10-2019, 07:19 AM   #32
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You can rule out it wasn't melted from some past incident that nobody checked?
It does seem like a one time, separate event to me. Considering the safety factor built into wire sizing calcs, I don’t see how #8 would melt and #6 wouldn’t.
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Old 12-10-2019, 07:22 AM   #33
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It does seem like a one time, separate event to me. Considering the safety factor built into wire sizing calcs, I don’t see how #8 would melt and #6 wouldn’t.
I completely agree. If the insulation is melting off of #8, then the insulation on #6 would still be getting severely damaged int he same situation.
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Old 12-10-2019, 07:38 AM   #34
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There is no set temperature. 70A sounds awfully low to melt the insulation off of #8, however, if that 70A was allowed to flow for hours it just might.

In connector tests that I have seen it take some time for 100A to melt the insulations off of #12 wire.
The insulation does have a set melting temperature but I know what you’re saying. Here’s how I see it: If you overdrive the conductor, you’re turning it into a heating element. If you don’t reach the melting temperature of the insulation, it won’t melt. The characteristics of the insulation may change (discolouration, etc.) but what bothers me is that it actually melted. I can’t see #8 melting even if it is undersized. Besides that, the fuses blew.

I’m thinking there was a separate event aside from motor operation.
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Old 12-10-2019, 09:04 AM   #35
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No, it's an old Nema starter, and I did check the numbers on the heaters. How do you test that ?
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IDK. Try undersizing the the heaters just to see them drop the coil out.

edit...Was the breaker sized properly? How old is it? (will it trip?)
Are the heater elements those bimetallic style that start with a B---?

What is the part number for the heater elements?

I've seen A LOT of starters over the years with the overloads sized/set to 125% of the motor nameplate, even though they should be sized to 100% of the nameplate since they are set to trip at 125%. Nobody usually notices the error until later, when something burns up. Sometimes years down the road.

It sounds as though this machine has the potential to be overloaded by operator input fairly easy, so it's definitely worth verifying it's correct in my opinion.


EDIT: A CC87.7 bimetallic looks like it could be 1-3 sizes over the size it should be for a 46 amp nameplate motor depending on which column you should be using on this chart:

https://www.google.com/url?sa=t&rct=...f9kR3YbtDMffQL

Take a look at the bottom of this pdf. It mentions how to do some of the sizing for Sq D's overloads.
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Last edited by Cow; 12-10-2019 at 09:14 AM. Reason: Found some info from Sq D
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Old 12-10-2019, 09:11 AM   #36
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Are the overloads the correct trip class for the machine?
A class 30 will allow an operator to bear down and grind like heck long enough to melt the wires over time and yet not trip the starter.

Our machine shop here did that with our bigger grinder, 10hp. The operator had leaned over the years just how long he could go before tripping.
All internal wires were high temp, except from the newer starter. They melted in the whip.
The original grinder wiring had a contactor inside the base. When that died 20+ years ago a starter was mounted on the wall. The grinder is from the 1940’s.


https://www.gt-engineering.it/en/Ins...ripping-curves
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Last edited by Wirenuting; 12-10-2019 at 09:25 AM.
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Old 12-10-2019, 09:14 AM   #37
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No, it's an old Nema starter, and I did check the numbers on the heaters. How do you test that ?
An older Square D?
Tap it with a screw driver and Klein’s.
Don’t try it unless you have a spare on the truck.
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Old 12-10-2019, 11:51 AM   #38
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Dorian. Do you remember my story about bypassing my electric meter with number 10 some years ago?
Ran the complete apt for two weeks with zero wire damage. Thats with range, HVAC ect....
I think number 8 could stand many more amps than 70. Way more.
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Old 12-10-2019, 12:10 PM   #39
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Wirenutting nailed this. The repeated bogging down of the load is probably the answer. I recently was amp checking a box manufacturing operation for a moving company. They build big hauling boxes onsite for moving furniture and the like and are pretty much one time use so these guys build seventy or eighty big boxes a day. The table saws were tripping often, not a voltage drop problem. It turned out to be the operators- they would bog the saw blades during ripping plywood sheets constantly. Blades would stop. #10 wires were melting. Sometimes the breakers didn't trip till stuff started smoking. Would not have mattered if I ran #6 to the saws, the operators are the problem. They are under pressure to hurry all the time. Very hard to communicate to them, they are all from an island chain out there where there are French Electricians and no speaky Englisky.
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Old 12-10-2019, 12:20 PM   #40
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Was it a surface Grinder? One that would take a pass, lift the head, move the table back, drop the head then repeat. These would do that to motors and wire because they allowed the heater and motor to cool between passes on heavy cuts. Think of starting the motor over and over, only motor don't stop just the heavy cut acts like starting current.
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