Wires overheating and melting the insulation

[Trawets]

I have 4 electric salamander heaters that are permanently installed on walls at my work. 2 are fed from one panel and 480/208 transformer and the other 2 are on a separate floor with its own panel and transformer. All 4 are wired in a similar fashion and are suffering from the same issue. The problem is the conductor insulation is melting at the disconnects on the line side and the breaker and wires are overheating (120 F +).

Here's the setup working from heater to breaker panel:
3 phase, 208 Dayton model 1RKT9 heater, 42 amps
5' to 10' of 6/4 SO cord
60 amp Siemens non-fused disconnect, cat # GNF322
150' of #6 THHN copper inside 1"emt (3 hots, 1 ground) ran in plenum drop ceiling
3 pole, 208 v, 60 amp Square D bolt on breaker

All terminations are 60/75 degree rated
voltage at panel is 215
voltage at disconnect is 211 while running
amp draw is A 41, B 41, C 39 (I think the fan is single phase)

I have no loose connections and I think all my calculations are correct. I plan on up-sizing the wire to #4 and replacing the breakers but that still has me scratching my head as to where I went wrong. Any help is appreciated!

Just to be clear, the 480/208 transformer is configured for a 208 Delta secondary, and the heaters are wired line to line with no neutral? That is why the fan current appears on only two lines?

 

[infinity]

211 volts should not make much of a difference. 120° F on a 90° C (194° F) conductor shouldn't be a problem.

 

[JFletcher]

I am leaning toward a termination issue at the line side of the disconnects... You said they are tight... Are they too tight? I would undo them, and check to see if they were over tightened and broke several strands on the wires, or vibration or another factor may be contributing. the wires may also barely be inserted into the terminals causing a poor connection. Perhaps the original installer cut a few strands off to make the wire fit easier?

Any chance you can post a picture or two?

 

[Sierrasparky]

Loose or incorrect torque at the line side terminals.

 

[Trawets]

The 120 F is after ten minutes of running.

I’ll take pictures tomorrow before I undo the connections, cut the wires and redo the connections.

 

[JFletcher]

The 120 F is after ten minutes of running.

I’ll take pictures tomorrow before I undo the connections, cut the wires and redo the connections.

Please do, let us know how it turned out.:thumbsup:

 

[Jraef]

I am leaning toward a termination issue at the line side of the disconnects... You said they are tight... Are they too tight? I would undo them, and check to see if they were over tightened and broke several strands on the wires, or vibration or another factor may be contributing. the wires may also barely be inserted into the terminals causing a poor connection. Perhaps the original installer cut a few strands off to make the wire fit easier?

Any chance you can post a picture or two?

Termination issue, almost guaranteed. SO cord is typically class G stranding (101 strands of 24), typical mechanical lugs are class B or C rated (37 strands max), meaning the lugs are not rated for high strand count conductors. Why? Because that is exactly what happens. It doesn’t matter how hard you tighten the lug, that type can’t push enough of the strands together tight enough to carry the rated current. There are a few mechanical terminal blocks that are class K rated, but typically you must terminate it using specifically rated compression lugs and dies.

 

[Little Bill]

Termination issue, almost guaranteed. SO cord is typically class G stranding 101 strands of 24), typical mechanical lugs are class B or C rated (37 strands max), meaning the lugs are not rated for high strand count conductors. Why? Because that is exactly what happens. It doesn’t matter how hard you tighten the lug, that type can’t push enough of the strands together tight enough to carry the rated current. There are a few mechanical terminal blocks that are class K rated, but typically you must terminate it using specifically rated compression lugs and dies.

OP said this was happening on the line side so I don't think the SO cord would be the problem. I do however agree that it sounds like a termination problem.

 

[masterinbama]

I agree it's the termination of the fine strand conductors. Ilsco makes crimp on lugs rated for welding cable. I would try them First before repulling the feeders.

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[Russs57]

Don’t overlook the disco. Been seeing more instances of a phase not making up all the time. Also been recent recalls from some brands.

 

[sameguy]

Meter both line load at the disco. To find your answer.

 

[Trawets]

Hope these pics help if they come through. I took these pics after 2 hrs of running. I also removed the arc guard on the disco and it was reading 188 F.
The transformer is 480 delta to 208 wye. The heater fan uses L1 and L3. No neutral is required.
I was the installer 6 years ago and I refuse to cut wire strands off to make it fit. The lugs are rated to #3. The wire is #6 made up of 19 strands.
While I can tend to tighten screws too much, I’m struggling to believe that I did it at 3 lugs at 4 separate disconnects. But it’s not impossible. I’m trying to talk my company into investing in an insulated torque screwdriver set.
I haven’t yet had the chance to cut and reconnect the wires.
I have not been able to find any recalls on any of the equipment.

Thanks. Any input is still appreciated!


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[LarryFine]

Looking at the IR pic, it looks like the heat is coming from the switch contacts, not the terminals. I recommend a new switch.

 

[Jraef]

I still think it's the high strand count wire, but the heat is rising through the disconnect contacts up into the line side conductors.

 

[Cow]

Your disconnect guts need to be replaced.

We use Siemens disconnects almost exclusively and I've had to replace several of these over the years that have been fairly heavily loaded over a long period of time because they start generating too much heat at the switching mechanism which in turn starts to overheat the terminations and wiring. You got 6 years out of them since your original install. So now you know they have a 6 year lifespan in this environment, if you want longer service intervals, replace with 100 amp disconnects.

I do not believe strand count is playing a part in generating the heat. For instance, we do work for large farms with potato storages, typically 60 amp disconnects with 60 amp fuses to cords running as much potato piling equipment as they can plug in. Fuses blowing are common, but I do not see symptoms of overheating where the SO cords are ran right to the disconnect terminals.

I know fine stranded wire should not be terminated in this manner, but the reality is, generally it is not a problem.

 

[jtinge]

If SO cord is used to connect the heater to the supply, shouldn't the cord be terminated in a plug and connected to a receptacle fed by the disconnect rather than hardwired to the junction box? This violates the "uses permitted" section of Article 400. Should have used flex conduit and Article 310 wiring instead.

 

[JFletcher]

First of all, thank you very much for providing pictures and such detailed troubleshooting... It is very much appreciated. I would go so far as to say what you have provided could be in a textbook for troubleshooting.

I looked up that model disconnect, I too found no recalls, nor any literature on expected lifespan switching under load. 6 years seems incredibly poor to me, and I don't imagine those switches saw even 2000 cycles during that time. Nevertheless, I do not discount Cow's experience with these models, and he may very well be ultimately correct in his post.

Are the heaters switched on and off with the disconnects? If so how often?

the infrared taken labeled 149° Fahrenheit seems to show the issue is starting near the top terminations... Do those lugs connect to the switching mechanism with that single Phillips head screw?

At this point, redoing the terminations and rechecking the terminal lugs is less time & expense than replacing the disconnects.

Thank you again for taking the time to post pictures and following up... It has been a long time pet peeve of mine when people ask questions and then never reply back with any follow up or solution. :thumbsup::thumbsup:

 

[Trawets]

Jtinge: my code book is at work but I will definitely look into that code when I go on Monday.

Jfletcher: the heaters are in cold areas of the building where pipes and sprinkler lines have froze in the past like our elevator pits and our generator radiator room. They may get switched maybe 10 times a year. On in late fall, off in spring and maybe a few times during winter to do preventative maintenance. I never stopped once to think of the factory connections at the lugs.

Everyone else: thank you for the advice and I will be taking it all into consideration as I move forward with correcting the issues.

If there is any more advice that anyone can think of, it is welcome. I will update you guys if and when I find out what is going on.


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[Russs57]

Am I the only one seeing a phase on the 20 amp 2 pole breaker also reading hot? Notice the discoloration on face of both the 60 amp 3 pole breaker and the 20 amp 2 pole breaker. They look like they may have gotten wet, or seen some contamination. I'd like to know what FOP test says at full load on both breakers. Granted that low voltage to a heating element shouldn't cause increased amperage.

And what is that goop in the bottom of the disco that looks like oil?

Doubt the loops in the wire on line side of disco are adding enough inductance to matter.

I'd say pull the arc chutes, re-terminate and re-tighten everything. Spray blades and line side contacts with contact cleaner. Inspect blades and abrade with gray scotchbrite if needed (but don't remove silver!). Squeeze line side contacts together with needle nose and apply some of that "red grease" sparingly to blades/contacts. Open and close disco several times and make sure all blades are fully engaging line side contacts.

Then give it a few days of operation and take some more infrared pics.

Like I said, I've been seeing a lot more disco's causing these problems over the past decade or two. Not a fan of plastic rotors for the blades.

PS, remove line side lugs, clean both mating sides, maybe add conductive grease, and reinstall.

 

[jtinge]

Jtinge: my code book is at work but I will definitely look into that code when I go on Monday.

You can also check out this thread on hardwired flexible cord.

http://forums.mikeholt.com/showthread.php?t=175866