Retirees hobby

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fisherelectric

Senior Member
Location
Northern Va
A retiree up the street has a plastic forming machine, used to melt and then form plastic sheets into different shapes. It uses a series of heating coils which slide over the work surface. He called me saying it blows the internal 30 amp fuses when it's on more than 5 or six minutes. He said he usually only has the heaters on for 2 or 3 minutes at a time. It is fed at a 30 amp fuse block which feeds the control circuits and then to a contactor that turns on the elements. The contactor is wired with 12 gauge THHN and rated 60 amps.I put an amprobe on the coils and they pull 36 amps. I asked him about the machine he bought which has no rating plates and no manufacturers name. He said it was a one of a kind prototype. The heat coils are wired together and back to the contactor with hi-temp (100 degree C) wire Type SWEF-2, also 12 gauge. I could replace the fuse block with a 60 amp block and run #8 to the contactor fused at 40amps, but I'm nervous about the SWEF-2 #12 feeding the coils. I have never heard of this type wire and don't know about the ampacity. He's been using this machine for several years.
 
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fisherelectric

Senior Member
Location
Northern Va
I'm not the retiree! Yet! The guy with the machine is, and in his seventies. This machine means a lot to him, he's trying to start abusiness with it, however I'm inclined to agree with Pierre. It's a pretty simple machine but seems to have some design problems. I hate to blow this guy off, but think maybe i should. Has anyone had any experience with type SWEF-2 wire? I think I owe this guy an expanation of what's wrong with his machine.
 

Rockyd

Senior Member
Location
Nevada
Occupation
Retired after 40 years as an electrician.
The letters may not be meant for civies...


Thinking that the nomenclature could be military specifications?
 

mdshunk

Senior Member
Location
Right here.
I was a factory electrician for a long time in a plastics factory, and I did maintain a number of thermoforming machines, so I think I can address this matter with a little bit of experience.

Two general items that seemed cause fuses to blow on this sort of equipment were bad heated terminations and worn contactor contacts. The permanent corrective action is:

1) Replace contactors with SSR's or Mercury contactors. The choice between the two depends on how often or quickly the temperature controller cycles the elements. Every couple seconds, choose an SSR. At least a minute between cycling the element on and off, choose a mercury contactor.
2) Wire the equipments leads between the contactor load side and the element with TGGT wire, sized for the connected load
3) Use nickel ring terminals at the element end, crimped with the crimper called out by the terminal manufacturer
4) use lockwashers on the nuts at the element studs.

The things on this list solve 90% of the fuse blowing issues due to overcurrent, assuming the machine was otherwise properly designed.
 
mdshunk said:
I was a factory electrician for a long time in a plastics factory, and I did maintain a number of thermoforming machines, so I think I can address this matter with a little bit of experience.

Two general items that seemed cause fuses to blow on this sort of equipment were bad heated terminations and worn contactor contacts. The permanent corrective action is:

1) Replace contactors with SSR's or Mercury contactors. The choice between the two depends on how often or quickly the temperature controller cycles the elements. Every couple seconds, choose an SSR. At least a minute between cycling the element on and off, choose a mercury contactor.
2) Wire the equipments leads between the contactor load side and the element with TGGT wire, sized for the connected load
3) Use nickel ring terminals at the element end, crimped with the crimper called out by the terminal manufacturer
4) use lockwashers on the nuts at the element studs.

The things on this list solve 90% of the fuse blowing issues due to overcurrent, assuming the machine was otherwise properly designed.


The SSR's are probably easier to find. We went away from using mercury contactors because they would explode every once and a while. And they are a pain in the neck to clean up.
I have replaced quite a few mechanical contactors with SSC's, they work well and can be cycled quite fast so as to controle temp to tighter tollerances.
TGGT wire or teflon coated wire without the fiberglass sheath will take more current than standard copper wire, I believe that the conductor is made of Nickle.
 

mdshunk

Senior Member
Location
Right here.
brian john said:
What was done with the mercury, we have a job where there are existing mercury contactors that are to be removed.
I always took them to my supply house (Hagemeyer). I think it was about 10 bucks a pole to dispose of mercury contactors. I take most of the hazardous nasties to the supply house, like PCB ballasts and emergency light batteries. Some customers want a CD (Certificate of Disposal) for these sorts of things, which the supply house can provide.
 
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