Failed 50 amp Plug

Discussion in 'Furnaces and their construction' started by Al2O3, Feb 7, 2022.

  1. Melterskelter

    Melterskelter Gold Banner Member

    Actually, it is not necessarily up to the consumer to look up the cited standards to confirm conformance. Intertek has put their stamp on it.

    “Intertek Group plc is a British multinational [2.7B GBP] assurance, inspection, product testing and certification company headquartered in London, England. It is listed on the London Stock Exchange and is a constituent of the FTSE 100 Index.”

    Looks like Intertek is the real deal. I bought a “super heavy duty” RV 3-conductor power cord for my kiln. Made in China. Distributed by a large company. Very well made. Not cheap. Made to the requested price point and requested quality point.

    I’m betting these are decent plugs. Of course, “Trust but Verify.” Kelly is onto the verify part, for sure.

    Denis
     
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Other than wire brushing the blades to keep them clean, which I'd prefer not to have to do or pay such attention, but not sure what one would do about it other than replace it. The only damage occurring to an inexpensive plug as there is a breaker on my rig and the feed circuit, neither of which have ever been tripped. The more serious issue is shock or fire hazard. As far as shock, I always turn the furnace off, remove the cord from the service outlet at the wall because the cord had an external grip, and then separate the plug and receptacle end of the cord. I never like the exposing the big blades while still energized. As for fire, that junction is always laying in the open on a concrete surface, and 95% of the time, out in my driveway, so not too concerned about that, and I'm never too far away during a melt. Now heat treat time is different.

    Sort of surprised this thread garnered as much attention as it has. I'm replacing the plug on my second furnace today so I'll snap a few more photos of the differences between the two I've noted.

    I want an IR camera, but my main motivation is to see if I can image a mold filling while in the flask during an active pour......that would be interesting. Pretty sure it would work with a non-metallic flask wall but not so sure through a steel wall, unless the sand would be too disruptive. It depends on the sensitivity and tunability of the camera. In a past life, we built cryogenic coolers for military IR imaging equipment. During lunch, we'd take the night sights outside and point them at cars passing by. With a couple of twists of the knobs, in full daylight, it would display the driver appearing to be suspended in mid air, the next brightest things were tire hoops that contacted pavement, then the engine which was very bright, and off the charts bright was the exhaust system running front to back with the exhaust plume......pretty cool.

    Best,
    Kelly
     
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Here's a side by side of the two plugs.

    6 Compare Plugs.JPG

    If you search Amazon and eBay for the cheapies, the older failed plug represents about 8/10 of what displays. Here's a link to the replacement.

    https://www.amazon.com/dp/B07DVZFBPM?psc=1&ref=ppx_yo2_dt_b_product_details

    Here's a comparison of the blades. Initially I thought the blades on the replacement were thinner, but they're actually about the same. The old ones are solid whereas the replacement's blades are thinner gauge folded double to about the same thickness from thinner stock. I like the lugs on the replacement blades much better.

    7 Compare Blades.JPG

    When I diassembled the second plug on my other furnace e-insert controller, I noticed pinched insulation in two places. Though never good, the one is between neutral and ground so other than minor increase in shock hazard, not much it could contribute to the fail. The pinch on the live red conductor couldn't go to ground. That ground conductor is precariously close to the live lug.

    8 Pinched Insulation.JPG
    9 Old Cap.JPG

    Diassembling this one did bring back a lot of annoying memories from when I assembled them 5 years ago. There isn't really sufficient room to route 6ga conductor inside the housing and the entrance strain relief had to be opened up to accommodate 6/4. The stuff I used on my equipment was only 7/8" OD and the drop cord was 1"OD, which would have had no chance with this plug. As delivered, I doubt it could have accommodated 8/4 without modification.

    Here's the replacement. Still a bit tight, especially on the ground leg but better than the other for routing and securing the conductors. I like the strain relief better as well.

    10 New Plug.JPG

    I buttoned it up and it's ready for service. Even though they're a bit suspect, I through the old blades in my electrical junk box.

    11 Save Blades.JPG

    Best,
    Kelly
     
  4. Smoking Shoe

    Smoking Shoe Silver

    Considering that I was taught that the electrons only 'flow' on the surface folded and thinner, but the same mass for heat distribution, should be better?

    The lugs on the new do look far more robust.
     
  5. ddmckee54

    ddmckee54 Silver

    Kelly:

    Be sure to check the connections periodically, and tighten things if needed. The strands in the conductors will tend to "flow" a little under the clamp pressure, and the connections may loosen up. The finer the strands in the conductor the more they will move around. Where I work we go through the substation connections, both medium voltage and low voltage, every year checking the connections to avoid that possibility.

    At one new installation that I was working on we had to do thermography on every power connection, verifying that the connections were good, before the owner would sign off on the installation. If we found a hot one it was probably loose and we had to fix it, that was one of the requirements of the contract.

    Don
     
  6. Jason

    Jason Gold

    The problem with the first plug is it's too damn small. They have enginerded every last bit of space to save that 1/8 of a penny. Cheap bastards. It's almost inevitable you will dork it up closing it.
    Look at the space inside the yellow one! There is enough from to park a truck in there.
     
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Quite a few hours on the new plug/receptacle now. Still look new and no detectable temp rise in use at 32amps. This concludes the (my) most highly analyzed plug ever thread..... LoL

    Best,
    Kelly
     

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