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Line power intermittent failure on my PET

Hugo Holden

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Joined
Dec 23, 2015
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Australia
My PET came from the UK. It was fitted with what is probably a standard UK power plug. Generally I like these plugs as they have very robust thick pins and they are rated to 13A. I also have outlets for these in my workshop, even though I am in Australia.

The line power cut in and out to my PET, it took me a while to figure out where the problem was. I had a similar problem with my SOL-20, but that bad connection was on the power transformer secondary connections where crimping had failed to some spade terminals. It actually corrupted some disk files and caused me a few headaches trying to find it.

In this case the problem was not what I expected.

Someone had decided that it was a good move to incorporate a fuse into the plug. There was a 13A rated fuse in there in series with the active wire. Not a bad idea as that fuse would help protect the cable. However, the spring clip of the fuse holder was hopelessly poorly spot welded to the brass plug pin and it had simply separated and the two surfaces were just sitting loosely together in the plug.

Line plugs are supposed to be designed by the best of the best electrical engineers, with electrical safety and reliability in mind. It goes to show one thing, if you are in manufacturing, think very carefully about the processes used in manufacture. How much variability is there in the particular process you are considering. For a spot weld it is a lot, especially if a Human operator is involved, less automated, for a threaded hole and a screw it is a lot less and probably less for a rivet.

Intermittent plugs like this, while not unsafe as an electrical hazard, can cause chaos with intermittent operation of appliances and computers.

edit:........ I just opened another brand of the same style of fused plug, but in this case they get the big green tick because they have riveted the fuse clips to the brass posts.
 

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Wasn't it standard practice for some manufacturers to ship product with no line plugs to customers in the UK? The customer was supposed to supply the plug.
In any case UK plugs are engineering (perhaps over-engineered) marvels compared to the stuff we get in North America. I doubt that Oz is much different in that respect. And ours are likewise rated at 15 and 20A.
 
Wasn't it standard practice for some manufacturers to ship product with no line plugs to customers in the UK? The customer was supposed to supply the plug.
In any case UK plugs are engineering (perhaps over-engineered) marvels compared to the stuff we get in North America. I doubt that Oz is much different in that respect. And ours are likewise rated at 15 and 20A.
It does seem that the engineering of basic electrical components has slipped. One other area I have noticed is the current ratings of switches, which appear to have become amazingly high for the size of the contacts & switch body.

One thing though which "took the cake" for over-rating, at least in my opinion, is a Hall current sensor in an SOIC IC package. It is rated to take 30A via two pins in and two pins out on the SOIC package.

Most AU plugs are 10A rated, of course with 230V here the currents are 1/2 for the same transferred power compared to 115V systems.

My favorite plug in AU & NZ is the Tapon plug (piggyback type) hard to get in AU now but still made by PDL industries in NZ. Every time I visit NZ I buy a box of them, they come in white, black and clear top. Great for low power workshop apparatus. Though they got abused by the public though, stacking many up on high current gear which is why I think they disappeared from the AU stores. Here is a picture of this marvelous plug:


 
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