General > General Technical Chat
Dangerous fuseholder wiring in variac
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Circlotron:
Opened up my variac to have a look inside and I noticed that the incoming mains active wire goes to the fuesholder connection that is closest to the front panel. This means that with the fuse removed, the live part of the fuseholder can be contacted by the user. Good idea to swap the fuseholder wires.
TimNJ:
Now that's an interesting design accident that I've never considered. I've used this style of fuseholder many times in my own projects, and never once thought about that. Though, I'd say most people will *probably* unplug the thing anyway, but who knows.

NiHaoMike:
I wonder why those variacs have a voltmeter that is too imprecise to adjust the voltage with rather than an ammeter that would actually be useful. Better yet, nowadays they should be using digital panel meters that can at least match a cheap Harbor Freight DMM for accuracy and precision.
Ian.M:
That looks remarkably similar to the far east 'red peril' variac user 'tkamiya' tore down here: https://www.eevblog.com/forum/beginners/shopping-for-a-variac-shopping/msg3066512/#msg3066512
and eventually decided to condemn for scrap as irremediably unsafe based on his findings here:
https://www.eevblog.com/forum/beginners/shopping-for-a-variac-shopping/msg3068574/#msg3068574  :--

If the wiper doesn't have a slip ring but is connected by an ordinary wire wrapped a couple of turns round the uninsulated steel shaft that flexes and rubs every time the knob is turned, yours is the same as 'tkamiya's and should probably also be condemned as eventually the insulation will rub through and the shaft go live.  If you want to keep it safely in service you'll need to add proper ground bonding straps between all its metalwork, an insulating sleeve on the shaft, and glassfibre sleeving over the wiper wire, (which for reliability should also be replaced with extra-flexible test lead wire of an appropriate CSA) to protect it from rubbing!  :popcorn:
wraper:

--- Quote from: Circlotron on July 14, 2020, 11:21:57 pm ---fuseholder can be contacted by the user. Good idea to swap the fuseholder wires.

--- End quote ---
That's basically how most of similar fuse holders are made. Swapping wires won't help much since it still will be connected through transformer anyway. You may argue that Australian mains plugs are polarized but I would not count on that.
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