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-   -   How Did They Du Dis? (https://www.electriciantalk.com/f2/how-did-they-du-dis-189457/)

ppsh 01-05-2017 10:04 PM

How Did They Du Dis?
 
Putting in a subpanel for a well pump, some outdoor lighting, etc.. Plugged in my pvc heater at the nearby GFCI, wrapped it on a pipe, and waited, and waited, 5 minutes on a piece of 1" sch 40 and still hadn't softened. A minute later I smell burning windings. Find the source of the smoke, its a 24vac multi tap transformer in a weatherproof enclosure, smoking and sparking. Kill the breaker and start opening all of the enclosures.

It was a 24vac, 40va transformer with a multi tap primary, 120, 208, 240v. Power going to the well equipment was 12/2 uf, powered forma a 2 pole 20. Transformer fed a water softener controller. Primary was wired using the 240 tap and common, as it should.

However, there was another wire pigtailed to the common on the primary side, and a wire hooked to the 120v tap, went underground thru sealtight, and fed the GFCI I plugged my PVC heater into.


It appears that they wanted 120v, and had no neutral, so Cletis discovered he could get 120v from attaching to the 120v primary tap on 240v fed transformer.

How did this even "work"?

Fishbulb 01-05-2017 10:54 PM

The primary winding was functioning both as a standard primary winding of the power transformer and as an autotransformer itself. You could safely supply a whopping 80 VA to the GFCI receptacle until the water softener switched on. I suspect your heating blanket was slightly over that?

dmxtothemax 01-05-2017 11:31 PM

Why would it not work ?
it is simply an auto-transfomer.
Not exactly best practice,
but it works.
not dangerous if not over loading the tranny.

:eek:

B-Nabs 01-06-2017 01:29 AM

Quote:

Originally Posted by dmxtothemax (Post 3521945)
Why would it not work ?
it is simply an auto-transfomer.
Not exactly best practice,
but it works.
not dangerous if not over loading the tranny.

:eek:

But there's yer problem right there.

dmxtothemax 01-06-2017 02:22 AM

What was the load ?

MechanicalDVR 01-06-2017 08:17 AM

Worked fine for years.....

I can hear the home owner now!

B-Nabs 01-06-2017 08:58 AM

Quote:

Originally Posted by dmxtothemax (Post 3522137)
What was the load ?

He said it was a PVC bending blanket, so at least 200W, which is already 250% over what that setup could handle. And those blankets can draw as much as 1500W depending on size.

Jlarson 01-06-2017 11:18 AM

What the hell are you doing blowing up such a fine piece of craftsmanship?

Someone worked really hard on that kludge.

dmxtothemax 01-06-2017 04:49 PM

Cletis wus ere !


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