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Hi folks,
I'm building tube amp with double primary winding power trans (2 X 120V). It will wired in series to get 240V input rating.
Question is : could I connect power switch between the winding, ie. ac in (live)-fuse-winding1-switch-winding2-ac in (neutral).
Would this OK and acceptably safe?
I want to wire this way because it's simpler in execution
Thanks in advace
Follow Ups:
Yes, use a DPST switch wired in the manner described by Tom.
(mains live > fuse > switch pole1)
(mains Neutral > switch pole2)
...An NTC thermistor after the switch (pole1) couldn't hurt! :-)
Cheers,
W
This is the most popular way and I know it's UL approved to do it that way and how I always do it in my projects. But some claim this is not the safest way.
Another idea is to run the HOT to the switch first, then to the fuse holder. The reason is that the fuse holder is totally dead with the power switch off (assuming a properly polarized cord and outlet). Even a back wired fuse can be dangerous if the fuse is good and separates from the cap while still in the holder. As for the power switch failing to ground, most approved power switches are designed not to do this and furthermore have substantial metal that should take out the building circuit breaker if they do fail to ground internally.
Food for thought!
Food for thought...Another idea is to run the HOT to the switch first, then to the fuse holder.
Synonymous scenario:
Installing the OPD AFTER the equipment mains disconnect.
Of course we agree on the "UL" approved method.Another scenario worth mentioning:
Putting the fuse on the mains N > one leg of the PT primary.
Switch the mains Hot > other leg of the PT primary.
In theory it will work; I've seen many manufacturers implement fusing this way.
I only advocate the "UL" method.
Good topic.
Edits: 04/18/14
Current safety standards call for live wire to connect to back terminal of fuse holder (to avoid exposing a "hot" terminal if fuse is removed), then side terminal to power switch, then to load. A second switch pole can be connected in the neutral, but the live or hot lead must be switched. I would recommend following this established practice.
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