What's the best way to hook up an Isolation transformer

[ixe13]

Hi,

I bought an isolation transformer (http://www.hammondmfg.com/169.htm model 169G) to bring down the 120/123 AC Volt coming out the wall outlet to 115 Volts for a pair of QUAD II.


My primary concern wasn't really to isolate but rather to bring the main AC down a bit. I suspect the transfo might be bit overkilled for the job, but then, I might find other uses for this thing later on...

1-Now, at the primary, There is no indication on which wire the hot and neutral from the main outlet are connected. both wires are black. I guess it doesn't matter, but I though I better ask...

2-At the secondary it's seems obvious, 0 volt is the neutral, ...right?

3-I will put this transformer into a steel enclosure. Should I isolate the transformer itself from the enclosure using rubber washer or something similar?

4-On the picture, you can see that there is a ground connection on this Transfo. Is it the transformer's frame that provide it ?

5-And lastly, what should I do concerning the third prong(Ground) from the main and the QUAD. Could be related to the question 4...

The QUAD do have the third prong connected to their Chassis.


Thanks in advance for any advices since I wont connect this thing before knowing exactly whay I'm doing. I did do some reaserch, but ended up more confuse than anything...

Yves

[DougL]

1-Now, at the primary, There is no indication on which wire the hot and neutral from the main outlet are connected. both wires are black. I guess it doesn't matter, but I though I better ask...

For your application, it does not matter.

2-At the secondary it's seems obvious, 0 volt is the neutral, ...right?

Correct. You are 2 for 2.

4-On the picture, you can see that there is a ground connection on this Transfo. Is it the transformer's frame that provide it

Yes

5-And lastly, what should I do concerning the third prong(Ground) from the main and the QUAD. Could be related to the question 4...

The safety ground should be connected to the input IEC, the output plug, the metal case and the transformer frame at a single point to prevent any ground loops.

HTH

Doug

[speakerfritz]

I checked the schematic and did not see the dot that normally is indicated if there was a polarity on the primary. the schematic shows both are black. so even if you wanted to differ on which is hot and which is neutral...how would this be done since they are both black...conclusion...on the primary side...it wouldn't matter.

[audiowize]

FYI - An autoformer is generally less expensive and a bit easier to wire, and I would gander a tad more efficient also.

[gingertube]

Sorry in advance Audiowize
- you just pushed one of my buttons.

Autoformers are in my view just "bloody" dangerous. I would be in favour of banning them entirely. The problem of course is no isolation between input and output.

Cheers,
Ian

[audiowize]

Do elaborate on your issues of not having isolation. If you're just adjusting voltages, I don't see the need for a second winding. As long as safety ground is maintained, I don't see the problem. In fact, a GFCI will trip from a problem with an autoformer, like your finger making contact. The same cannot be said for such an instance on the secondary of an iso transformer.

[ixe13]

I tryed a variac and the bloody thing was leaking 20 Volt AC between any of the output prong and the frame... even turned off...

Now Theory is not my strong point, but I dont think this is right.

And Ive read quite a bit about variac on different forum, and since it's a good thing in a lab, I didnt really wanna put this thing in my livingroom for all kind of reason...


Thanks for the comments

Yves