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Wiring an Isolation Transformer

I found a pristine, never been used, Topaz (Square D Company) 91018-31 1.8 KVA Ultra Isolator Line Noise Suppressor for $40. Other markings include .0005pF, 50/60 Hz, 120/240, Indoor Type 1, Enclosure Class 1-80 Insulation. However, it has no receptacle or chord.

My first question to the forum, is how to wire it? Could I just take a short extension cord, cut in half, wire the male end to the output side and the female end to the input side? Should I use bare wire under the screw terminals, or should I crimp/solder on spades? What wires go on what screw terminals? Some suggest balanced is the way to go. But some suggest this cuts the power in half, some suggest it doesn’t. Here is an example I found of balanced wiring:

Input:
Neutral (white) to H1
Hot (black) to H4
Ground to chassis

Output:
Hot 1 (white) to X1
Hot 2 (black) to X4
X2/X3 center tap connected to chassis ground and outlet ground.

Is this all there is to it? I am a complete newb when it comes to electrical work. Is this something I can do myself, or should I hire an electrician? Any assistance would be greatly appreciated.
cpalcott

Showing 4 responses by herman

herman
2,215 posts
 
First of all, if you are not sure how to do this I seriously suggest you enlist the help of someone locally who can help. It is possible to kill yourself or burn your house down if you screw up with electrical work.

To run it balanced you'll need to connect it as you stated but also jumper H2-H3 on the primary otherwise no current can flow. That puts the 2 primary windings in series and also the 2 secondaries so it is a 1:1 transformer.

The full VA rating at 120VAC assumes you are running the 2 primaries as well as the 2 secondaries in parallel so each winding carries half of the current.. Running balanced you will have them in series so VA rating is half since full current runs through each winding, not half of it.

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herman
2,215 posts
 
Was it..... Was his mind made up?... Set in concrete?

Having a bad day? No need to be snippy. I said "if." I didn't say set in concrete,, I didn't say his mind was made up.

BTW I'm still curious how it is less isolated wired as 120-120.

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herman
2,215 posts
 
Yes, I did read it.

It doesn't say anything that I can find about 120-120 having less isolation, in fact it says "The advantage of operating a Balanced Input or a Balanced Output is noise reduction as a result of the balanced line common mode noise rejection."

As far as I can tell their argument against going balanced has to do with safety and adhering to code, which are both valid concerns, but your point about "less isolation" isn't discussed as far as I can tell. I would be interested to hear the explanation if you would be so kind to provide it..

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herman
2,215 posts
 
Please explain
120V in 120V out will not yield all that much isolation. Better to wire the xfrm 240V in, single ended 120V out.

If the purpose of the exercise is to have a balanced secondary then he has no choice but to wire it as stated above. You can't have a 240 primary and balanced 120 secondary. Granted, you can argue that balanced might provide no benefit, but he won't know until he tries it.

Wiring it 240-120 means he will need to run a 240 line to it. I didn't gather from his initial post he was wanting to hire an electrician to run new lines.

And why does 120-120 not "yield all that much isolation"?

I didn't know there were varying degrees. I thought it was either isolated or it was not. How can it be less isolated as 120-120?

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