Isolation xfmr correct polarity orientation test

I guess I got lost in your post. I thought you wanted to know why you didn't measure 60 - 0 - 60 referenced to ground when it was floating.

I have a 4.2kva Topaz iso to connect into my system. Here is the information off the plate. I have inserted periods to separate the 2 colums.

INPUT SIDE................OUTPUT SIDE
126v H4 dot................120v X2 dot
120v H3...................
114v H2...................
000v H1......................X1
S1.............................S2
CHASSIS...................CHASSIS

The input side has a chassis lug, an S1 lug (this is the shield covering the primary winding), an H1 lug (for common), and H2-H4 lugs (hot lugs which allow one to adjust for a slightly high or low input voltage to get 120v on the output). H4 has a polarity dot.

The output side has a CHASSIS lug, an S2 lug (for the shield covering the secondary winding), an X1 lug (for common), and an X2 lug (hot). X2 has a polarity dot.

The question is: "How should this be wired?"

On the INPUT side, I would assume that the CHASSIS is grounded, and that common connects to H1 (which is already grounded at the sub pannel), and that hot goes to H3 (in my case).

On the OUTPUT side, I would assume the ground wire from the outlets goes to CHASSIS, X1 goes to the outlet common, and X2 goes to the outlet hot.

Where do the shields get connected?

I have been advised that the secondary common, X1, is left floating or it will compromise the iso's ability to isolate and filter out the garbage.

Any assistance here would be appreciated!

Could I ask you a few questions?

Sub panel?
Is this for the output of the iso unit? Or the input?

4.2kva at 120V input.
Xfmr is good for 35 amps at 120V.


Wire size to feed the xfmr. 125% of 35A = 43.75A... #6awg min. What is the total distance from the feed panel to the xfmr, if it is not being fed from the subpanel?

Does the unit have it's own primary safety disconnecting means? Is the unit insite of the panel it will be fed from?

What is the nominal Ac 120 voltage measured at a kitchen receptacle? 115V, 118V, 120V, 125V, ?

If the xfmr is going to be fed from the subpanel.
How big is the wire size feeding the sub panel?
How far is the sub panel from the main electrical panel?

Aprox how much load, amps, watts, va, will you be connecting to the xfmr?

If the unit is to be fed from the sub panel, does the xfmr unit have it's own individual overcurrent devices, breakers or fuses, on the output to protect it from the loads to be connected to it?

>>"I have been advised that the secondary common, X1, is left floating or it will compromise the iso's ability to isolate and filter out the garbage."<<
>>>>

Not by any licensed electrician.
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Are you going to install and wire this yourself?

Jea48,
Hi, I am an electrical engineer by training and have quite a bit of experience in AC wiring, although not certified. So, I feel confident doing this if I can fully understand the hookup.
The 4kva iso is fed from a 60amp breaker (single phase) in the main panel, and feeds a subpanel, all with #6awg wire. The main panel, iso, and subpanel sit within 2 feet of each other.
The subpanel has dedicated circuits, each having 3 - #10awg solid conductors, with the hot and common twisted and star grounds at the subpanel. The circuits average about 15 feet in length.
The "idle" load on the iso is about 500w, with almost 80% of that being the tube amp. The peak load, worst case, is about 2000w, or less than 50% of the iso rating. If iso loading is a concern, I could move the tube amp and subs outside the iso, but on the same phase.
The normal voltage is 121-122v, and is quite consistent over 24 hours.
I will send you an AC power distribution and conditioning architecture diagram separately via email (and to anyone else who would like to see it).

Below is my response to a member on another forum. I attemped to to speak more in layman terms.
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Jon, I have to admit I did a lousy job on my presentation of this thread. I should of kept it simple and to the point. I should of left out all the voltage measurement values. They only confused people, and the issue.
The test is a simple way to check the polarity, phase relationship, of the secondary output of an isolation transformer to the AC grounded system the transformer is fed from. I have used this test procedure for years in commercial and industrial applications. It has never failed.
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Example:

Test procedure.
Primary
I connected the primary of the single phase isolation xfmr to 123V from the electrical panel in my home, connected to (L1) and the neutral. The two primary windings are parallelled, (H1&H3) connected to the Hot. (H2&H4) connected to the neutral.

Secondary
I had to series the two secondary windings to achieve 120V. X2&X3 tied together insulated. X1 and X4 floating with a difference of potential between them of 124Vac.

I measured the AC voltage from each of the two floating secondary leads, X1 and X4, one at a time to the equipment ground or to the line neutral. The lowest AC voltage reading of the two will become the neutral and be bonded to earth ground. The lowest voltage reading was from X4 to equipment ground.

I then bonded X4 to the equipment ground. X4 is now the neutral, the grounded conductor. X1 the Hot conductor. X1 to ground measures 124Vac.
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Now if every thing is correct I should be able to measure from the new X4 neutral to the electrical panel neutral and the reading should be 0. The reading was 0.

Next measurement to take is from new Hot conductor, X1, to L1 of the electrical panel. If the secondary polarity of the isolation transformer is correct, in phase, with the electrical panel L1, the difference of potential should be 0 or very close to it. The difference of potential was 1.8Vac unloaded. Good.

Is this really of any importance?? Probably not if all of the audio connected ic equipment is fed from the output of the xfmr. What if the transformer is only to feed the preamp, and the Amp is plugged directly into the wall recept. Notice I used L1, line one, for my test. The xfmr is fed from L1 and I would assume the power Amp would be connected to L1 from the electrical panel.
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What would the result if I had Bonded X1 to ground instead of X4 of the secondary of the transformer?
I did so,
X1 bonded to ground now the neutral, the grounded conductor.
X4 is now the Hot conductor. X4 measured to ground 124Vac, should be...

Measurement from X1, new neutral, to the line neutral, electrical panel, 0 Vac. Ok.
Measurement from X4, Hot, to electrical panel neutral 124Vac..ok
Measurement from X4, Hot, to L1 of the electrical panel, 248Vac....

Real power?? You bet! I connected a table lamp with the three way bulb set on 150 Watts across the Hot X4 and the panel neutral, it lite full brilliance. I wished I had a couple pigtail lamp sockets on hand, but no such luck. I took the plugs of two lamps and series two of the blades for the next test. With the two 150 watt bulbs in series and a couple of make shift pigtails I connected one end of the series two lamps to the hot X4 of the xfmr secondary, and the other to L1 of the electrical panel. They lit full brilliance.
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I tried to use the most direct way of explaining the test procedures.
I hope it came through that way. My attempt was to explain in layman terms best I could.
The actual test was preformed with two three wire cord and plug connected to the same electrical duplex outlet. The outlet is fed from L1 but the results would of been the same for L2, of the electrical panel. Primary of xfmr was connected from one cord and plug. Test measurements for the electrical panel reference taken from the three leads from the other cord and plug. Polarity, continuity, of both cords and plugs are the same.
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If we have learned from experience that audio equipment that is connected together by ICs should be connected to the same line. Then should not all isolatation transformers have their output polarity, phase relationships, in sync the same? Or at least as close as possible?

I would appreciate your comments Jon.
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>>"It can take just a bit of a load to read near correct voltages, and this is related to how much capacitive coupling there is between the primary and secondary, and how much capacitive imbalance there is between the various windings/taps. Very little capacitive coupling (which usually indicates a higher quality transformer, or one designed specificaly for a low amount of capacitive coupling) require very little loading to get nearly correct voltage readings."<<
>>>>>>>>>>>

Jon as I had stated earlier in a post I did connect the three way lamp set at 150W for a load on the xfmr. The only other heavier load I could think of was a 1200W cloths Iron. One hell of a transformer all I can say. Unloaded the output was 125V. With the Iron connected the voltage dropped to 100V With the secondary windings in series my 2kva xfmr was a 1kva. I quickly took my test readings from the two floating 120V secondary leads though the readings were a little lower when measured to the equipment ground one was high and the other was low. The readings matched the polarity orientation of the xfmr leads.
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Jim