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PostPosted: May 2nd, 2020, 3:23 pm 
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Joined: January 15th, 2015, 7:19 am
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Location: Baltimore MD
I bought this iso tranny on web last year and I needed to change out the outlets for better quality ones, plus I added a filter.
what I am curious about that when testing with one of those plugin mains testers it shows and open ground.
you can see in the picture that all grounds are connected and I verified with a meter that there is continuity.
also, I get a voltage reading between neutral and ground on the outlet socket of 60 or so volts.
I am reasonably certain it's wired correctly but I must have made an error somewhere
Attachment:
iso1_WEB.jpg
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Attachment:
iso2_web.jpg
iso2_web.jpg [ 31.57 KiB | Viewed 1775 times ]

Attachment:
iso3_web.jpg
iso3_web.jpg [ 41.96 KiB | Viewed 1775 times ]


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PostPosted: May 2nd, 2020, 3:24 pm 
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Location: Baltimore MD
here is the schematic of the tranny
Attachment:
isoxformer_web.jpg
isoxformer_web.jpg [ 24.67 KiB | Viewed 1773 times ]


you can see that I wired brown and orange to neutral and red and yellow to hot
the filter is my version of a felix...... just x1 caps across mains and a common mode inductor in series then another set of x1 caps
this is another one but essentially the same
https://www.audionervosa.com/index.php?topic=6727.0

any help would be greatly appreciated


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PostPosted: May 2nd, 2020, 3:37 pm 
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Did you make sure you have the right orange and yellow?

Roscoe

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PostPosted: May 2nd, 2020, 3:57 pm 
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Paul, a meter will lie to you in a situation like this. Between conductors with no electrical connection, a random voltage will be read on a high impedance meter due to capacitive and inductive effects between the conductors. You need to add a load across the terminals, then measure voltage. When in doubt, two pigtail lamp sockets in series with 100 watt or so bulbs works well for up to 240 volts. Since you measured 60 volts, a single socket with a high wattage lamp will work. Measure across the lamp while in operation. You'll probably get a zero volts reading if the two leads are not connected to the same winding, or if a winding is open.


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PostPosted: May 2nd, 2020, 3:59 pm 
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there are two groups of cables coming out of the tranny one group has additional black insulation the other does not
I assumed (I know I can get into trouble here) that they were grouped by primary and secondary
I cant imagine it would work it this was not the case


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PostPosted: May 2nd, 2020, 4:02 pm 
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Sorry first do the test above with a lamp, then , if the lamp does light, check that the primaries are in parallel. If you apply 240 volts to thg he 120 windings and they are in series, each secondary will only produce 60 volts.

But probably, the ground is not connected to the secondary center tap, probably floating.


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PostPosted: May 2nd, 2020, 4:11 pm 
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thanks
I wired according to the schematic
two primaries in parallel for 117VAC in
I will do the lamp test later.
there is a ground wire coming out of the tranny and it is grounded with everything else. Maybe I should remove that ground


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PostPosted: May 2nd, 2020, 4:34 pm 
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My guess is that the ground coming out of the transformer is connected to a static shield and not connected to any of the windings. Also, to positively identify the windings disconnect all leads and use an ohmmeter to identify which leads are for which windings. The leads going to a particular winding should show low DC resistance. If you connect to one lead from each of different windings the ohmmeter should essentially show an open circuit.

A reason why the plug tester may show a bad ground is that most of the simple testers check the ground by assuming it is tied to neutral at the load center and the tester passes a small current from the hot to the ground and therefore to the utility neutral which lights up the indicator. Since you have floating secondaries there is no way for the hot current to get back to the box. For that to work you would have to tie your floating neutrals to the ground in the box. If you have the normal ground tied to the box which you should have for safety you will then have broken the isolation you are looking for. BTW in your scenario, with floating windings with no neutral to ground connection, the ground does no good against secondary faults but will still protect you against a fault from the primary to your body. If you had a fault that connected your body to both sides of the floating winding you would be in big trouble. But then again, if you got across a hot and neutral of a normal circuit you would also be in trouble. In that case a GFI would not help because the current in the hot and neutral lines would balance. A GFI protects you against a hot to ground path, not a hot to neutral path which is very unlikely.


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PostPosted: May 2nd, 2020, 4:43 pm 
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Pelliott321 wrote:
here is the schematic of the tranny
Attachment:
isoxformer_web.jpg


you can see that I wired brown and orange to neutral and red and yellow to hot
the filter is my version of a felix...... just x1 caps across mains and a common mode inductor in series then another set of x1 caps
this is another one but essentially the same
https://www.audionervosa.com/index.php?topic=6727.0

any help would be greatly appreciated


It is an isolation transformer so you are isolated from the building ground hence the reading. My guess.

Otherwise, schematically, the drawing shows separate windings, but it just might be one secondary winding with multiple taps so you could possibly get 60-vac readings between the "neutral" and hot.

It's not really a neutral like in a panel-board but the circuit return.

Stu? Can you step in? You might have experience with this issue from your work experience.

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PostPosted: May 2nd, 2020, 7:25 pm 
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Joined: January 15th, 2015, 7:19 am
Posts: 1226
Location: Baltimore MD
the ground is not isolated all grounds on all sockets are grounded to the chassis
there is a green/yellow wire coming from the tranny that is not shown on the schematic. I assumed that it should be grounded also


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