Isolation transformer

I am not there today. I did double check the wire connects on the primary side. The only un used wires are the wires for a 240 connection on the primary side. These are 2 brand new transformers from Larson in which they sent a video of them testing voltage from hot to neutral getting 230 volt. Which I do have was just concerned about the 120 to ground but it could be my meter.

Also I used a fused disconnect in the first place for ground fault protection when the neutral was grounded. Now I landed both hot and neutral on the single phase terminals of the disconnect and fused them. I understand if there is a fault to ground on one of these legs. It should not cause a shock hazard. But if both shorted together, it would blow the fuses. I have no details on the filters as they are also European. I am waiting to hear how the clients testing goes. If all goes well today, I’d assume I treated this transformer as an isolation. And my meter was reading phantom voltage. I left the grounding electrode unhooked. If they do have problems, I am going to bring up the situation with current on the electrode.
 
If you connected N to ground and bonded them to the disconnect, there should be zero volts from N to ground, they are connected together. Also, there shouldn't be a fuse in N.
 
I did have zero volts to ground when I had them bonded and I also had them on a neutral block together and bonded. But when I measured current on the GEC I then un bonded everything and treated it as an isolation transformer. The client then tested his equipment and it worked. I then put the neutral that’s un bonded on the other pole of the disconnect and fused it. If it doesn’t have to be fused I can return and wire nut it through. I just want it to be safe. I also don’t know who has wired up the stuff inside the chamber but it seems like this is where and why I’m receiving current on the GEC. Anytime I turn on a single pole 20 amp plug that is filtered through the filters I’m receiving some short of current on the GEC. If their tests go good today and equipment works with the neutral not bonded I’m going to leave it how it is.

It just confused me I was getting 120 on both hot and neutral to ground when it is an isolation transformer. I appreciate everyone’s help.
 
If you have actually bonded the transformer "N" terminal to ground you should measure a nominal 240V regardless of the meter impedance.

Bonding the transformer does not change if from being an isolation transformer, it makes it an ungrounded transformer. Measuring voltage to ground on an ungrounded transformer will show varying voltages when using a high impedance meter.
 
Cursitti said:
So I should be fine with it ungrounded? And yes I’m probably getting false readings from meter
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I suspect either that the RF filtering will be poorer without the transformer grounding, _or_ the RF filter itself provides grounding and the combination of two ground points created your 3.5A current flow on the GEC.
 
The RF filter has a ground lug for the line and load. And it also has a lug to ground the outside case along with the RF cabinet having a lug. And yes I’ve been thinking since the other contractor connect to the ground bar for these ground points and I connected my electrode to it before hand I am now getting that current from the filters as well. The client has not told me yet about their tests. Grounding the neutral on the secondary should get rid of noise but I have no idea until they tell me. I suspect even if everything goes well they wont tell me and the system will just continue to be ungrounded.
 
Cursitti said:
So I should be fine with it ungrounded? And yes I’m probably getting false readings from meter
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I think it should be grounded. It is not unusual for equipment manufacturers to have some internal power line/surge filters connected to ground.

The NEC requires ground detection schemes on ungrounded systems.
 
So what do I do about the the current on the GEC if the filters are possible also contributing to this?
 
Cursitti said:
Grounding the neutral on the secondary should get rid of noise but I have no idea until they tell me. I suspect even if everything goes well they wont tell me and the system will just continue to be ungrounded.
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Code issues aside in the OP you stayed that you needed a neutral so how can you use an ungrounded system?

Cursitti said:
So what do I do about the the current on the GEC if the filters are possible also contributing to this?
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I don't see how that has anything to do with current on the GEC. If you have a 2-wire secondary with one side grounded what path is the GEC providing for current return?
 
They say I need neutral but their equipment works but they stated that was for the filter.

There is current on the wire even without the transformers on. Like I said when i turn the single phase filters on ill get about .34 amps on the GEC.
 
Cursitti said:
They say I need neutral but their equipment works but they stated that was for the filter.

There is current on the wire even without the transformers on. Like I said when i turn the single phase filters on ill get about .34 amps on the GEC.
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Is it possible that you really mean EGC not GEC?
 
jim dungar said:
You have a 2 wire transformer output, so you technically do not have a neutral at all. However your transformer wiring diagram calls one terminal "N".
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Correct, by definition it would not be a neutral but electrically it wouldn't change anything.
 
infinity said:
Correct, by definition it would not be a neutral but electrically it wouldn't change anything.
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Yep. But some people think there is something special about having or not having a neutral which is probably why the transformer chose that designation rather than the more traditional X1 and X2.
 
Yes i told the client this tech wasn’t a neutral and he said basically whatever gives them 230 to their equipment he’s cool with lucky when i grounded it i found there’s was current. I did tell him though i would like to come back and find out why there is current on the grounding electrode. My guess is because they have all the chamber grounds and filter grounds tied to the bus bar I’m tied to. Something can’t be wired right within the chamber or the filters might be causing this issue. When i turn off all power to the 120 volt loads the current disappears on the grounds they also ran.
 
Yes i told the client this tech wasn’t a neutral and he said basically whatever gives them 230 to their equipment he’s cool with lucky when i grounded it i found there’s was current. I did tell him though i would like to come back and find out why there is current on the grounding electrode. My guess is because they have all the chamber grounds and filter grounds tied to the bus bar I’m tied to. Something can’t be wired right within the chamber or the filters might be causing this issue. When i turn off all power to the 120 volt loads the current disappears on the grounds they also ran.
 
The manufacturers description of the transformer is a little off from the diagram and seems odd to me;
the MT-ISX-FP-1P-208V-5KVA-220V.EU-N3R-50HZ isolation transformer is a single phase unit with a primary voltage of 100 V Split Phase. It also provides a secondary voltage of European 230 V single phase. This transformer takes 100 V split phase (two 104 V legs, L+L+N) and converts it to 230 V single phase (L+N). This L+N model is considered European 230 V.
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'L+L+N' to me suggests a 3 wire primary side. and the 'L' + 'N' on the secondary suggest that N is already bonded to the case. If not I would think it would have X1 and X2.
Based on the diagram (assuming its correct) I would think it should say something like "the MT-ISX-FP-1P-208V-5KVA-220V.EU-N3R-50HZ isolation transformer is a single phase unit with a primary voltage of 208 V Single Phase. It also provides a secondary voltage of grounded 230 V single phase where N is bonded to the case.."
 
@Cursitti I think you are on the right track with this. You have a system that is 'working' but you have a measurement that seems off, and you want to get to the bottom of it.

The system is probably designed for European 230V, where the grounded conductor is actually the neutral of a 400/230V wye system. So calling the grounded N conductor 'neutral' conveys the essence of what is going on even if it is technically not a neutral.

About the several amps of current going to 'ground', it isn't clear to me if you have this current going to a ground electrode, or circulating between 'ground' points on different pieces of equipment. You are probably going to have to map out all of the 'ground' wires (egc, gec, signal ground, RF ground... doesn't really matter what they are called, if they are supposed to be at ground potential and are connected together), and then measure the current on each of these to get a picture of what the source of this current is.

-Jonathan
 
winnie said:
@Cursitti I think you are on the right track with this. You have a system that is 'working' but you have a measurement that seems off, and you want to get to the bottom of it.

The system is probably designed for European 230V, where the grounded conductor is actually the neutral of a 400/230V wye system. So calling the grounded N conductor 'neutral' conveys the essence of what is going on even if it is technically not a neutral.

About the several amps of current going to 'ground', it isn't clear to me if you have this current going to a ground electrode, or circulating between 'ground' points on different pieces of equipment. You are probably going to have to map out all of the 'ground' wires (egc, gec, signal ground, RF ground... doesn't really matter what they are called, if they are supposed to be at ground potential and are connected together), and then measure the current on each of these to get a picture of what the source of this current is.

-Jonathan
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I’m just waiting on a reply back from client i expressed my concerns but if they want to leave the transformer ungrounded it’s out of my hands. As far as if they wanted it to be grounded i told them i will need time to troubleshoot where this current is coming from. I appreciate your input. I just wanted to make sure I was on the right track because sometimes I second-guess myself on stupid things.
 
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