Why do I read voltage here?

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brother

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This is an ungrounded system, transformer. 480 to 120/208. the secondary is not grounded (x2) I used a digital meter and got 150volts from one conductor to ground. the other side i actually got 101 volts dc!! No there is nothing wrong with my meter.

On another ungrounded system I got 60 volts to ground, and the other conductor gave me 58 volts to ground. The system is a little newer than the previous one. so why do i get these readings here on a digital. On a solenoid meter (wiggy) I get nothing of course.
 
Capacitive coupling. No ungrounded ac system is truely ungrounded. I had one of my shipmates in the navy die when he contacted a 480v ungrounded delta system when his screwdriver slipped off an adjusting screw for a pressure control relay while he was standing in a steel deck.
 
If you don't attach a wire from a power system to planet Earth, then the voltage between any of the system's various wires to planet Earth can, well, "Float like a butterfly, and sting like a bee." :)
 
brother said:
so why do i get these readings here on a digital. On a solenoid meter (wiggy) I get nothing of course.
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That happens so we can say "That's why I use a wiggy unless I need to know the specific voltage, and then it needs a load to be reliable."
 
iwire said:
I agree, but why are these Wye systems ungrounded???
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This is a hospital, where they they have isolation systems. I was done with a job at a house now doing work at a hospital. Noticed that some of the older systems (probably installed back in late 60's) and there was a concern about the system losing its intergrity. the newer systems had less of capacitance coupling it seem than the older ones.

I think one of the older ones need to be replaced because the voltage to ground (even though its ungrounded system) seem a bit high even compared to the other older systems. Either that or something has gotten grouned somewhere. All the equipment was unplugged.

What do think?? Whats the life exspentancy of isolation/ungrounded systems in operating rooms?? if these systems are over 42 years old should it be replaced??
 
Well your meter has a high impedance makes voltage readings by tiny currents in your wiring due to inductive coupling or capacitive coupling as stated .

You will see voltage on dc setting on ac wiring but its not correct and odd voltage will be found .

But capacitive is less and inductive is more so on that transformer voltage not grounded a wiggy does not measure because its a low resistance meter just a coil meter no current no voltage .

Induced voltage is the same as capacitance coupling in this case without a ground on that transformer not grounded.

Meaning the wiring connected and the taps and connections change voltage on each phase to earth ground by the resistance of each the capacitance of each and the placement of wiring in conduits running out off the secondary with no load . Its the load of wiring the load of the coils and the load of insulation on your conductors .


Wiring is a capacitor between neutral and a hot with no load connected!

Its also between earth and hot ! Your meter is the lite bulb its a load but inductive is total different then capacitance coupling!
 
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Brother, since these transformers are serving OR's there should be an alarm (today it would be a LIM) somewhere in the space, this was done even 40 years ago. In the newer systems your readings of 60 and 58 is normal with a high impedance meter due to the fact that the LIM has already created a high impedance fault to ground.

I am wondering if the reason you're seeing a DC voltage is that you might be seeing one side of some component in an alarm.

Roger
 
TOOL_5150 said:
What is the difference between induced voltage and Capacitive coupling?
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Well, the reactance of inductance rises with an increase in frequancy, while the reactance of capacitance drops with an increase in frequency.

Inductors tend to pass steady voltage and resist changes in current, while capacitors tend to block steady voltage and pass changes in current.

Inductive coupling is an electromagnetic coupling between conductors, while capacitance is an electrostatic charge between conductors.
 
LarryFine said:
Well, the reactance of inductance rises with an increase in frequancy, while the reactance of capacitance drops with an increase in frequency.

Inductors tend to pass steady voltage and resist changes in current, while capacitors tend to block steady voltage and pass changes in current.

Inductive coupling is an electromagnetic coupling between conductors, while capacitance is an electrostatic charge between conductors.
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I had to read that twice, but now I see the difference. Thanks Larry.

~Matt
 
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