chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
Could someone explain the voltage irregularities common to ungrounded systems? Why does this occur?
Thanks
Thanks
Ungrounded system voltage
- Thread starter chris kennedy
- Start date
- Status
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
100129-2146 EST
Chris:
Consider something very simple. One isolated 120 V secondary. Also have this transformer have a Faraday shield between primary and secondary.
There is a small amount of capacitance between the grounded shield and the secondary. There is also leakage resistance from the secondary to the shield.
Next run a piece of Romex from the isolated secondary with three wires that is 100 ft long. Two of the wires are connected to the floating secondary. The other wire is connected to a source of 120 V relative to ground.
Turn off the power to the floating secondary. Now you have a voltage divider from the ground referenced 120 thru a parallel RC in series with another parallel RC of different values. The first parallel RC is from the cable capacitance and leakage resistance to the pair of wires to the isolated secondary. The secondary parallel RC is the secondary capacitance to the Faraday shield and its parallel leakage resistance. The component values will determine the voltage reading of the floating secondary relative to ground.
Turn on power to the floating secondary and the analysis is more complex. But the same basic idea.
.
Chris:
Consider something very simple. One isolated 120 V secondary. Also have this transformer have a Faraday shield between primary and secondary.
There is a small amount of capacitance between the grounded shield and the secondary. There is also leakage resistance from the secondary to the shield.
Next run a piece of Romex from the isolated secondary with three wires that is 100 ft long. Two of the wires are connected to the floating secondary. The other wire is connected to a source of 120 V relative to ground.
Turn off the power to the floating secondary. Now you have a voltage divider from the ground referenced 120 thru a parallel RC in series with another parallel RC of different values. The first parallel RC is from the cable capacitance and leakage resistance to the pair of wires to the isolated secondary. The secondary parallel RC is the secondary capacitance to the Faraday shield and its parallel leakage resistance. The component values will determine the voltage reading of the floating secondary relative to ground.
Turn on power to the floating secondary and the analysis is more complex. But the same basic idea.
.
- Status