unacceptable voltages

[waltermitty]

we installed a 480VOLTS 3 phase 5HP pump. The pump has a 2 wire high temp sensor in series with the overload heaters in the starter which is 830 feet away from the pump. With the pump not running we recorded a voltage of 625 volts from the temp sensor to ground ! Can anyone explain what is going on?

 

[buddhakii]

What are the voltages at the source?

 

[jim dungar]

we installed a 480VOLTS 3 phase 5HP pump. The pump has a 2 wire high temp sensor in series with the overload heaters in the starter which is 830 feet away from the pump. With the pump not running we recorded a voltage of 625 volts from the temp sensor to ground ! Can anyone explain what is going on?

If the circuit you are measuring is not bonded to ground, it is possible that you are reading a capacitive coupling or phantom voltage.

 

[dbuckley]

It could be real; voltage drop across a primary neutral, to local ground rod 830 feet from where the supply neutral point comes from.

To eliminate this you could temporarily run 830 foot of extension cords from where the starter is to have a remote ground and measure the voltage there from ground to ground and from both grounds to the sensors. Just be careful; if its real, a ground to ground shock of that magnitude will at the very least hurt.

Edited to add - if it is real then you need to make sure the wire is rated for the appropriate voltage and I'd advise a warning sign.

 

[hurk27]

In a ungrounded delta I have seen stray voltages like this, without ground fault monitoring system which tend to keep the stray voltages down its possible to pick up stray voltages off the primary's. you see this in older plants.