voltage from ungrounded surfaces to ground

[jmoore56]

Have a 400 amp, 120/240 single phase service with (2) two hundred amp panels. Voltage from any surface connected to the concrete or earth is about 5 volts. When two large 240v heaters are turned on the voltage increases to about 110 volts. when one heater is turned off the voltage drops to about 85 volts. With no heaters and just 115 volt lights the voltage drops back to about 5 volts. Any ideas

 

[LarryFine]

When it's the "typical" open neutral, line-to-line loads should have no effect. Is it possible that your heaters have any line-to-neutral loads in them? For that matter, do the heaters heat properly? If so, that rules out a line problem.

My take is that you do indeed have a "typical" open neutral, and, while lhe line-to-line voltage should stay at 240v, the line-to-neutral voltage should be shifting. Measure the line-to-neutral voltages while using your heaters again.


Oh, and welcome to the forum. :smile:

 

[brian john]

Check the heater elements and current at the heater, place an amp clamp around the feeder and see if you read current on the cable when the unit is on.

If you have a shorted element you might have this situation, too early to think of other options.

I have seen this happen with resistive heaters.

 

[jghrist]

Is the EGC intact? Properly bonded to the heaters and to the panel ground?

 

[wirenut1980]

My guess is you have a fault on the heater circuit or the heater element itself is faulting to earth. As suggested, check to make sure EGC is intact from the heater all the way to the main and you have proper neutral to ground bond at the main. There could be improper neutral to ground bond causing neutral current flow on the ground which elevates the voltage with respect to reference ground. But the heater would have to have line to neutral loads.

 

[weressl]

Have a 400 amp, 120/240 single phase service with (2) two hundred amp panels. Voltage from any surface connected to the concrete or earth is about 5 volts. When two large 240v heaters are turned on the voltage increases to about 110 volts. when one heater is turned off the voltage drops to about 85 volts. With no heaters and just 115 volt lights the voltage drops back to about 5 volts. Any ideas

Hook up a 110V/45W lightbulb between the same points. If it lights up, you got ano open ground. If it doesn't its capacitive coupling. (for the heck of it measure the miliAmps through the unlit bulb.)