Analog Ground Fault Amp Meter

[Saturn_Europa]

Does anyone know how these analog Ground Fault Amp meters work? Its mounted right next to the 208/120v 3 phase step down transformer. I cant find much documentation online.

 

[hillbilly1]

Usually large CT(s) stepping down the amps to milliamps.

 

[winnie]

The meter itself is just used as an indicator. It takes a 0-1mA DC input (from _any_ source) and that moves the needle. The _scale_ happens to be very non-linear and say 'amperes ground fault'.

Somewhere else in the system there are the CTs that @hillbilly1 describes. This might be separate CTs on each circuit conductor, a CT around the ground-neutral bond, or a big CT surrounding all the circuit conductors. There will also be a device that takes the CT output and processes it to that 0-1mA DC signal.

Maybe call and get more info: https://www.branom.com/shop/category/electrical-756

-Jon

 

[jim dungar]

Usually large CT(s) stepping down the amps to milliamps.

The meter says its input is VDC, therefore there is some type of 'transducer' feeding it.
Most likely the transducer takes a CT (0-5AAC) input, although it may have some type of sensor input, like for a Rogowski coil, that actually measures the ground current.

 

[hillbilly1]

The meter says its input is VDC, therefore there is some type of 'transducer' feeding it.
Most likely the transducer takes a CT (0-5AAC) input, although it may have some type of sensor input, like for a Rogowski coil, that actually measures the ground current.

Maybe a rope ct with power supply? I think the CT’s on those are millivolt output, but probably could be configured as a dc output instead of data.

 

[synchro]

There might be a current sensor such as the following one that's sold by the same company Branom as on the meter pictured above. This sensor apparently has internal electronics to take the AC current from its CT and convert it to a 0-1.0mA DC current using an appropriate amount of nonlinear compression so that a wide range of currents can be easily viewed on an analog meter.

https://www.branom.com/shop/m-194-s...1623?page=2&category=868#attr=4894858,4635774

https://www.branom.com/web/content/product.datasheet/8253/product_datasheet/M-194 SP.pdf?download=1

And here's an analog meter from Branom similar to the one pictured above:

https://www.branom.com/shop/st70dc1...161894?category=869&search=0-1ma#attr=4608210