Ground Fault Sensor Specs

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steve66

steve66

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Illinois
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Engineer
I understand that there are two types of ground fault sensors: One that measures the current on the N-G bonding jumper, and one that goes around all 4 wires (3 phases and neutral). What are the advantages or disadvantages of each type? Which would you specify?

Also, are there any other important items you would specify for a service with ground fault protection?

This is for a 480V, 3000 amp service for an industrial type facility. Mostly all motor loads.

Thanks in advance:
Steve
 
Very few 480V systems use a residual ground fault scheme (sensing the current on the N-G bond).

By far and away the most popular scheme is the zero sequence scheme (measuring current in all of the circuit conductors. Stand-alone units encircle all the conductors, while integral units (i.e. electronic breakers) use a separate CT for the neutral, but still "sum" the currents together internally to the device.
 
jim dungar said:
Very few 480V systems use a residual ground fault scheme (sensing the current on the N-G bond).

By far and away the most popular scheme is the zero sequence scheme (measuring current in all of the circuit conductors. Stand-alone units encircle all the conductors, while integral units (i.e. electronic breakers) use a separate CT for the neutral, but still "sum" the currents together internally to the device.
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Sensing on the neutral ground bond is ground return? I THOUGHT

Zero Sequence single sensor encompassing all phases and neutral.

Residual is 4 seperate sensors one on each phase and neutral? I THOUGHT

When busing permits Zero Sequence is the most common method, as noted this is a large Current Sensor commonly called a window CT based on the large size. CT secondary is usually 1000/1 in.


Other items

Single phase protection, Under Voltage, Blown Fuse trip, Reverse rotation, with some of these a capacitor trip device should be included for tripping.
 
brian john said:
When busing permits Zero Sequence is the most common method, as noted this is a large Current Sensor commonly called a window CT based on the large size. CT secondary is usually 1000/1 in.

That just got me thinking: with a 3000 amp service, I'm probably going to have 8-10 sets of wire, or about (40) 600 KCM wires.

Do they make window CT's that large?

Steve
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Click to expand...
 
Very cool. Thanks for the link Brian John.

10" x36": Still with 40 cables, the electricians that install this big stuff must feel like you are weaving a scarf with 600 KCM cable. My hat's off to you guys that wrestle this stuff.

It also looks like the split core is worth specifying.

Steve
 
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