Ground Fault Detection (Option 1 vs Option 2)

[EricElec]

So I have a situation where I need to replace an existing 200A fused disconnect with a CB that can also detect ground faults, the 2 options I see are:

1. CB with a shunt coil connect to a ground fault detection relay connected to a Window CT

2. Install a CB with a Electronic trip Unit (LSIG) and set the parameters necessary for ground fault detection

I am thinking option 2 is better in the sense that the CTs are enclosed inside the MCCB? An external CT with a GF Relay would be more expensive to install/supply in my mind.

 

[jraef]

The window CT option was the only viable choice up until relatively recently. But it still is better if you ALREADY have a CB and need to upgrade it to having GFP, or you cannot "trust" your technicians with an adjustable trip circuit breaker. Since you are retrofitting an older FDS, I would recommend doing it with the electronic trip CB with GFP if you can. Much simpler.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[davidbeach]

Solidly grounded system or an impedance grounded system? If impedance grounded you may find better sensitivity with the separate CT. Otherwise I'd go with the breaker to have a system with fewer components and therefore fewer things to go wrong or stop working properly.

 

[rcw retired EE]

If there are any phase-neutral loads, a neutral CT that matches the breaker is needed. Verify that the neutral is only bonded to ground upstream of the neutral CT. Also the CT must be installed with its polarity in the correct direction per the breaker installation instructions.