just curious how this works. I have seen it with double ended substations (M-T-M) configurations, but I recently saw a one-line that had a double ended substation and another derived system connect to it (basically a back-fed brkr.) connected to a generator switchboard my question is how do they set up the ground fault when the one brkr is normally open but still n&grd. connected. I believe they would use the a/b contacts on the PCB's to enable / disable the trip units GFI function and orient the CT's the correct way to sum neutral currents?? I may be totally wrong just curious..
Ground Fault Multiple Derived Sources
- Thread starter Mike01
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zog
Senior Member
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- Charlotte, NC
Sparring design? Thats pretty common.
simmilar
simmilar
thanks no not a sparring design this will be a M-T-M double ended sub each end has a generator feeding a LVPCB that is in the normally open position but the generator is a SDS so how do you detect ground fault when you have a non energized SDS??
So would my general assumptions be correct??
simmilar
thanks no not a sparring design this will be a M-T-M double ended sub each end has a generator feeding a LVPCB that is in the normally open position but the generator is a SDS so how do you detect ground fault when you have a non energized SDS??
So would my general assumptions be correct??
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brian john
Senior Member
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- Retired after 52 years in the trade.
With a Main Tie Main it is common to use a ground return GFP with 3 separate CTs one for each source and one for the tie. There are aux contacts on each main switch/circuit breaker that control which CT operates and how they sense current depending on which main is feeding the load.
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It sounds like you have a Main-Tie-Main-Generator system.
A modified differential ground fault (MDGF) system uses a combination of breaker contacts and CT orientations (sometimes even multiple CT's) to properly account for the different fault current and normal neutral current paths.
If care is not given to the GF design, it is possible to have an overly sensitive GF which trips "early", an overly insensitive GF which does not trip when it should, or nusiance trip signals being sent to the devices which are turned off. All of these conditions can exist in the same M-T-M lineup.
A modified differential ground fault (MDGF) system uses a combination of breaker contacts and CT orientations (sometimes even multiple CT's) to properly account for the different fault current and normal neutral current paths.
If care is not given to the GF design, it is possible to have an overly sensitive GF which trips "early", an overly insensitive GF which does not trip when it should, or nusiance trip signals being sent to the devices which are turned off. All of these conditions can exist in the same M-T-M lineup.
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