GFI relay in ATS

[chris kennedy]

I just got home from a trouble call about partial power at a health care facility I finaled a few months ago. 3 phase 480 ATS MTS. Both MDP and MTS have 1000 GFI amp mains. Short time delay is set at .1 sec. as per my PE. I found B phase jack from POCO dropped about 6:30 pm tonight. The ATS showed a ground fault happened at 10:48 AM. This tripped the GFI relay in the ATS which also is set at .1 sec. GF pickup on breakers is set at .1s 30. So there was no transfer. The relay was factory preset(Lakeshore). I will contact my PE tomorrow. Any input?

 

[wirenut1980]

I don't know enough about this to give a defintive answer, but I would start by looking at whether the transfer switch switches the neutral, and how the grounding is set up between the generator, transfer switch, and main service. There is a good article on the EC&M website about this type of situation resulting from incorrect grounding and bonding.

 

[hbendillo]

You're throwing way to may abbreviations around for me. Does MTS stand for manual transfer switch and POCO the power company? Anyway, isn't there an exception in the code for installing ground fault protection on a critical and life safety branch feeder? Not sure about equipment branch. If so I would disable the GF and just have it alarm instead of trip the breaker.

Are you saying the facility lost B phase at 6:30 PM?

 

[chris kennedy]

You're throwing way to may abbreviations around for me. Does MTS stand for manual transfer switch and POCO the power company? Anyway, isn't there an exception in the code for installing ground fault protection on a critical and life safety branch feeder? Not sure about equipment branch. If so I would disable the GF and just have it alarm instead of trip the breaker.

Are you saying the facility lost B phase at 6:30 PM?

Yes to all this except critical care. This facility is dental, blood test free scripts baby formula ect. I,ll be right back.

 

[chris kennedy]

Sorry bout that. Here is a very interesting quote from the 2005 Handbook. This is commentary following 230.95.

An alternative to installing ground-fault protection may be to provide multiple disconnects rated less than 1000 amperes.

Now read 90.1(C). Mabey just design suggestions?

 

[hbendillo]

Looking back at your original post I have a question. Does this facility have two transfer switches, one manual and one automatic, or just one manual transfer switch?

So we have a transfer switch which obviously has two feeders, one normal and one emergency, both rated 1000 amps and protected by 1000-amp GF protected circuit breakers right? The transfer switch also has a circuit breaker which is on the load side and also has GF protection? The circuit breaker in the ATS is the only one that tripped?

 

[brian john]

It is not the factories responsibility to set the GFP, this is or should be part of a coordination study. I cannot imagine a hospital project with adjustable trips and no coordination study.

Check with the design engineer, to see's who was suppose to supply this imporatnt document.

 

[steve66]

If you have ground fault protection on an health care main, I think you also need another level of ground fault protection (or maybe that is for hospitals only, I can't remember.) It's in Article 517.

At any rate, the transfer switch should have switched apon loss of the B phase. I'm not sure why you would have ground fault protection in the transfer switch??

Are you sure a breaker on the load side of the transfer switch didn't trip?

 

[brian john]

Is this ATS/MTS actually an isolation bypass ATS, an ATS with a manual bypass for service and or emergency manual operation? Or are these parallel switches that feed common load with one in a normally open position?

The key is how theses two systems are tied, location of CT's, interlocks.

Several issues play into this, as noted are multi-level GFP systems installed with zone selective operation? (the GFP closest to the fault opens as well as sending a restraint to upstream devices) or are they trying to avoid cascading of CBs with a ground fault by coordination?

You gave the time settings what are the current values of the involved devices?