ATS Replacement in Hospital

[cdcengineer]

We've been working with a local hospital to replace some existing ATS units in a 40 year old section of the hospital. These were originally installed as 3-pole switches as the Essential Electrical System was installed as non separately derived based on the grounding methods.

When the hospital completed an addition which more than doubled it's size two years ago, the designing engineer specified 4-pole switches for the new ATS and requested that the contractor alter the Essential Electrical System (ESS = Generator) grounding creating a separately derived system. I wondered at the time what that might do to the many existing 3-pole switches. I thought ground loops might be created where objectionable current might cause problems. No problems were noted by the staff.

Anyway, now that they are replacing some of the existing 3-pole switches with 4-pole, I wondered why code would not require that all the 3-pole ATS be replaced when the grounding of the ESS?

Does anyone have any personal experience with situations such as these? Any input is greatly appreciated.

 

[templdl]

Yes, this can be an issue that is often overlooked.
This has been my experience when addressing both ATS as well a ground fault applications:

I depends upon how the nuetral and grounding conductors are configured. To understand what you have you may have to ring it out to find out where the neutral is grounded.
You may not need to use a 4p ATS if the neutral and ground are not tied together at the generator. If they are and the generator becomes the point at which the neutral and ground are tied together then you would have to have a 4p ATS to disconnect the neutral from the normal source where it had been grounded to the ground at the generator.
I have found that when I've spoke with technition who are trying to locate and solve grounding issues in older hospitals that it is not unusual to find the neutral grounded at more than one locations becaouse of their age and additions that they have gone through. This was more of a problem 30 years ago though and those issues may have been addressed and resolved nd are probably less likely to be a problem. But never the less it suold be confirmed that grounding meet the current NEC requirements.

 

[cdcengineer]

Thanks for the post. I head to the site today, so we'll see what we find out after some investigation.