Grounding SDS back to substation

[__dan]

According to the electrical engineer on this job, he's stating that NOT using a bonding jumper at the transformer, and instead doing it at each switchgear connected to the transformer secondary makes each switchgear it's own separately derived system. He claims that's the way it should be...

He is also claiming that it's not abnormal to see current going over the ground. Either (a) in a non-linear scenario like ours where we're using a lot of phase to neutral current and (b) even in a 3-phase 480v roof fan he claims we will see leakage to the ground. I have conflicting opinions on this from multiple electricians lol

There's quite a bit lost in translation there, what he said coming through an intermediary.

Having been in this situation one of the first thing I would do is look up his name with the State to see if he has a license. You may have to repeat the search going up the food chain at the outside Engineering firm to see who has a license and who does not.

It becomes a liability issue. Generally engineering firms do not send a guy with a license to a job and the ones they do send who you may be talking to, look them up to see if they have licenses. Some work is regulated by statute and who is an Engineer is a statutory definition. Applies variously. hardware board or programming design, no. Work inside the building footprint, maybe yes or no by jurisdiction. Changes to the building footprint above a certain sf limit, yes usually also by jurisdiction.

That's my first guess. The guy you reference as having spoken to is probably not the guy with the license, and may have no license at all. That's when liability would fall on the next nearby guy who does have a license.

"Separately Derived" applies to the system as a whole, through the wire and busbar connections of what is connected to it.

So you are able to fully disconnect transformer 1 from its loads and "connect" 1's loads to transformer 2, assuming you have only done the three hot wires.

If the neutrals of system 1 and 2 were left as solidly connected, you have two "Separately Derived" (grounded separately derived) systems, connected together, with two N to G bonds when there should be only one N to G bond.

I believe I detected two blowoff type answers in your last post when one is my limit (the shared neutral load current on the parallel grounding path is "objectionable"). I would check the guy who said that to see if he has a license, usually they do not. If that is the case the liability would fall on you if you are the first guy in line with a license.

This scenario is very predictable and it is predictable trouble.

 

[tortuga]

Post photos of the GE switchgear namplates and the transformer(s).
One issue I have run into moving the N-G bond is some older gear has a "for use only as service equipment" restriction.

 

[__dan]

Another thought.

Scenario so far as understood. You have moved transformer 1's loads to transformer 2 because of trouble running transformer 1. Apparently this was not provided for in the original design, usually by an interlocked tie breaker or ATS.

Possibly the 1's three hot wires were disconnected but 1's neutral and system bonding jumper were not, and left solidly connected, creating (one) SDS with two or more N to G bonds.

If you want to mitigate by going to an SDS with one N to G bond, I am thinking you would not lift or remove 1's system bonding jumper. Leave that there, the next guy will have no idea what you have done.

You would want to disconnect 1's neutral at the same point where 1's three hot wires are disconnected. I am guessing you have 1's 3 pole breaker just turned off and locked. I'm thinking, the easiest possible thing to do, is lift the supply neutral from 1 at the same location.

This by itself no one would guess to look for or check, making that alone a problem. There would have to be signage and documentation.

You can verify the effectiveness of the change by Amp clamping 1's system bonding jumper, both before and after, the opening of 1's neutral connection to the other (2's) SDS. All the split paralleled neutral current should go away from 1's system bonding jumper, but likely there will be some remaining non zero noise current which itself could be large.

I would not touch it without having an approved engineering change for the work. It's a huge problem the next guy would never guess 1's neutral was lifted at the same point the breaker was opened and locked off. A 4 pole ATS might do that for him but he would have no idea how it works.

Then of course they will blame every past and future problem on that change and not their own stuff. Have them tell you what to do, but know who has the license for it and who knows what they're doing.