Isolation ground

[a10jp]

In one of our facilities, we are serving the IM server room via an isolation transformer, which according to the are supplied with a separate ground, different from the distribution panel.

Is this called an isolated ground, where it is a separate ground path fed directly from the substation grounding?

Similarly, on both the standby power panel and the distribution panel, the TVSS are also to be connected to the common substation ground, which would satisfy the code of a bonded system for this facility. I confirmed with the designer, and he stated that this separate ground are to be fed from the substation ground, which confirm my understanding where the ground should be connected to.

However in Japan, grounding system are very different. Everything has a separate ground, meaning each a separate path to the ground via a ground electrode.

Had a discussion on this subject with a Japanese engineer, and he explained that the best method to comply with the code is for each of these separate system with separate grounding to be bonded at a common ground terminal. Sort of like you ground every individual system to a common ground terminal (the substation ground). Does it sound correct?

The contractor stated that the TVSS should NOT be connected to the substation ground, since it is a surge path, and it should be kept separate fromm the normal system ground. He stated the same thing for the isolation transformer for the IM room, which he said should have independent grounding, and not to the bldg substation.

I do not believe this satisfy the code, doesn't that make the bldg have different ground potential, at the normal substatsion ground, isolation transformer, TVSS?

 

[rbulsara]

Not familiar with japan, but your understanting is correct and the japanese is wrong, even by long stretch imagination of twisting engineering principles. I doubt japansese codes are that bad. I suggest you look up the official versions of japanese code by yourself and seek a professional opinion from some one expreienced in japan.

 

[a10jp]

One additional question I have concerns the location of where bonding take place. From the substation (which is close by the facility), which has its own grounding, do we only carry the neutral (which is grounded) to the main service panel, at that point the building will connect to its own ground, and the incoming neutral from the substation will be connected to the service panel at the neutral or grounded terminal?

FOr in door dry-type transformer, does the chasis grounded (which is only for the casing) get bonded to the system ground too?

 

[fsmyth]

NEC's Article 250 goes into a bit of (cloudy, as
usual) depth on this. It depends on whether any
one (or more) of the systems is(are) considered
"separately derived", it seems. It does show an
example of a system with all grounds brought back
to a common point.
There have been great and mighty discussions and
treatises on the same subject in regards to noise
suppression and/or isolation. Google is your friend.
<als>

 

[a10jp]

I have attached a diagram below of what I intended to accomplish. Scenario 1 is what I want to do as I believe it complies with NEC for system bonding. However, since the bldg does not have a good and well-defined ground grid, it makes things difficult as everything must comes out of the substation.

A little info on the substation. Besides the 208V transformer, it also has a 400V, 400KVA and a 210V, 150KVA as well.

The distance between the substation is about 100M. I am worried the local ground rods will create a virutally independent ground from the substation.

The local Japanese facility engineer opposed to connect the TVSS to substation ground. Instead he wants to have completed isolated ground(ground rods) without connection to substation, so the surge path can be isolated.

Any opinion?

http://us.f1.yahoofs.com/bc/6806c083/bc/My+Documents/Grounding+Sketch-revised.pdf?bf13ZTDBWVh_DAhm

 

[a10jp]

http://us.f1.yahoofs.com/bc/6806c083/bc/Share/Grounding+Sketch-revised.pdf?bflVbTDB97ExDAhm

Let's try this link.