Picture of safety and service earthing 2

[AusLee]

Hello,

I have put a picture for a small installation on the following address:

http://lndang2.tripod.com/

This picture shows that the neutral bar of the transformer is connected to earth bar, and separately, the neutral of the generator is connected to earth.

Only the earth of the transformer is passed on to the ATS.

The reason is: in case both earths (from the generator and from the transformer) are passed to the ATS, then suppose i am working on normal power from the transformer, in this case i will have electricity flowing into the generator through the unintterrupted earthing line, and consequentlyt putting its (dead) neutral point at the same voltage as the neutral of the transformer which can (?)electrify the generator?

When i run from the generator, the earthing of the neutral and the earthing of the earthing bar in the ATS are not the same.

Is the picture correct or does it have something dangerously wrong?

 

[davidbeach]

What's missing is that the ground system around the generator and the ground system around the transformer must be connected to each other.

 

[AusLee]

Thank you, but just one question: in this case the neutral of the generator will be permanently connected to the neutral of the transformer. This is before any circuit breakers are encountered in the circuit, then if someone is working on the generator, and something happens on the public network, an over voltage of some sort, would the local earth be still enough to keep the operator safe, even if he is working on an "offline" machine?

In case it is still ok and nothing happens to the operator, is the scheme in the picture litterally wrong (separate earths for each source) or it can work?

 

[davidbeach]

No, the neutral is switched at the ATS (it is isn't it - not entirely clear but if not switched there would only be one neutral bar with all three connections) and so the neutral is only connected to ground at the generator when the generator is supplying the load and is only grounded at the transformer when the utility is supplying the load.

If you don't connect the grounds, your service technician will be exposed to one "earth" on the generator frame and a different "earth" in the surrounding electrical system. Those different earth potentials could be enough to cause serious harm. That's why the NEC and other electrical codes require all ground systems to be bonded.

 

[waross]

In addition to Davidbeaches comments, Your generator seems to be grounded with a seperate grounding grid. When running on the generator any neutral current must pass through the ground grid. There are a lot of reasond why this is not a good idea.
There are at least two acceptable options.
1> Run ground cables from the generator to the ATS and/or the MDB. The neutrals should be switched. Only one connection should be used between ground and neutral at one time.
2> Move the connection between neutral and ground to the ATS or to the MDB. (Remove the neutral/ground jumper from the transformer.) With this scheme the neutrals do not have to be switched.

These recommendations are for a normal installation.
There may be exceptions for installations where very large distances separate the transformer, generator and ATS.
Danger from "Hot" neutrals is not usually present. There are exceptions, and incorrectly connected grounds may at times make an installation more dangerous rather than safer.
respectfully