Hi, and welcome to ECN.
I can't speak for Russia, but in Europe in general there are different neutral/grounding arrangements for utility supplies. Briefly:
(1) TN-C-S, the closest there is to the American system, with a neutral-ground bond at every service entrance and thus multiple grounds on the neutral where one xfmr supplies several premises. (Also known as PME -- Protective Multiple Earthing -- in the UK, and equivalent to the Australian MEN system.)
(2) TN-S. Neutral is grounded
only at the xfmr, and a separate protective grounding conductor runs back to that point. No neutral-ground bonds are used at the service panel or anywhere else. Still found in the old parts of many British towns, but I don't think it's that common elsewhere.
(3) TT. Supply neutral is grounded, but the EGC/grounding system of the building is not bonded to the neutral at all. It is connected to a local ground rod only.
You might like to look at
these diagrams in the reference area to see the arrangement of the different systems. They're drawn from a British perspective, but the basic principles apply to European as well.
When it comes to a control xfmr, you have what in NEC terms would be described as a separately derived system. Is this part of the HVAC panel itself, or a stand-alone unit which then uses building wiring to distribute the 220V power? That could affect any code requirements in different countries (e.g. the latter might come under the code whereas as integral xfmr would be part of the equipment rather than the building wiring and thus not covered).
Certainly if installing a xfmr as a stand-alone unit here to step-down from 415V to 220-240V it would be normal to bond one side of the secondary to ground.
[This message has been edited by pauluk (edited 04-20-2004).]
