General Box Wiring questions (older box, berlin)

[stew2]

Hi
(Photos) http://www.flickr.com/gp/14322092@N06/8Tsw01

me and my wife and kid moved into a [new] flat in berlin. our last flat had single-phase wiring, and old ceramic fuses. In the last flat, I successfully replaced all the old ceramic fuses in the old flat with proper MCB's and RCBO/RCCB/RCD's, with some help from an electrician in the ROI.

Our new flat has the typical (for berlin semi-renovated) old fuse-box; the twists are it has three-phase wiring coming in from the meter. The ROI electrician is not very familiar with 3-phase. There is an 18kw 3-phase continuous hot water heater for the kitchen sink and bathtub. The feed for the hot water goes out from the electrical box, directly above the second set of main fuses. (see photos)

Some of the single-phase wiring is current (modern, three-wire), some of the wiring is the original copper [two-wire, no earth]. It's a mixed bag.

My question are:
In the 3-phase portion: why are there two fuses for each phase? Is it some kind of safety thing? (refer to photo)

Since the three phase wiring feeds a hot water heater, should[n't] this ideally be covered by an RCD instead of fuses?

I have a 4-pole RCD, for the three phases and the neutral. This can simply replace the massive room these two pairs of three fuses are taking up in the box?

I've looked up the specs for a similar 3-phase 230v 18kw heater. Each phase is supposed to be covered by a 50amp fuse, but what is the rating of the RCD supposed to be?

Single phase: I want the I've installed on the porch to be covered by an RCD - and the outlets in the bathroom and the light. And the outlets in the kitchen too. Where is the best place(s) to put in the RCD's? There's more room in the existing main electrical box if I can replace the bottom two rows of fuses with a single RCD.

Regards.

 

[fluffy2560]

I've got something similar here in Austria. In our case, the 2nd set of fuses are in a box at the front of the house, not inside. This is a safety provision so that the Feuerwehr (fire brigade) can come and switch off the power in the event of something nasty happening. I suppose in your case, the 2nd set of fuses are to allow one to work "somewhat safely" with the house wiring and make a distinction between the power company's "side" and your "side". I would have thought a 3-phase isolator would have been nicer than their fuses - then you'd know it was off. Fiddling about with electricity is always dangerous and their proximity to each other means taking extra extra care to not accidentally touch any of the phases.

Regarding the RCD, in my house, each phase goes into one of the switched poles and the neutral goes into the neutral. Then you've got on the other side of the RCD connections to each phase for whatever you want. If you want 3-phase for your water heater, you can have "3 x MCBs " linked in/wired in parallel (one per phase) going off to the water heater as L1, L2 and L3 (see also my post on my cooker L1, L2, L3 in the same forum). With the rest of the power for the house, you can use each phase individually taking into account a level of diversity per set of MCBs per phase. I think this is quite odd but it seems to work and once you understand it, it's pretty easy stuff. With each phase you can treat it as basically as normal electricity and follow the normal "rules" - e.g neutral, earth etc.

One needs to make sure there is no possibility for phases to come into proximity with each other - e.g. sockets in the same room on different phases. Keep as much physical distance as possible. In my house, we've got one MCB per room. Essentially each room is on a different phase with as much distance as possible between them.

Just be really careful with the 3-phase, it's 400V and it'll blow your fingers off or kill you stone dead. If in doubt, get an electrician.