Longish query - circuit breakers in consumer units

Hi,
about to add new circuits and need extra circuit breakers.
Screwfix lists type B and C (what happened to Type A)?
Both are shown as ISO rail fitting.
So:
will almost any circuit breaker fit any consumer unit (CU was replaced six years ago) because they are an ISO standard fitting, or is it a case of loads of different fittings?
Consumer unit is Siemens Stratus 200 Breakers are all marked 5sx21 Ratings are B32 or B6 (so presumably a 'B' type breaker).
See http://www.siemens-industry.co.uk/news/pressrel.asp?ID 8 - apparently they are miniature circuit breakers.
See http://www.siemens-industry.co.uk/distribution/alpha200.asp - RCCB, switch, or split load.
Now I am more confused instead of less.
http://www.chelsworth-lodge.nildram.co.uk/Electrics/DSC00113.JPG
http://www.chelsworth-lodge.nildram.co.uk/Electrics/DSC00114.JPG
These show my incoming power and the consumer unit.
I have (it looks like) two switches for incoming power (LHS), plus an RCCD (RHS).
How do I tell if this is all on the RCCD, or if the lighting (LHS) is switched - which I would presume is a split load (from reading the FAQ). It looks like a split load setup. Is the cut in the busbar easily visible?
This brings me on to connecting in the new wiring (13 amp ring main and immersion heater on a direct circuit).
As I seem to have two switches on the main switch, I presume one is for the lighting side, and one for the power via the RCCD. So I presume that I could keep the lighting running with the power side off whilst I connect in the new cables.
(1) I turn off the main switch on the consumer unit - darkness reigns. (2) Remove the cover (3) Turn on the lighting side again so I can see what I am doing without using a torch. (4) Pull the RCCB for extra safety? (5) Connect in the new wires (6) Add the new mini-RCBs (7) Power up power side (RCCD back in) with cover off and extreme care then test the new circuits. (8) Power everything off again and re-install the cover. (9) Power up and celebrate. (10) Go round resetting all the clocks, CH timers etc.
Any advice much appreciated - main issue is 'do the type B RCDs from Screwfix fit these units - answer please in time to place the order today :-)
TIA Dave R
P.S. Included the picture of the power side because I seem to have three blocks on the inbound side - one is used for the meter and two spares. I know there used to be storage heaters - unused sockets in the wall and a very nasty charred CU in the garage before we had all this replaced - so that would explain one extra service, but what was the other one for? Is it usual to have the incoming service split into 3? A relic of the old multiple fuse box setup? I note there is no isolating switch between power in and the CU - would this be a good idea or is the switch on the input side of the CU adequate?
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Always use Type B, unless you have a specific reason to use a lower protection rating (you don't!). There is no Type A, although I'd like to buy some if they made one. They'd be very useful for large pure resistive circuits, such as cookers.

You'll see that the switch on the left has the two handles connected together. This is because it is a double pole switch that switches both the Neutral and the Live at the same time. It should cut power to the entire consumer unit.

I wouldn't. There will be live busbars in the consumer unit, protected only by your incoming service fuse. I wouldn't want to short that out by dropping my screwdriver. Turn off the main isolator (left hand switch) before doing any wiring up.

Most makes will fit most boards. However, many will claim that you should not do so, or that it will invalidate the guarantee. If you are worried, then buy Siemens ones, if you can find them.

Yes. Electricity is generated and transported around the country in three phases, 120 degrees apart. Large industrial motors use all 3 phases as they can maintain constant power throughout the mains cycle. A standard domestic electricity supply uses one of the 3 phases selected at random by the electricity company, often fused at 100A for a modern installation, although older ones may be 40A or 60A.
With electrical heating installations, such as storage heaters, you would typically have a 2 or 3 phase supply as they draw too much power for a standard domestic cutout. So your guess is probably correct that you did once have a 3 phase supply. It was probably all removed when all the Economy 7 gubbins were removed and a single phase meter installed.
BTW, I'm slightly worried by some of your questions. You might want to consider doing the main wiring up of the circuits and then get an electrician in to test and make the final connections. You need some very expensive test gear to do the circuit testing, not a 2.99 multimeter from Maplins.
Christian.
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<snip>

** I would if I could - it is the obvious safe solution. However I can't seem to Google any suppliers. Hence the question about universal fit ** <snip>

Thanks for the prompt response and good advice. I have read the FAQ on testing a circuit - it says "You need a low resistance ohm-meter with good resolution, say a range of 0 - 2 ohms with divisions of 0.05 ohm. ". Is this the really expensive test gear you mention? If so, how much is 'very expensive' likely to be?
I am pretty confident that I can safely connect to a consumer unit - I have done so several times in the past just not to one of these new fangled fancy gizmos you young fellas seem to favour these days :-)
On reflection, as you suggest, keeping the lighting power on may not be the greatest move - I was lured by the joys of electric light instead of a torch :-)
If the test gear is unreasonably expensive I will chat to our local electrician about commissioning the wiring.
Cheers Dave R
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To do it properly, you need a continuity tester capable of 200mA test current (NOT a multimeter!), an insulation resistance checker capable of 500VDC, an earth loop impedence tester and an RCD tester. You can get the whole lot for around 600 quid. Of course, most people don't seem to do it properly.
The most important part is the continuity/insulation resistance tester, which are normally on the same instrument. The cheapest of these are around 200 quid new. I got mine for 35 quid on eBay from someone who thought it was a broken electronic thermometer. He admitted afterwards that he sold it because it gave him a nasty electric shock when he was playing with it. (500V does that!)
Christian.
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On Mon, 3 Nov 2003 13:43:04 -0000, "David W.E. Roberts"

I've implemented a fairly simple solution to deal with this, which is a small maintained emergency light.
These can be obtained from electrical wholesalers quite inexpensively and are a fluorescent tube fitting with electronics and a battery backup which lasts 3 hours. I installed a small 8W one immediately above and in front of the consumer unit in a cupboard. It is charged from a lighting circuit and is switched on normally when the door is opened.
However, it will also come on, powered by battery, if the power fails or is deliberately turned off to do work.
This is much better than playing around with torches in confined spaces or leaving the power on and working on the CU live. I've seen the melted remains of a fairly substantial screwdriver in the bottom of a CU after it managed a short between the bus bar and the metal case..........
.andy
To email, substitute .nospam with .gl
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wrote:

the
torch
I have a battery light on the wall by the CU - not as elegant as your solution but better than nothing (as long as it is checked regularly).
Just looked on Screwfix and they do one for 21 - so I've added this to my order.
Thanks Dave R
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The following are claimed to stock Siemens:
http://www.rexelsenate.co.uk / http://www.neweyandeyre.co.uk / http://www.ac-electrical.co.uk /
Some of the websites are pretty useless, though.
Christian.
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All done now.

<snip>
the
off
*** ..errr...yes - having taken the front off there is no way I would work on it with the power up! ***
<snip>

this
*** Yep - switch on the input side seems fine to isolate everything ****
The scariest thing was the huge black spider which had taken up residence inside the CU which made me jump more than a jolt from the mains :-)
The 'pattern' RCB fitted well, but squeezed the blanking plates up a fraction.
Thanks to everyone for helpful advice.
Cheers Dave R
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So you've never touched the mains before then?
Mungo
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residence
When hooking my finger round a plug, touching banjaxed wiring etc. I get a serious quiver up my arm (no archery jokes please). This doesn't make me jump much at all - just quiver gently.
Large black spiders, however, do produce large involuntary muscle contractions and distinct motion in an away direction.
:-)
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