DIY Doctor


Postby yount03 » Fri Dec 03, 2010 9:33 am

Dear Sir/ Madam…

I have been looking on your website regarding MCB, RCD & RCBO`s and what is the difference and the best to use.

I have a large 3 bedroom house with 3 floors, I want to use 1 consumer box to run the house with the latest technology..

Below is what I need for my house:-

70 Sockets
30 lights
65 Spotlights
6 Fans
1 Electrical Shower
3 Outdoor Lighting

I was thinking of making 4 different rings to split each floor + kitchen, can you please advise which I can or should use MCB, RCD & RCBO`s

Thanks in advnace

Much appreciated
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Simply Build It

Postby ericmark » Sat Dec 04, 2010 9:28 am

Thought I had answered this but here goes again.
Assuming not on a TT supply then the RCBO is best route. It reduces the chance of a faulty item tripping out whole house but more to the point they stop the build up of leakage from loads of IT equipment used today all which seem to have filters in them which cause some small leakage.

The 30ma RCD at 40ms comes in a few different forms. In the consumer unit the units able to handle between 63A and 100A will normally be passive that is they will not auto trip with a power cut. Some have warning lights to show when the tripping current is being approached and some will even auto reset them selves after checking line is clear however at over £300 each unless the house had disabled living there who were unable to manually reset they would not be used.

Also in the consumer unit we use the RCBO in UK mainly these only open the line conductor and there are some places where this is not allowed and or not recommended in Europe the twin pole type is more common. But of course twin pole RCBO's are twice as thick making the consumer unit twice the size. We also tend to split the consumer unit into two or three sections with some circuits grouped together and some circuits having their own RCBO to control them.

Away from the consumer unit volt drop can be a problem and it could under fault conditions be enough to stop the RCD working so we use the active type. This means if there is a volt drop they switch off anyway. Also handy where motors are used i.e. lawn mowers as if the power fails then returns the lawn mower will not re-start. Also the remote RCD's built into plugs and sockets are normally double pole so using a 10ma active RCD built into a plug or socket for lawn mower is still a good idea.
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Postby russell fields » Sat Nov 12, 2011 12:32 am

how can voltAGE drop stop an RCBO operating?
also RCBOs that take up one space can be double pole.
russell fields
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Postby sparx » Sat Nov 12, 2011 3:29 pm

Whilst some comments made are relevent, ie Hager ML range of RCBO's are double pole single module devices does this mean anything to you?
Without wishing to be rude are you competant to do this work? will you be paying your Local Authority Building controls £250+ inspection fee and do you have the test equipment to read and fill in the required installation certificates?
I mention this since by asking the question you are obviously not a registered electrician who can self certify.
To do the work without notifying first is illegal under Part P of said regs. and if done may negate your house insurance and would give problems if you later want to sell up.
In short, answer to your original question:
RCBO's give combined overcurrent and earth leakage protection to each individual circuit, best but most expensive option, (my house has this set up).
Two RCD's in a consumer unit plus MCB's is another popular way of complying with regs, probable cheapest and most used option.
Or a combination of one RCD combined with mcb's for part of board and some RCBO's for other circuits.
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