consumer units


Postby karl neville » Sun Mar 28, 2010 9:14 pm

hi was looking at split consumer unit and wanted to know how the feed from the main double pole isolating switch fed the mcbs is it done using the busbar ?and can i feed all my rcd circuits from 1 rcd or does each circuit have to have one ie sockets outside , cooker , shower ring main ?sorry if this sounds a bit of a silly question thanks karl
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Postby jackhawk » Mon Mar 29, 2010 4:55 pm

Hi Karl, no such thing as a silly question. I know!! If you are going for a split load CU you want two RCDs for each side. EG: All your down stairs circuits and lights up, and all your upstairs circuits with lights down. 30mA RCD at the start of both splits. Get a CU that is pre wired, saves a lot of messing about. Most are and can work out cheeper.

Regards

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Postby moggy1968 » Sat Apr 03, 2010 10:12 pm

but bear in mind this work is notifiable under part P and that once installed an installation cert and schedule of test results must be completed.
not having these may lead to problems later with insurance and the sale of the property as they are a legal requirement.
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Postby ericmark » Mon Apr 05, 2010 7:39 am

A consumer unit is a type tested distribution unit and as such you can't change from manufactures design. That includes only fitting MCB's and RCBO's which are recommended.

Although as a competent person I could fit a distribution unit then the house could only be sold to another electrician so in real terms we have to fit consumer units and follow the manufactures instructions.

There are a number of split load designs from the special types for storage heaters to the triple split to allow two RCD's and also some either unprotected by RCD or using RCBO's.

However assuming a TN supply I would go for non split unit and all RCBO controlled circuits as this will produce far less tripping then any other system.

With a TT system the need for twin pole switching of RCD's at the moment causes problems with non split consumer units normally sold in UK. As a result the option is normally restricted to single split and two RCD's.

There are other options including auto resetting RCD's but this is very expensive and not really an option except for specials like where disabled people live in the house.

However first point has to be what earthing system one is using? TT means an earth rod. TN-C-S is often referred to as PME and together with TN-S means the electric supplier also supplies the earth.

It is these points which mean consumer unit changes are not DIY jobs. Main thing it needs £750 worth of testing equipment to both pre-test before starting and re-test after completing. In theory the LABC should test this for DIY people but even if they do you don't get paperwork. And often they try to force you to get tests done.

Really speaking the provision for DIY people to fit their own consumer unit is really so I can fit my own where I do not normally work on domestic but have a full test kit in garage and C&G 2391 + 2382 and can sign my own paper work. It is not so Joe public can fit their own unit.
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