by ericmark »
Thu Aug 07, 2008 7:06 pm
Sorry not made it plain. The boxes are used in many places not just homes and they are made to be flexible so it can be configured as required. There are four standard versions.
Those with one neutral rail will be used with either MCB’s where no RCD is required or RCBO’s where earth leakage is required. But RCBO’s are both expensive and in most cases only switch the “Line” the “Neutral” being left connected so both for cost and in some cases regulations other options are used.
Before July the single split consumer unit was popular as not all items had to be protected by RCD’s and now these are being sold off cheap and special items like the lights, and smoke alarms are supplied through RCBO’s on non RCD side and less critical items through group RCD.
Again to reduce cost a duel RCD board is used this is to get around the requirement that the supply should be split into circuits to prevent inconvenient tripping and danger and it suggests lights and sockets should not be on the same RCD for same area.
Then a further progression where three neutral bars are used and two go through RCD’s and one is intended for use with RCBO’s.
An RBCO is a MCB and RCD combined but in most cases it does not switch neutral. Some specials clip on to existing MCB so you can use B, C, or D type but most come as one unit. The price can be from £13 to £40 for basic same unit according to make and one has to be careful when selecting what make to use. Now they are being used more the price is going down you must remember many of the regulations controlling their use have only been in force for a mouth or so and even electricians are not quite sure where what is required. As many have not yet studied the new regulations and sat the C&G2382 exam which shows they know how to read the book.
I hope I have explained this time and near everything has RCD protection but not all in the same way.
Eric
