RCD/MCB help

[Spectric]

Once upon a time there were no RCD's and everything hanging of a couple of rewirable fuses in porcellan holders!! Infact people used adaptors that pluged into a lighting bayonet fitting to power an appliance such as an iron!!

Then we had a single RCD for many years, it provided a new level of electrical safety but the issue was that when it tripped it left you in total darkness, not a good situation to be in especially if you are taking something out the oven.

So the split board appeared with two RCD's and the theory was that if the circuits were shared between the two RCD's then total darkness could be avoided, but only if the property was wired bearing this in mind.

Now the solution is no RCD's and use RCBO's, one for each circuit and now you have a system where each circuit has its own protection and if one trips then you don't have the situation where say a bulb blows, takes out the RCD, heating goes off and pipes freeze.

Having two lighting circuits is not new, it is the way I wired any property and often in larger ones with the kitchen and hallway seperate again. But sometimes having to rewire a property is not open to decision if it is in such a state as to be deemed no longer fit for purpose, but current best practice does not have to be retrofitted to existing servicable installations and if you have a single RCD then so be it until the time for a rewire.

 

[stuart little]

That explains what happened to me when replacing a socket in my loft, N & E touched = 'CLICK !' WTF!

 

[guineafowl21]

I can't agree with that statement for several reasons. First, you have no idea on the size or type of his property. Second, you are applying 'current' best practice. The newer regulations suggesting, for example, split upstairs lighting from downstairs lighting is more a question of convenience IMO then electrical safety. Thirdly....rewiring a whole house ? You must be joking. The hassle etc. Replastering. Redecorating.

That’s quite a hard-line response to a suggestion. I guess that’s how forum arguments start.

A board change, without total rewire, could well be feasible in his case. It would stop all the circuits being at the mercy of one faulty appliance; certainly worth of consideration, especially for hobby woodworkers.

 

[moosepig]

Thanks for all replies, folks. My house had a new CU fitted in 2005; the sockets are on their own RCD so at least the lights stayed on. Might investigate double pole MCBs for some circuits - sparky job, naturally. Just seems daft to me that the only way of isolating circuit doesn't really isolate it... whoever mentioned ease, cost and convenience nailed it I think

 

[Spectric]

If you look at reg 537.14 then you will see double pole isolation is only required in a domestic installation with a single phase TT supply, this is one where the means of earthing is provided at your installation and supply is often from overhead lines and pole transformer. If your supply is TN-S or more likely TN-C-S which is a protected multiple earth system then double pole isolation is not required. In a domestic enviroment the only person who would benefit from having all two pole MCB,s or RCBO's would be an electrician carrying out periodic test and inspection as it makes testing easier and also reduces the risk from borrowed neutrals.

 

[moosepig]

In a domestic enviroment the only person who would benefit from having all two pole MCB,s or RCBO's would be an electrician carying out periodic test and inspection as it makes testing easier and also reduces the risk from borrowed neutrals.

...or a competent DIYer carrying out permitted work who doesn't wish inadvertently, unexpectedly and suddenly to power down the rest of the house's sockets?

 

[Spectric]

That is very limited to only work that is not notifiable which means nothing that impacts or changes the original design intent so light fittings, switches and socket fronts. Anything else requires testing, so you need test equipment and this is not cheap. With current consumer unit design using single pole protection then any circuit can be isolated to a level that will allow the DIYer to perform these task providing they have the means to prove dead, the circuit not them.