I am going to replace my consumer unit with a modern one, the one at present is well out dated, has mcbs but no rcd protection for the whole house. problem i have is the old wireing red black green do not or will not reach most of the terminals in the new box. all the old wires will enter from the back from one hole in the wall and plastered, no slack in the wires either. will it be OK to butt extension wires onto some of the old wires, a re wire is not feesable, a lot of advise would be helpfull. would block screw terminals be accepable for inspection?

Butt crimps properly installed everytime. Dont be tempted to use choc blocks and I would not use wago's either but thats just a personal thing.

thanks sparky jim, studying for part P. just wondered where we stand regarding joining the wires in a consumer box?

I have used the shrink covered butt crimps which do a very neat job. But one needs the correct jaws to ensure the crimp is correctly applied. In all my time as an electrician only one firm I have worked for ever calibrated the crimp pliers. That was GEC Large Steam Turbines who I worked for in Sizewell and Connah's Quay power stations. But it did raise the question as to matching cable size to the crimp used. 1.5mm, 2.5mm, and 6mm cable in red, blue, and yellow crimps is normally not a problem. But 1mm and 4mm cable is really too small to fill the red, and yellow crimps and needs special pliers to ensure it is correctly crimped.

GEC issue crimp pliers would impress a number onto the plastic so an inspector could check if the correct pair of pliers had been used.

So although a correct used crimp is fine one must use the correct pliers for the crimp. With the blue crimp for example there are different jaws for the shrink type to non shrink type and to be certain one would have to use same make of pliers and crimp.

Personally I just look at the crimp and give it a small tug although really one should not tug at them. Only the test crimp made to calibrate should subjected to any force.

thanks ericmark! i have a decent set of crimpers that wont release till correct pressure is reached, slots colour coded, although some times it's hard getting the pressure to release the jaws,lol

I have two sets of crimp pliers which have a over centre mechanism which controls the pressure. One the standard one where you need to completely close to re-open. The other set looks like a pair of mole grips. Latter has not been used for years but has a locked adjustment at end of grip. The other pair has a dial to adjust the pressure.

What I have talked about with a number of sparks is under pressure is something which we can see or at least feel as when we tug the crimp will come off. However over crimping needs one to remove the crimp and inspect the cable to see the effects. I have seen where the cross sectional area was reduced due to the crimp pliers being wrongly set.

However the consensus was that although the cable was crushed it was unlikely to cause overheating as a result so was not really a problem. What we considered was more of a problem was the oxide and the thin plastic coating put on cables where under low light conditions it can easy be missed.

So I am quite happy to use my over centre crimp pliers even though not calibrated.

However I had a lot of problems using crimps with motor vehicles because of the very close contact capillary action tends to keep them wet and with the salts acting as an electrolyte the electrolytic action can quickly cause them to fail.

With motor vehicles I found connector strips in junction boxes worked better.

I think therefore one must use some thought as to what one is doing and not just follow an instruction set. There may be situations where using a junction box does a better job than the crimp specially where the crimps make the space in the consumer unit crowded.

With non domestic I have built my own panel with a din rail full of connectors to address the problem of short cables. However for domestic we should use type tested units.

I have argued with my son over the enclosure in my house which holds the two RCD's. He says it not allowed in a house as there is not an Instructed, Skilled or Competent person on site. However I pointed out to him, I am classed as Competent, so is my father-in-law next door but one and so is he. Also my father was the Technician Engineer in a 1000MW power station and my son-in-law studied for his degree in electrical engineering so every house hold in the family has a competent person resident.

However I have found the more knowledge I gather the more I realise that I don't know. And one can get totally bogged down with regulations so I have been looking at this smiley while I was typing so can't resist.