Planning new CU

[ACDC]

I'm planning to replace my old cu (re-wirable fuses, no rcd) with a new split load one.
Obviously I'm going to put the ring and electric shower circuits on the rcd side, but what about the immersion, cooker and central heating?
I've looked at other split load cu's and some have these 3 circuits rcd protected, others don't.
Any advice?
Thanks.

 

[securespark]

As your experiences show, it varies from spark to spark.

Some put cookers on rcd if they are elderly (the cookers, that is!), others put CH + Imm Htrs on RCD because the "use" water. Others put them on the non-protected side because they are essential and therefore will not be lost in the event of a trip.

 

[ban-all-sheds]

Cookers can be prone to earth faults where a bit of moisture gets into the elements. Enough to trip an RCD, but so little that it would evaporate away and cause no danger. As it's one circuit it's easy to move though, and whatever you end up planning, you will have spare ways on each side, won't you....
I'd advise having a fair few spare positions - you don't have an RCD right now, and you may uncover problems that you never knew you had before. Being able to move sockets etc back to a non-RCD position until you get the problems resolved is a lot better than having no power until you get the problems resolved...

Separate non-RCD radial for the fridge/freezer highly recommended.

Are you having mains powered smoke alarms?

MCBs are prone to nuisance tripping when lamps blow - you might like to think about using Type Cs for the lighting circuits, or alternatively pick a brand of CU where you can get modular fuse-holders to use instead of MCBs.

One very important point - if you have a TT supply you must use a 100mA time-delayed (Type S) RCD as your main incomer, and all sockets must be on a 30mA RCD, not just the downstairs and outside ones.

Have you thought about how you will isolate the supply in order to connect the tails?

 

[ACDC]

Thanks for your advice- I like the idea of the freezer on its own non rcd radial.
The earth system is PME and the smoke detectors are battery run.
There is no isolator between the meter and the cu, so if I'm going to change the cu myself ( haven't decided for sure yet) I will carefully pull the service fuse.

 

[ban-all-sheds]

I will carefully pull the service fuse.

And while it's out, you'll fit an isolator for future use, won't you...

 

[Careful_Bodger]

BAS - would you fit the isolator in the outside meter cabinet? (In its own IP40 box, say.) Do the regs allow/recommend this?

On the matter of 'pulling the fuse', I ws recently told that REC rules require their employees to use gauntlets and a face guard while doing this. Is it really such a perilous activity? - not withstanding the legal rectitude!

 

[ban-all-sheds]

BAS - would you fit the isolator in the outside meter cabinet? (In its own IP40 box, say.) Do the regs allow/recommend this?

AFAIK, the box and insides thereof are REC property, so if you are fitting an isolation switch of your own it should be inside your property, after the tails have entered your house. More convenient there, anyway.

On the matter of 'pulling the fuse', I ws recently told that REC rules require their employees to use gauntlets and a face guard while doing this. Is it really such a perilous activity? - not withstanding the legal rectitude!

I don't think it's that hazardous, as long as you take care, but there are always different rules when an employee is asked to do something - an employer can't just say "you be careful, now". I wonder how many of their people use the safety gear they've been issued with? Of course, if they don't, and they are hurt, then provided their employer can show that they were issued it, that they were given safety training, that there was an official policy of using it, with supervisory checks and disciplinary procedures for non-use, then the employer is in the clear.