Does electric shower require RCD?

[Spark123]

Did you have to file the keyway off to get it to fit, or did it just go in wonky? Neither of these methods are advisable. It is normally only the position next to the switch that can accept anything over 30A.

 

[RF Lighting]

a quick note here. we had a BROWN 100A wylex board with a wooden back. how rare is that???

Is that the one that has 4 fuses to the left of the main switch, and one to the right?

Have come across a few of these, but they are pretty unusual.

 

[RMS]

I only just stripped one of these out today, it had 5 BS3036 fuses on the left and one on the right which always seems to be the cooker or shower. The back was hollow.

 

[Adam_151]

to get ² as in mm² , just hold doen your left alt key and type 0178 on the numberpad with your other hand

I've seen pics of the wylex boards described, I belive the fuseway on the right is designed to be able to handle a 45A cartrisge fuse for a range cooker, and they sometimes get used for showers

I can't see why not, nothing wrong with crimping an extension on cables in a fuseboard as long as its done properly, unless anyone can come up with a reason why pyro cores can't be crimped for some reason I've overlooked or some things

 

[RF Lighting]

I can't see why not, nothing wrong with crimping an extension on cables in a fuseboard as long as its done properly, unless anyone can come up with a reason why pyro cores can't be crimped for some reason I've overlooked or some things

Crimping extentions onto pyro cores is pretty common, as it saves stripping sometimes as much as a meter of pyro outer, then trying not to twist the cores while you fit the pot, then fit meters of sleeving. Also it is nearly always nescassary to extend the short earth tails on the newer pots.

 

[The Jeep]

Thanks guys, that's useful info (about the ² character) and about crimping to pyro cores.

I know it's correct practice to put the highest rated MCB nearest to the main switch, but does it really make any difference? I thought it was just anal good practice!

By the way, I feel confident that the main incomer can take the additional load of adding a shower, as it's protected by a 60A HBC fuse downstream, which I believe can handle a lot more current than that over short periods (any opinions on that?). Ultimately, its main function is protecting the pyro incomer and cables up to the CU from overcurrent and therefore overheating. If the total current draw in the flat is too great, that fuse would blow (no built-in protection on the main switch on this old board), and as long as I don't change the rating of that fuse, then the level of protection is not compromised.

But how do I determine if the old fuse board (probably 1960s) is up to taking, say, a 40-50A rewirable fuse? I'm pretty sure you do get them with those higher ratings, so what would be the limitation? The bus bar?

 

[RF Lighting]

I know it's correct practice to put the highest rated MCB nearest to the main switch, but does it really make any difference? I thought it was just anal good practice!

I don't think it will make any real difference on todays consumer units, but on the older type boards (read wylex) the busbar was designed to only carry certain amounts of current over very short distances.

By the way, I feel confident that the main incomer can take the additional load of adding a shower, as it's protected by a 60A HBC fuse downstream, which I believe can handle a lot more current than that over short periods (any opinions on that?).

This is correct, but you should not be designing circuits to be overloaded, even for a short periods of time.

Ultimately, its main function is protecting the pyro incomer and cables up to the CU from overcurrent and therefore overheating. If the total current draw in the flat is too great, that fuse would blow (no built-in protection on the main switch on this old board), and as long as I don't change the rating of that fuse, then the level of protection is not compromised.

Check the size of the incommer pyro. You will be suprised at the current cayying capacity of pyro compared with twin and earth.
If you look on the gland or pot of the pyro it will have the conductor CSA written on it. This is written like : 2L2.5 4L6
The first number is the number of cores that the pyro has, the letter AFAIK is to indicate light duty (L) or heavy duty (H), the second number(s) is the CSA of the cores.

do I determine if the old fuse board (probably 1960s) is up to taking, say, a 40-50A rewirable fuse? I'm pretty sure you do get them with those higher ratings, so what would be the limitation? The bus bar?

You need to look at how much load is currently running of this baord, and the maximum current rating of the board. If you overload the board them you risk burning out the main switch or busbar, and although it is rare, it does happen. I've seen it and it scary how close to a full blown fire that house had.
An alert homeowner saved the day and nearly killed themselves in the process, but thats another story.

 

[Adam_151]

But how do I determine if the old fuse board (probably 1960s) is up to taking, say, a 40-50A rewirable fuse? I'm pretty sure you do get them with those higher ratings, so what would be the limitation? The bus bar?

The busbar connections fuse clips, from the POV of the busbar and main switch if they are rated at 60A it doesn't matter how that 60A is devided for all those parts care...

Way to tell, is wylex boards with a 60A main switch were not meant to handle circuits over 30A

 

[Adam_151]

You need to look at how much load is currently running of this baord, and the maximum current rating of the board. If you overload the board them you risk burning out the main switch or busbar, and although it is rare, it does happen. I've seen it and it scary how close to a full blown fire that house had.
An alert homeowner saved the day and nearly killed themselves in the process, but thats another story.

C'mon RF....

 

[Spark123]

The reasoning for putting the highest fuse next to the main switch I have read somewhere on here was for eddy currents, although I think the reason for only having one keywayed is so only 1 large fuse can be installed per board.

OK ready for the bedtime story

 

[Steve]

no, my 100a brown wylex board had 8 ways, all to the left of the main switch. no "high load" fuseway.

 

[Adam_151]

For anyone wondering about the wylex fuseboxes with the higher rated fuseway.... http://www.harmel.co.uk/cu1.jpg

 

[WabbitPoo]

but i agree anything that your using wet and naked and is liable to be sprayed with water should be RCD protected.

Does that include the wife?

 

[Spark123]

but i agree anything that your using wet and naked and is liable to be sprayed with water should be RCD protected.

Does that include the wife?

We were leaving that post for Ban-all-sheds reply, now you've gone and spoilt it

 

[The Jeep]

OK, so what do you do when you have to rewire and update (i.e. new appliances, electric shower) an ex-council tower block flat that's protected elsewhere by a 60A HBC fuse locked in a cupboard? OK, I got the FB key and removed said fuse to allow me to install a new CU, but that CU came, as most of them do, with a 100A main switch breaker, which will never see any action as, if the worst comes to the worst, the 60A will go first, leaving the poor tennant in the dark wondering what the f@#k happened and why there's nothing they can do to put things right at the CU.

Well, today, I ran everything in the flat at full tilt and measured a maximum of 73A on the incomer (using a clamp meter). Nothing was getting remotely warm (except the kitchen and bathroom) and I'm sure even a few more amps could be pulled as the 60A fuse is a huge beasty. The Pyro, incidentally, is 10mm² (love this secret ASCII code!) which is good for +/- 90A, depending on which table you look at in the regs.

So either I leave things as they are, buy a spare 60A and tell them to call me if it all goes dark and I'll come out for a small fee with my FB key & fuse, or I try to find a smaller main switch breaker (60A) which will, hopefully, trip first. Maybe better a bit of nuisance tripping than blowing the big guy. Actually, I doubt that would ever happen and I can just move on and forget it... but my advice is, folks, don't work on tower block flats. stick to good old houses with 100A incomers.