new shower

[just add water sparks]

A friend of mine had a shower unit pack up,and had a spare shower unit from a previous house move.I went round to inspect the old unit which was a 10.5kw shower.I looked internally in unit to my surprise to see it fed by 4mm,i looked at the back wall of the shower wall to see how it was fed as it dangled from the ceiling with no clips or trunking via a DP switch.Obviously the previous cowboy found the cable short and decided to extend this by a switch.I further investigated the mcb size obviously concerned about overheating and to my surprise it was a 32amp mcb,so how on earth did it function when you would have logically thought it would have drawn at least 40amps????????.So would the 9.5kw shower (spare)realistically work,NOT THAT i would condone that sought of thing.As i would install to regs and manufacturers spec.The 4mm would be protected by the 32amp mcb which is adequate.

 

[Billythekid]

whats the point of having a breaker rated at 32a,if it doesn,t trip even at 48a?
it wouldn,t be doing its job protecting overload surely?

This is why it's so important to size the cpc adequately, as often the cpc has a smaller csa than the live conductors. It's all well and good installing a cpc that will take a relatively large inrush of current (low resistance fault) for a short duration, but how about a small overload/fault of high resistance over a much longer duration?

 

[ayjay]

You need to look at the bgb, which is the current wiring regulations, we all go by it. A mcb ( circuit breaker ) will take more than its rated at for a set amount of time, their rated as a b c d . The graphs in the book of regulations will make it clear to you.

h,mmmm the little green book---
hi will , what about using a wire fuse like we used to to? or even a cartidge fuse? at least the blow nearer the over current, it seems to me that these so called "trips" are no good
if it says 32a/ or what ever ,thats when it should disconnect, not 46a ffs

 

[kingeri]

This is basic stuff, surely. Overload protection shouldn't even be an issue if the correct size cable is selected. The MCB/fuse's most important job is to protect against fault current!

 

[just add water sparks]

You need to look at the bgb, which is the current wiring regulations, we all go by it. A mcb ( circuit breaker ) will take more than its rated at for a set amount of time, their rated as a b c d . The graphs in the book of regulations will make it clear to you.

Will i started off with the orange , yellow ,brown and blue and goodness know how many other coloured books including accompanying on site guide books,Brian Scadden books,The electricians guide to part "p",books by John Whitfield,Part "p" doctor by Alan Lynch e.t.c e.t.c please read post no.12 again.How many pages on the BGB are different from the BRB ?and why cannot i read updated ammendments from whatever source?

 

[electric will]

I don't know. I know nothing.

 

[electric will]

The graphs in the bgb for the amount of current vs time for fuses and breakers to disconnect is the same as the graphs in the brb, and I bet the haven't changed in the earlier editions of the regs, although some fuses have been took out and other mcb's been added. Back to the old bs3036 fuse wire say rated at 30 amps when too much current flows though it, the wire takes time to heat up and Melt causing disconnection. Mcb's work in the same way, electrics like heat, it takes time to heat something up and melt it

 

[Geordie Spark]

oh dear should i be tarred and feathered lol Why the hell should i fork out for forkin £65.00+ when i can look at amendments.It beggars belief on here when some people nit pick!!!!!! this game is expensive enough changing books so quickly with amendments.To some degree its a money generating exercise

My thoughts too. Cheers mate!! :17:

 

[HandySparks]

How many pages on the BGB are different from the BRB ?and why cannot i read updated ammendments from whatever source?

Because the IET isn't going to publish amendment sheets for 17th Edn Amdt 1. There are changes to too many pages (although many are just the odd word here and there).

 

[electric will]

h,mmmm the little green book---
hi will , what about using a wire fuse like we used to to? or even a cartidge fuse? at least the blow nearer the over current, it seems to me that these so called "trips" are no good
if it says 32a/ or what ever ,thats when it should disconnect, not 46a ffs

So whats the need for, type b,c and d breakers? Are you saying every over current protective device should disconnect at exactly the rated current?

 

[ayjay]

well somewhere near it,will-p
wire fuses do
cartridge fuses do it better, whats the point of an mcb that doesn,t trip at just above its rated current?
a 32a mcb that will stay in at 48a for a certain time! the 4-0 mm,twe cable will be overloaded
perhaps i,m wrong, but all i can say is, if a breaker has 32a written on it, it should trip at say 33a,