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.

 

[telectrix]

don't forget that a 32A MCB will quite happily take 48A for up to an hour before tripping.

 

[Billythekid]

The load also varies from unit to unit, i.e some units have three or four seperate elements. These are controlled by a few things (again dependant on unit), temperature of incoming water/ temperature of outgoing water/ users chosen heat setting, etc. And as above, not many people shower longer than 15mins. Hope this helps.

 

[just add water sparks]

thanks i appreciate you taking up your time ,in my ignorance where abouts does it give reference to this in brb for future reference.It is great when people bounce back with info

 

[electric will]

In my opinion It's not a good idea running that cable at over 40 amps even on a 32 amp breaker,
like telectrix says it can take an hour to trip it, that cable will probably be in insulation and I can see the shower be used for one person after another, so that shower coud be on for quiet some time.

 

[just add water sparks]

yep of course Will i did not want to complete this mess!!!as a matter of fact because the install looked so bad i checked the cable run in loft.There was 6" of insulation which brings me to two another confirmation's.Am i correct in saying that if a cable is clipped direct to the side of the joist then it negates the de-rating factor as this dissipates any heat.How do you guys size the difference between 4mm and 6mm visually.Apart from having small pieces with you to compare.I know this sounds a daft question but 2mm dif. needs a bionic eye.

 

[just add water sparks]

re my post no.4 does it show in any tables in brb for 32amp mcb taking 48amps just for ref purposes not obviously as design guide please telectrix

 

[Spazz]

re my post no.4 does it show in any tables in brb for 32amp mcb taking 48amps just for ref purposes not obviously as design guide please telectrix

Out of interest why are you working out of the BRB??? we are now on the BGB!

 

[Amp David]

re my post no.4 does it show in any tables in brb for 32amp mcb taking 48amps just for ref purposes not obviously as design guide please telectrix

Page 301 of the BGB shows you the time/current graph for type B 60898 MCBs

 

[telectrix]

which shows that a 32A MCB will trip in around 1000secs. at 48A. that's 16minutes.

 

[ayjay]

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?

 

[just add water sparks]

Out of interest why are you working out of the BRB??? we are now on the BGB!

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

 

[just add water sparks]

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?

seems logical can anyone answer that one please????????????????

 

[electric will]

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.

 

[ayjay]

hi-- "just add water",in reply to your q- people at the top, writing regulations, need to keep their highly paid jobs! simple-
so-- they keep inventing - first the red then the green
what could be a better job!
a frigging yellow one next
then a mauve

 

[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.