Shower cable breaker question

Y

youngsparky

Hi all,
My girlfriends mum shower has gone faulty she is planning on a new one. Done some investigating and it's a 9.8 kw on a 6mm on a 32a breaker. Why hasn't the fuse bin blowing?
I havent done any cable calcs as of yet.
Any ideas just curious?
Cheers
 
Mcb's have a fusing ration of between 1.2 and 1.6, so dependant on its type, age etc etc it could take anything between 38.4 and 51 amps to trip it, the shower will pull around 40-42 amps depending on the supply voltage and VD, cable calcs wont really tell you a lot as apart from VD, there is nothing in there that will affect the current drawn, cable calcs are all about the current carrying capacity of the cable.

however, the cable is undersized for the size of the shower so its probably a good job its only a 32a breaker
 
youngsparky said:
Hi all,
My girlfriends mum shower has gone faulty she is planning on a new one. Done some investigating and it's a 9.8 kw on a 6mm on a 32a breaker. Why hasn't the fuse bin blowing?
I havent done any cable calcs as of yet.
Any ideas just curious?
Cheers
Click to expand...

It's a short duration overload, my daughter could make it trip with a long duration overload!
 
I'm wondering whether or not it's on a mains water feed or a header tank. I've seen plenty of old showers burnt out due to inadequate water pressure after they've been fitted by a less than concientious plumber (or spark!). New showers will normally not attempt to heat the water if there is insufficient pressure, so if you fit a new one and it won't get warm you may have the culprit.
Just a thought.
 
Last edited by a moderator:
High Tower said:
.

however, the cable is undersized for the size of the shower so its probably a good job its only a 32a breaker
Click to expand...


Possibly not - clipped direct it can be up to 47A. As IQ said it is probs fine for showers of 15min duration but the mcb could trip if the whole family want a go one after the other :)
 
pushrod said:
Possibly not - clipped direct it can be up to 47A. As IQ said it is probs fine for showers of 15min duration but the mcb could trip if the whole family want a go one after the other :)
Click to expand...

Very true!!

However when was the last time we seen a shower cable clipped direct,with no de-ration factors applied. The normally always run through Walls, voids and insulation at some point.
 
Run in masonry still counts as clipped direct. I came across the very same thing some time ago and thought 'hold on this can't be right' but when i sat down with the brb it turned out ok and the shower had been working ok for years. I could have put it on a bigger mcb but thought why fix it if it ain't broke lol
 
pushrod said:
Run in masonry still counts as clipped direct. I came across the very same thing some time ago and thought 'hold on this can't be right' but when i sat down with the brb it turned out ok and the shower had been working ok for years. I could have put it on a bigger mcb but thought why fix it if it ain't broke lol
Click to expand...

Yea I know that chased is the same method, I'm just always wary of 10kw showers on 6mm2 as a shower cable almost always runs into insulation etc etc

The op is by his name still learning hence I made the comment of the mcb holding because of it's fusing factor and was saying it was probably a good job that it was on a 32a as if it was a 40a then the cable would possibly be working at the top of it's tolerances

Having said that the diy'ers in the slums round here install 10kw showers on cooker flex so it's all good
 
before condemning the 6mm. i would 1. ensure it wasn't buried in insulation. 2 clamp meter the cuurent drawn. bet it will be under 40A, nearer 35A.
 
I agree with telectrix also to get it at it's max 10kw it would be peel your skin off the water would be to hot to stand under
 
for the mother- in-law , a good earth to the shower basin is essential.
 
And from the earth term in the shower unit along the hose to the shower head just to be sure
 
used to be on the old rubber cable and horsehair & lime plaster. modern cable/plaster no problem, but capping is advisable due to plasterers being let loose with sharp tools.
 
yes it would require RCD if less than 50mm deep.
 
can be metal or plastic - just a bit of protection for when it is plastered. Also gives the theoretical chance that you could always pull a new length of cable in :rolleyes:
 
SPARTYKUS said:
6mm2 will take alot more than 47A
Click to expand...

And there lie's the problem with DIYers We have be trained from the very start of our training, that cables need de-rating according to the environments in which the cable is installed. Whereas in reality the cable can and will draw far more than than it's de-rated calculated value. In this situation as regarding a shower installation, the over current will only generally be drawn for short periods of time... So the cable is probably not being stressed to extremes and the 32A MCB isn't receiving sufficient time to trip the over current section within the MCB... So to the householder/DIY'er
everything is Sweet!!! AS has been stated, the problems come when the usage changes, like when children become teenagers, especially of the female variety (though there are quite a few male teenagers that are more like tarts in the bathroom...lol!!)

Is the installation alright then?? ...No of course it's not, We know the very real dangers of these situations, but you try telling DIY Joe that after years of reliable service that he got it all wrong!!! It's the same old story, and your looked at as though your just wanting to make an extra few quid at his expense and for no obvious benifit!!!!....
 
Last edited by a moderator:
Thanks lads this discussion has helped me with a similar problem ;

neutral at the back of the double pole switch has melted insulation & the back of the switch. 10 mt run of 6mm to a 9kw shower on a 32a mcb. So gonna replace the cable with 10mm t+e, replace double pole switch & run from a single shower rcd.

So does it need tested too?

Thanks for the input ;-)
 
No the new installation from the shower RCD to the shower itself.
Continuity.
Insulation resistance tests.
Zs test.
RCD test.
And test Ze at origin so you know you gotta a good earth.
And it's notifiable. :D
 
and that is if it's 9kwatt. optimistic manufacturers always use 240v to make their product appear more powerful than it actaually is . i've yet to see a 9kw shower pull more than 35A anyway.
 
If your unsure wether to re run the cable or tighten connection. Do what you think is safest.
I always like to leave a job knowing it's the safest it could ever be
 
youngsparky said:
If your unsure wether to re run the cable or tighten connection. Do what you think is safest.
I always like to leave a job knowing it's the safest it could ever be
Click to expand...

Spot on attitude .......................though at my age leaving the site with it working is always a bonus
 
hmmmm.... how many electricians does it take to change a light bulb? answer-- 35.






1 to change the lamp, 2 H&S suits to ensure safety, 1 friend to post a thread, 1 to safely dispose of the old lamp and 30 to discuss alternative ways of doing the job
 

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Shower cable breaker question
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