Shower circuit

[flukey]

just been to see a shower replacement job.
whoever fitted existing one has used immersion circuit and it goes like this.
20amp mcb, 2.5 cable to airing cupboard, 6mm cable to double pole ceiling pull, 6mm to shower.
customer says the existing 7.5kw shower has functioned happily for years

 

[TFGtv]

My own house had a similar arrangement!

About 15' of 2.5mm to the pull switch... 6mm to the shower...

Circa 1998, West Lothian Council 'electricians' had fitted the shower unit for the little old lady who used to occupy the house!

I only got suspicious when I opened the box to add another MCB for some outside lights.... And saw the solitary 2.5mm cable running into the 30A breaker! When I complained to the council they denied everything claiming that the old lady must have done it herself! And that in the face of a pre-entry inspection report before we bought the place!

 

[flukey]

My own house had a similar arrangement!

About 15' of 2.5mm to the pull switch... 6mm to the shower...

Circa 1998, West Lothian Council 'electricians' had fitted the shower unit for the little old lady who used to occupy the house!

I only got suspicious when I opened the box to add another MCB for some outside lights.... And saw the solitary 2.5mm cable running into the 30A breaker! When I complained to the council they denied everything claiming that the old lady must have done it herself! And that in the face of a pre-entry inspection report before we bought the place!

what size shower did you have on yours

 

[TFGtv]

what size shower did you have on yours

To be honest I don't remember... It was a Mira I remember that much. And I think it would be bottom of the range; certainly it wasn't very powerful.... As you can imagine on discovering how it was wired I disconnected it immediately.... Which then caused SWMBO to insist that the very NEXT job I done was to replace it along with most of the bathroom!

 

[kung]

The joys of being a spark ay ! its like a 8mm pipe feeding the rising main !

 

[flukey]

The joys of being a spark ay ! its like a 8mm pipe feeding the rising main !

it gets better kung. just checked tritons website and its actually an 8.5kw shower

 

[sparks1234]

Yes, my dad has a shower fitted by dolphin about 30 years ago, been running on a 2-5, i think it is a 7 Kwatt, dont know what size breaker it is on but never had a problem, not to say its right of course

 

[super_stuey]

Hi guys sorry to dive in on the thread, any chance you could explain in laymans terms why it is so bad to be wired in 2.5mm? I take it is to do with cable current carrying capacities? (mouthful!!)

Im only a wee 2330 level 2'er at the mo and weve not done it at college yet so would be nice to have a minor headstart!!

Cheers guys sorry 4 asking stupid questions!

 

[sparks1234]

2.5 twin and earth is rated approx at 24 amps , this depends on installation method and the conditions you install it in, generally rule of thumb is a max of 20 amp MCB for a 2-5 T & E.
7.5 Kwatt shower is about 33 amps and if you get up to the 10.5 Kwatt shower, they are around 45 amps, usually a 6mm or a 10 mm cable for the larger showers or longer distances.

 

[Mr Mark Sparks]

thats the thing with flukeys job its wrong but with a 20a mcb the cable is correctly protected doesnt make it right though

 

[super_stuey]

right thanks guys I think I understand. So the 2.5 being rated at 24 amps is that basically the current it can take without overloading/melting?

And the ampage of the showers I take it your using I=W/V where V=230 volts right?

 

[sparks1234]

got it

 

[flukey]

thats the thing with flukeys job its wrong but with a 20a mcb the cable is correctly protected doesnt make it right though

you are quite right saying that the 2.5 is correctly protected on a 20 amp mcb but can you imagine putting that on the certificate when i fit the new shower going back tomorrow to put it right and fit the shower

right thanks guys I think I understand. So the 2.5 being rated at 24 amps is that basically the current it can take without overloading/melting?

And the ampage of the showers I take it your using I=W/V where V=230 volts right?

you got it. an 8.5kw shower will demand 37amps and should therefore be on a 6mm feed

 

[super_stuey]

Happy days thanks for your help guys.

Stu

 

[spark1]

Cable being subject to overload.........serviceable life of cable shortened

protective device being overloaded.....serviceable life and reliability being compremised.


I have found in the past that if undersized cable is used on a shower it can show as overheating at terminations.....usually at the isolator switch prducing burn out.

If an undersized circuit breaker is used this usually shows itself by tripping when one person uses the shower immediatley after somebody else....the circuit breaker already having been close to its thermal trip limit by the first use of the shower.