shower cable

[jimmie74]

Hello a friend of mine wants to upgrade their shower to a 9.5kw model.

They already have a 6mm shower circuit in place and in use that was installed when the new c/u was fitted, with a 40amp c/b. The cable run is 15 metres and mostly clipped direct apart from the 3 odd metres where it is chased in to a wall. I make this installation reference method B and in the electricians guide to the building regs page 31 table 2.3.1 says a 6mm cable installed ref method B rating is 38amps and on page 49 table 4.1.1 6mm cable should be protected by a 32amp c/b.

I know this was done by 16th edition but was it that different to the 17th edition.

My mate is trying to avoid fitting a new shower cable but wants a bigger shower, but regs says 6mm for showers up to 7.2kw and 10mm for showers up to 9.6kw.

Can anyone shed some light on this please?

 

[sparkytim]

First check shower rating at 230 volts

9.6 kw is probably rating @ 240 volts

as this is a fixed load then BRB Pg 74 433.3.1 (ii) allows ommision of overload protection so 6mm ok on 40 A MCB

 

[SPECIAL LOCATION]

Hello a friend of mine wants to upgrade their shower to a 9.5kw model.

First I assume 9.5Kw is the rating on the box?

typically the "box ratings" are at 240v nominal...

NOT the 230v nominal (what BS7671 works to)

thus 9500w/240v = 39.5A (approx)

small print on the box probably says less than 9.5kw @ 230v?.

So typical load is around a 6ohms 40A load. 40A MCB going to be fine.

They already have a 6mm shower circuit in place and in use that was installed when the new c/u was fitted' date=' with a 40amp c/b. The cable run is 15 metres and mostly clipped direct apart from the 3 odd metres where it is chased in to a wall. I make this installation reference method B

[/quote']

Chased into wall is not method B...

'B' is more of the in conduit, or trunking or single cores in conduit in a wall etc.. etc..

Re read pages 261 .. 265 BS7671.

BUT.

PVC clipped direct into a masonry wall (i.e. chased in) is still method 'C'

look at number 57 on page 264 of BS7671.

So cable method is 'C'...

Now page 50 of On-Site-guide says 40A radial circuit, 6.0mm cable, method C, should be no problem for 15m circuit length.

A 6.0mm cable method 'C' is rated up to 46amps... so your 40A max should be no problem.

and in the electricians guide to the building regs page 31 table 2.3.1 says a 6mm cable installed ref method B rating is 38amps and on page 49 table 4.1.1 6mm cable should be protected by a 32amp c/b.

I know this was done by 16th edition but was it that different to the 17th edition.

My mate is trying to avoid fitting a new shower cable but wants a bigger shower, but regs says 6mm for showers up to 7.2kw and 10mm for showers up to 9.6kw.

Can anyone shed some light on this please?

I would guess there are zillions of 9.5k showers running on 6.0mm with no problems.....

Providing you keep the MCB at 40amp, AND it is RCD protected, I cant see any major problem..

If re-wiring were being considered then obviously 10.0mm would be the preferred way to go providing for future upgrade of shower.

ut the kettle on

 

[netblindpaul]

One thing though Specs, what if Manuf' instructions state min 10mm!

17th requires compliance with Manuf' insstructions!

Even though all else is OK.

Paul

 

[SPECIAL LOCATION]

One thing though Specs, what if Manuf' instructions state min 10mm!17th requires compliance with Manuf' insstructions!

Even though all else is OK.

Paul

Think you will find a lot of manuals have a "summary" version of the regs tables.

and still give a 6.0mm option for 9.5k..

NO safety issues with a cable that can carry 46A

fused at 40A

with a 39.5A load

over 15m length

that typically only runs for 10 -15min at a single run.

IF some of those factors were changed then maybe reconsider...

But I know of loads of 9.5k showers running happily on a 6.0mm

As said if rewiring stick in a 10mm..

But if cable is existing and all tested out good IR etc..

stick the shower in...

any problems and the 40A MCB or 30ma RCD will do their job!

thats what they are there for.

 

[Theorysparky]

One thing though Specs, what if Manuf' instructions state min 10mm!17th requires compliance with Manuf' insstructions!

Even though all else is OK.

Paul

dont forget either that the big red book is not law

all you need to do is justify your methods if it came to it

40amp mcb for a 6mm cable good enuff

also bear in mind that to reach the 40amp the shower needs to be set at max temp.....

have you tried that recently ????? dont its flipping scalding

 

[jimmie74]

Thanks for the speedy response sparkytim and special location,

Yes the spec for the Triton Inscription is 9.5kw@240v and 8.8kw@230v.

I must admit I have never seen a c/u like my mates but then again i'm new to all this, it has a RCCB in place of a main switch.

Thanks again for the info, my wife tells me to go on the forum but i'm always scared of asking silly questions and getting replys like "well if you don't know you shouldn't be doing it"

Many thanks people

 

[netblindpaul]

Therory,

I am more than aware the BrB is not law, and I am a strong exponent of the fact.

However, if you went against the BrB, and, the Manufacturers instructions you may find a problem in justifying your actions.

Even though you are almost certainly correct in what you have put in your posts.

One other thing though, as I understand the function of a normal electric shower, the element runs at a constant current/temperature with the water flow being controlled to give the required temperature.

I've not yet seen one with electronic controls on the element, even my own "advanced" triton, only has 2 basic relays between the elements and the mains, one element for low power, 2 for high power.

 

[Theorysparky]

Therory,I am more than aware the BrB is not law, and I am a strong exponent of the fact.

However, if you went against the BrB, and, the Manufacturers instructions you may find a problem in justifying your actions.Even though you are almost certainly correct in what you have put in your posts.

Paul

Fair point

 

[SPECIAL LOCATION]

Thanks for the speedy response sparkytim and special location,Yes the spec for the Triton Inscription is 9.5kw@240v and 8.8kw@230v.

I must admit I have never seen a c/u like my mates but then again i'm new to all this, it has a RCCB in place of a main switch.

Thanks again for the info, my wife tells me to go on the forum but i'm always scared of asking silly questions and getting replys like "well if you don't know you shouldn't be doing it"

Many thanks people

Your wife speaks wise words young Skywalker,

wise will you be, to follow her guidance!

Silly questions?

that only applies IF you do ask a silly question......!!!!

Your question was IMHO well written...

logically presented..

and a perfectly sensible... If you don't know the answer..

then ASK is the sensible thing NOT the silly thing...

NOT asking is the idjuts solution.

PS... we are still waiting to find a silly question...

cuz there ain't one!

except maybe...

how's Deke gonna keep control of Brian!?

:coat

 

[SPECIAL LOCATION]

One thing though Specs, what if Manuf' instructions state min 10mm!17th requires compliance with Manuf' insstructions!

Even though all else is OK.

Paul

Typical Manufactures instructions....

9.5Kw ok with 40A mcb....

40A load OK on 6.0mm method 'C' clipped direct.

Extracts from a Triton book...

many other manufactures instructions are similar.

:coffee

 

[jimmie74]

Thanks special i've just found this aswell from triton.

9.1 The current rating will be reduced if the cabling is bunched with others, surrounded by thermal loft or wall insulation or placed in areas where the ambient temperature is above 30

 

[SPECIAL LOCATION]

One other thing though, as I understand the function of a normal electric shower, the element runs at a constant current/temperature with the water flow being controlled to give the required temperature.

I've not yet seen one with electronic controls on the element, even my own "advanced" triton, only has 2 basic relays between the elements and the mains, one element for low power, 2 for high power.

A lot of Electic showers have Dual elements...

e.g. 4 position switch...

OFF

COLD ONLY

HEAT #1 Single element sometimes called summer setting

HEAT #2 Dual element often called winter setting

On a 9.5k shower each element is typically 12ohms.. (6ohms two in parallel)

so one element on is approx 20A (230 or 240)/12ohms

Both elements on approx 40A (230 or 240)/6ohms

When running at the warmer temperatures they will actually switch off for short periods with the internal thermal cut-off.

IF you actually put a clamp meter on a shower cable it is not often running full whack for the whole of the shower period.

and even when it is at full load, due to the shorter periods of full load operation it is not too much of an issue...

say compared with an electric oven that me be switched on for a longer period during cooking.

:coffee