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John Rumm
 
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Default Wiring for A Whirlpool Bath

Tim Blank wrote:

Hi,
I have just purchased a whirlpool bath. The Instructions for the bath state
that it needs to be wired accordingly (spelling and gramar reproced from the
orginal!)


Does this bath have any electrical heating capability? It sounds like it
could be in electric shower territory for power consumption when
heating. If it is simply a pump however then it seems unlikely that it
needs the best part of 7kW just for that!

"Conneecting to the mains:

For the pump power supply, bring and electrical line using a waterlight lead
of a 6 x 25mm section protected by a 2 x 16A magnetothermal switch and
equipped by a 30mA differental switch. The earth wire muct be absolutely
connected to an earth hold. The resistance of the eart hold much not exceed
3ohm, this electrical line must uniquely serve the bathtub"


Oooo nice ;-)

Guessing at some of the terms:
"magnetothermal switch" = MCB
"30mA differential switch" = RCD

the 2 x 16A seems odd - perhaps it does mean 32A. That would also tie up
with a 6mm^2 CSA cable (assuming the distance is not excessive). No idea
where the 25mm comes into it.

The "The resistance of the eart hold much not exceed 3ohm" seems an odd
requirement to specify on a circuit which is also RCD protected. (might
make more sense on a circuit that relies on EEBADS protection only - but
then the 3 ohm figure would be too high to provide fast enough
disconnection of the MCB (a quick look at fig 3.4 in Annex 3 of BS7671
suggest Ze would need to be = 1.5 ohm for a 32A MCB). I think you can
ignore this bit since you have the RCD (and since you will probably
exceed this requirement by a good margin anyway)

To get this right, you will need to go back to basics and read the
actual current loading or power rating off the plate that should appear
somewhere on the bath.

"this electrical line must uniquely serve the bathtub" sounds like a
suggestion that there be an equipotential bond run back to the CU. This
is not actually a requirement under BS7671, the CPC in the feed cable
would be adequate on its own. The whole bathroom should still be cross
bonded so as to ensure it is an equipotential zone however.

Now...

I plan to instal the bath by running and RCD protected Fused Spur (Screwfix
14770) from one of the sockets located in my lounge (small flat). I will


If we are talking about a high current drain setup then you will need a
dedicated circuit. Even a 16A fixed load would be inappropriate to feed
from an ordinary ring circuit.

then have a pull cord located in the bathroom or wall mounted switch in a
cupboard next door which will sit between the bath's pump and the FCU. Is
there any problems with doing this?


This bit is fine - the ceiling switch would be better since it is in the
same room as the bath and hence allows it to be used for isolation
(assuming = 3mm contact separation and it being two pole) without
complex lockout requirements (i.e. there is little danger of someone
turning back on while someone else is maintaining the bath). It would
also probably need to be of the shower isolator type to handle the
current requirements if they are large as we suspect.


--
Cheers,

John.

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