I've been renovating the G/Fs bathroom this week, upon going to turn off
the shower supply, I found that it was supplied from a really old fuse
box, as well as looking like it is a spur from the cooker supply.
There are no RCDs anywhere in system.

To make the shower a little safer, I would like to fit a RCD to it.
Would something like this be suitable:
http://www.screwfix.com/prods/69659/

I presume, to fit this, I would disconnect the supply to the pull
switch, fit the supply to the RCD, then the output to the pull switch?

Ta for any thoughts.
Alan.
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To reply by e-mail, change the ' + ' to 'plus'.

On Sat, 22 Nov 2008 21:36:26 +0000, (A.Lee) wrote:

I've been renovating the G/Fs bathroom this week, upon going to turn off
the shower supply, I found that it was supplied from a really old fuse
box, as well as looking like it is a spur from the cooker supply.
There are no RCDs anywhere in system.

To make the shower a little safer, I would like to fit a RCD to it.
Would something like this be suitable:
http://www.screwfix.com/prods/69659/

I presume, to fit this, I would disconnect the supply to the pull
switch, fit the supply to the RCD, then the output to the pull switch?

Ta for any thoughts.
Alan.

Is the cooker still in use?
Where does ths cooker cable come from ? A CU?
Is the cable in use up to the job iro the shower rating?

wrote in message
...
On Sat, 22 Nov 2008 21:36:26 +0000, (A.Lee) wrote:

I've been renovating the G/Fs bathroom this week, upon going to turn off
the shower supply, I found that it was supplied from a really old fuse
box, as well as looking like it is a spur from the cooker supply.
There are no RCDs anywhere in system.

To make the shower a little safer, I would like to fit a RCD to it.
Would something like this be suitable:
http://www.screwfix.com/prods/69659/

I presume, to fit this, I would disconnect the supply to the pull
switch, fit the supply to the RCD, then the output to the pull switch?

Ta for any thoughts.
Alan.

Is the cooker still in use?
Where does ths cooker cable come from ? A CU?
Is the cable in use up to the job iro the shower rating?

You are in dangerous territory. How old is the installation? What wattage is
the shower? what size is the cable?

Whilst it may not be very safe now, you may be opening a can of worms.....!

John wrote:
I've been renovating the G/Fs bathroom this week, upon going to turn off
the shower supply, I found that it was supplied from a really old fuse
box, as well as looking like it is a spur from the cooker supply.
There are no RCDs anywhere in system.

I'm not an expert but I'm also learning about 21st centruy house
electricks..
and in my sister's flat someone had hotwired a shower onto the cooker
circuit...

If a cooker needs a 30amp fuse and the shower needs 20 amps
and if you want them both on at the same time
that would mean you'd use a 50amp fuse
which means you could have 30amps over current on the shower before the fuse
blows-
so that's not much protection,
I'd get scared and put in a new wire with RCD for the shower.

I think under part P a competent electrician has to install a new bathroom
circuit,
but over half the work is the planning and the measuring
and drilling holes in the walls and fixing conduit routes
which I plan to do myself first.

--
[george]

A.Lee wrote:

I've been renovating the G/Fs bathroom this week, upon going to turn off
the shower supply, I found that it was supplied from a really old fuse
box, as well as looking like it is a spur from the cooker supply.

Just looking like, or is it actually on the cooker supply?

Is there a cooker on it as well?

What is the rating of the shower (usually given in kW)

And what size was the fuse?

And what cable is in use? You can find out by measuring it and looking
up the size he

http://wiki.diyfaq.org.uk/index.php?...es#Cable_Sizes

There are no RCDs anywhere in system.

Prior to the 17th edition regs[1], there were plenty of cases when an
electric shower could be adequately protected and safe even without a
RCD. So don't read too much into there not being any at the moment.

I would be more concerned about checking that the cable and fuse rating
are appropriate for the size of shower.

[1] The need to protect cable runs will probably require a RCD anyway now.

To make the shower a little safer, I would like to fit a RCD to it.
Would something like this be suitable:
http://www.screwfix.com/prods/69659/

I presume, to fit this, I would disconnect the supply to the pull
switch, fit the supply to the RCD, then the output to the pull switch?

In effect - often these are positioned close to the CU rather than close
to the shower though.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:
A.Lee wrote:
I've been renovating the G/Fs bathroom this week, ....[shower supply]
looking like it is a spur from the cooker supply

Just looking like, or is it actually on the cooker supply?

Thinking about it, I was slightly sidetracked by the 'Cooker' on the
separate fuse. It is in fact a gas cooker, which obviously replaced the
previous electric cooker, so should be no problems with overloading the
cable.
It is a 30A fuse, with the relevent cable (6mm iirc).

There are no RCDs anywhere in system.

Prior to the 17th edition regs[1], there were plenty of cases when an
electric shower could be adequately protected and safe even without a
RCD.

But wouldnt fitting a RCD be much safer than it being protected only by
a fuse?

In effect - often these are positioned close to the CU rather than close
to the shower though.

Fitting it at the shower end would be far easier, but yes, I suppose I
could replace the separate fuse box for the cooker at the incoming
supply end.
Ta
Alan.
--
To reply by e-mail, change the ' + ' to 'plus'.

wrote:

On Sat, 22 Nov 2008 21:36:26 +0000, (A.Lee) wrote:

I've been renovating the G/Fs bathroom this week, upon going to turn off
the shower supply, I found that it was supplied from a really old fuse
box, as well as looking like it is a spur from the cooker supply.
There are no RCDs anywhere in system.

Is the cooker still in use?
Where does ths cooker cable come from ? A CU?
Is the cable in use up to the job iro the shower rating?

See other reply, I was hoodwinked by seeing 'cooker' on the fuse, and a
separate 'cooker' switch in the kitchen.
Alan.
--
To reply by e-mail, change the ' + ' to 'plus'.

In article , A.Lee
writes
John Rumm wrote:
A.Lee wrote:
I've been renovating the G/Fs bathroom this week, ....[shower supply]
looking like it is a spur from the cooker supply

Just looking like, or is it actually on the cooker supply?

Thinking about it, I was slightly sidetracked by the 'Cooker' on the
separate fuse. It is in fact a gas cooker, which obviously replaced the
previous electric cooker, so should be no problems with overloading the
cable.
It is a 30A fuse, with the relevent cable (6mm iirc).

There are no RCDs anywhere in system.

Prior to the 17th edition regs[1], there were plenty of cases when an
electric shower could be adequately protected and safe even without a
RCD.

But wouldnt fitting a RCD be much safer than it being protected only by
a fuse?

I'd guess that 3/4 of all/old electric shower installations don't have
RCDs and I've yet to hear of any Daily Whail exposes on grannies being
killed off, so the old concept doesn't seem that flawed to me, provided
! that the shower is wired and earthed correctly.

Mine is on an MCB only and I am perfectly happy with that, it's even one
of the early Dolphin ones with a direct and uninsulated heating element
in the water flow.
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

A.Lee wrote:
John Rumm wrote:
A.Lee wrote:
I've been renovating the G/Fs bathroom this week, ....[shower supply]
looking like it is a spur from the cooker supply

Just looking like, or is it actually on the cooker supply?

Thinking about it, I was slightly sidetracked by the 'Cooker' on the
separate fuse. It is in fact a gas cooker, which obviously replaced the
previous electric cooker, so should be no problems with overloading the
cable.
It is a 30A fuse, with the relevent cable (6mm iirc).

OK, so sounds like you need a label upgrade on the fuse then! ;-)

There are no RCDs anywhere in system.

Prior to the 17th edition regs[1], there were plenty of cases when an
electric shower could be adequately protected and safe even without a
RCD.

But wouldnt fitting a RCD be much safer than it being protected only by
a fuse?

I think it is one of those "feel good" things - you may think the RCD
offers better protection, but if you actually think through the possible
fault scenarios it is less clear cut.

Being a fixed appliance the chances of you making direct contact with a
live part are very slim (unless you plan on live working maintenance
while taking a shower!). Its not as if there are any blades or exposed
flexes etc. That then leaves indirect contact. The shower is probably
plastic cased, which means no shock from that. So, the final possibility
is insulation failure on the heating element creating a fault to earth.
If the equipotential bonding in the shower room is up to scratch, that
should ensure that you can't be exposed to a dangerous potential for the
duration of the fault, and the fuse should open within 5 seconds (and in
all probability much quicker).

The times the RCD would certainly help, include situations where the
earth fault loop impedance is high - but then again we are only talking
about a 30A circuit here - so even a rewireable fuse will open in time
with a fault current a tad under 90A. It would also be good where the
equipotential bonding is not good enough (or missing)

In effect - often these are positioned close to the CU rather than close
to the shower though.

Fitting it at the shower end would be far easier, but yes, I suppose I
could replace the separate fuse box for the cooker at the incoming
supply end.

Might be neater. Note that these separate enclosures include overcurrent
protection as well as RCD, and you don't really want to devices cascaded
since you are not going to be sure which will trip in the event of a fault.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In article , fred writes

Mine is on an MCB only and I am perfectly happy with that, it's even one
of the early Dolphin ones with a direct and uninsulated heating element
in the water flow.

eeeek! That can't be right, can it? It sounds as if you're saying the
live element is immersed in the water?

On Mon, 24 Nov 2008 13:31:17 +0000 someone who may be Mike Tomlinson
wrote this:-

Mine is on an MCB only and I am perfectly happy with that, it's even one
of the early Dolphin ones with a direct and uninsulated heating element
in the water flow.

eeeek! That can't be right, can it? It sounds as if you're saying the
live element is immersed in the water?

What do you think would be the problem?

Some heaters (not showers) work by passing electricity through the
liquid to be heated.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

When I was an apprentice we used to boil a cup of tea by placing two metal
plates in either side of a large pint mug and connecting the plates to the
mains. It works but don't try this at home children cos if you plug in too
many it blows the mains fuse. :-).

Sam
"David Hansen" wrote in message
...
On Mon, 24 Nov 2008 13:31:17 +0000 someone who may be Mike Tomlinson
wrote this:-

Mine is on an MCB only and I am perfectly happy with that, it's even one
of the early Dolphin ones with a direct and uninsulated heating element
in the water flow.

eeeek! That can't be right, can it? It sounds as if you're saying the
live element is immersed in the water?

What do you think would be the problem?

Some heaters (not showers) work by passing electricity through the
liquid to be heated.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

In article , Mike Tomlinson
writes
In article , fred writes

Mine is on an MCB only and I am perfectly happy with that, it's even one
of the early Dolphin ones with a direct and uninsulated heating element
in the water flow.

eeeek! That can't be right, can it? It sounds as if you're saying the
live element is immersed in the water?

:-D, I wondered if anyone would do a double take.

On the basis that a picture is worth a 100 . . .

http://i36.tinypic.com/34t95bc.jpg

V clever little design, transparent plastic case in two parts with a
central divider, keeping the two elements apart and forming a narrow
channel for the water to pass over the coiled resistance wire elements.
Unsurprisingly, the cold water enters on the blue flexible plastic pipe,
flows left along the bottom and returns to the right along the top
channel, exiting on the red.

The plastic inlet & outlet pipes are a good 50cm long so there's a good
long 'insulating' path through the water from live to the heavily earth
bonded metal in let & outlet fittings.
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

In article , fred writes

V clever little design, transparent plastic case in two parts with a
central divider, keeping the two elements apart and forming a narrow
channel for the water to pass over the coiled resistance wire elements.
Unsurprisingly, the cold water enters on the blue flexible plastic pipe,
flows left along the bottom and returns to the right along the top
channel, exiting on the red.

Looks a fairly modern design (plastic cable ties, brown for live, blue
for neutral etc.) but the concept still scares the **** out of me.
Reminds me of those toasters from the last century with drop-down sides
that exposed the live elements.

--
(\__/)
(='.'=) Bunny says Windows 7 is Vi$ta reloaded.
(")_(")

In article , Mike Tomlinson
writes
In article , fred writes

V clever little design, transparent plastic case in two parts with a
central divider, keeping the two elements apart and forming a narrow
channel for the water to pass over the coiled resistance wire elements.
Unsurprisingly, the cold water enters on the blue flexible plastic pipe,
flows left along the bottom and returns to the right along the top
channel, exiting on the red.

Looks a fairly modern design (plastic cable ties, brown for live, blue
for neutral etc.) but the concept still scares the **** out of me.
Reminds me of those toasters from the last century with drop-down sides
that exposed the live elements.

Installed 1983 the sticker says, so 25 years old.

I see where you are coming from with the scary concept idea but water
really isn't that good a conductor. IIRC 6mm is the safe air clearance
distance live to earth so 500mm (along the plastic pipe) of water should
do just as well.
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

fred wrote:

Mike Tomlinson writes

Looks a fairly modern design

Installed 1983 the sticker says, so 25 years old.

and a 1971 patent.

A.Lee wrote:

But wouldnt fitting a RCD be much safer than it being protected only by
a fuse?

It should be perfectly safe without an RCD provided that:

(i) the earth fault loop impedance (Zs) is low enough to ensure that
the fuse/MCB will blow/trip in less than 5 seconds in the event of an
earth fault, *AND*

(ii) SUPPLEMENTARY BONDING is in place in the bathroom, including
bonding between the earth terminal of the shower unit (or nearby
isolation switch) and any metal water pipework, particularly pipework
feeding the taps of a metal bathtub over which the shower in question is
used.

Supplementary bonding can be omitted under the 17th ed. if the relevant
conditions are met (RCDs for all bathroom circuits including lights and
main bonding in place for the building as a whole). If the shower has
no RCD the conditions are not met and the bonding becomes vitally
important to keep the shower outlet and your tootsies at more or less
the same voltage...

--
Andy

In article , fred writes

The plastic inlet & outlet pipes are a good 50cm long so there's a good
long 'insulating' path through the water from live to the heavily earth
bonded metal in let & outlet fittings.

Isn't that highly dependent on the composition of the water though? Say
if the water became more conductive, oh, as a result of iron sediment
contamination from a disturbed mains pipe, wouldn't that be rather
dodgy?

I assume such a design would be illegal now.

In article , Mike Tomlinson
writes
In article , fred writes

The plastic inlet & outlet pipes are a good 50cm long so there's a good
long 'insulating' path through the water from live to the heavily earth
bonded metal in let & outlet fittings.

Isn't that highly dependent on the composition of the water though? Say
if the water became more conductive, oh, as a result of iron sediment
contamination from a disturbed mains pipe, wouldn't that be rather
dodgy?

That's a good point and I believe it could cause damage to the shower
but I think it would still be safe given the following:

1. Cold end is live, hot end is neutral so an increase in conductivity
of the water would result in and effective short on the element but the
end closest to the user would be still be at neutral potential.

2. The outlet pipe is earthed so that even with a neutral fault and
having water with increased conductivity, the output should still be at
earth potential.

I'm open to be convinced otherwise though, but please don't try too hard
to convince me, I like my little backup shower heater ;-)

I assume such a design would be illegal now.

That wouldn't surprise me.
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

In article , Andy Burns
writes
fred wrote:

Mike Tomlinson writes

Looks a fairly modern design

Installed 1983 the sticker says, so 25 years old.

and a 1971 patent.

Yes I noticed that and tried to search for the details of the patent but
I got bogged down in rubbish sites, did you find a detailed listing?
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

fred wrote:

and a 1971 patent.

Yes I noticed that and tried to search for the details of the patent but
I got bogged down in rubbish sites, did you find a detailed listing?

Try
http://v3.espacenet.com/publicationD..._GB&CC=GB&FT=D

--
Andy

In article , Andy Wade
writes
fred wrote:

and a 1971 patent.

Yes I noticed that and tried to search for the details of the patent but
I got bogged down in rubbish sites, did you find a detailed listing?

Try
http://v3.espacenet.com/publicationD...9710616&NR=123
5849A&DB=EPODOC&locale=en_GB&CC=GB&FT=D

Thanks, a bit dry sic but worth a read, emphasis appears to be on flow
regulation and anti-scald rather than the uniqueness of the uninsulated
element but the need for long insulating flow tubes is mentioned.

Application first filed 1967.
--
fred
BBC3, ITV2/3/4, channels going to the DOGs