Hi All

Is there a formula I can use to calculate the appropriate RCD size for a
circuit? I am about to use an old electric shower supply to feed a 1.7Kw
storage heater. Its the only thing on the circuit (or is it a spur :-) and
currently has a 30amp RCD on it.

I assume 30amp is way too much for a little storage heater but how do
calculate what to replace it with? Same applies to a circuit that I'm
putting a hand drier on and so on...

Thanks

Tony

In article ,
enuff wrote:
Is there a formula I can use to calculate the appropriate RCD size for a
circuit? I am about to use an old electric shower supply to feed a 1.7Kw
storage heater. Its the only thing on the circuit (or is it a spur :-)
and currently has a 30amp RCD on it.

RCDs aren't current dependant - although you need one of a suitable
current carrying capacity.

I'd guess you mean an MCB?

To work out the load, divide watts by volts, so in the case of your heater,

1700
---- = 7.4 amps
230

I assume 30amp is way too much for a little storage heater but how do
calculate what to replace it with? Same applies to a circuit that I'm
putting a hand drier on and so on...

Normally, the MCB in the CU protects the house wiring. The fuse in either
the plug or the FCU (fused connection unit) protects the appliance -
although if there is only the one appliance on the circuit - like say a
cooker or immersion heater, the MCU can protect both.

--
*It IS as bad as you think, and they ARE out to get you.

Dave Plowman London SW 12
RIP Acorn

Is there a formula I can use to calculate the appropriate RCD size
for a circuit?

An RCD is a device that detects imbalances in the neutral and live flows.
Typically, you use 30mA for a final circuit, or 100mA time delay for whole
house arrangements (only when required). However, I think you really mean
MCB, which is a device that cuts out when a certain level of overload
current or short circuit current has been drawn.

For a resistive load, you divide the 240V power consumption in watts by 240.
The heater specifications should give outputs for 240V and 230V. Assuming
the 1.7kW is rated at 240V, this will give just over 7A. A 10A MCB would be
good here, although 16A MCBs are frequently used. Check the installation
manual to see if it (or its flex) requires protection at a certain level.
The manufacturer's recommendation should override any calculations or
assumptions you make.

The hand drier circuit will also have a reactive element due to the fan
motor. However, this will not be significant compared to the resistive
element of the heater. In any case, the things are typically no greater than
3kW so that they can be fitted on a 13A FCU. Use a radial circuit with at
least 16A capacity, with an FCU connecting between. A device such as this
normally shares a circuit with other devices, perhaps on a 32A ring final
circuit.

If you really do want a dedicated circuit, then it may be possible to use
the 16A MCB and avoid the FCU. However, you MUST check the installation
instructions to ensure that this provides adequete protection to the dryer.
Many will allow this, as continental European final circuits are often rated
at 16A with no subsequent fuse protection, unlike UK systems, and many
manufacturers prefer to have a single version of an appliance to sell
throughout the European market. You may need a DP switch anyway for
maintenance, so little saving will be made.

Christian.

In uk.d-i-y, enuff wrote:

Is there a formula I can use to calculate the appropriate RCD size for a
circuit? I am about to use an old electric shower supply to feed a 1.7Kw
storage heater. Its the only thing on the circuit (or is it a spur :-) and
currently has a 30amp RCD on it.

I assume 30amp is way too much for a little storage heater but how do
calculate what to replace it with? Same applies to a circuit that I'm
putting a hand drier on and so on...

Doesn't seem like you mean RCD (residual current device), which is a safety
device protecting against current which has been sent out of the live
conductor going anywhere other than back along the neutral, but rather an MCB
(miniature circuit breaker) - modern version of a fuse, wot you've probably
got a row of in your consumer unit (modern-speak for 'fuse box').

Yes, there's a simple formula relating watts to current; watts = volts *
amps, so your 1.7kW heater will pull about 7A. (Easier still rule of
thumb: each 1kW means 4A near as dammit).

*But* if you're confused about RCDs versus MCBs, unsure whether the
thing feeding the storage heater is a circuit or a spur (a bit like
asking whether something is a tree or a sessile oak), you should probably
spend a while in the library or a tenner or so at Amazon to read up some
more on electrickery-as-she-is-practised before getting too ambitious.
(That hand drier you mention - will it be in a bathroom? If so, how about
its supplementary bonding? you know that the minimum conductor size for
that depends on your earthing arrangements, don't you? which Zone will it
be in? This little litany is not meant to intimidate, but to help you
calibrate where your current level of competence is compared to that needed
to do the works you have in mind).

HTH - Stefek

"enuff" wrote in message
...
Hi All

Is there a formula I can use to calculate the appropriate RCD size for a
circuit? I am about to use an old electric shower supply to feed a 1.7Kw
storage heater. Its the only thing on the circuit (or is it a spur :-)
and
currently has a 30amp RCD on it.

I assume 30amp is way too much for a little storage heater but how do
calculate what to replace it with? Same applies to a circuit that I'm
putting a hand drier on and so on...

Thanks

Tony



Thanks all

You're all right, its an MCB. I'm learning, slowly...

I'm leaving the existing 30amp in and then changing it to a 10 after the
weekend. Stefeks right to question the hand-drier positioning and the
bonding which I plan to have handled by a competant electrician who is doing
a lot of work here over the next 2-3 weeks.

The drier I have in mind is a proper commercial jobby from TLC...

http://www.tlc-direct.co.uk/Products/MRE88ACS.html

Surely these are designed to go within reach of sinks etc?

Tony

In uk.d-i-y, enuff wrote:

The drier I have in mind is a proper commercial jobby from TLC...

Surely these are designed to go within reach of sinks etc?

Yup. Regs don't have an explicit distance limit for appliances from sinks,
just "be sensible" wording (i.e. don't put it where it's likely to get
regularly splashed if that'd be bad for safety). They are prescriptive
about minimum distance from nearest edge of bath or shower: need to be
out of arm's reach, specified as 60cm (two of our quaint English feet,
metricated ;-) But your electrician will know all about that.

Cheers - Stefek

wrote in message
...
In uk.d-i-y, enuff wrote:

The drier I have in mind is a proper commercial jobby from TLC...

Surely these are designed to go within reach of sinks etc?

Yup. Regs don't have an explicit distance limit for appliances from sinks,
just "be sensible" wording (i.e. don't put it where it's likely to get
regularly splashed if that'd be bad for safety). They are prescriptive
about minimum distance from nearest edge of bath or shower: need to be
out of arm's reach, specified as 60cm (two of our quaint English feet,
metricated ;-) But your electrician will know all about that.

Cheers - Stefek

Stefek

Thats what i thought, just thinking of the local McDonalds etc

I'm the poor s*d who's going to be putting the damn thing in! I'll just run
a 6mm earth from it and leave it ready to attach to an existing pipe. I
assume thants whats needed, if so I have a box of earth clamps.

Tony

In uk.d-i-y, enuff wrote:

I'm the poor s*d who's going to be putting the damn thing in! I'll just run
a 6mm earth from it and leave it ready to attach to an existing pipe. I
assume thants whats needed, if so I have a box of earth clamps.

More than good enuff ;-) - always ass-U-ming the existing pipe is already
bonded to other metalwork in the bathroom...

cheers, Stefek

I'm the poor s*d who's going to be putting the damn thing in! I'll just
run
a 6mm earth from it and leave it ready to attach to an existing pipe. I
assume thants whats needed, if so I have a box of earth clamps.

Also, if like MacDonalds, it is a toilet room only with no bath or shower,
then supplementary equipotential bonding is not required.

Christian.

Christian McArdle wrote:
I'm the poor s*d who's going to be putting the damn thing in! I'll
just run a 6mm earth from it and leave it ready to attach to an
existing pipe. I assume thants whats needed, if so I have a box of
earth clamps.

Also, if like MacDonalds, it is a toilet room only with no bath or
shower, then supplementary equipotential bonding is not required.


Our local macdonalds has these sinks which are basically like holes in
the wall with a drainhole in the bottom. You stick you hands in and a
(PIR?) sensor detects your hands and squirts some soap on them. A couple
of seconds later it turns on the warm water and gives you about 10
seconds of water. A couple of seconds after that something else in there
starts blowing hot air on your hands. All without having to take your
hands out of the hole in the wall...

On Mon, 19 Jan 2004 13:13:13 -0000, "R W"
wrote:

Our local macdonalds has these sinks which are basically like holes in
the wall with a drainhole in the bottom. You stick you hands in and a
(PIR?) sensor detects your hands and squirts some soap on them. A couple
of seconds later it turns on the warm water and gives you about 10
seconds of water. A couple of seconds after that something else in there
starts blowing hot air on your hands. All without having to take your
hands out of the hole in the wall...

Hell, those are the washbasins???? And there I was thinking they were
an automatic bidet.....

Never did figure out how to stop the front of my trousers getting wet!


PoP

Sending email to my published email address isn't
guaranteed to reach me.

Our local macdonalds has these sinks which are basically like holes in
the wall with a drainhole in the bottom. You stick you hands in and a
(PIR?) sensor detects your hands and squirts some soap on them. A couple
of seconds later it turns on the warm water and gives you about 10
seconds of water. A couple of seconds after that something else in there
starts blowing hot air on your hands. All without having to take your
hands out of the hole in the wall...

Oh my God! didn't people get lazy these days? Soon they'll put robots
on the tables so you don't get tired eating

(OK I know it saves them money by not having to clean up after the
place has been used a few times...)

PoP wrote:
On Mon, 19 Jan 2004 13:13:13 -0000, "R W"
wrote:

Our local macdonalds has these sinks which are basically like holes
in the wall with a drainhole in the bottom. You stick you hands in
and a (PIR?) sensor detects your hands and squirts some soap on
them. A couple of seconds later it turns on the warm water and gives
you about 10 seconds of water. A couple of seconds after that
something else in there starts blowing hot air on your hands. All
without having to take your hands out of the hole in the wall...

Hell, those are the washbasins???? And there I was thinking they were
an automatic bidet.....

Never did figure out how to stop the front of my trousers getting wet!



Just give it a quick shake before you put it away...

On Tue, 20 Jan 2004 08:35:19 -0000, "R W"
wrote:

Just give it a quick shake before you put it away...

It's easier to kick the drops off.....

PoP

Sending email to my published email address isn't
guaranteed to reach me.

On Mon, 19 Jan 2004 17:03:02 +0000, PoP wrote:

On Mon, 19 Jan 2004 13:13:13 -0000, "R W"
wrote:

Our local macdonalds has these sinks which are basically like holes in
the wall with a drainhole in the bottom. You stick you hands in and a
(PIR?) sensor detects your hands and squirts some soap on them. A couple
of seconds later it turns on the warm water and gives you about 10
seconds of water. A couple of seconds after that something else in there
starts blowing hot air on your hands. All without having to take your
hands out of the hole in the wall...

Hell, those are the washbasins???? And there I was thinking they were
an automatic bidet.....

Never did figure out how to stop the front of my trousers getting wet!



Seems to be a modern trend for designing whbs and urinals which look
as much like the other as possible.
On one occasion it was only when trying to figure out how and where to
wash my hands that I realised I'd just ****ed in the sink!

--
Niall

On Tue, 20 Jan 2004 21:23:57 +0000, Niall
wrote:

On Mon, 19 Jan 2004 17:03:02 +0000, PoP wrote:

On Mon, 19 Jan 2004 13:13:13 -0000, "R W"
wrote:

Our local macdonalds has these sinks which are basically like holes in
the wall with a drainhole in the bottom. You stick you hands in and a
(PIR?) sensor detects your hands and squirts some soap on them. A couple
of seconds later it turns on the warm water and gives you about 10
seconds of water. A couple of seconds after that something else in there
starts blowing hot air on your hands. All without having to take your
hands out of the hole in the wall...

Hell, those are the washbasins???? And there I was thinking they were
an automatic bidet.....

Never did figure out how to stop the front of my trousers getting wet!



Seems to be a modern trend for designing whbs and urinals which look
as much like the other as possible.
On one occasion it was only when trying to figure out how and where to
wash my hands that I realised I'd just ****ed in the sink!

Bachelor flat was it ?? I'm told that that is normal behaviour in
those :-)

..andy

To email, substitute .nospam with .gl

On Tue, 20 Jan 2004 21:37:30 +0000, Andy Hall
wrote in response to

"****ed in the sink"

Bachelor flat was it ?? I'm told that that is normal behaviour in
those :-)


I'm told - by someone who moves in such exalted circles - that in one
of the Bachelor Rooms at Balmoral that there was a little notice above
the somewhat grubby hand sink saying "Go on! Everybody else does"

(The room of necessity being at the far end of a rather draughty and
apparently uncarpeted corridor")

The Dook's idea of fun?
Barley Twist
(Please put out the cats to reply direct)

In article ,
Andy Hall writes:

Seems to be a modern trend for designing whbs and urinals which look
as much like the other as possible.
On one occasion it was only when trying to figure out how and where to
wash my hands that I realised I'd just ****ed in the sink!

Bachelor flat was it ?? I'm told that that is normal behaviour in
those :-)

Aston Mathews in Islington had a combined WHB/Urinal in their
showroom, which must be the ultimate bachelor flat accessory.

--
Andrew Gabriel

On 20 Jan 2004 21:58:18 GMT, (Andrew
Gabriel) wrote:

In article ,
Andy Hall writes:

Seems to be a modern trend for designing whbs and urinals which look
as much like the other as possible.
On one occasion it was only when trying to figure out how and where to
wash my hands that I realised I'd just ****ed in the sink!

Bachelor flat was it ?? I'm told that that is normal behaviour in
those :-)

Aston Mathews in Islington had a combined WHB/Urinal in their
showroom, which must be the ultimate bachelor flat accessory.

Wasn't this the thing where the WHB was above and the water from
washing the hands went down and flushed the urinal?




..andy

To email, substitute .nospam with .gl

On Tue, 20 Jan 2004 21:37:30 +0000, Andy Hall
wrote:

On Tue, 20 Jan 2004 21:23:57 +0000, Niall
wrote:




Seems to be a modern trend for designing whbs and urinals which look
as much like the other as possible.
On one occasion it was only when trying to figure out how and where to
wash my hands that I realised I'd just ****ed in the sink!

Bachelor flat was it ?? I'm told that that is normal behaviour in
those :-)


Nope, public bog. Which was only deserted when I went in :-(

I did hear of a party in a student flat where there was one bloke
wazzing in the bog and another 3 lined up along the bath, when someone
else walked in, saw the situation and shied off. "It's OK mate, just
use the bath" said one of those doing just that. "You B******s, I LIVE
HERE, that's *my* bath!"

Last seen at the local supermarket, buying them out of bleach and
Dettol...


--
Niall

In article ,
Andy Hall writes:
On 20 Jan 2004 21:58:18 GMT, (Andrew
Gabriel) wrote:

In article ,
Andy Hall writes:

Seems to be a modern trend for designing whbs and urinals which look
as much like the other as possible.
On one occasion it was only when trying to figure out how and where to
wash my hands that I realised I'd just ****ed in the sink!

Bachelor flat was it ?? I'm told that that is normal behaviour in
those :-)

Aston Mathews in Islington had a combined WHB/Urinal in their
showroom, which must be the ultimate bachelor flat accessory.

Wasn't this the thing where the WHB was above and the water from
washing the hands went down and flushed the urinal?

That's it -- all one piece of porcelain though.
If you're careful, you could have a wash and **** at the same
time, but it might take a little practice...

--
Andrew Gabriel

On 20 Jan 2004 23:42:56 GMT, (Andrew
Gabriel) wrote:

In article ,
Andy Hall writes:
On 20 Jan 2004 21:58:18 GMT, (Andrew
Gabriel) wrote:

In article ,
Andy Hall writes:

Seems to be a modern trend for designing whbs and urinals which look
as much like the other as possible.
On one occasion it was only when trying to figure out how and where to
wash my hands that I realised I'd just ****ed in the sink!

Bachelor flat was it ?? I'm told that that is normal behaviour in
those :-)

Aston Mathews in Islington had a combined WHB/Urinal in their
showroom, which must be the ultimate bachelor flat accessory.

Wasn't this the thing where the WHB was above and the water from
washing the hands went down and flushed the urinal?

That's it -- all one piece of porcelain though.
If you're careful, you could have a wash and **** at the same
time, but it might take a little practice...

There was a joke about a sailor and a marine involving that, but I
can't remember it......



..andy

To email, substitute .nospam with .gl

In article , PoP
URL:mailto
On Tue, 20 Jan 2004 08:35:19 -0000, "R W"
wrote:

Just give it a quick shake before you put it away...

It's easier to kick the drops off.....

Don't you mean "spin dry" ?

--
AJL Electronics (G6FGO) Ltd : Satellite and TV aerial systems
http://www.classicmicrocars.co.uk : http://www.ajlelectronics.co.uk