Immmersion Heater Switch
 

I'm sure this can't be right.
The fused switch that controls my immersion heater is very hot.
I know that some heat will be generated in the cabling as the element gets
hotter, but the switch itself gets too hot to touch.
I've checked the connections inside the switch, and they all seem secure.
Does anyone have any other ideas why this switch is so hot?

Also, is it usual for an immersion heater circuit to be spurred off a ring
main, or should it be on it's own dedicated circuit wired with a higher
rated cable?

Thanks
Paul

In an earlier contribution to this discussion,
Paul S wrote:

I'm sure this can't be right.
The fused switch that controls my immersion heater is very hot.
I know that some heat will be generated in the cabling as the element
gets hotter, but the switch itself gets too hot to touch.
I've checked the connections inside the switch, and they all seem
secure. Does anyone have any other ideas why this switch is so hot?

In order to generate heat within the switch, the current flowing to the
immersion heater must be meeting some resistance. If the wires are all
secure, the resistance must be coming either from the switch contacts or
from the fuse not being a tight enough fit in the fuse holder. Either way,
if it's got seriously hot, it will never be the same again - and must be
replaced.

Also, is it usual for an immersion heater circuit to be spurred off a
ring main, or should it be on it's own dedicated circuit wired with a
higher rated cable?

I'm not sure about the legality. It's generally considered to be good
practice to have a dedicated circuit - with its own breaker - for the
immersion heater. However, I suspect that a lot *are* spurred of a ring
circuit. Mine certainly is - but I'm not too worried, because my immersion
heater is for emergency use only, with all hot water normally being heated
by gas throughout the year.
--
Cheers,
Set Square
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In article ,
Paul S wrote:
The fused switch that controls my immersion heater is very hot. I know
that some heat will be generated in the cabling as the element gets
hotter, but the switch itself gets too hot to touch. I've checked the
connections inside the switch, and they all seem secure. Does anyone
have any other ideas why this switch is so hot?

Most likely IMHO the fuse and fuse contacts. Replace the fuse with a new
one and pinch up the contacts slightly if you can, checking they are clean
and not corroded.

But you might just change the entire FCU - they're not expensive.

--
*Modulation in all things *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Set Square wrote:
I'm not sure about the legality. It's generally considered to be good
practice to have a dedicated circuit - with its own breaker - for the
immersion heater. However, I suspect that a lot *are* spurred of a ring
circuit. Mine certainly is - but I'm not too worried, because my
immersion heater is for emergency use only, with all hot water normally
being heated by gas throughout the year.

And unless it's fed off the same ring as the kitchen, the chances of the
ring being heavily loaded these days is low.

--
*Laugh alone and the world thinks you're an idiot.

Dave Plowman London SW
To e-mail, change noise into sound.

"Paul S" wrote in message
...
I'm sure this can't be right.
The fused switch that controls my immersion heater is very hot.
I know that some heat will be generated in the cabling as the element gets
hotter, but the switch itself gets too hot to touch.
I've checked the connections inside the switch, and they all seem secure.
Does anyone have any other ideas why this switch is so hot?

Also, is it usual for an immersion heater circuit to be spurred off a ring
main, or should it be on it's own dedicated circuit wired with a higher
rated cable?

Thanks
Paul



Get it replaced and make sure the wire ends are nice and shiny and the
terminals are tight. Best use a decent make such as MK,

On 15 Oct 2004 "Paul S" wrote:

I'm sure this can't be right. The fused switch that controls my
immersion heater is very hot. I know that some heat will be generated
in the cabling as the element gets hotter, but the switch itself gets
too hot to touch. I've checked the connections inside the switch, and
they all seem secure. Does anyone have any other ideas why this
switch is so hot?

Either there's some arcing going on (can you hear any fizzing sounds
from the switch?) or there is some contact resistance which is
generating heat. Try taking the switch off and using some switch cleaner
on it. Make sure the terminals are screwed up onto copper, not
insulation. If that doesn't work replace the switch.

Also, is it usual for an immersion heater circuit to be spurred off a
ring main, or should it be on it's own dedicated circuit wired with a
higher rated cable?

I've always had the immersion heater on it's own dedicated circuit with
a 15amp fuse and 1.5 mm^2 cable. I don't see why you can't spur it off
a ring main as long as you're not running other powerful equipment off
it at the same time. For example immersion heater + electric kettle +
3kW fire would overload the ring main and blow the 30amp fuse.

--
Richard Porter
Mail to username ricp at domain minijem.plus.com
"You can't have Windows without pains."

I've always had the immersion heater on it's own dedicated circuit with
a 15amp fuse and 1.5 mm^2 cable. I don't see why you can't spur it off
a ring main as long as you're not running other powerful equipment off
it at the same time. For example immersion heater + electric kettle +
3kW fire would overload the ring main and blow the 30amp fuse.

The Regs are pretty explicit about immersions and similar water heaters
needing their own dedicated final circuit. The reasoning is, AFAIUI,
that when you do use that immersion, it's pulling a beefy 15A for a
sustained period (more than half an hour from cold, 20mins plus to
refill after a bath or similar). That's a substantial enough part of the
design load for the ring that it shouldn't be sharing with other
appliances: other water-heating appliances (kettles, washing machines,
dishenwashen) pull similar amperages but for a notably shorter time.
Only electric heaters pull similar long-lasting loads, and even those
are more often thermostatically controlled (not so many 3-bar electric
heaters sold these days!). And the "worst case" for a ring, safety-wise,
is a long, sustained overload - your 30A MCB will pass 40A for A Very
Long Time Indeed without disconnecting, but currents that big,
especially if unevenly distributed in the ring, can cause heating in the
cables and at joints which go beyond the realms of the Safe And Sensible.

As others have mentioned, these days our houses typically have lots of
small loads on the ring, and use of the immersion is more of a
backup/emergency thing than the usual way of heating hot water; so you
can often get away with sharing the immersion with the upstairs ring
(and it's what the Professional did in our current place when putting in
a new ring for an extension, with no spare ways in the CU). But it does
violate a direct and clearly-stated provision of the Regs, so shouldn't
be done lightly - or at all, depending on how smart you think you are...

Stefek

In article ,
James Salisbury wrote:
Get it replaced and make sure the wire ends are nice and shiny and the
terminals are tight. Best use a decent make such as MK,

I'm not convinced MK is worth the considerable extra cost - unless to
match an existing installation, looks wise. All these things conform to
the appropriate BS and should be equally capable of carrying their stated
load.

--
*Don't use no double negatives *

Dave Plowman London SW
To e-mail, change noise into sound.