electriciantrackworld – installing a timer switch for an immersion heater

Morning all.

I’m after a bit of sparky assistance please.

I’m looking to replace the simple on / off switch on my immersion heater with a timer switch, i.e

This:

with something like the Time Guard 7 Day Fused Spur Time Switch from Maplin

Is this simply a case of switching of the power at the mains, unscrewing the current switch from the wall, disconnecting the wires, wiring up the the timer switch and attaching it to the wall, switching on the power and away we go.*

Or is it more complex than that, and by complex I mean will the above steps result in electrocution / fire / death etc.

The immersion heater has a switch on the consumer unit so I don’t think it is on a fused spur.

Many thanks in advance.

*This I can do. When it comes to electricity changing a lightbulb / wiring a plug is currently my limit of knowledge.

Is this simply a case of switching of the power at the mains, unscrewing the current switch from the wall, disconnecting the wires, wiring up the the timer switch and attaching it to the wall, switching on the power and away we go.*

Basically yes.

As long as your current immersion heater is 3KW or less then the Maplin switch will be ok.

The immersion heater has a switch on the consumer unit so I don’t think it is on a fused spur.

What is the rating of the fuse for this? It should be 13A or less, otherwise you need to put a 13A fuse before that Maplin timer switch.

^ wot flaps said.

Check the rating of the heater and the supply. The switch will need to meet the same or greater specification.

I fitted one of these to handle up to 16A supply
http://www.timeguard.com/products/time/immersion-and-general-purpose-timeswitches/ntt03-24-hour-7-day-compact-electronic-immersion-heater-timeswitch

Cheers guys.

Yes its a 3KW immersion heater.

Here’s the fuse on the consumer unit:

Is that going to work OK?

Thanks again.

16A, so as the maplin switch is rated to only 13A (IIRC) you really need a 13A fuse between the two (or just buy a 16A timer switch).

The Maplin unit has a 13A fuse. That said Stoner’s unit looks abit better than the Maplin one, also I’d be tempted to add it in series with the switch so you can easily isolate it

@nickjb – couldn’t I isolate it by just flicking the switch on the fuse on the consumer unit?

I think I’ll go with Stoner’s recommendation.

Oh, and dont forget to use sufficient cross sectional cable/flex for the 16A rating too (if you cant reuse whats there to connect to the heater without changing it)

@nickjb – couldn’t I isolate it by just flicking the switch on the fuse on the consumer unit?

Yes, you can but I much prefer to have some means of local isolation for every appliance as well, especially as the timer switch has no ‘off’

I’m hoping there will be enough flex behind the current switch so I can wire the new one straight in without the need for additional flex.

More flex = more faff = more potential for disaster.

The 16A MCB is fine.
13A fuse in the timeguard timer.
Should be a straight swop.
Ensure the conductors are in good condition, they have a habit of getting hot and breaking down. Ensure that the connections are done up tight when you fit it as loose connections can be a fire risk.
Isolate by switching off the 16A MCB but you should check it actually does isolate it. MCBs can (rarely) fail to isolate and the board might be wrongly labelled or it has been swopped to another MCB.
If in doubt isolate the whole house with the big red switch.

Rich.

Cheers Rich

The board is correctly labelled as if I switch of the MCB the light on the current immersion switch doesn’t light up.

I’ll switch off with the big red switch though just to be safe.

Either of the Timeguard units would be suitable. It just depends on whether you want fuse protection.

Re you MCB’s in your consumer unit, I would investigate whether these are affected by the Wylex product recall from the other year. The 16A part number seems to correlate.

Evening all.

So, I have the timer switch ready to install.

At the moment there is an earth wire connected to the back of the on / off switch plate. Do I just disconnect that and attach it to the earth terminal at the back of the wall box? This is the view:

I’ve had a look behind the wall box and the earth terminal isn’t attached to anything.

Ta in advance.

You really should have an earth to your immersion heater.
I know it should be connected to earth (eventually) by the main bonding, but that wont work too well if a plastic fitting has been put in the pipework somewhere.
Where does the earth cable you’ve got come from?
And what is the supply cable – is that just 2 core (L+N, or is that the earth), or is it the outgoing flex that has no earth?

There should be two cables in that come out the wall and attach to the existing switch. The brown and blue from the consumer unit will go to the “feed” terminals (Live and neutral respectively)on the new timer, whilst the brown and blue to the immersion will go to the “load” terminals on the timer. This should correspond to what’s on the existing switch.

What you will probably find is that the earths of the two cables are actually run together in the green/yellow sleeving. It’s not easy to see from your pictures but you should see them both together if you look closely. If this is the case then that is good because as alanl says the immersion heater will need to be earthed and these two connected via the terminal on the switch is achieving this.

Now, the timer may or may not have an earth terminal on it. If so, just connect the existing two earths in the yellow/green sleeving into the terminal on the timer – ignore the one in the plastic pattress on the wall.

If there is no earth terminal on the timer, use the terminal in the plastic pattress (the one you’ve highlighted) as the connection point for the earths.

In either case ensure that they are both secure in the terminal as this will be necessary to give good earth continuity all the way from the consumer unit to the immersion heater.

Any questions, just ask.

Rich.

Rich

Many thanks for that explanation.

Here’s the end of the earth wire(s):

The timer switch doesn’t have an earth terminal so I’ll go ahead and attach the earth wire(s) to that.

You can see the two bare copper wires – one from each of the two cables. Put them into the terminal on the white plastic back box as highlighted above and Robert as they say will in fact be your father’s brother.

I had something similar at my flat but for an electric towel rail in the bathroom with the switch and timer in the old airing cupboard in the hallways.

Fitted a timer switch (toolstation) and also an isolation switch as I like to have both. They were wired into the old immersion heater circuit that was now redundant as a combi was fitted.

All done as part of a new CU unit and some other bits and bobs, I just installed all the wall boxes and let the electrician wire and install everything as it was all notifiable.