Wiring a 48 Hour Time Clock

[Darkness]

I've got a new water heater tank fitted outside and I currently have it connected to a socket via plug. My 48 hour time clock arrived yesterday so I need to fit it so that the heater comes on during the night.

Should I connect the clock to a 20a Isolator etc and use a 16A MCB at the cu?

Or like some chap suggested, spur of the neighbouring socket and use a fcu with 13a fuse?

I prefer the first method.

The clock is 3.8kW single phase, 16A max.

Cheers for any help.

 

[jwilliams]

Or like some chap suggested, spur of the neighbouring socket and use a fcu with 13a fuse?

The clock is 3.8kW single phase, 16A max.

Is that a reasonable answer?

 

[Darkness]

Not Really. Do you agree or disagree with the FCU?

I've seen some fitted with an Isolator hence why I mentioned it plus the fact I've a 20a Isolator lying here doing nothing.

 

[jwilliams]

Not Really. Do you agree or disagree with the FCU?

Not an expert, but I wouldn't run a 16A load through a 13A fuse.

 

[Darkness]

It's been running on a 13a fuse/plug for the past 2 weeks fine.

With the timer, it will run for a couple of hours every 2nd day.

I've a spare 32a mcb in my cu not being used so I wonder if I can still use that with the 20a Isolator acting as the breaker?

 

[Spark123]

jwilliams, I think you have your wires crossed, the 16A is the maximum current that the clock can handle. As long as the clocks rating is higher than that of the load then the clock is suitable for use.
Darkness, I take it you have a 3kw immersion heater? If so it is better fed from its own circuit from the consumer unit.

I've a spare 32a mcb in my cu not being used so I wonder if I can still use that with the 20a Isolator acting as the breaker?

An isolator is a switch, not a protective device. You will need a 16A MCB in the CU to adequately protect the circuit.

 

[jwilliams]

jwilliams, I think you have your wires crossed, the 16A is the maximum current that the clock can handle.

Ah, you're quite right. Really must stop trying to do 4 things at the same time

 

[Spark123]

Darkness,
I take it you are aware of the building regs (Part P England/Wales) re this type of work? It might fall into the category of being a special installation (outdoor power circuit), is the water heater actually outside?? adding a new circuit is notifiable in any case.

 

[Darkness]

Cheers folk.

Yes it's pretty much an immersion heater. I'll have to get a 16a mcb then.

Is 1.5mm 3 Core Heat Resistant Flex still to be used despite it's near enough outdoor location?

btw, I am exempt from Part P. Lucky Me.

 

[Spark123]

The link from the switched flex outlet plate to the immersion needs to be in heat resistant flex. All the fixed wiring can be done in 2.5mm twin + earth depending on its length and installation method.

 

[Darkness]

I had a good look at the heater and timer switch to see what's needed and I'ts just dawned on me it's a double immersion heater which needs a 32a supply. I only had the one wired with a plug.

I have the 32a mcb but the 20a Isolator is no use now.

Now the biggest problem is the timer switch which is rated 16a max. How do you get around this one? The heater supplier stated its the correct timer for the tank.

Unless I just wire the one immersion and have it on the timer much longer. I doubt there will be much difference in running cost apart from the speed the tank is heated which isn't a factor.

 

[securespark]

Is it an E7 system?

 

[Darkness]

The intention was to change to E7 but I'm still wondering if its beneficial to me yet.

Y?

 

[Spark123]

I believe the intended purpose for the twin elements is the bottom one is run on E7 and heats the whole tank of water up at night. The top element is on a normal daytime rate and used to heat the water at the top of the tank as required and is supplied via a boost switch.

 

[Darkness]

Your probably right.

I'll hunt for the documentation of the heater and confirm what you've stated but I expect you to be correct.

btw, should I bother with an Isolator?