Air source heat pump/immersion heater query

[Welderpaul]

Here's the insides...

Does that look correct for the new bit?..

And measured just because I can, immersion pulls 11.5 A

 

[sparkysy]

yes your drawing will work, I was suggesting using your new timer to switch the contactor so instead your switch live from the new timer would link into terminal A1 and your neutral if it is the way you have drawn it is already connected with the link form terminal 3 to terminal A2 so wouldn't need to put one in from the new timer output. If you get what I'm saying?!
Sy

 

[Welderpaul]

I get you yep. Any particular benefit of doing it either of the two ways?

 

[sparkysy]

Not particularly no, the way I described will see no heavy load through the timer as the contactor is doing the heavy switching, will make the timer last a lot longer! Oh and one less wire!

 

[Neilj]

I'd agree with @sparkysy on the wiring, the timer contacts won't be rated very high in terms of current so you're better off wiring it so your additional timer triggers the contactor, same as the existing one does. Then all the high current switching load is handled by the contactor.

 

[Welderpaul]

So like that yeah?

 

[sparkysy]

Yep that's it spot on!

Afaik in response to @Neilj those timeguard timers are capable of 16a resistive load.
They are good timers and I have used them for immersion heater control many times with no issues. But would still be best in this case to use the contactor as in @Welderpaul 's last diagram!

Hope it all works and you get some extra heat!
Sy

 

[Welderpaul]

will need 2 supplies 3kw on each using 2.5mm and fed of 16 amp mcbs

No point rushing these projects...
Does an immersion require a fused spur, or is just a switched spur ok?

 

[dobbslc]

I found 13 amp switched spurs on a 3KW immersion get hot and start to melt so I now use a 20 amp double pole isolator but you have to be sure the flex and 2.5mm cable is protected at the DB properly.

 

[brightspark]

No point rushing these projects...
Does an immersion require a fused spur, or is just a switched spur ok?

if on a 16 amp supply just a double pole switch spur required

 

[brightspark]

I found 13 amp switched spurs on a 3KW immersion get hot and start to melt so I now use a 20 amp double pole isolator but you have to be sure the flex and 2.5mm cable is protected at the DB properly.

you can use 1.5mm heatproof flex on immersion heaters as you say the 13 amp fused arent realy up to the job /the 20 amp double pole switch is best but will be on a 16 amp breaker the 1.5mm flex is rated for 16 amp

 

[dobbslc]

That's basically what have except 2.5mm flex.

 

[Welderpaul]

Great thanks chaps.

 

[Welderpaul]

Not related, other than its another lecky question. Is the DNO fuse inside the centre block under the meter? It looks like the only way of accessing it is to unscrew the end caps

We'll ignore the leaking pitch for now.

 

[Bornfree]

I think it would be in the left hand cast iron lump.

 

[sparkysy]

Definitely in the cast iron enclosure to the left.
I would get your Dno to look at that, all the ones I have come across like that have been upgraded. They can go with a big bang when opened!
The thing under the meter is just to prevent access to the tails and connections.

 

[Welderpaul]

Ah, ok. great I will speak with them. What age do you think the service head is?

 

[Bornfree]

Ah, ok. great I will speak with them. What age do you think the service head is?

1960s to early 1970s

 

[sparkysy]

Yes I'd have said 60s,
Most of the ones that have been changed have had the main cable cut in the road and a new PME cable installed with a new cut out.

 

[Welderpaul]

Yes I'd have said 60s,
Most of the ones that have been changed have had the main cable cut in the road and a new PME cable installed with a new cut out.

Whats the likely size of the substation fuse on the other end of the incoming PILC?..