Drayton wiser hub wiring

[btjtaylor]

Hi all

I am planning an installation of the Drayton Wiser hub to my Baxi Assure 36 boiler - can someone sanity check my wiring?

Here is the current wiring (there is a weather sensor and associated wiring which was never connected - as far as I can tell it doesn't matter at this point):



I plan to wire off the boiler's wiring connection points and pass the flex through the hole that the unused weather compensation cable comes through as it's much easier than trying to get another cable into the FCU - according to the boiler manual this is acceptable if the load is under 1a - I couldn't actually find the power consumption of the wiser hub online but im sure it won't be significantly more than other programmers etc - certainly nowhere near 1a:



Hopefully this is correct?

Also attached pages from the boiler manual dealing with the connections:



Thanks in advance
Ben

 

[CBW]

Hard to work out on your drawing if correct, but you might also be able to use opentherm. Make sure you get Kit 1 for a Combi. The Wiser states 2 amp but a 1 in brackets, so unsure what this means. Opening the boiler forms part of the combustion circuit and needs to be checked for safety afterwards

 

[RandomGrinch]

The Wiser states 2 amp but a 1 in brackets, so unsure what this means.

This is the switch rating of the relays - the DC value is usually in brackets and is less than the AC rating. With AC, a sudden break caused by a switch (the relay) changing state, is less likely to cause a sustained arc than DC, hence the rating for AC load is higher.

- I couldn't actually find the power consumption of the wiser hub online

The power consumption is listed at 6.2W max, way less than an Amp!



A general note, you seem to have a black wire still connected to terminal 1, and extending to a terminal block - as this will still be a switched live, it will be safer to disconnect this wire, in the same way the grey wire is. For neatness and safety, you can park the ends of the grey and black wires in a spare terminal block.
If you are using a new cable to the Hub r, it is no longer acceptable to sleeve and use an earth cable in the flex as a switched live. You would need a 3 core plus earth cable; ensuring the earth's are connected, even if unused.

But as @CBW says above, you may wish to investigate the benefits of using opentherm.

 

[btjtaylor]

Thanks for the replies both - I have had a look and the boiler does indeed have OpenTherm terminals and the wiser kit appears to support this using the kit I intend to purchase. Would the boiler typically need any kind of configuration to enable this functionality? The manual doesn't really explain it.

From doing a bit of reading I *think* I don't need the switched live connection if using opentherm - is that correct? In that case I think I can use a single 4 core + earth cable and use 2 of the cores for the OpenTherm connection. I did read somewhere its not really recommended to do this but it seems like a lot of people online have done this without problems and it may be difficult to get a third cable into the boiler as there's just 2 glands for this purpose (the other one will be used to feed the fused spur)

Edit: On this video they have 2x cables going through a single gland so I am ok to keep high/low voltage separate as recommended (seems sensible anyway). Seems best to run a 2 core + earth for the power and then a seperate 2 core for opentherm.

 

[RandomGrinch]

From doing a bit of reading I *think* I don't need the switched live connection if using opentherm - is that correct?

Correct.

I think I can use a single 4 core + earth cable and use 2 of the cores for the OpenTherm connection. I did read somewhere its not really recommended to do this

It isn't recommended, and isn't best practice, considering the potential destruction to the boiler and controls, should mains voltage get to an extra low voltage PCB.
However, as the insulation is rated for the highest voltage the cable will carry, there shouldn't be a problem. Just double check your connections, before turning anything on!

 

[stem]

The Wiser states 2 amp but a 1 in brackets, so unsure what this means.

The first number is the rating for a 'resistive load' (e.g. heating element) and the figure in brackets is for an 'inductive load' (e.g. motor). Only don't ask me if a Baxi Assure 36 boiler is inductive or resistive.

 

[RandomGrinch]

The first number is the rating for a 'resistive load' (e.g. heating element) and the figure in brackets is for an 'inductive load' (e.g. motor). Only don't ask me if a Baxi Assure 36 boiler is inductive or resistive.

Yes, sorry, I was mistaking the markings for the contact voltage ratings (which are usually more obvious on relays).

I would guess the resistive load rating has slightly more relevance when connected to the boiler, than say if the hub was controlling a pump

 

[btjtaylor]

Revised diagram based on opentherm (getting a bit messy now - wish i'd saved a version with no wires drawn on, or used visio!). Black cable disconnected that goes to fused spur, i'll put that into a connector block or similar at the boiler end so as not to have a random potentially live cable flapping around in the backbox



This matches visually with the Baxi video where they have connected their Opentherm-based controls in the same manner so think i'm all set

 

[RandomGrinch]

i'm all set

Yup, though no need for the link between L and Com on the hub.

Good luck!

...and the boiler should be checked for gas safety after replacing the cover!

 

[btjtaylor]

Good point, i'll get rid of that

Boiler is due a service anyway so i'll get it checked out at the same time

Thanks!