Switching an immersion heater from Loxone 16a Relay

[Aaron]

Hopefully an elementary question but want to check my thought process please.

I understand that usually an immersion heater (3kw for instance) has a dedicated MCB and radial to a 20a double pole isolator where the immersion flex is connected.

I would like to control my immersion from my Loxone Relay Extension although a little unsure how best to achieve this.

While a 3kw immersion should draw less than 13a and thus be suitable for for the 16a relays (actually 20a according to the relay documentation), I want to ensure the relay is protected during fault.

Ready in place I have a 16a RCBO and dedicate 4mm T&E. Should I fuse the connection at the isolation point? A 16a fuse seems ideal but their scarcity suggests this is not a common approach.

As I type this, I think the question is more generic: How best to protect the mains relays in a Loxone implementation?

thanks

Aaron

[Rob]

I have a set of dedicated RCBO's in my Loxone cabinet to provide full protection to the mains circuits being switched by my relay extension.

I have mains coming in from consumer unit through a 2pole 100A isolator and then fed through the RCBO's to the relays and then on to the equipment.

The important thing to remember with RCBO's is that you can't common the neutrals from different RCBO's so you need a different set up from the usual neutral busbar.

I use a number of 5-way WAGO 221 connectors as mini "neutral busbars" and works fine.

[Jamie Blackman]

Hi Aaron,

The best way I can think is to use a contactor. The immersion will still be fed by the RCBO but you can connect a contactor to loxone so it switches on when it gets the command. This means that loxone is the switch and the load is all on the fuseboard.
We use them a lot for the door switches in hotels so when you take the card out when you leave it cuts the power but the full load can't be all on the key device.

Link below...

https://www.tlc-direct.co.uk/Products/CMREL230slash20slash20.html

Cheers
J

[Aaron]

Thank you for the advice Gents.

Rob - I have a very similar set-up. 100amp double pole and dedicated RCBO's before the Loxone relay. While I know that the RCBO will activate if the immersion tries to draw too much power under a fault condition, what I'm unsure upon is whether this fault current would have already 'fried' the loxone relay before activating. I have seen installations with the 24v side fused so wondered if something similar is typical on the 230v side (or if the MCB/RCBO) is sufficient?

Jamie - Great idea concerning the contractor and seems like an ideal solution (maybe for the cooker too; correctly rated). Presumably these would be mounted centrally before distribution rather than at the appliance end (or does it not matter)? Just seems a bit of a waste to require a contactor behind an already beefy and expensive relay.

[DavidL]

You should be fine with the dedicated Loxone relay extension. If you were using a miniserver or other extension relay, I’d suggest using an external relay/contractor for this.
I personally use a separate, fairly inexpensive, relay that loxone switches to power the immersion.

Just a couple of notes for you, you may find that 4mm isn’t necessary depending on your cable routing and installation method. Clipped direct, 2.5mm is usually sufficient.
Make sure you provide a double pole isolator where your immersion terminates to your cable from your relay. The regulations state “immersion heaters should be supplied through a switched cord-outlet connection unit complying with BS 1363-4”

David

[Flux]

On all my digital output i used the following contactor, peace of mind and the ability to take Loxone out of the loop if nec. 

finder 22.32.0.024.4340

[Aaron]

Thanks All

I think the Contactor is a sensible option although I bought the relay second hand so I'd probably be spending out to protect something which is worth less than the protection (on an individual relay basis).

As long as a fault on the relay doesn't fry the whole 24v side I think I'll be fine. I'm probably also putting faith in expecting Loxone to know what they are doing by offer a 16a relay in the first place (although I did read in the relay documentation they are actually rated at 20amps).

@DavidL - Thanks for the general advice. I've done the whole house on 4mm LSOH (a somewhat nuisance to work with in hindsight!) usually protected with flexible steel conduit. Just need to replace the existing isolator.

Great help and advice as always!

[Brad]

Anyone have advice on where to get latching 10vdc contactors for the US market? I was initially going to be using the relay extension for a larger load like you were but realized that if the loxone extension was down then I'd lose power to the rooms I put the outlets on the loxone relay. I have a slew of unused analog outputs that I'd like to control some latching relays from.