Demista pads powered by a 24v SELV transformer, with cabinet hinge used as a conductor

[mc_nebula]

I'm working on a site in the UK where a joinery company will be installing bespoke vanity cabinets.
The cabinets will have MDF/mirrored doors with a demista (heated pad) laminated between the mirror and the MDF door.
The Demista is powered by a 24v SELV transformer, located behind a small panel in the cabinet, in the normal way.

There is a cable, run from the transformer, via a routing, into a tiny pocket behind the Blum hinge mounting plate, in the cabinet side.
The cable is terminated with a spring connector, which is clamped by the Blum hinge mounting plate, see attachment mountingplate.png

There is a corresponding cable and spring connector in the 35mm round drilling for the actual Blum hinge, which would be clamped by the hinge - see attachment hingeplate.png

The 24v power for the demista is intended to flow through the hinge itself - the actual metal body of the Blum hinge will be energised with 24v, from the SELV transformer.
The hinge at the top of the door would be positive and the hinge at the bottom would be negative from the SELV transformer.
The hinges are around 80cm apart.
The door itself will be lacquered MDF.

There is a lot of debate at the moment over the acceptability of using the exposed metal body of the hinge as a conductor.
The on-site electrician doesn't have a problem with it, but I am just slightly uncomfortable.

Does this comply with UK regs?
If it doesn't, please can someone point me in the direction of the regulations it contravenes?

Many thanks in advance!

 

[DPG]

Has anyone tested it electrically? Not just with an ohmeter, but using a tester which feeds a current through to test it under stress. Similar to an earth bond test, but obviously this is not being used as an earth.

Any high resistance will create heat and a) waste power and b) possibly be fire risk

Also, what effect will the ingress of damp and moisture make to this joint? Bearing in mind it is only pressure holding the contacts against each other.

Having said that, it's a clever idea.

 

[mc_nebula]

Has anyone tested it electrically? Not just with an ohmeter, but using a tester which feeds a current through to test it under stress. Similar to an earth bond test, but obviously this is not being used as an earth.

Any high resistance will create heat and a) waste power and b) possibly be fire risk

Also, what effect will the ingress of damp and moisture make to this joint? Bearing in mind it is only pressure holding the contacts against each other.

Having said that, it's a clever idea.

I'm assured that the joinery company have done extensive long term testing under load.
I don't have it to hand, but I have seen a table of acceptable pad sizes for this set-up, including the current draw. They also specify the wire size that should be used, and I also recall that they advise against using 12V Demistas because of the increased current that they draw, compared to the same size 24V pads.

I'm not an electrician - I am a curious construction project manager, and certainly not qualified to comment on the overall set-up - hence my post here!

Getting another spark onto site won't be an option for now - this isn't directly my responsibility, and at this stage, it would ruffle far too many feathers, as I am sure you can imagine!


Assuming the joinery company have done appropriate testing, and the hinge isn't introducing high resistance or getting hot, how would this setup sit within the regs?
Something about it just makes me feel slightly uneasy. I'm being told it's fine, but my unease makes me want an informal second opinion.
Are you really allowed to have exposed extra low voltage conductors in zone 2 of a bathroom?

 

[davesparks]

would this setup sit within the regs?
Something about it just makes me feel slightly uneasy. I'm being told it's fine, but my unease makes me want an informal second opinion.
Are you really allowed to have exposed extra low voltage conductors in zone 2 of a bathroom?

You mention that it is fed from an SELV supply so there won't be a shock risk. I can't see any reason within the regulations why this should be a problem.

I don't like it as a setup, but that's personal opinion and not regulation.

 

[mc_nebula]

You mention that it is fed from an SELV supply so there won't be a shock risk. I can't see any reason within the regulations why this should be a problem.

I don't like it as a setup, but that's personal opinion and not regulation.

Hi Davesparks, thank you for your reply.

A colleague has mentioned 414.4.1 as not being satisfied just now.
I'm not an electrician, but I don't think they are interpreting this correctly.
Could you look at this?

edit to add that there is a 24V LED strip in the same cabinet.
This is an IP rated LED tape, fed from a different SELV transformer.
The tape is housed in an aluminium extrusion, with a plastic diffuser clipped in.

Could this bear relevance to the regulation noted?