12V & 5V 'Structured Cabling'?

[B Wilde]

Hi, I'd appreciate any expert advice on this;

I'm having my house rewired and keen to get minimise wall warts/power adaptors for the various permanent smart home fixtures that I'm inevitably going to burn cash on over the coming years (i.e. 5V (USB) wall fixtures like NEST thermostats, RING alarm panels etc as well as 12V accessories like doorbells and blind motors).

Is there any practical or regulatory reason I couldn't / shouldn't run 12V feeds back to a central 7A 12V DIN transformer in my CU for blinds and 12v kit (and then use a small step down to 5V where required for permanent USB devices)? I believe the max run will be about 35m so hopefully, voltage loss will be negligible.

I respect this is only what people have done with doorbells for years but didn't want to overengineer if there's a smarter way others are addressing the proliferation of low voltage, permanent tech. I plan to use power-over-ethernet PoE wherever possible for network stuff.

Thanks in advance..

Ben

 

[Harry Bloomfield]

Is there any practical or regulatory reason I couldn't / shouldn't run 12V feeds back to a central 7A 12V DIN transformer in my CU for blinds and 12v kit (and then use a small step down to 5V where required for permanent USB devices)? I believe the max run will be about 35m so hopefully, voltage loss will be negligible.

No reason at all, apart from the issue you mention above, of volts drop due to distance. A 12v 4mm main around the house might be all you need, to get around the volts drop issue.

 

[mattylad]

The idea of 12v to 5v adapters is going to be the same as having 240vac to 5vdc adapters.

Realistically how much would use 12v?
These days most stuff use a 5vdc source.

 

[Swwils]

Just run cat5 or 6 to every location.

CU not the best place, terminate it at network location.

Inject what you need.

 

[ericmark]

USB is a problem as there is hand shaking, where the outlet and the device work out charge rate, so as said really does not matter is dropping 12 to 5 or 230 to 5.

However as I have found to my cost smart devices do fail, not had a 5 volt outlet fail yet, but have had smart sockets and light switches fail, so now look for plug in devices rather than built in.

I have wired a farm house on the Falklands 12 - 0 - 12 volt for battery powered lighting, but it was a lot of work, and only really worth it as 230 volt was on the generator.

Nest thermostat gen 3 uses it's own heat link for the power to the thermostat, and also same wires are used for data, so better if hard wired to heat link, there is an option to use wireless and USB powered cradle, but if rewiring better to use power from heat link, so data goes on same cable.

My son wired his house with idea of as much hard wired as he could, however simply can't buy TRV heads which can be hard wired, there are some designed for under floor heating hard wired, but it seems in the main we have no option, I have been moving to Zigbee was using Energenie, also have bluetooth, and my idea of keeping to one system did not last.

Many years ago in the days of the fax machine I wired the house with phone/fax double sockets, one internal and one external so if the fax went faulty I could easy swap phone sockets, idea was when a fax is received it would auto disconnect phones so better signal for fax, today all redundant, phones all wireless, and fax long gone, had to disconnect as it was reducing broad band speed, it seems best laid plans of etc.

So main thing is have anything with electrolytic capacitors so easy replaced, they don't last for ever, so having them hard wired is not a good idea.

 

[B Wilde]

No reason at all, apart from the issue you mention above, of volts drop due to distance. A 12v 4mm main around the house might be all you need, to get around the volts drop issue.

very helpful thanks. RE: 4mm, are you suggesting 4mm flex or 4mm T&E? If T&E that's considerably larger than I imagined

 

[B Wilde]

The idea of 12v to 5v adapters is going to be the same as having 240vac to 5vdc adapters.

Realistically how much would use 12v?
These days most stuff use a 5vdc source.

thanks, I was thinking of the 12v blind motors I've got to drive (about 5 of them) and the Ring alarm accessories that use 12-24v. For the 5V, i had planned on using very small inline 12>5v regulators inside patress boxes behind the equipment - I've not found 240v alternatives that are either small enough or UL certified or quality I'm willing to trust. If you know of any i'd appreciate a steer.

 

[JohnW2]

thanks, I was thinking of the 12v blind motors I've got to drive (about 5 of them) and ...

They sound like things that might draw a fair bit of current, hence a potential voltage drop issue with long cable runs. Do you know the the power or current of the motors?

Kind Regards, John

 

[Swwils]

Run 2 cat 6 to every location for return.

 

[Robin0577]

I totally agree that for things like the blind motors you're going to need a high current supply and pretty heavy cables.

For smart home devices that are purely electronic and don't contain motors or other high current components, your best bet is most likely to choose devices that operate on standard 48v PoE. Things like cameras, wifi access points, etc. That may mean ditching popular domestic brands like Nest and Ring, and choosing slightly more professional quality products. You simply need to choose a network switch with enough power capacity for all your devices.

Edit to add...

If you have a 5/9/12v device that you want to power from standard PoE, just use one of these. https://cpc.farnell.com/tp-link/tl-poe10r/splitter-poe-tl-poe10r/dp/CS23514

 

[mattylad]

[QUOTE="B Wilde, post: 5009963, member: 278368" UL certified[/QUOTE] Are you in the UK or in the states?

UL certification is a US thing.

 

[plugwash]

Given a length and acceptable proportion of power loss, halving the voltage quadruples the required cable size. So what would be a negligable current in a 240V system can become a very significant issue on a 12V system.

 

[Harry Bloomfield]

very helpful thanks. RE: 4mm, are you suggesting 4mm flex or 4mm T&E? If T&E that's considerably larger than I imagined

Either type will do. Volts dropped will depend upon the loads applied and how much drop is acceptable along the cable route. With such low voltages combined with distances, volts drop always needs to be considered, rather the current rating of the cable.

 

[B Wilde]

I totally agree that for things like the blind motors you're going to need a high current supply and pretty heavy cables.

For smart home devices that are purely electronic and don't contain motors or other high current components, your best bet is most likely to choose devices that operate on standard 48v PoE. Things like cameras, wifi access points, etc. That may mean ditching popular domestic brands like Nest and Ring, and choosing slightly more professional quality products. You simply need to choose a network switch with enough power capacity for all your devices.

Edit to add...

If you have a 5/9/12v device that you want to power from standard PoE, just use one of these. https://cpc.farnell.com/tp-link/tl-poe10r/splitter-poe-tl-poe10r/dp/CS23514

thank you for this - I've not come across this device. It seems to be exactly what i was after!

 

[B Wilde]

Either type will do. Volts dropped will depend upon the loads applied and how much drop is acceptable along the cable route. With such low voltages combined with distances, volts drop always needs to be considered, rather the current rating of the cable.

thanks again.