Using CAT5 Cable for Volt Free Thermostats

[Paul Waterhouse]

Hi All,
Long time reader but this is my first time posting a question. I have Googled the heck out of this and can't find a definitive answer, I'm hoping you guys can help.

I have a 6 zone underfloor system controlled by a Raspberry Pi running a system called Pi-Therm and it works brilliantly. I have a digital temperature sensor each zone, these connect to the Pi using Cat5 ethernet cable, the Pi then controls the zones via a bank of relays and switches the boiler and zone valve at the right times etc...

We are now selling the house and whilst explaning to the new buyer how the system works they glazed over and I started to have visions of me providing 24hr support when they couldn't figure out how to boost zone 3 for 30 minutes - you get the idea.

So, what I proposed was to replace the "smart" system with something less "smart". I will replace the whole Pi system with a wiring centre and the sensors with cheap, simple programmable stats (Salus RT500?). My question is, can I run volt-free stats over the existing Cat5 cable or do I need to try and pull 1.0mm T&E to each stat?

I know that Cat5 cable can handle 48V as that is what power-over-ethernet uses but I guess that the big question is more about the current limitation of such thin cable (AWG 24 I believe). Also, I don't want to sell the house and there be any repercussions, I'd rather do the job right than hear about it from some suit in 12 months time!

Cheers,
Paul.

 

[Welder]

If you are simply using the Cat5 to switch something like 12v via a local (assuming self or locally powered) stat then it will be fine provided its not too long a run and you don't get too much volt drop. I'd be perfectly happy running 500ma through it.

 

[ShaunCorbs]

Aslong as it's bolt free your fine

 

[Welder]

As in Usain???

 

[Paul Waterhouse]

Yeah, wouldn't want Usain Bolt in my heating system

Thanks for the advice, I presume that if I use volt-free stats I also need a volt-free wiring centre??

 

[ShaunCorbs]

Correct or one that can do some do both

 

[Welder]

All wiring centres are volt free till you add some!

All terminals can be isolated so its simply more about making sure you don't intro voltage where it's not needed. Remember some contacts are specifically designed for AC or DC or if the same are used are differently rated.

 

[Chuck]

I know that Cat5 cable can handle 48V as that is what power-over-ethernet uses but I guess that the big question is more about the current limitation of such thin cable (AWG 24 I believe).

0.58A per core according to the table towards the bottom of:

Category 5 cable - Wikipedia

Personally, I'd sell the system as is and let the next owner decide what to replace it with. If I did decided to replace it, however, I'd replace the CAT5 with mains-rated cable. There's no guarantee that someone in future won't replace the thermostat with a 240V one and they may not notice that the wiring is the wrong type.

 

[Welder]

0.58A per core according to the table towards the bottom of:

Category 5 cable - Wikipedia

Personally, I'd sell the system as is and let the next owner decide what to replace it with. If I did decided to replace it, however, I'd replace the CAT5 with mains-rated cable. There's no guarantee that someone in future won't replace the thermostat with a 240V one and they may not notice that the wiring is the wrong type.

Call me a liar for 80ma

At the end of the day you are selling your house. So long as you are honest and provide details what have you to worry about? No one can legislate for idiocy? So, based on your thinking, you may as well pull 10mm through just in case they attach a 10KW shower to the end of the cable

Do it properly with what you have but do it right by detailing what's done and leave it so they HAVE to find it. End of.

 

[Chuck]

Call me a liar for 80ma

I didn't. I simply cited a source for the figure because the OP asked for a 'definitive answer'.

 

[Welder]

I didn't. I simply cited a source for the figure because the OP asked for a 'definitive answer'.

Sorry Chuck, I realised you weren't really having a pop. Just messin.

 

[Paul Waterhouse]

Do it properly with what you have but do it right by detailing what's done and leave it so they HAVE to find it. End of.

Good point Dave. I am inclined towards hanging volt-free stats on the exising cable and documenting the work for future reference as it's not exactly conventional.

I was starting to think stuff it, just leave all the exisiting kit in place along with a large print copy of the instructions but we really want to keep our buyer sweet. She's a cash buyer, we've been trying to sell for a while and we've totally fallen in love with the place we're buying so I was trying to grease the wheels and keep things on track. If all it costs me is a couple of hundred quid and a short day of labour I'm as happy as the proverbial pig...

 

[Mark K]

Hi All,
Long time reader but this is my first time posting a question. I have Googled the heck out of this and can't find a definitive answer, I'm hoping you guys can help.

I have a 6 zone underfloor system controlled by a Raspberry Pi running a system called Pi-Therm and it works brilliantly. I have a digital temperature sensor each zone, these connect to the Pi using Cat5 ethernet cable, the Pi then controls the zones via a bank of relays and switches the boiler and zone valve at the right times etc...

We are now selling the house and whilst explaning to the new buyer how the system works they glazed over and I started to have visions of me providing 24hr support when they couldn't figure out how to boost zone 3 for 30 minutes - you get the idea.

So, what I proposed was to replace the "smart" system with something less "smart". I will replace the whole Pi system with a wiring centre and the sensors with cheap, simple programmable stats (Salus RT500?). My question is, can I run volt-free stats over the existing Cat5 cable or do I need to try and pull 1.0mm T&E to each stat?

I know that Cat5 cable can handle 48V as that is what power-over-ethernet uses but I guess that the big question is more about the current limitation of such thin cable (AWG 24 I believe). Also, I don't want to sell the house and there be any repercussions, I'd rather do the job right than hear about it from some suit in 12 months time!

Cheers,
Paul.

A volt free thermostat means it doesn't supply any voltage, the voltage will come from whatever you are going to control with it.

In order to make something work with a volt free switch (in your case a thermostat) you supply a voltage, it switches that voltage through, or not, and a current flows to operate whatever you are switching.

For example a light switch is a volt free switch.

So if you try to create a traditional system here with your existing cat 5 wiring, you will be switching 230v. Cat 5 cable is not suitable for that, regardless of the current.

Theoretically, you could transform the whole system down to under 48v (24v would be easiest, transformers and relays are readily available) and use relays switched by the 24v to switch the 230v where it is needed, i.e. at the pump and boiler.

 

[Paul Waterhouse]

A volt free thermostat means it doesn't supply any voltage, the voltage will come from whatever you are going to control with it.

In order to make something work with a volt free switch (in your case a thermostat) you supply a voltage, it switches that voltage through, or not, and a current flows to operate whatever you are switching.

For example a light switch is a volt free switch.

So if you try to create a traditional system here with your existing cat 5 wiring, you will be switching 230v. Cat 5 cable is not suitable for that, regardless of the current.

Theoretically, you could transform the whole system down to under 48v (24v would be easiest, transformers and relays are readily available) and use relays switched by the 24v to switch the 230v where it is needed, i.e. at the pump and boiler.

Aahh, Light bulb moment! Right, I am playing along at home now . Sorry guys, I was a bit slow on the uptake

So I had a look at low voltage wiring centres - wow £120 or so! As I already have a mains voltage wiring centre and a roll of 1.0mm cable, and as most of the wiring is pretty easy to pull, I am thinking I'll just use what I have. It'll take me half a day to pull all the new cables and the other half of the day to wire it all up and test it (then another day to program all the stats! ).

Many thanks for all the help guys, very much appreciated.

 

[Welder]

To be honest Paul, from your response above, I now realise you do not have the knowledge or understanding I had assumed. Yes I know assuming is something one should never do...

If you had not worked out the basics, as Mark described, then I'd suggest you ask someone qualified to do it to ensure it is safe. Remember, just because you sell the place, today you are legally liable for some considerable time post event. You cannot apply 'caveat emptor' in the same way anymore. I'm concerned that putting this lot in may be considered minor works electrically and so must be certified.

 

[Mark K]

To be honest Paul, from your response above, I now realise you do not have the knowledge or understanding I had assumed. Yes I know assuming is something one should never do...

If you had not worked out the basics, as Mark described, then I'd suggest you ask someone qualified to do it to ensure it is safe. Remember, just because you sell the place, today you are legally liable for some considerable time post event. You cannot apply 'caveat emptor' in the same way anymore. I'm concerned that putting this lot in may be considered minor works electrically and so must be certified.

As a NICEIC commercial qualified supervisor, I would say minor works would not cover it.

 

[Welder]

As a NICEIC commercial qualified supervisor, I would say minor works would not cover it.

So what would?

 

[Mark K]

So what would?

Minor works is intended for modification of an existing circuit, or replacement of a single device. Personally, I think this would fall under adding a new circuit.

It's always open to argument, and you could say the feed to the original controls was the circuit, and adding on the wiring centre and stats constitutes modifying that circuit. I wouldn't as it's quite extensive, more that one device etc.

I think you'd need an Electrical Installation Certificate rather than a Minor Electrical Installation Certificate.

 

[Paul Waterhouse]

To be honest Paul, from your response above, I now realise you do not have the knowledge or understanding I had assumed. Yes I know assuming is something one should never do...

If you had not worked out the basics, as Mark described, then I'd suggest you ask someone qualified to do it to ensure it is safe. Remember, just because you sell the place, today you are legally liable for some considerable time post event. You cannot apply 'caveat emptor' in the same way anymore. I'm concerned that putting this lot in may be considered minor works electrically and so must be certified.

That's fair comment Dave and I take your point. I can see how some of my posts may portray me as less than competent.

If it is beginning to look like I'll need a certificate I'll give my sparky friend a call and see what his take is on the whole thing.

 

[Chuck]

'll give my sparky friend a call and see what his take is on the whole thing.

I think you'd be better off giving your solicitor a call first. I think you'll find they say don't touch the system if the buyer has already seen house. It'll just be a matter of including the usual boiler plate in the contract that says that the seller makes no warranties about any system and the buyer must commission their own surveys and tests, and rely solely on them.

Don't worry about providing 'IT Support' to the new owner. Don't offer this as part of the sale and once the sale has completed don't answer their calls.

 

[Mark K]

I think you'd be better off giving your solicitor a call first. I think you'll find they say don't touch the system if the buyer has already seen house. It'll just be a matter of including the usual boiler plate in the contract that says that the seller makes no warranties about any system and the buyer must commission their own surveys and tests, and rely solely on them.

Don't worry about providing 'IT Support' to the new owner. Don't offer this as part of the sale and once the sale has completed don't answer their calls.

Personally, I agree with this, homes are going smart now, be upfront about how it's a step forward.

Paul - If you really want to be proactive, spend that day you were going to spend re-wiring it carrying out normal tasks on it, like changing times, extending for half an hour and write out a cheat sheet for each one and give it to the new owner.