Hive thermostat replacing old danfoss

[Dan42]

Hi,

Can someone give me some guidance please. I'm replacing a faulty danfoss central heating thermostat/timer with a single channel hive on a combi boiler. The danfoss was a battery powered unit so only had two control wires going in to it, one into a terminal marked 3N/O and the other into 1 COM. I've replace the cable with some four core to supply the hive receiver with live and neutral it requires and just taken these both from the junction box after the switched fused spur that supplies the boiler. For the two control wires I've gone into the common terminal on the hive with one and the heating on (NO) with the other. Both of these wires coming from the boiler are black, so I've no idea which is which.

Problem is the receiver unit isn't lighting up as though it isn't getting power. I've tried switching the two control wires around to see if it was because these were wrong but it doesn't make any difference.

 

[Taylortwocities]

Is there a timer on your boiler that controls the time for heating? You’ll need to set that for always on.
Re your 4-core cable. That needs to be 4-core plus earth.

 

[Dan42]

Hi,
No, no separate timer, the danfoss was the thermostat and programmable timer. As for the cable, why would I need 4 core plus earth? The hive receiver doesn't need an earth.

 

[Deleted member 267285]

The earth is there to protect the cable, and maintain continuity. If your hive isn’t lighting up for power then it’s not the switching (control) wires doing this. Check your L and N connections.

 

[Taylortwocities]

Do you have a two probe voltage test device? A multimeter would do.
You need to test if you actually have 230volts between L&N on the Hive.

 

[Dan42]

Yep, schoolboy error, I had my blacks and browns mixed up, I blame bad light and old eyes

Just to clarify on the earth, based on the two replies, you are both saying to connect this regardless? The hive installation info states that the receiver is double insulated and doesn't need an earth. There is an earth terminal on the hive back plate, but it suggests that this can be used if required, i. e., just somewhere to park the earth wire if needed.

 

[Taylortwocities]

Fixed mains cabling must contain an earth (CPC). Even if the device is double insulated. It’s a basic requirement.

 

[Deleted member 267285]

Fixed mains cabling must contain an earth (CPC). Even if the device is double insulated. It’s a basic requirement.

I didn’t think a receiver for a wireless thermostat was classed as fixed?

 

[RandomGrinch]

I didn’t think a receiver for a wireless thermostat was classed as fixed?

There seems to have been some discussion about what constitutes fixed wiring in the past!
Here's an example:

What is the definition of fixed wiring or an appliance

Following on from the pond thread, it has always been my understanding that the fixed wiring ends at the socket, switch, SFS, light drop ect. Are you saying that if i had a cooker hood connected to a SFS, the cooker hood would become part of the fixed wiring?

www.diynot.com

I am happy to be corrected
But, in some circumstances, I think it may depend on your setup. If you had a receiver right next to the boiler and FCU, the cable wasn't clipped, and the receiver had a suitable enclosure - I think it would be easy to argue that it was an appliance connected to the FCU; it is beyond the extent of the fixed wiring.
However, even though the Hive receiver is double insulated, I don't think you could say the same for its baseplate!
"Best practice" may be to earth this one

 

[ericmark]

Hi,
No, no separate timer, the danfoss was the thermostat and programmable timer. As for the cable, why would I need 4 core plus earth? The hive receiver doesn't need an earth.

A circuit protective conductor shall be run to and terminated at each point in wiring and at each accessory except a lampholder having no exposed-conductive-parts and suspended from such a point.

Don't shout at me I didn't make the rules, it changed in 1966.

It has caused many problems with down lights moving from extra low voltage to low voltage, as unless some thing goes wrong and the hole is too big, down lights are not suspended.

I have seen loads of work done by plumbers where they have failed to fit an earth, mainly thermostats, both wall mounted room thermostats, and tank thermostats, and even used the green/yellow with out over sleeving, but just because a plumber gets it wrong does not mean we can copy them.

 

[RandomGrinch]

Don't shout at me I didn't make the rules, it changed in 1966.

Yes, but often quoted is:

"fixed wiring means all conductors forming part of the electrical installation between the place of entry at which supply is obtained and any point of outlet;"

Which suggests an FCU 'could' be a suitable 'outlet', where the definition of fixed wiring ends.
Hence the discussion I linked to in the previous post

I think one of the deciding factors for me, (may be!) - is the receiver still safe if it was removed from the wall?

With a Nest heatlink - Yes, there are cable entry points and cord grips. This can easily be compared to a portable appliance.

In the case of the Hive - No!

 

[ericmark]

Yes I do see your point on fixed, this is still a problem in kitchens in Wales where technically if you use an extension lead and nail in some cable clips to keep the cable off the counter, it need notifying, I think that is going too far, and I would never offer my LABC £100 plus vat because I had nailed in a few cable cleats, better to use screws for the cleats, this was challenged in a court case, over a picture on the wall, nails are permanent and screws temporary.

We can also argue the point over what is new. If we transfer a circuit to another overload device then it is not a new circuit, and if we then use the old over load device to supply some thing else that is also not a new circuit, as the circuit existed in the past. We all know the Part P rules intends that to be considered as a new circuit, but until there is a court case, and we have case law, we can claim it was an old circuit.

The same goes for

Single-core cables that are Coloured green-and-yellow throughout their length shall only be used as a protective conductor and shall not be over-marked at their terminations, except as permitted by Regulation 514.4.3.

people have said this means with multi-core you can over-mark, but I think this is wishful thinking, and not really following the sprite of the regulations.

Electrical installation (abbr: installation). An assembly of associated electrical equipment having co-ordinated characteristics to fulfil specific purposes.

more general install means "place or fix (equipment or machinery) in position ready for use."

In general to be portable it needs to be under 18 kg or have wheels, and can be moved while being used, so the Nest thermostat display can be portable, but when used with the trim plate and base so plugged in to a unit fixed to the wall there is a provision on the heat link for an earth to run with the 12 volt DC power to the display (they don't call it a thermostat even though it is).

I have never run an earth with extra low voltage, however not sure if technically permitted, the old thoughts were should a dog knock over a standard lamp in the living room which smashed as it landed on the radiator then unless the radiator is earthed that live connection could be transmitted to another room, however it has been since 2008 permitted not to bond all pipe work within the home as long as protected with a RCD.

I assume the thinking is that in the main the RCD will disconnect before we can touch a live part, if there is a good enough return path for us to get a shock. And if the return path is not there, we would not get a shock anyway, like with the birds on the power cables.

I have many times refereed to the Emma Shaw case, however her home did not have RCD protection, so I do see why today we should expect homes to be RCD protected, but when the English landlord law came out, we saw how many homes are still not RCD protected, and I have argued myself how BS7671 is not retrospective.

So with that in mind, if a new thermostat is fitted with a low voltage (230 volt) supply, does it need RCD protection?

 

[EFLImpudence]

So with that in mind, if a new thermostat is fitted with a low voltage (230 volt) supply, does it need RCD protection?

No.

Sockets are the only 'things' (appliances or accessories) that are required to have RCD 'protection' otherwise it depends on the cable installation method and location.

 

[ericmark]

So since sockets not allowed in bathrooms, no need for a RCD for bathroom supplies?

Think you may have made an error.

 

[EFLImpudence]

ALL circuits to the bathroom - and even just passing through - require RCDs.