Central Heating & Hot Water wiring

[orval]

Hi there!

I am wiring up a new heating and hot water system that is being installed by a plumber. I've recently moved into the house and I'm re-wiring it, with the appropriate building control inspections of course. I figured I'd save £680+VAT by doing the wiring for this new heating system myself.

So; I have a 3 channel programmer and there are 3 zone valves. One for hot water -- sealed cylinder, one for upstairs radiators, and one for downstairs UFH.

The UFH manifold and control panel, UFH zone valve and the programmer are under the stairs. The boiler (Rayburn 480CD) is in the kitchen. The hot water cylinder is in the loft.

The boiler requires a 3A fused spur, as does the UFH control panel. It would be possible to supply these from the downstairs ring main. But the attic has it's own ring main, and I assume it would be a bad idea to connect the heating junction box (Honeywell 42002116) to that supply. Seems wrong to do this from separate rings.

I do have space in my CU, so I did wonder whether I should have a dedicated ring (or radial) circuit for this stuff.

Any advice?

Thanks in advance,
Orval

 

[holmslaw]

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[orval]

That confirms what I thought. Thanks!

Not including earths, there are five connection points on the boiler. Two are Mains Live & Neutral and two are Pump Live & Neutral. The last one is Switched Live.

According to the diagram in the boiler's installation manual, I take a fused spur from the ring to the Mains connections. The Pump connections are connected to the pump. (I suppose the boiler controls when to pump and when not.)

What I find odd about this is that the FSU will isolate the Mains input but the Switched Live could still be live. To isolate that you have to use the FSU in the attic. So I can use those warning signs but I don't like it.

Is there some kind of switch that could isolate Mains and Switched Live at the same time?

 

[holmslaw]

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[orval]

If I only have one isolator there will be some very long cable runs after it. Is that allowed/advisable?

 

[holmslaw]

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[orval]

If I only have one isolator there will be some very long cable runs after it.

Lifes a beetch and then you die.

I don't really mind the work or the cost. What I want to make sure about is the regs. Doesn't an isolator have to be within reach (or "reasonable" distance) from the thing it is isolating? Seems odd to have an isolator in the kitchen for stuff in the attic!

I'm curious, how does the CH control panel control the water temperature to the rads and the ufl? I believe max temp for ufl is about 60°C, but you need about 80°C for the rads. If you end up with 80°C water on the ufl it will ruin the pipe.

There isn't a CH control panel. Upstairs rads are just controlled by the programmer and a thermostat. Anyhow, the temp is controlled within the manifold. It mixes water from each side of the manifold. I.e. with the cool water that has been under the floor and back.

 

[matt1e]

Hi Orval
basically you take a live supply to the rayburn from the spur
connect the pump directly to the rayburn
take a 3 core + earth from the rayburn connected to L,N and S/L to the first wiring centre this will give you a live and neutral for controls (programmer etc) and a switched live back to the rayburn (all isolated via the heating spur)
daisychain another 3core and earth from the first wiring centre to the next one
wire the stats and zone valves to the relevant wiring centres
the stats are wired to power the valves open
the valves end switches are all wired in parallel and connect live to switched live which will then fire the boiler

Google "s-plan plus" which is basically what you are doing but make sure you do connect the pump to the rayburn and not the wiring centres, as it needs to overrun

I'm curious, how does the CH control panel control the water temperature to the rads and the ufl? I believe max temp for ufl is about 60°C, but you need about 80°C for the rads. If you end up with 80°C water on the ufl it will ruin the pipe.

Hi holmslaw
you are correct that the UFH needs to be lower temp but it ruins the floor not the pipe if it is too hot plus the fact that you dont need the water as hot for underfoor anyway as its more efficient
the UFH circuit will (or should in this situation) have its own manifold fitted with its own pump and a thermostatic blending valve which will control the temp of the water in the UFH circuit

Matt

 

[orval]

Thanks Matt. V useful. I get the daisy chaining idea, but I still don't like the idea of having stuff in the attic isolated in the kitchen. What about having another isolater in the attic? They'd be in series then, which seems weird. Would the regs allow this?

 

[matt1e]

Thanks Matt. V useful. I get the daisy chaining idea, but I still don't like the idea of having stuff in the attic isolated in the kitchen. What about having another isolater in the attic? They'd be in series then, which seems weird. Would the regs allow this?

no they would be in parallel and yes you could fit local isolators to each wiring centre if you wanted to, but to have total isolation you would have to make sure that any isolator fitted is
a) triple pole and
b) isolates all further wiring centres fitted down stream also as any zone valve fitted anywhere can energise the switched line

its a bit over kill to be honest as you wont normally be going anywhere near them unless there's a fault, IMO an "isolate elsewhere" sticker would surfice
put it this way any sockets etc fitted in your attic wont have local isolators either! are you comfortable with that?

Matt

 

[bernardgreen]

If I only have one isolator there will be some very long cable runs after it. Is that allowed/advisable?

With the very low currents involved voltage drop along long runs will not be a problem.

Having a single point of total isolation and the safety it creates is worth having. There is also value in having an isolator at boiler, tank and other nodes as long as they are wired in series and each one totally isolates the entire system.

It is also worth considering indicator neons to show when there is power to the system.

 

[orval]

Right! Nearly have it sussed.

I'm going for one isolator btw.

My last puzzler is that I need one switched live from the programmer in the cellar to the cylinder stat in the attic; and another from the prog to the room stat in the hall. Is it okay to use twin & earth leaving the neutral unconnected? I've seen that double insulated live plus earth cable but it seems quite hard to get hold of.

 

[matt1e]

Right! Nearly have it sussed.

I'm going for one isolator btw.

My last puzzler is that I need one switched live from the programmer in the cellar to the cylinder stat in the attic; and another from the prog to the room stat in the hall. Is it okay to use twin & earth leaving the neutral unconnected? I've seen that double insulated live plus earth cable but it seems quite hard to get hold of.

yes its ok but better to terminate the spare core and make it safe rather than cut it off
you wont need singles, it will be a better job to to run the programmer and stat cables to their nearest wiring centres then link the cores through the wiring centres to their destinations, far neater and easier for future fault finding/upgrading etc

Matt

 

[securespark]

If I only have one isolator there will be some very long cable runs after it. Is that allowed/advisable?

With the very low currents involved voltage drop along long runs will not be a problem.

Also, as you have a 1362 3A fuse feeding the system, you are allowed a much higher EFLI than you would from the supplying circuit. Can't remember what it is, it's down in the van and I ain't going down there now!!

 

[AndyPRK]

sometimes 5 core flex is used for heating systems. Surprised its not been mentioned.

Like this for example
http://www.ebay.co.uk/itm/0-75mm-5-...al_Components_Supplies_ET&hash=item23158d0536