Regarding the elect. supply to a new gas central heating system... Is it ok to run a T&E from a dedicated mcb in the CU to supply both the boiler and the pump?
What should the termination be on the wall? Does it need some kind of isolator (as in eg an electric cooker DPole switch) . thanks
I have done exactly this.
I used a 6A MCB in the consumer unit. Ran 1.5mm2 T&E from this to a double pole Fused neon connection unit in a pattress box.
Then onwards to the wiring centre that your pump, boiler, thermostats and valves connect to.
PLace a label on the switched FCU to indicate its a an isolator for the whole system.
You should also place a FCU on the supply cable to the boiler and place this adjacent to the boiler and label this "BOILER ONLY" Isolator.
This was on the advice of the gas engineer so that they can quickly turn off the power should the need arise. In my case, there is 240 mains on the zone valves so hence the labelling as flicking the boile ronly isolator won't cut the power to the zone valves.
Obviously if your system isolator switch is next to the boiler, then the situation described won't arise, but I suppose an issue would arise for anyone working on the pump or zone valves if these are in a seperate room to the boiler.
Most boilers would require triple pole isolation and not a FCU for local isolation (they usually have permanent live, switched live and the neutral).
Even if you did not need the triple pole isolation and could get away with double pole isolation a non fused double pole switch next to the boiler would be recommended.
And the OP MUST have a switched fused spur somewhere that will control ALL of the boiler controls and the pump.
In message , dave writes
Yes. Generally the whole of the CH is supplied from one feed as they are then all the various its are connected up via the various controls etc.
Switched FCU.
Then a feed from there is normally taken to the wiring centre where everything is connected up.
Yes.
Normally a flex outlet for the boiler (perhaps with neon), and then a main double pole switch somewhere that will isolate both the boiler, the pump, and any other mains control equipment such as 3 port valves etc.
My admittedly quite old electrical system has a fused spur from the kitchen ring main. I think I have a 3 rather than a 5 amp fuse.
I presume that would conform to current regulations but I can't claim any specific knowledge.
There is a lot of benefit in running your heating system on your own MCB and even on a RCBO instead. You then have integrity of supply so that a falut elsewhere in the house does not lead to loss of heating during a cold snap.
My CU has 13 RCBOs. as the boiler and dassociated controls are on their own RCBO, I can have all of the other 12 RCBO's trip due to overload, earth leakage what have you, but still have power to my boiler. I have automatic frost protectino on the boiler so hopefulyl will prevent burst pipes.
I think a dedicated RCBO for the heating only is a a small price worth paying for that extra level of assurance during deepest winter... Particularly when you see how much devastation leaking water can cause.
My particular boiler has earth, permanent live, permanent neutral and a a pair of volt free connections. These volt free pair goes to all the microswitches in the zone valves so I don't have a switched live per se as ARW points out.
Agreed, but then its quite easy to turn off the water in the first place if you're going away for any length of time.
Fair enough, but one significant risk during cold snaps is a power cut.
In order to cater for this, everything in my system is powered from a single 13A plug - which can be unplugged from the ring main and plugged into a generator instead. [And yes, the genny does have an earth spike and has one side of its output tied to earth to keep my boiler's flame ionisation detector happy].
It also means that I can achieve total isolation of the system by pulling the plug.
For clarity, I was not suggesting otherwise. On its own circuit is a very good idea. Note that single module RCBOs, and normal MCBs don't by themselves provide isolation though - so you still need a double pole switch somewhere,
But how is power supplied to the valves?
Yep, that is allowed.
I have a wiring centre fed by a FCU with neon.
two 2-port zone valves, two programmable room thermostats connect to this along with a five core cable for the boiler. (one of each for each floor of house.)
The programmable thermostats control the zone valves directly, the two microswitches within the zone valves are wired in parallel straight to the volt free contacts to the boiler.
The boiler needs permanent live and permanent neutral as its a combi boiler otherwise we get no hot water :-)
Which is fine...
Ideally you want one switch you can turn off that isolates the whole system.
(especially as a combi with zone valves is relatively uncommon)
Bet you could not do that with a Y plan:-)
I already have this (the Neon FCU) in the airing cupboard which also has the 2 zone valves and the wiring centre.
Then there is 5 core cable going from airing cupboard to the boiler in the kitchen.
Hence the need for a isolator switch next to the boiler for anyone working on the boiler to be able to turn off power quickly without needing to run to the airing cupboard.
probably could actually, replace the tank stat with a 2nd room stat, and and relabel the HW on the timer to be the 2nd heating zone.
The boiler can be reconfigured to work with switched live instead of volt free switching contacts.
To be honest, having two programmable room thermostats, two 2-port zone valves etc is actually simpler to wire, understand and fault find than a Y plan.
One advantage of a Y-plan, is that not all valves are closed during the pump run-on. With two zone valves you would probably need a bypass valve.
But bear in mind that the cylinder stat on Y-Plan is a change-over switch - not just on/off - so your second room stat would also need changeover contacts. [In reality, most do, so that they can be used for both heating and cooling applications].
correct.... i do have a automatic bypass valve for that reason.
And what sort of isolation switch would you now need next to the boiler;-)?
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