oil c/h & h/w: pump, timer, stats, etc. usually off same fuse?

[Harry Davis]

Are all the electrics for an oil central heating and hot water system (pump, timer, stats, etc.) usually all off a dedicated mains fuse? Or all on the same fused spur from one of the rings?

Or is it common for one of the appliances to be on one ring, another on another, etc.?

The reason I ask is that we suffer from constant power cuts, and I'm considering giving myself the option of another supply, either from a standalone diesel generator or from batteries, thereby enabling us to keep the heating going. I'd like to have the electrics for the heating system on their own plug, which could be plugged either into a mains socket or a socket powered by another supply.

Thanks in advance!

Harry

[fred]

In article , Harry Davis writes

It should all be fed from the same point, it is a safety requirement so that anyone working on the installation can go to a single location and isolate the system without the risk of electrocution from some other source of power back feeding into the control wiring.

Which ever way you go, make sure you have enough headroom in your genny or inverter to feed the motor and magnetic loads that make up most of the c/h system. Others may be able to offer hands on advice but my guess would be that 100% headroom would be required at least.

[meow2222]

Better to find out how yours is fed. And quicker. It should all be of one point, but of course shoulds aren't always followed.

Motors draw many times run current during startup, and are the main load on a modern CH system.

NT

[Dave Liquorice]

The entire heating system should be fed from a single fused supply, be that from a ring or direct from the CU. There are so many things switching things on/off based on time or temperature that to have things fed from multiple supplies would be down right dangerous. You might think you've isolated something and test it, but time passes or the temp changes and your "dead" circuit becomes live...

That's what I've had here for quite a while, unswitched socket and 3A fuse in plug top. Absolute isolation of all heating related stuff when unplugged (the plug is next to the board with all the stat receivers, time switches, solar controller etc). Enables it to be plugged into extension lead from generator when the mains fails.

[The Natural Philosopher]

hey should be all of one fused spur.

Whether its a dedicated ring or not is up to whoever cabled the thing up. Normally its on another ring as the power draw is small.

Never unless its been bodged.

Do the job properly and use a changeover on the spur and a properly wired in generator.

[Dave Liquorice]

'tis true but they are small motors. Circulation pump

[Dave Liquorice]

Opens a whole new can of worms regarding earthing. You have to be absolutely sure that the bonding of generator chassis and "neutral" and generator chassis and your supplied true earth connection are all low enough to enable any fault protect to still operate within the prescribed times. Not to mention that a small genset probably won't be able to supply enough current under fault conditions either.

Personally I go for a floating L and N supply from the genset and ignore the lack of true earth. I only connect some appliances to the genset via extension cables. Those are heating, fridges/freezers and the fish tank.

[Martin Brown]

Indeed. Although it is *all too common* to find that some DIY idiot has bridged either a ring main or in my house a *lighting* circuit to allow the CH pump to be switched on manually from the living room. Back boiler on the main room fire (now a wood burning stove).

Fortunately we spotted the problem before it killed the boiler service engineer. I always test supposedly isolated mains circuits with a neon screwdriver but until then I had never seen one fail.

The total electrical load for my CH is relatively modest. I'd guess a

1kW generator or inverter would do it at a pinch. I have a 2kW unit.

The really difficult loads are the fridge and freezer. The compressor motor is an absolutely evil high current load as it starts up.

[John Rumm]

Not a problem with all of them, but IIUC, some boilers won't flame sense correctly without an earth reference.

Changeover switches are easy enough on TT properties, but get a bit more complex on TN ones.

[Dave Liquorice]

Not a problem in the context of this thread. Oil boiler, flame sense is optical, ignition a BFO spark. B-)

[harry]

I have a small wood burning stove with a hot plate. Needs no gas, electricity and I can store wood. You can run out of oil too.