On 04/11/2012 14:52, fred wrote:
In article , Harry Davis
writes
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.?

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.

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 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.

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.

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.

--
Regards,
Martin Brown