I've just been looking at some really cheap generators for emergency use. I
was thinking about one of the sub-100 Pound jobbies. I just want a light or
two plus enough power to run the gas central heating system in case there is
a power cut.
I was wondering about wiring this up. I deally, what I would like to do is
simply run up a lead with a standard plug at each end.
Then, in the event of a power outage:
1. Switch off the mains supply, hopefully isolating the house from the
national grid (as I really can't hope to power the whole country from my
2. Switch off everything in the house apart from the central heating.
3. Plug cable into both the genny and one of the 13 amp power sockets around
4. Start genny.
Sounds too simple, so what's wrong with that?
Does a standard consumer unit isolate both the live and the neutral?
There's a *really big* switch in a box in the garage - large grey box with a
sort of door handle on the front. Is that likely to isolate both? Should I
just open it up and have a look?
Does it matter if you don't isolate the neutral? Isn't that at earth voltage
What does a cheap 500w generator do when someone turns on a 3 kw fire
upstairs by mistake?
Any help most gratefully received. BTW I did google for this, but I could
not find a reply to the question I put. Perhaps it's obvious that it won't
a) It's illegal
b) It's highly dangerous for all concerned
One moment of aberration with plugs and switches, which is easy in the
dark and you run the risk of electrocutiing yourself or possibly some
unfortunate engineer working on restoring the supply.
Don;t even think about doing this.
Yes, but this is not relevant.
Yes it does.
Trip a breaker, blow a fuse or burn out the generator.
The only way to do this safely is with the correct type of switchover
isolator specifically meant for the job.
To email, substitute .nospam with .gl
On at least two counts.
Part VI of the Electricity Safety, Quality and Continuity Regulations
Switched alternative sources of energy
21. Where a person operates a source of energy as a switched
alternative to a distributor's network, he shall ensure that that
source of energy cannot operate in parallel with that network and
where the source of energy is part of a low voltage consumer's
installation, that installation shall comply with British Standard
22. - (1) Without prejudice to regulation 21, no person shall
install or operate a source of energy which may be connected in
parallel with a distributor's network unless he -
(a) has the necessary and appropriate equipment to prevent danger or
interference with that network or with the supply to consumers so far
as is reasonably practicable;
(b) has the necessary and appropriate personnel and procedures to
prevent danger so far as is reasonably practicable;
(c) where the source of energy is part of a low voltage consumer's
installation, complies with British Standard Requirements; and
(d) agrees specific requirements with the distributor who owns or
operates the network.
(2) Sub-paragraphs (b) and (d) of paragraph (1) shall not apply to
a person who installs or operates a source of energy which may be
connected in parallel with a distributor's network provided that
sub-paragraphs (a) and (c) of paragraph (1) are complied with; and
(a) the source of energy does not produce an electrical output
exceeding 16 amperes per phase at low voltage;
(b) the source of energy is configured to disconnect itself
electrically from the parallel connection when the distributor's
equipment disconnects the supply of electricity to the person's
(c) the person installing the source of energy ensures that the
distributor is advised of the intention to use the source of energy in
parallel with the network before, or at the time of, commissioning the
Without the proper switchgear, prevention of parallel operation cannot
Secondly under the Electricty Acts, a license is required to generate
electricity for supply to the grid, although there appear to be
specific exemptions for local wind etc. generators with appropriate
However, I think that the 2002 Act covers it.
Plus, if one were to do this, put power into the network and kill
someone, it might be a touch tricky defending a charge of manslaughter
That does seem to cover all the possibilities that I thought of before
asking the question. I thought there might be a standard that these
generators are usually built to. Thanks for confirming in a slightly
roundabout way that there isn't.
Giving this some more thought, I fully accept what you said. There's too
many things that have to be done right. As I see it, the main safety issues
a) The connecting cable could potentially have live pins exposed
b) Relies on nobody turning the main switch back on again
c) Relies on the main switch working
Make a mistake with b or c and you could really hurt some poor contractor
working in the rain to restore power. (In practice, this is only a problem
if a small part of the supply has been isolated, so you would probably get
away with the error, but I agree that's not the point.)
That's enough to be going on with, along with it being illegal, or have I
missed something important?
Thanks for being patient with me.
| Giving this some more thought, I fully accept what you said. There's
| too many things that have to be done right. As I see it, the main
| safety issues are:
| a) The connecting cable could potentially have live pins exposed
| b) Relies on nobody turning the main switch back on again
| c) Relies on the main switch working
| Make a mistake with b or c and you could really hurt some poor
| contractor working in the rain to restore power. (In practice,
| this is only a problem if a small part of the supply has been
| isolated, so you would probably get away with the error, but
| I agree that's not the point.)
Bear in mind that although your generator would be putting out 240V, it
could be backfeeding a transformer where an electrician working on the
isolated supply-side terminals would be rather startled to suddenly find
I take the point that it's unsafe, but isn't this scenario very unlikely
indeed? Surely it could only happen if every other house apart from mine is
isolated from the path to the transformer? If the other houses in the street
are still connected up, then the load on the generator will cause it to
stop, burn out, or whatever.
The times I've seen them at work on overhead plant is that they short
all three phases together and then connect that to an earth stake and
only remove it when the work is done and the line is to be re-energised.
Rather sensible and I suppose a practice born out of past adverse
On Sun, 19 Sep 2004 15:06:24 +0100, tony sayer wrote:
You've missed out the long handled volt stick they wave about before
they attach the earthing bonds via long handled insulated tools.
I'm not totaly convinced that such bonding would protect from back
feeding from a portable generator connected by the highly dangerous
double plug method. The load presented may well make the genny
struggle and possibly trip/stall but if there wasn't much load where
is the circuit via earth?
There is no decent connection from either phase of the generator to
earth unless you deliberatly install an earth spike and bond that to
one of the generator phases. Granted one phase might be connected to
the generator chassis and that might be resting on the ground and
might be making a good low impedance connection but thats rather a lot
of "mights". Remember there is no RCD the only disconnection device is
the overload trip.
Dave. pam is missing e-mail
Yes but it's not fail safe, it relies on the RCD being plugged in and
not removed if/when it "nuisance" trips. And you still need to bond
one of the generator phases to chassis and local earth rod so that
things are correct for the house wiring, ie "neutral" can't float
significantly away from earth.
Dave. pam is missing e-mail
No problem. I just didn't want to see you hurt yourself.
You've highlighted the risks exactly
What you could do, and would be a reasonable solution if you wanted
something simpler would be:
a) Put in some additional wiring and outlet sockets at critical places
like CH, Freezer etc. You'd need a plug/socket for the CH for this of
b) Wire these to the generator and in the event of a power cut, you
move the appliance plugs over to the emergency circuit.
You still have to be sensible about not overloading the generator, but
there would be no risk of powering the mains.
c) Put in some emergency lights in strategic places. The 8w
maintained fluorescent type are quite inexpensive and reasonable for
this. You can switch them on and off if you want use as a normal
light but then they come on when the power fails.
I put one in the cupboard where my consumer unit is for example.
To email, substitute .nospam with .gl
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