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.
From the subsequent discussion, you're now well aware of the dangers of doing it in the way originally suggested.
One point which I don't think has been made (forgive me if I have missed it) is that of voltage stability and waveform. It seems to me a distinct possibility that a cheap generator will produce all sorts of voltage variations and spikes as loads are added or removed. If this is so, any sensitive electronic equipment being powered by the genny - and I include things like the control PCB in a central heating boiler in this category - could be damaged, somewhat defeating the object of the exercise.
At the start of last winter, I bought a Honda generator (somewhat more expensive than the ones discussed here!) as a precaution against power outages. This actually generates DC, and produces "mains" - with a (claimed!) very high degree of voltage stability - by means on an inverter. It also has a 4-stroke engine and fairly good silencing - so the idea is that it shouldn't annoy the neighbours too much if it is running for a few hours - and might *even* be useful for caravanning in remote locations.
I do not intend to connect the genny to the house mains - but rather to unplug certain items from the mains and plug them into the genny instead. In order to facilitate this, I have modified the power supply to the central heating - which is now fed from a 13A plug in the utility room rather than from an FCU in the airing cupboard. My genny can produce about 1600 watts - which should be sufficient for the heating controls, a couple of freezers, a TV and a few lights - and even a microwave oven if most of the other load is temporarily removed.
I have also sunk an earth spike in the garden, to which the genny's earth lead will be attached.
I had no need to use it last winter - but it's a peace of mind thing. I guess that I had ought to run it every now and then, to make sure it still works!
That reminds me of the days when I was a student, and was housed in a
17 story hall of residence. Rooms only had the old 3 amp round pin plugs: there were 13 amp plugs in the corridors, which frequently resulted in large amounts of steam, after people put the kettle on for a coffee, and then became otherwise engaged.Groups of rooms shared a single fuse, and different groups were on different phases. Fuses blew frequently - it wasn't difficult to overload them, and the wait for the electrician to come around was rather tedious. Someone (almost certainly a scientist/engineer - that's all there were at the Uni, apart from opticians and journalists) once had the bright idea of making up an extension cable with two plugs on, and powering one group of rooms from the adjacent one. Unfortunately it was still plugged in when the electrician replaced the fuse.
Normally three phases are run from the substation to the local area, so in practice only every third house is connected to a give phase.
.andy
To email, substitute .nospam with .gl
The bugger. I set a practical examination for medical students once, which also had a "though experiment" section. Since it was impossible in the time scale to set them a typical experiemtn in immunology which could take weeks to do, they ere asked to outline the steps leading up to the laboratory work, then do the lab. work.
it involved creating antibodies to a component of human white blood cells, adding either a radiocative or a fluoroescent marker to the antibodies and then incubating the cells with the antibody _in vitro_.
About 80% of medical students would perform all the steps correctly except the last one. They all wanted to inject the radiocative material into the patient. And they all looked a bit bemused when the demonstrators explained to them that it could be done outside the human body. Standard medical reflex I reckon, see a syringe, squirt something into human being.
I thought they normally shunted the circury in fault fxing?
No. Not really. They all have regulated internal supplies.
The esy way to do this is to simply find way of feeding the genny to the CU busbars via its own mains switch and even RCD, and then deselect incoming mains, and as many house circuts as are not immediately required.
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 experiences.
Not on a cheap likely chinese 500w unit no.
Tim..
Correct!
I have the above, and i also have a secondary double pole 100A safety switch after the main fuse before the changeover switch as added protection of not zapping some poor bugger on the line.[1]
[1] Use a 10kva diesel unit.Tim..
You'll probably find that the freezer wont start with a 500w max generator suppling it- the compressor is almost a dead short when stationary.
Tim..
I believe, depending on which supply system your house is supplied with (TT, PME, TC-S etc etc) that when running with a conventional generator through a change over switch etc, that you should have the neutral and earth connections at the generator bonded together and an earth spike.
Thus the neutral is referenced to 0 potential and not floating at 115v as it would be without this. If a fault to earth occured you could well get a 115v shock if this isnt the case.
With a 240v inverter type generator, am not sure if the above should apply. Probably not...
Tim..
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.
As a rule of thumb a motor needs about 2 to 3 times it's running rating to start. 500/3 = 160W, close but higher than most normal freezers so it'll probably be OK provided there isn't much else on at the same time.
Just looked at the fridge/freezer (140W) ordinary fridge (110W) and upright freezer (90W).
You *must* bond one of the generator phases(*) to the chassis and to a properly installed earth spike with suitably rated cable. This earth also needs to be connected to the installations earth again via suitably rated cable. I'd also feed the generator in via an RCD.
What you do with this local earth and the supply earth when running from the generator is the problem and does depend on the type of you have. With PME, ie the supply earth is locally derived and neutral is bonded to it at the supply point then I think it's pretty safe just to tie them all together and not worry about it. Where the supply earth comes in as a seperate wire or connection I'm not so sure about. You cannot relie on the supply earth under fault conditions (power cuts = faults, who knows what the enginneers will do to fix the fault).
You'd more likely get the full output of the generator, the fault would pull that phase down to earth, if you picked up the other phase, ouch.
No one phase still needs to be designated "neutral" and bonded to local earth.
(*) The alternator generates two phases 180 degrees apart, until you designate one "neutral" and bond it to local and installation earth you have the potential for all manner of weirdness with the installations live and neutrals being anywhere from 0 to 230v with respect to earth.
The comedy element comesin when you have two fridges/freezers on one generator/inverter that automatically transfers over from the mains on power failure. It'll work fine - until they both try to start at once.
Wouldn't a generallised safe solution be to plug a RCD into the generator, to have an earthing spike going from the chassis/local earth to ground, and plug the load into the RCD?
In message , Grunff writes
I keep thinking about wiring my genny up to the house and it is the thought of the change over system that has been delaying me.. I've had a brief look around and was considering a contactor, relay, rather than a manually operated switch for convenience. But if the cost is vastly different then that would be the overridding decision maker. Are there any reputable on line suppliers of such things? The incoming mains is fused at 100A and has a fused switch before the CU so interfacing should not be too hazardous. The genny is 7.5KVA Thanks for any advice.
Which way round is that and what's it going to protect?...
In article , Bill writes
We've used one from RS components, was around 70 quid IIRC
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