Backup Power (by alaric)
As I have mentioned before, we have a petrol genset that we use to keep things going during our frequent power cuts. Immediately after the flood, too, when we had to shut down the house power since one of the outlets was submerged, I ran the computers off of the genset.
However, it is a pain to have to run the nice cable I made around the house, reach behind a filing cabinet to unplug the UPS that feeds the computers from the wall and plug it into the generator cable, unplug the fridge freezer, stretch cables about, etc...
So the logical next step would be to fit a second consumer unit, move the 5A lighting circuit over to it, and run a 15A circuit to a few strategically placed sockets around the house - where fridges and freezers are likely to ever be, and of course, up in the office where the computers live, and where the incoming phone lines are (where the ADSL router goes).
This consumer unit can run from a single 30A fuse in the main consumer unit (the slot currently taken by the lighting circuit will do nicely), but via a pair of 32A IEC 60309 connectors. The circuit from the main consumer unit would come out via a female socket, and the feed into the new consumer unit via a male socket.
Then the two can be connected by a short length of 32A cable with appropriate plugs on each end. And when the power goes down, I can turn the emergency circuit off with the master switch on the secondary consumer unit (because it's bad to use a plug and socket as a switch, interrupting a flowing current and arcing in the process), unplug from the useless incoming circuit, and plug into the genset's output... The genset can only produce about 10A; in practice, that's more than enough to run everything, and it has a 16A outlet on the front, but I'd feel compelled to see if I could find a 10A circuit breaker nonetheless, since with proper sockets stationed about the house, it might be easy to accidentally overload it. But I'm designing the system around a standard 15A socket circuit and a 5A lighting circuit, so that in future, I can get a bigger genset and power more stuff without needing to rewire it all.
What I wonder, though, is if this arrangement would actually be legal under the stringent UK wiring laws. As far as I know there's nothing wrong with having a 32A socket coming from a 30A fuse (after all, a standard 15A circuit feeds many 13A outlets); the question is, is it OK to have a lighting circuit and a set of outlets coming from a consumer unit fed from a 32A inlet socket?
I hope so, since it'd really make switching over to backup power easier than it currently is. And since anything I connect between those two sockets isn't a fixed part of the house wiring it would, I presume, not be governed by regulations, so fiddling with alternate power sources (such as turbines and battery arrays) would be a lot easier.
Building Maintenance | alaric | 
Sun 16th Sep 2007 9:30 pm
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By Matt, Mon 17th Sep 2007 @ 1:46 pm
just watch out that if somehow two devices became connected to each other - network switch? - and the two end computers were on different supplies, different phases (or out of phase), then fun might occur!
By alaric, Mon 17th Sep 2007 @ 1:51 pm
As long as the neutrals are commoned, I think that sort of thing is OK. If you have two 240v supplies that are 240v RMS against the same neutral but out of phase, then after going through a PSU, they'll produce the same 12v or whatever compared to the same 0v line. I think!
However, if I had two mains connections to the house, I don't think I'd be able to common the neutrals since they could come from different transformers with different neutral connections, so commoning them could in principle cause large currents to flow...
But if I set up anything of my own that makes electricity to use the same neutral as the mains incomer, all should be well 😉
By @ndy Macolleague, Tue 18th Sep 2007 @ 1:21 pm
You needn't worry about low voltage stuff. Sometimes you have a floating output on the LV side of the transformer. Things like Ethernet are happy to wander between equipment connected to different phases. Normally (always) the cabling is decoupled from the equipment by isolating transformers in the socket.