John Summerfield wrote: > > In the event of a quake, it seems to me prudent to cut HT and mains, but > then generator sets automatically starting up would tend to negate the > action. > Not really - before you cut the mains, you switch the generator set control to off instead of auto. The transfer switch and remote generator controls are normally located right by the mains - it makes the wiring so much easier. It can get more complicated in data centers, or large buildings where only specific sections are connected to backup power. (Things like elevators and emergency lighting...) But they are also not unattended installations. > I occasionally hear about events involving live wires on the ground > following accidents and fires. It's bad news, especially for the poor > kid that picks one up. > This should not be a problem with even a home generator setup. This is because any setup should disconnect from the incoming line while using the generator. (A setup for a farm, or designed to power several buildings is different. You can have overhead lines between the generator and different buildings.) You need to do this not just for safety sake, but because if you don't, you will overload your generator because you are trying to power your neighbors as well. Any auto-start setup that does not include a transfer switch to automatically take care of this was designed/installed by an fool. For that matter, even manual-start setups should have it. The practice some people use with a double-mail cord to connect the generator to the house wiring after pulling the mains is not a safe practice. I have installed a few backup generator setups over the years, especially in preparation for y2k. The risk from a proper installation in not significantly greater then when you are powered off the mains. The main added risk is that fact that you are running some kind of engine to power the generator, and it has some type of fuel system. This is slightly less risky then running a car engine. (It is not moving, and the fuel tank/lines are normally better protected.) If your generator runs off of propane/natural gas, then the added risk is probably less. You would probably have that fuel source on location anyway. Now, what is scary are the battery banks used to power a large UPS installation. I have seen too many installations where there is no short-circuit protection on the battery leads. When you have a bank that produces 120V, and has the short-circuit potential of several thousand amps, the results of a short can be interesting. Then again, they will usually vaporise enough copper to clear the short. But the plasma created while doing so tends to be hard on the rest of the equipment located there. There is a fair amount of heat, as well as light and RF generated when you vaporise a few cubic inches of copper. (I have seen 6" of 1/4" x 6" copper bus missing.) A setup with a couple of 12V deep discharge batteries and an inverter is dangerous on a lower scale. But it does have an added danger that is often overlooked when it is a home-brew setup. When you charge the batteries, the produce hydrogen gas, and that is explosive. If you do not have proper ventilation, you risk an explosion. The biggest danger is when charging after heavy use, but even normal maintenance charging produces some. This is why you have to add water every so often - it gets broken down as a byproduct of charging. Mikkel -- Do not meddle in the affairs of dragons, for thou art crunchy and taste good with Ketchup!
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