In reply to a post by Ignitionnet:

Are they still running the generators in the winter and selling it into the grid?

Remember that being the bane of my life working for an OLO - slightly dodgy rectifiers / UPS so when the exchange cut from mains to generator all the colo'd DSLAMs would bounce, then again when the generator run was done.

" Are they still running the generators in the winter and selling it into the grid?"

Never heard that one , they do run them up now and then to make sure all is ok with them years ago that was a mates job.

Bout seven or eight years ago all the exchange generators were firing up a bang on 4pm. Ignition is right. The country was short of power and BT had a generator in every town and village...

Yes, 4 o'clock. Remember well it getting to 3:55 and counting down before the monitoring lit up with red.

Yes the 2nd backup line does need to be tested. They go out of service, are decommissioned and are never commissioned.

If I get the response that you had then I just say, ok, you are so confident that it works lets go to the computer room and YOU pull the main cable. Lets see if this works. That normally gets someone to think about if this service is working or not. It also means they are not confident about the overall 'backup contingency' and I then attempt to implement 3 mth tests until they are just happy to test on request. Its all a confidence thing.

Yes they still do at some places. Thames Water also do the same thing.

Its not all just about selling power back out it also cuts there electric bill on some large sites. Google electrical triad periods and that should explain how it all works and why its done.