Every depot has an uninterruptible power supply in its network cabinet. We bought them in a single programme in 2020 after a run of short power cuts, and the business case was simple: the network should ride through anything under half an hour.
In January one of our northern depots lost mains power for twenty five minutes during the evening shift. The UPS did exactly what we had bought it for. The switch stayed up, the access points it powers stayed up, and every scanner in the building could see the network. None of them could reach the warehouse system. The router for the depot's internet circuit sits on a shelf beside the cabinet, plugged into a wall socket, and the carrier's line terminating unit next to it shares the same socket. The depot stopped picking for the whole cut and for another twenty minutes afterwards, while the router booted and the line resynchronised.
We checked the other depots. At fifteen of them something on the path between a scanner and our data centre had no protection at all: routers, carrier equipment, a firewall in a different room, and at two sites the dispatch label printers, which meant that even with a connection nothing could leave the building. We had protected the cabinet we specified in 2020. Everything added or moved since had gone wherever there was a free socket.
Then we tested the units themselves on a Sunday morning, which nobody had done since installation. Nine of the twenty two ran for less than a third of their rated time. Batteries age whether or not they are used, and none of ours were on a replacement schedule, because the status light on every unit was green.
We now draw the power path for each depot in the same way we draw the network path, from the scanner to the data centre, and everything on it is either protected or has a recorded reason why not. Carrier equipment goes inside the cabinet, and our standard site drawings now say so. Batteries are replaced every four years regardless of what the unit reports, and each site has a timed mains off test every spring. The dispatch printers now have their own small units.
Protecting the equipment on our list was the easy part. The outage came from a box that had never been on it.
– Serguey Shinder
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