Shades of Grey

We had some electricians in at work today, pulling in some large cables in preparation of a forthcoming upgrade. The cables are 300mm² steel wire armoured, capable of handling more than 500 Amps. (By comparison, domestic wiring for sockets uses 2.5mm²). Eight of these cables are used for our main building supply and they are extremely un-bendy. I often think that the work of an electrician is as much about mechanical engineering as electrical engineering.

Then, a couple of hours later, the lights went out. This always gets us worried, as whilst we have big power systems to take care of this, it causes a fair bit of disruption of non-critical systems. After a quick trawl round various places, we found the reason, one of the electricians had accidentally operated the main switch. He had put it back on immediately, but as we have a backup generator system, the control gear immediately took over and transferred the load onto the generator after a short interval. (Short, but it felt quite long at the time, some twenty seconds or so). The reason he had tripped it was a rather silly one and there is a clue in the photo shown here.

He had been at the top of the ladder manipulating the aforementioned large cables and as he had come down the steps, he accidentally put his foot on the trip switch part of the main circuit breaker, which had immediately sprung over to the off position. He was very apologetic and extremely embarrassed! Next time, he might not buy his footwear here…