You don’t have to be a genius to understand phase rotation. Anybody, mechanical engineer (even a Natal graduate) can see how it works: take the three phases from a three-phase supply and connect them to a motor. The motor will run, say, clockwise. Then turn the supply off, change over two of the phases, and the motor will run in the opposite direction.
Now, children, it’s very very important that, when you do changes to the wiring of a big factory or other premises, you keep the phase rotation the same as it was. Let’s imagine that the transformer of a factory is changed – if the phase rotation is wrong, the motors will all go the wrong way round when the power is switched on. In other words, for example, cranes will go up when the operator pushes the ‘down’ button – which is not good.
Since it is such a simple concept, it is absolutely standard (in the city that I work in, Cape Town) that the average contractor and engineer forget about phase rotation. The contractor thinks that it’s a kinda engineer thing, sorta rotating vectors an’ all, while the engineer thinks that it’s not the engineer’s problem. It’s all not helped by the fact that the meters we have to measure phase rotation are sup- plied either by the Germans or the British. German meters have a little wheel connected to a tiny motor, which spins clockwise. The motor drives a disc. On the disc are written the letters R,S and T, all at 120 degrees to each other around the edge of the disc. Looking at the letters, they appear in the order R, S and T, while the disc spins clockwise.
The British have a similar disc with the letters R, W and B, and, as you look at the letters, they appear in the order R, W and B, while the disc spins anticlockwise.
To help us all, the representation of the German disc with R, S and T (clockwise) represents the same phase rotation as the British disc with R,W and B (anticlockwise). It’s just a different form of representation. But this is where the whole thing unravels: people think that it is the actual direction of the spinning disc which shows the correct phase rotation, not the order in which the letters appear. And the RST, as against RWB, confuses them.
All this reminds me of a cruel trick we played on Ockert the appy. We convinced him that, if the phase rotation of a power supply was wrong, then everything electrical worked backwards. We said it wasn’t German phase rotation or British, but French. So we rewired his drill so that it rotated the wrong way. We changed the site stove so that when the control knobs were turned to ‘off’, the phases were full on, and when at ‘max’, they were off. We changed the site gantry crane so that ‘up’ was down and ‘left traverse’ was ‘right traverse’. We rewired the welding machine so that ‘maximum amps’ was zero and ‘low’ was maximum. In the evening, we served him hot beers since we said the fridge was working like an oven. We kept it up for about two days before we let on.
Twenty-four years later, I met him at a conference. He is now head of electrical research at a huge petrochemicals firm. After he got his trade, he went to university and got a degree. He remembered our tricks on him with some clarity. He must have, since, as I began my presentation (it was on computational methods in acoustic measurements), I toggled the first slide. Instead of the correct picture, there was a picture of a beautiful girl wearing almost nothing. I went beet red. The next slide was the same. The computer guy came and sorted it out. At lunch I sought Ockert out. Had he done it? Oh, he said, did you know in my new job they taught me to speak French? Nope, I didn’t. Well, he said, “La vengeance est un plat qui se mange froid,” Which, I knew, means “Revenge is a dish you should eat cold . . .”