ECN Forum Forums General Topics of the Trade General Discussion Area My Favorite Electrical Myth

Per minute? I make that about 0.4Hz!

It actually turns off 100 times a second and 120 times a second in the Americas (twice per cycle). I guess we are more impatient.

Not a typo. We have a new Anglais bar owner here. My mate Phil calls him Methusela, as he reckons he must be 700 years old to have done all the amazing yarns he tells. According to M, it is 50 times a minute. Mind you, he also led a platoon of 70 British SAS squaddies in Vietnam, which must have been a bit of a surprise to Lyndon B. Johnson and PM Harold Wilson!

I caught that as well. It's amazing how many people don't stop to think that the number of zero-crossings per second is double the frequency.



Can you imagine the size of transformers you need for that?



Ah, he must be related to somebody I know. Got called to do his national service, you know. Except that by all accounts he was born in 1950 -- I guess he must have lied about his age.

We had one like that where I used to work. Depending on what day he told the stories, he was either an Army Ranger, Navy Seal, Special Forces, Green Beret, and served in either the Army, Navy, Air Force, Marines, CIA, or anything else that sounded impressive.

He also told stories of incidents on construction sites that weren't survivable after you thought about it for a few minutes, like the lead-lined door to an X-Ray Room falling on top of him during a hospital project.

Yep, compulsory national service ended in the U.K. around 1960, and I think the last intake was a year or more before that. His rifle must have been as tall as he was!

This same guy claims to have driven trucks for "over 25 years." When you deduct the number of years he claims to have spent doing other jobs since then, it works out that he must have started at about 14. Pretty impressive considering that you have to be 17 to even get a regular car license, and 21 for an HGV license!

Oh, and he's absolutely hopeless when it comes to electrical things as well. He really shouldn't be let loose near anything with wires.

One of the funniest things I've ever seen on TV, a few years ago there was a programme called The Red Green Show, there used to be a segment on there with a guy called Hap Shaughnessy, good lord were some of his stories tall!.

There is also something that I have seen engineers forget. There are no "zero crossings" in 3 phase (L/L).
When you use SSRs and other triac devices they will always be opening under load even when you are only using 2 phases and thinking it looks like single phase. The only way to get a zero crossing is to go line to neutral.

Ah, the Red Green Show. Harold got married again for us on the 300th show Saturday night (again). I enjoy these reruns and watch it more faithfully than anything else on TV. At times one half of one hour of TV watched during some low TV weeks.

Funny that my wife thinks I McGiver things when all I know, I learned from Uncle Red.

A zero crossing is the point where the instantaneous voltage is zero. Unless there is a DC component, you'll have zero crossings with any AC waveform. I don't understand why you say there are no zero crossings in 3 phase L/L.