Reply to post: Re: Once more, with feeling

Re: Once more, with feeling

> the request was made because the customer wanted the circuits limited to 10a absolute max, not 10.005 and --> definitely not 20!

In which case the customer understands even less what fuses/breakers are there for than your wiring fiend.

No.

Many power supplies and plug boxes and other things have a rating for V and A. They are built so that at the max of those they should be able to cope, but they don't have to cope above those levels. Most have a safety/fudge factor built in, so a 10A 250V plug box could survive happily at 11A. Few would survive at 15A though.

I have watched transformers in TV's melt down and some actually get hot enough to catch fire, I recall some cheap Chinese[1] import TV's (at a time when the Phillips "Griax" (GR1AX) 14" TV was popular but suffering a "go to full volume when a bright white screen was displayed" fault - same chassis was in their 'space helmet' tv around '91/'92) that had a 10a fuse in them, but no thermal fuse in the under-rated and poorly made transformers. Even worse, when you turned the TV "off" the power was shunted through some hefty ballast resistors instead of actually turning the supply off, IE the PSU of the TV was always running at 'full noise'. Some of these transformers would literally have a melt-down, and some of them could be sending out flames while still well below 10a. I cannot recall any more on the brand details above what is in here (did fix many of the GRIAX's, fitting 2 diodes on the board where they should be but the factory had cheaped out and used wire links instead).

Many other people have had experiences of stuff catching fire while drawing a lower current than the fuses or breakers would trip at, and some people know that they can protect themselves better by using a lower-rated breaker, within the confines of the ratings of attached devices rather than twice the confines.

Your reply only shows you completely missed the point of the exercise, and why the customer wished to significantly reduce the available energy to the 'threat', hence vastly reducing the risk of a fire :) Sometimes personal safety means slowing way down and 'driving to the conditions', not blundering along at the legal limit.

[1] I'm quite certain they were Chinese-made but may've come from elsewhere. One of the larger store chains sold hundreds of them, which gave the starting-to-die repair industry a big boost for a while.