Re: You're just....


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Posted by David Sherman on Wednesday, September 19, 2007 at 14:23:43 :

In Reply to: Re: You're just.... posted by MoparNorm on Wednesday, September 19, 2007 at 13:26:03 :

Yep, those Westinghouse (now Zinsco) breakers that were popular 25 years ago also have a nasty habit of failing short. But once you have components failing to do what they're supposed to do, especially protection devices, all bets are off. Running heavier wire to the motor isn't going to make a bit of difference if the breaker fails, other than to maybe make some bigger sparks.

As to the 5 feet, the guy said he was putting the compressor right next to his panel. I didn't see any need to repeat that or ask for a detailed spec. "Right next to the panel" is an accurate enough spec to tell me we didn't need to calculate voltage drop.

Titles don't mean much to me either, but what does mean something to me is being able to back up one's design decisions with some kind of reasoning. At the very least, one can refer to the code book. At best, anybody building anything has enough understanding of basic principles to do a few calculations so that whatever he's building is big enough and strong enough to do the job, but isn't wasteful of materials. If I had to, I could figure out based on the resistance of the wire and the permissible voltage drop (his motor will run on 208 volts, so if he has 240 at the panel, he could lose 30 volts and it would still work) just how long he could run a given gage of wire. It's no different than calculating the dimensions of a beam needed to span a given distance with a given load.

I get a little tired of guys looking at something and saying "it needs to be bigger" based on absolutely nothing. It's real easy to say "that porch post should be a 8x8" or "that wire should be #6" or "that slab should be 10" thick". If "engineering" means being able to do a little figuring to back up your decisions, then everybody who builds anything well should be a little bit of an engineer.



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