Booms, Busts, and Recoveries Message Board

STOCKTALK

We've detected that you're using an ad content blocking browser plug-in or feature. Ads provide a critical source of revenue to the continued operation of Silicon Investor. We ask that you disable ad blocking while on Silicon Investor in the best interests of our community. If you are not using an ad blocker but are still receiving this message, make sure your browser's tracking protection is set to the 'standard' level.

Strategies & Market Trends : Booms, Busts, and Recoveries

Public Reply Prvt Reply Mark as Last Read File

Previous 10 Next 10 Previous Next

To: maceng2 who wrote (65827)	7/2/2005 7:28:32 PM
From: Slagle	Read Replies (2) of 74559

PearlyButton Re: "third wire earth is dangerous" The idea of the third wire is not to protect you from electrical shock in the first place but to make the clunky thermal overload work better. And this was an innovation added to US practice only after the first thermal breaker type load centers began to replace the older fusible load centers that had been used from the beginning. You can make a melting element fuse that is very accurate and repeatable. The early generation thermal overloads were anything but accurate but were most likely to work with a good solid current surge and they needed the help of a solid ground path to make them work better. High current semiconductors are still protected with fast acting fuses, and thermal overloads are much better now than 45 years ago. Better, but still not good enough to protect a semiconductor. Practice here, just like what is used in Asia and elsewhere now used only two conductors till the late 1960's. The 1970 OSHA workplace safety act demanded the third wire and this got lots of folks killed, especially in factories. Here is the danger: Imagine a typical refrigerator sitting on a wooden floor. With third wire grounding the metal housing of the appliance is connected to ground by a copper conductor. If you stick your finger in the interior light socket or touch any live part of the wiring while touching the grounded case with the other hand you stand a good chance of being electrocuted. With a two wire system the frame of the fridge would not be grounded and you would be unharmed. Dry rubber or leather shoes will protect you that way, even if standing on concrete. You can hold a live wire, even a live 480 volt control wire in your fingers, no problem, unless you touch something grounded. The original idea of grounding the case was to help the early thermal overloads work better and not burn the house down. Breakers are better now and the practice should be abandoned. The main problem is 115 volt in the first place. And the particular problem here is the UL dictatorship that prevents the adoption of better wiring devices that are in use elesewhere. With a 220 volt system the tiny wire used makes much better and more reliable connection. Connections are always the problem. And the tiny #14 or #16 wire used is so soft and flexible that even if there is heating due to overload little mechanical stress is transmitted to the connection. With the clunky #12 solid that you need for a 115 volt branch circuit connections are always a problem. The dimensions and general construction of most wiring devices we use here in residental and commercial applications; toggle switches, recepticles, handiboxes ect. date from about 1920. The UL dictatorship prevents the use much better and innovative wiring devices developed elsewhere. And for the highest level of shock protection you really don't need a third wire at all. With a "ground fault" type current interrupt you can simply look for a difference in current between conductor L1 and L2 and trip as soon as a difference is observed, within a half cycle if need be. But for most stuff that is not needed. Slagle

Report TOU Violation

Share This Post

Public Reply Prvt Reply Mark as Last Read File

Previous 10 Next 10 Previous Next