Tweakers' Asylum

Posted by jea48 (A) on September 19, 2008 at 21:48:12

In Reply to: RE: I removed the GFCI in my Equitech, installed all P.S. Audio outlets... posted by howard on September 19, 2008 at 12:50:24

>>I've touched it many times without any problems(it sits on the floor next to the CRT). What situation could arise that would aside from spilled liquid that would cause a shock? <<
>>>>>>>>>>>>>>>>>>>

Glen B touched on a couple of the problems in his first post that for some reason he deleted.

One of the examples Glen gave was an incandescent lamp.

If you look at a lamp holder the center contact connects the hot conductor and the outer shell of the lamp holder connects to the neutral, the grounded conductor. The plug on the cord of the lamp is polarized so the plug can only plug into the receptacle so the shell of the lamp is always at ground potential. So if you change the light bulb in a lamp, whether the switch is on or off, you should never receive an electrical shock if your fingers are touching the shell of the bulb and lamp holder as you screw the bulb in or out as some other part of your body may be grounded. It is a safety thing.

But you can't say the with a balanced power system. If a lamp is plugged into a receptacle fed from a balanced power system the shell will be hot with a difference of potential to ground of 60Vac.. 60 volts will kill you just the same as 120V. That is why NEC says certain types of light fixtures shall not be fed from a balanced power system.

And just to make it as idiot proof for someone who does, just one of the reasons NEC requires GFCI protection.

Again Glen touched on the fact that audio equipment may only break one Line and install a fuse only on that Line.

So if the switch is open the flow of current is stopped and the equipment is off. As Glen said with the balanced system the other side of the Line feeding the equipment is still Hot. Glen stopped at this point, not sure why.....

So the switch is open the unit is off. I agree.

But what if on the Line side of the switch/fuse for what ever reason a ground fault occurs...... No problem the fuse blows, current flow stops.

But wait a minute......, the other Line is still Hot, And there still is current flow. From the Hot Line through the primary winding of the equipment power transformer on out through the ground fault out the equipment grounding conductor back to the source. Not sure what happens if only 60 Volts is now feeding your preamp. Again with GFIC protection this cannot happen.

Using the same example as above, and for what ever reason, the equipment ground becomes open after the fuse blows.... Don't know why but it happened.

Maybe at the time the fuse blew you was out getting a beer or something. You come back into the room, no sound what the hell. You lean down and rest your hand on another piece of grounded equipment and touch the NOW HOT CASE of the preamp. You will have 60Vac going across your heart.

Far fetched? Maybe..... But with GFCI protection it should never happen.

Bottom line, just be careful.

Edits: 09/20/08