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In Reply to: RE: Fuse Holder posted by Steve O on June 06, 2016 at 06:04:08
With the fuse in tact, both of the tags are going to be hot regardless. If the fuse blows one is hot, then you unplug it. If touch safety is a concern, both should be heat-shrinked. However, you are talking about an environment where there is exposed voltage everywhere so that is kind of like wearing a 1 inch square bulletproof vest.
Follow Ups:
Standard engineering practice is to run the line or hot lead to the rear of the fuse holder.
The reason is that when the fuse is removed, the exposed front ring terminal is not hot. This is to protect the end user.
Once the chassis is open, all bets are off although many do insulate the internal connections as well.
I always put the switch first before the fuse to keep everything dead if I am too lazy to unplug. I can't imagine changing a fuse on a hot piece of equipment, but it probably is an every day occurrence.
Chip647 is absolutely right, put the switch first, much more important than which of the two terminals the hot (make sure it is hot and not neutral) is connected to. The only time I've been shocked, working on this stuff for 20 years, is when I turned an amp off, and changed a fuse when the fuse was first (DUH). Sometimes you take a shortcut when thinking (amp off), this practice helps some.
twystd
and hot to the tail end cause it is further away from stuff like the chassis that could touch the terminal closest to the cap. is easy enough to unplug before working on stuff...neglect that, and your thought process pours chlorine into the gene pool.
Switch failure would then pop the fuse, and hopefully not deliver a resistive heating process that results in an acute thermal event...LOL
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
You can still complete the circuit with your other hand when the switch is off.
"You can still complete the circuit with your other hand when the switch is off."
How? FenderLover's schematic is correct. And FWIW, you're supposed to pull the line cord before replacing a mains fuse. No amount of precautionary wiring inside an amp can substitute for proper safety practices.
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Buy Chinese. Bury freedom.
"No amount of precautionary wiring inside an amp can substitute for proper safety practices."
That is certainly true, however there is the possibility (inevitability in my case) of a brain fart. If the fuse would have been wired after the switch I wouldn't have been shocked. Sometimes it's best to make things as idiot proof as possible, at least when it comes to safety.
twystd
The right type of power entry module can solve this problem for you. I haven't EVER been tempted to touch a metal fuse cap with the line cord plugged in. And just to cover all the bases, it is NOT safe to place the switch ahead of the fuse. Safety demands that the fuse should be the FIRST thing the hot mains wire is connected to.
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Buy Chinese. Bury freedom.
Fuses are simple and reliable. Switch contacts do get welded/arced together. I do a lot of electrical testing at work. Trust me, you don't want to bet your life on a switch or circuit breaker to actually shut of power.
So yes, fuse holder first. Fuse holders should have a line and load side. When in doubt check with the manufacturer.
When a switch arc welds itself on and the fuse is blown, it is no more dangerous than having the fuse first, in both cases if you are not smart enough to unplug the unit, there is a potential for shock when changing the fuse. The way around this is to not have an external fuse access..
What will happen if the switch arcs internally to the chassis? If you're lucky, the house breaker will blow quickly. If not, the internal green earth wire might open and you get electrocuted the next time you touch the amp. Or, maybe the earth wire stays good long enough for the wiring in the amp to catch on fire. Or the wiring in your house. Take a look at any UL equipment and you'll see that NOTHING precedes the fuse. This is what's required to protect users from defects and most mishaps.
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Buy Chinese. Bury freedom.
I don't think I'm getting this. You cannot get a shock from the fuse holder, IF the switch is off. If the switch is on... you can get a shock from the fuse holder, no matter if it's before or after the switch.If you are touching both the neutral and hot lines, you will get a shock. I'm wondering if the OP got a shock from the residual charge in the main PSU caps. This can happen no matter what position the switch is at.
Edits: 06/08/16
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