"Compromise" ground switch

[John]

http://www.bustedgear.com/faq_Amp_shocks.htm


I came across this while googling. It seems it would be useful for anyone that gigs a lot with the dubious wiring I hear about in clubs and whatnot. Is it safe?

[shooter]

Is it safe?

Looks like it should be as long as the ground pin on the line plug IS connected to chassis

[kagliostro]

There are special capacitors that if burn didn't short

do a search for class j and class x capacitors

If they burn they open like a fuse

Use one of those with the mod

EDIT: see here for a brief explanation

http://www.kemet.com/Lists/Filestore/EvoxRifaRFIandSMD.pdf


Here you can get a bit more info

http://www.kemet.com/Lists/FileStore/900%20Series%20Product%20Training%20Module.pdf

Franco

[frankenxtein]

A simple outlet tester can be had for about $5 and being sure the Hot and Neutral  doesn't get switched in outlets. My home had a few outlets that were wrong and the ground was for decoration. I still have a rule shoes are required here in the "Home" studio , when using any kind of electrical gear ...... drummers being an exception , the mics don't touch the kit.

Any type amp in a bad wired outlet is not safe imho. Those ground lift switches don't even get used much on direct boxes here.

[kagliostro]

Ciao Frankenxtein

to me that isn't a ground lift, the capacitor short to the chassis (and after the mod to ground) the noise present on the line

the switch is there as in many country you can reverse the plug on the outlet (one exluded is England that has a special plug)

using the switch you can swap the connection (may be I have not understand you correctly, language problem)

--

The principal problem isn't on the shop, is when someone is playing thru the amp and the cap short, don't you ?

Franco

[jjasilli]

A simple outlet tester can be had for about $5 and being sure the Hot and Neutral  doesn't get switched in outlets. My home had a few outlets that were wrong and the ground was for decoration. I still have a rule shoes are required here in the "Home" studio , when using any kind of electrical gear ...... drummers being an exception , the mics don't touch the kit.

Any type amp in a bad wired outlet is not safe imho. Those ground lift switches don't even get used much on direct boxes here.

The problem I see is what Shooter already mentioned. If the outlet's ground, say at a venue, is "mere decoration", then there is no chassis-to-earth safety ground.  In that case, the "Improved Ground SW" recreates the dangerous condition we're trying to avoid. 

[frankenxtein]

"Set the 3-position switch to the safe, center-off position most of the time and only activate it when you absolutely need it.  You can use a "center-locking" toggle switch to make sure it doesn't get flipped accidentally."  If it makes noise something is wrong and dropping the ground doesn't have a safe position.

I never liked those switches and don't own anything that has one. Everything  I've built has the IEC jack or a grounded 3 prong cord. The only place that would have me to play would be a dive and you never know  that little tester is pretty cool. If I go to someones brand new home to play I'd whip that out first. Even if you told me Brown & Root did the wiring themselves. People make mistakes. My old house has two wire wiring. Things that shocked me as a kid Washers , Refrigerators , I grounded those outlets , some outlets in the bedrooms still are not grounded. Those decorative ground pins are .... well.   

Funny how the vintage collectors item type things are , touch one solder joint and it's no longer vintage. Amps sitting around with dead tubes , bad caps , dried out crusty wiring. Non polarized cords , even 2 prong polarized worries me. I've been shocked a few times over the years with SS junk. This new found hobby has me seriously checking for stray voltage everywhere. Those new caps really do hold that charge well   

[kagliostro]

Use an Y class capacitor

or better, no switch, no capacitor and use one of this



Franco

[pompeiisneaks]

Have one of those ever gone bad?  I've wondered that, I know they're a built in cap etc, but is there any way to 'fix' it if the x2 cap goes out or do you just replace the whole thing?

[sluckey]

You would probably never know if a cap failed because the Class X and Class Y caps are designed to fail open circuit. But there are also two series connected inductors. Those will fail open if too much current flows through them. Then you will have to replace the unit.

[John]

So, the "compromise" switch is safe as long as the outlets do have the 3rd hole ground?  And if they don't, nothing is "safe" anyway. I was actually thinking this would be a useful addition in amps that are used by working musicians. The code is the code, but I'd wager there's plenty of stages not correctly wired as far as hot/neutral goes, and this would help reduce hum in those cases?

[kagliostro]

I think that those Y capacitors that are specifically designed for this use can be sufficiently safe

after of all they are used in a lot of new circuits that respects a lot of safety standard requirements

Franco

[sluckey]

So, the "compromise" switch is safe

There's nothing dangerous about that circuit as long as you use a Class Y cap ***AND*** your chassis has a proper earth ground connection. The danger lies with the building ground. Anything that compromises the building ground, ie, improperly wired outlet, broken ground wire, or even a loose clamp on the ground rod at the service entrance, sets up a dangerous situation. Even if the cap is working properly, you will get a nasty sting when the switch connects to the hot side of the line and your hands are on the strings and your bare feet are on the ground. The lower your body resistance, the nastier the sting. A .047µF cap looks like a 56K resistor to 60Hz. That 56k resistance is in series with the resistance of your body and it's tied to 120V. If the cap shorts, then you get the full 120V across your body. That can be fatal!

Bottom line... A properly grounded building wiring system makes it all safe. Compromise that, and nothing is safe. You cannot control the building wiring! For this reason, I would not connect a cap from the AC line to chassis.

[John]

For this reason, I would not connect a cap from the AC line to chassis.

Ah hah, that's what I really needed to know. Hum is annoying but not lethal.

[kagliostro]

An italian friend give me this explanation

The Death Cap was used when the outlet where without a ground connection and there wasn't a 3 wire cord, the chassis, if floating, may happen to be connected to the Live via parasitic capacitances and this could sort in some noise

To avoid this, the chassis was ideally connected to the neutral, but being the outlet reversible it was possible to unwittingly connect the chassis to the Live instead than the neutral, to solve this problem were used the switch and the capacitor

Today, says my friend, that chassis is connected to ground via the third connection pin on the outlet, the switch and capacitor have no more reason to be used

I don't know if really things are as told, but seems a reasonable argumentation

Franco

[John]

Yes, the only reason I was considering this is when playing somewhere that the outlets are wired backwards; that is, the hot and neutral are reversed. Thought it might help with some hum issues. But, if those outlets are wires backwards, it's more than possible the ground wire was "forgotten".

[PRR]

> somewhere that the outlets are wired backwards; that is, the hot and neutral are reversed.

That does not matter if you have a solid ground. Unless you complicate with haphazard cap connections.

If there is really no ground, just beware, and complain to the management.