Security issues power switch wiring

[shocki]

When I check out the wiring of the power switch most of the time it looks like this.
http://www.ceriatone.com/images/layo...sCeriatone.jpg

I see the power switch is connected at 2 points.

When I check out German layouts most of the time I see the switch connected at to 4 points.
http://www.brieskorn.de/int/Guitar__...uxe_layout.pdf

So they are connected the N and the L side. Not just the L side. I think this is due to security reasons in Europe.
It seems this should be done cause the power plug could be plugged in the other way around so L and N changes. This would make sense. But the plug cannot be connected the other way around in the US? Is this correct?

[soundguruman]

When I check out the wiring of the power switch most of the time it looks like this.
http://www.ceriatone.com/images/layo...sCeriatone.jpg

I see the power switch is connected at 2 points.

When I check out German layouts most of the time I see the switch connected at to 4 points.
http://www.brieskorn.de/int/Guitar__...uxe_layout.pdf

So they are connected the N and the L side. Not just the L side. I think this is due to security reasons in Europe.
It seems this should be done cause the power plug could be plugged in the other way around so L and N changes. This would make sense. But the plug cannot be connected the other way around in the US? Is this correct?

Security? That an interesting way of describing it...
In the US, we have One hot wire and one neutral. The neutral is also tied to safety ground at the circuit panel.
We shut off (open) just the Hot wire and the circuit is OFF. The only thing left connected is neutral, zero volts.
So we only need a single pole switch. (two terminals)

In Europe, (generally speaking, varies according to country) the power is two phase. Two hot wires and no neutral. No zero volt wire.
So, they use a double pole switch to disconnect two hot wires. (four terminals)

That's really all there is to it...it just disconnects ALL the hot power, whether one hot wire or two.

It's a bit confusing at first. See, here in the US, we call two phase power "single phase." That's really incorrect.
We have two hot wires for a 220 volt supply and we call it single phase. There are actually two hot wires, and two phases.
Silly Americans.

[R.G.]

In theory, USA residential power plugs are powered by Line (120Vac nominal), Neutral (0V nominal) and Ground (safety ground). In theory, all you have to do is interrupt the line side, and you're safe.

However, there is a significant portion of outlets that may be wired incorrectly, with line and neutral reversed. This makes the amp a hazard for any technician working on it unless the tech has previously tested the actual AC wall plugs he uses. I have long advocated every musician to carry one of the simply plug-in testers for AC outlets. These tell you if the wall socket is wired correctly.

But I consider it downright silly and shortsighted to have an on/off switch with two poles available and only break one of the AC lines. If there was any evolutionary justice, this would eliminate people who only wired one pole of such a switch from the species, but I fear we cannot rely on
Darwin's Ghost to help us with this.

In theory, it's OK to just break the line. In practice, it falls somewhere in the middle between wildly optimistic, stupidly trusting and downright dim to only break one side if there's already a two-pole switch there, as most power switches are.

Perhaps there is a reason to blame history. Back in the dark ages when all amplifiers were built in caves, electrical distribution was only line and neutral in the USA, and probably other places. Highly regarded vintage amps with two-wire line cords were built during this time. In a setup like that I would still prefer to break both sides of the AC power, but many of these amps have a single break switch and a fuse, often with the fuse in the non-switched side of the AC line. When third-wire ground is available, it's foolhardy to not change this over to breaking both sides of the AC line and fusing the side that is nominally the Line side.

So - it's best to break both sides, no matter what your AC power line looks like. That's my story and I'm sticking to it.

[bob p]

In theory, it's OK to just break the line. In practice, it falls somewhere in the middle between wildly optimistic, stupidly trusting and downright dim to only break one side if there's already a two-pole switch there, as most power switches are.

In the past couple of days I saw a porn shot of an amp by a boutique builder who shall remain nameless, where he used a DPDT switch, fed the hot AC to both poles, and left the neutral AC supply uninterrupted. I guess he's hoping that nobody will ever plug into a mis-wired outlet.

I think the reason he did this is because he's thinking that wiring the hot AC across two poles will prolong switch life. Didn't make sense to me. I don't think that arcing is going to be a problem with 120 VAC.

[Gingertube]

Its one of those extra safety things - I did my electronics training in a major Aussie Hospital (Biomedical Engineering Dept). The Medical wiring standards were different than domestic equipment standards and it was REQUIRED that active and neutral wires of the mains were switched AND both active and neutral were fused.

I build Guitar Amps this way still, but its just a hang over from my training. However, as anyone who has worked as a roady or a musician in some of the dingy hotels and clubs can tell you, the electrical wiring in these places can be "a bit sus". AS stated by posters above, if they have managed to swap the active and neutral wires then the fact that both are switched and fused is a good thing - right?. Double pole switching is a good start.

Cheers,
Ian

[bob p]

if they have managed to swap the active and neutral wires then the fact that both are switched and fused is a good thing - right?. Double pole switching is a good start.

I agree completely that it's a good idea. what I don't agree with is the boutique builder who used a double pole switch to divide the hot mains across both poles while leaving the neutral mains unswitched. seems pretty stupid to me.

[shocki]

Just to complete this. This is not a problem for the user but for the technican who thinks the amp is turned off but actually is not. Correct?

[Steve Conner]

Correct. The user shouldn't be poking around inside the chassis at any time, so it doesn't matter if the power switch isolates the circuit completely or not.

That's what the "Danger High Voltage, No User Serviceable Parts Inside" sticker is for, to help the manufacturer disclaim responsibility if the user does take it apart and kill himself.

My personal opinion is that a technician should always remove the plug from the outlet before assuming the innards of the amp are dead, so it doesn't matter if the switch is single pole or double pole, because he's not relying on it for isolation anyway. However, in my own builds, I've always used double pole switches breaking both live and neutral.

In medical electronics, if some piece of equipment is hooked up to a patient, and it malfunctions and starts to leak current and fry the patient, then the power switch is the natural first port of call. So it makes sense to specify it as a safety isolator.

[shocki]

My personal opinion is that a technician should always remove the plug from the outlet before assuming the innards of the amp are dead, so it doesn't matter if the switch is single pole or double pole, because he's not relying on it for isolation anyway. However, in my own builds, I've always used double pole switches breaking both live and neutral.
.

I totally agree.

[soundguruman]

Correct. The user shouldn't be poking around inside the chassis at any time, so it doesn't matter if the power switch isolates the circuit completely or not.

That's what the "Danger High Voltage, No User Serviceable Parts Inside" sticker is for, to help the manufacturer disclaim responsibility if the user does take it apart and kill himself.

My personal opinion is that a technician should always remove the plug from the outlet before assuming the innards of the amp are dead, so it doesn't matter if the switch is single pole or double pole, because he's not relying on it for isolation anyway. However, in my own builds, I've always used double pole switches breaking both live and neutral.

In medical electronics, if some piece of equipment is hooked up to a patient, and it malfunctions and starts to leak current and fry the patient, then the power switch is the natural first port of call. So it makes sense to specify it as a safety isolator.

Of course Steve. The mains should be entirely disconnected, not just switched off.
In the old Fenders, it was a single pole switch. In the new ones, it's double polled.
And that is the new NEC code standard, which must be followed.

In newer construction of the passed 20 years, there has been a big effort underway to make certain that the polarity of the plug cannot be reversed.
The inspectors won't let people occupy the building unless this has been pre- verified at every power receptacle.
Even the ground wire must be a separate path, no more using the conduit as the ground conductor. (this conduit ground used to be the accepted standard)...

And NOW, enter the era of UN-grounded guitar strings. The bridge and strings are no longer grounded to the amp.
You are no longer holding a return ground path in your hands.
Therefore you will not be shocked if you touch a hot wire. (grounding your body guarantees you CAN be shocked).
If you are NOT grounded, then you cannot be shocked.
EMG and several others are adapting this new standard. I believe you should disconnect your guitar bridge ground, and join the trend. I have.

[Steve Conner]

Disconnecting the bridge ground is good for safety, but it can make your guitar hum more, as your body becomes an antenna for hum, instead of a grounded Faraday shield. One compromise I've heard proposed is to put a capacitor in series with the bridge ground. But if you have metal covers on your pickups, those will still be grounded.

In the UK, we've been installing 3-prong grounded outlets since the 1950s, so it's a non-issue. "Death caps" and polarity switches never existed here. I think the 240V line voltage made us more safety-conscious.

[soundguruman]

Disconnecting the bridge ground is good for safety, but it can make your guitar hum more, as your body becomes an antenna for hum, instead of a grounded Faraday shield. One compromise I've heard proposed is to put a capacitor in series with the bridge ground. But if you have metal covers on your pickups, those will still be grounded.

In the UK, we've been installing 3-prong grounded outlets since the 1950s, so it's a non-issue. "Death caps" and polarity switches never existed here. I think the 240V line voltage made us more safety-conscious.

Disconnecting the bridge ground could save your life.
If you are using humbucking pickups, this should not cause more hum. If you are using single coil, it may well increase the noise for sure.

[bob p]

This is not a problem for the user but for the technican who thinks the amp is turned off but actually is not. Correct?

RG made some important points. Disconnecting one side of the mains isn't good for users either... especially if circumstances are that it turns out to be the neutral side that's being switched.

[bob p]

However, in my own builds, I've always used double pole switches breaking both live and neutral.

Steve, you've got hot-hot mains in Scotland, right? So when you're interrupting both sides of an AC line, you're interrupting two hots, right? Not hot and neutral? Or have I got it wrong?

[R.G.]

The bridge ground doesn't have to be disconnected, just made unable to electrocute you.

There is a scheme for doing this that involves putting a 220K or so resistor bypassed for RF reasons with a ? 0.01? 1KV? or so ceramic cap. The 220K is a "short circuit" compared to the normal resistance of many feet of air when you're not touching another conductor, and an "open circuit" suitable for keeping you from being killed if the other conductor is hot to the AC line. The cap shunts RF buzz at line frequency and two-times-line frequency to ground. I've implemented this on a couple of my guitars and it works well. The strat had a lot of hum pickup with a hard-wire bridge ground, and this disappeared with the resistor/cap and the cavity shielding I did.

Steve Sez:
My personal opinion is that a technician should always remove the plug from the outlet before assuming the innards of the amp are dead, so it doesn't matter if the switch is single pole or double pole, because he's not relying on it for isolation anyway.
Absolutely. But every tech I know of has violated this, many times over.

This is a lot like putting a bleeder resistor on all filter caps. This and some other things are what I think of as "amplifier hygene" and ought to be like brushing your teeth. You just do it until it's automatic. It's good for you, good for the amp's owner - especially if the amp's owner is ... you ...