Security issues power switch wiring

[loudthud]

In Europe, (generally speaking, varies according to country) the power is two phase. Two hot wires and no neutral. No zero volt wire.

I have questions about this. Is it balanced or floating? Is there a breaker on each side of the line at the breaker panel? What happends if one side shorts to ground? What about in countries where they have 3 phase?

In the US 120V, circuits have only a single breaker on the hot side at the breaker panel. On 240V circuits there is a breaker on each side but they are joined together so that when one side is over current, both sides are disconnected. On three phase circuits (like I have at work) all three phases are disconnected.

[g1]

There is 220V (or 240) single phase (sometimes called split phase) or 208V triple phase. There is no two phase. And I'm not even an electrician .

[Merlinb]

In Europe, (generally speaking, varies according to country) the power is two phase. Two hot wires and no neutral. No zero volt wire.

Are you sure about this? I have never heard of such wiring in Western Europe...

[Merlinb]

When I check out German layouts most of the time I see the switch connected at to 4 points.

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?

The power switching rules vary by country, even when they have equivalent mains wiring and non-reversible plugs. The rules also change frequently in order to generate more revenue for the certifying agencies.

In Britain the current legislation is for a single switch in the live wire;another switch in the neutral wire is expressly discouraged, but other countries demand a switch in both, as you have observed.

[R.G.]

In Britain the current legislation is for a single switch in the live wire;another switch in the neutral wire is expressly discouraged, but other countries demand a switch in both, as you have observed.

Do the safety powers-that-be give a rationale for that? People whose job it is to give new and "safer" regulations sometimes think strangely.

[Merlinb]

Do the safety powers-that-be give a rationale for that? People whose job it is to give new and "safer" regulations sometimes think strangely.

The only explanation I've heard is that with two switches you could have a situation where the live switch goes faulty and stays closed, while the neutral is open, creating the illusion that the unit is isolated when it isn't. I don't know if that's the 'official' position on the matter. Seems like six of one and half a dozen of the other if you ask me!

[R.G.]

Wow.

As I said, the Safety-Enabled-Prognosticators think oddly.

I am fond of inserting a neon voltage indicator (or two or three) on the back of the power switch on my stuff. At least there would be *two* faults required before you would not have fair warning of a hot incoming line. Both the switch and the indicator would have to be bad.

Of course, this could be sidestepped with "testing hygene" where you have the habit of always checking for AC power at the switched side of the power switch to AC safety ground each time you stuck your hands in.

Of course, I'm also the kind of guy that doesn't trust a meter til i make it show me something in the way of a reading before I look for no reading to be safe.

My early experiences with being shocked and also designing power supplies led to a test twice, live once philosophy.

[Steve Conner]

Like most other European countries, we have power distribution by 400V 3 phase plus a neutral wire. Each house gets one phase and neutral, giving 230V. So no, we don't have "two hots". Larger buildings get all four wires, so they have three hots with voltages that don't add up.

Merlin, safety regulations for mains-powered equipment are harmonised across Europe now, according to the Low Voltage Directive. So British practice for wiring a power switch shouldn't be any different to European practice. In particular, many European countries use the phase and neutral system, with plugs that can be inserted either way round, which defeats the argument for "knowing that the unit is isolated" with a single-pole switch. (the switch could be in the neutral today)

[Alex/Tubewonder]

Also, installing a IEC power inlet in the amp instead of cable straight in through a grommet gives you a redundancy in power disconnection. Just unplug the mains cable from the amp and be safe even if power switch might be disfunctional.

[bob p]

In particular, many European countries use the phase and neutral system, with plugs that can be inserted either way round, which defeats the argument for "knowing that the unit is isolated" with a single-pole switch. (the switch could be in the neutral today)

Thanks for clarifying that, Steve. When I was travelling in Europe I remember seeing the "Europlug", which was a two-pin non-polarized plug, which I thought was inherently dangerous. I definitely wouldn't want that hooked up to any appliance that only switches one side of the line power (like an electric razor or the boutique amp I described above). This situation becomes particularly dangerous when people are crossing borders and using converter plugs with their appliances.

As I understand it: the Europlug shouldn't ever be seen on an amp anyway, as it is only permissible for Class II devices (double insulated and double switched), and guitar amps not being double-insulated would qualify as Class I devices that require chassis grounding.

Appliance classes - Wikipedia, the free encyclopedia

I didn't see anything specific about a double switching requirement for Class I appliances in what I was reading, but if you're forced to use a polarized plug like the UK's BS-1363 then I guess double switching is not absolutely necessary.

As others have said, double switching is still a good practice, whether it's required or not.

[R.G.]

Like most other European countries, we have power distribution by 400V 3 phase plus a neutral wire. Each house gets one phase and neutral, giving 230V. So no, we don't have "two hots".

At the next level up, the USA does have two hots. The incoming line is three phase and usually splits at the distribution line to three isolated 240Vac phases, each of which is center tapped. Most houses get both "hot" ends and the neutral coming in from only one of the 240Vac outputs, and their neighbors get the others.

The house/office/etc. is as a practice wired with one half (120Vac) and neutral to the outlets, and any two outlets may have 0V or 240Vac between the two hot lines, depending which incoming phase they happen to be wired to back at the breaker panel.

The electrician is supposed to wire things up so that the two hot sides are semi-balanced for 120Vac users. Heavy power users like electric stoves and furnaces get both hot lines. The neutral going back to the distribution transformer only carries the difference between the currents of the two hot lines. This can be anything from zero up to the full line current, depending on the balance.

A fun thing happens if the neutral going back to the distribution trannie gets high resistance or open. The voltage at any one socket is then determined by the balance of loading between the two hots and the in-house neutral. A heavy current user on one side of the incoming 240Vac pulls its side down and the other side's voltage rises until the currents balance since the current in the neutral which balances these things can't eat the difference. So if you have a high-resistance neutral at the distribution box, the voltage on any wall socket can drop precipitously if it's on the same side of the 240 as, say, a refrigerator, toaster, or hair dryer. A wall socket on the other side can shoot up to dramatically high voltages as the two sides of the two hot lines must add to 240.

I believe there was a guy with hum and reliability problems posting here a while back that did in fact find his house had a high resistance neutral giving this problem to his amp.

Maxwell's Demon must have been laughing over that one.

[Enzo]

A friend of mine was amazed when he found that his back porch light would not come on, but if he left the switch on, and then pushed a slice down into his toaster, the light came on. Toaster didn;t get very hot though.

[R.G.]

Hey! Kewl! His whole HOUSE was a light-bulb limiter!

[bob p]

Hey! Kewl! His whole HOUSE was a light-bulb limiter!

I found a setup like the one Enzo described when I was re-wiring my GF's house in Chicago for an attic conversion. Someone had done some "home cooking" wiring upgrades to put an outlet on the exterior of the back porch to run the electric lawn mower. The mower didn't seem to have much oomph. You had to flip the light switch on the back porch to enable/disable the outside socket, which wasn't properly wired for a wet location.

When I opened the box, I found only a black wire and a white wire; the light bulb was in series before the outdoor socket, so that it limited the amount of current that could flow to the mower. I yanked the circuit apart, disabling the outside socket which wasn't grounded. They didn't like that.

Interestingly, one apartment in that two-flat had remained unoccupied for years because of an electrical failure that took out the second floor's branch circuits. I found the failure point -- it was a short in one of the boxes in a closet that caused a fire that was limited to the box. fortunately the closed box and the thinwall conduit limited the air supply to burning wire insulation, and the fuses blew out in time to prevent the housefire.

I really like that idea of keeping an OHSA circuit tester in your gig bag.

[R.G.]

I really like that idea of keeping an OHSA circuit tester in your gig bag.

Better than any black cat bone or mojo hand, or other magic amulet. The plug tester DOES work sometimes if you do the right incantation - that is sticking it into the outlet you're about to use while saying "will me and my amp survive this?"