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Yes, they operate if there is a low resistance fault path to earth and remove the touch voltage risk but it's the local earth that provides the protection by causing the device to operate. If a person provides that fault path themselves then I'm afraid the MCB isn't going to be much help. I...

Exactly. They serve the same protective purpose as a wire or cartridge fuse - they serve to protect the cable against overcurrent.

Think about that one. For an MCB to trip you have it exceed its rated current.

Not if you're in Scotland :P

In that they prevent fires, yes. If you're in the s/c path with sufficient current flowing through you to trip the MCB then you're probably dead anyway.

Oh and when I was a kid and those bloody dangerous double adaptors for table lamps and the like (plugs into the bayonet connector in place of a bulb, provides an inline socket for the bulb and one off at 45 degrees to plug something else into) still existed, I stuck my thumb in the 45 degree...

An MCB will also detect live to earth faults if the design current is exceeded. RCDs protect people, MCBs protect cables.

Testing and setup of a valve power amp. Measuring the DC rails (650v nominal) at the main decouplers (around 100,000mfd combined) some idiot dropped a steel chassis piece right by my ear and the next thing I remember was picking myself up off of the floor about 6 feet from where I was...

Correct. The circuit is made between phase (live) and neutral. The earth or cpc is there to help protect against fault conditions not as a part of the circuit. The term short circuit therefore relates to live and neutral.

Neutral to earth, yes. Live to neutral, no - that's what the MCB is for.

Basically, yes. America uses a 110v split phase system with a centre tapped transformer as shown in the diagrams. This produces 2 110v lines at 180 degree phase that can be summed to give 220v if necessary.

Just use an FCU then.

BAS is referring to the way that the cable has been terminated in the consumer unit - if that's wrong then you'll definitely need an electrician to have a look. Does the switch that trips have a test button or not?

Oh I'd quite happily let evolution take care of that. :wink:

I think BS means is it the MCB that's tripping, the thermal switch on the immersion thermostat or an RCD - in other words what protective device is tripping?

If it's switchable, it provides a means of preventing unauthorised use of the outlet. Not a bad idea really.

First one would be: If you have to ask for basic safety tips then ask yourself should you really be considering doing it yourself? Second would be: No matter how trivial the job seems to you, always isolate the circuit and prove it dead using a suitable meter. If you don't know how to then...

Actually BAS, you get on your anti-downlighter soapbox with tedious regularity. It may only have been one post in this thread but there have been many others. Constantly rehashing this view contributes nothing to threads whereas the *constructive* help that others, including myself, post does...

That's normally the error seen when the OS is fully loaded. Are you sure it ran from startup (before Windows loaded)?

Have a read of this article: http://en.wikipedia.org/wiki/Electricity_meter The section on tampering and security should give you more information.