"blackboab" wrote in message
ups.com...
Bob

AC current changes direction 50 times a second so the current must
first flow one way - live to neutral - and then the other way - neutral
to live.

It changes direction because the live varies first positve with respect to
neutral and then negative with respect to neutral. The neutral wire is
(roughly) at earth potential and stays there (more or less - in practice
under no fault conditions, there may be a few tens of volts (ac) or so on
the neutral depending on the generating and distribution arrangements.

It's the size of the voltage with resepct to earth, not its sign that causes
the toucher problems.

I did say the neutral wont electrocute you under no fault conditions. It is
true, as another poster pointed out, that, if the neutral retrun becomes
disconnected in a circuit somewhere neutrals between there and an appliance
will rise to 240V if the appliance is on, giving, clearly, the risk of
electric shock - this is a fault condition though.

As a practical example, our incoming mains supply comes overhead in a
concentric cable. The centre inner core is the live. The outer sheath is the
neutral. They are insulated from each other (obviously) and insulated
overall, to guard against a) the outer becoming live under fault conditions
b) unwanted neutral leakage currents to earth (which can be quite high where
the impedance is very low and c) corrosion of the netral sheath. When my
meter was moved, they reconnected live. The outer insulation and neutral
sheath were removed/unwound and pulled back with no protective gear. The
inner was then cut with a pair of extremely insulated cutters!

I have held neutrals many times under no fault conditions.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)