Tingle from metal lamp = dangerous?

[daestrom]

Basically, Double insulated is a little misleading, but in UL/CSA
parlance, it means that the internal wiring is such that it would take TWO
faults to occur, either of which would stop the product from working,
before anything could become electrically dangerous to the user. Usage
conditions are also taken into account.
Among other things it also means that there cannot be any exposed metal
on the product. ALL exposed metal must be grounded, which become a
non-essential in double insulated products.

It also means it doesn't need a third "prong", and the blades do not have
to be polarized on the two-blade plug, and it does not need a 3-hole
outlet.

Not entirely true. The classic example is a double-insulated inexpensive
power drill. The chuck that holds the bit is metal, and is not grounded.
The tool does not have a third prong grounding conductor. But it meets the
definition of double-insulated because the chuck is insulated from the motor
by nylon gear-drive. And the windings on the motor are, of course,
insulated from the motor frame. So it would take two faults, just as you
said. It has no third prong, also as you said. But the exposed metal parts
are *not* necessarily grounded.

daestrom

 

[The Natural Philosopher]

Bill Woods wrote:

What does "double insulated" mean in actual practice?

I guess its a derivative of the literal term. There are 2 layers of
insulation between live and metal casing or user, wire ends are cable
tied together so that if one comes out it doesnt wander far enough to
touch anything dangerous, and the insulation test v is much higher. No
earth connection is used.

Thats the meant-to. In practice there are plenty of [[]] products that
do not meet the above at all, japanese stereos and spotlights
especially.


NT

Originally it meant a transformer with not only insulated wire, but an
actual sheet of something insulating between primary and secondary.
I think it then gort extended to the above specs.