Nate Nagel wrote:
Hi all,

got a real puzzler. Bought and old canister type vacuum off eBay and it
arrived today. Hooked it up, started testing it out, seemed to work
fine. Vacuumed the kitchen and dining room (tile floor) then got to an
area rug in front of the sink. Switched to the power head and it worked
OK for a minute or so and then tripped its built in circuit breaker. I
noticed when it was operating that the light bulb flickered a little
bit. Reset it, tried it again, same thing, but this time I grabbed the
(steel) wand instead of the rubber coated end of the hose and got that
unmistakeable tingle of AC. I whipped out my trusty Fluke and can't
seem to find anything in the wand, hose, etc. where either of the power
leads are shorting to steel; same thing with the body of the vacuum
itself. I even metered between both prongs of the power cord to the
vacuum case, still nothing. I *suspect* that the issue is with the
power head, but there doesn't seem to be anything amiss there that I can
identify with a meter - if nothing else, there's no way for even a short
to the case to get to the wand, as there is no possible electrical
connection between the body of the power head and the wand (the
connecting piece is plastic.)

May have a wire hose stiffener 'slinky' embedded in the plastic.
How is the wand head powered? Does it have an external cord or what?


The one thing I did not do was to hook up
the power head and operate it and measure the voltage from the wand to a
known ground; I didn't want to smoke the thing completely and then have
the seller tell me that I damaged it.

Why not test it? It's already smoked.
Since you said it worked for a minute or 2 then I would suspect an
intermittent short. Which you may never be able to see on the meter.


I'm inclined to just box the whole thing up and send it back for a
refund, but I'm quite honestly puzzled - can anyone come up with a
reasonable explanation as to how this could happen, given what I saw
with my meter above? This is really perturbing me, usually I can come
up with a reasonable explanation as to why something failed the way it
did, but I don't get this one.

To make matters weirder, the vacuum was plugged into a GFCI protected
outlet and the GFCI didn't trip. Or can one still feel a tingle below
the threshold fault current for a typical GFCI?

A GFCI will only detect a current imbalance from hot to neutral. If you
are NOT grounded and make a hot to neutral connection through your body
then you will be shocked all day until you let go. In most cases this
shock is unpleasant but not lethal as you are able to reflex and pull
away and hopefully not fall off a ladder or something.

A GFCI is designed to trip when it detects that some or all of the
current is not returning to the neutral. In most cases the current would
be leaking to ground such as a grounded metal frame of an appliance.
The GFCI will trip if you grab a hot wire and you are grounded in
some way such as when you are also touching a metal pipe, duct or
concrete floor. This prevents a severe, paralyzing and often fatal
shock which can happen under these conditions.

In your case the vacuum is not grounded and you were not grounded so the
GFCI did not, and should not trip even under short circuit conditions.

Kevin








nate