stars1234 wrote:

History:

In a ealier topic, I wrote of my old house, built in 1952 + remodeled
by someone who knew even less than I. It has no grounds and is a
general mess, I think even according to code back then -people tell
me the electrician and the building inspector were "friends."

Thirty years ago, when I bought this house, the person inspecting it as
well as myself saw the standard, three prong, grounded outlets and
thought all was okay; but he didn't check to make sure they worked
and I was too young to know to tell him to. After all, he was the
inspector.

It wasn't until sometime later; when I found a few, two slot,
non-grounded outlets, I became suspicious. And my suspicions are
correct. Someone replaced nearly all the outlets with three prong,
polarized, grounded ones, but no ground to connect them to and no way
to fish a ground to them.

Here's Today's problems and a few questions:

I got a laptop computer for Christmas. It uses an AC to DC adapter
(transformer) to get power and recharge the computer's batteries.

Unlike most modern electronics, this one has a non-polarized socket for
the charger and the power cord is non-polarized, non-grounded too.
Neither is there any kind of marking, such as a white stripe along the
cord that lets me know which is the hot/neutral side. From what I've
read, a white stripe usually indicates it is the polarized side (the
neutral) and goes into the longer slot on the wall socket. The longer
slot is always neutral. Is that right?

The instructions say, plug the charger into the computer and then that
into the wall socket.
When I did it, there was an arc from the wall socket's left slot. I
thought that's strange. (This is one of the three prong, polarized,
grounded (but not really) sockets.)

I left it plugged in for a day or so. I unplugged it. Later, when I
plugged it back in, without paying attention to the orientation of the
plug, there was no spark. I thought, "strange," again. So, I flipped
the power cord plug over, plugged it in that way and sure enough, a
spark from the left slot of the wall socket. --bright blue and snappy.

Obviously, the left (tall) slot of the wall socket is hot (which I
think is backwards according to code?). And with no white stripe on
the power cord that plugs into the transformer, then no polarized
socket on the computer: two round holes, instead of a square and round,
I can't tell which is hot/neutral and what should go where, but I
sure didn't like the arc at the wall socket.

Looking at the power cord's plug, the tip of the prong that got the
zap, is a bit black and melted.
Of course, I don't want to destroy the very expensive computer.

1) Does it matter which way the power cord goes into the outlet?
With nothing polarized, I don't know what to do. Or does it matter?

Spark, no spark? destroy my computer or is it okay, no matter which
way it goes into the AC?

2) Further checking the wall sockets, looking at them from the front
(ground down), I find some take a polarized plug's neutral prong, (I
think that the wide one), fits into the wall socket's tall, left
slot; for others wall sockets though, the tall slot is on the right. .

I assume that the wall sockets that take it on the right are turned
upside down, so no harm done-as long as it's wired correctly.
(I'm off to Lowes to get an outlet checker.)

3) I tested a three prong, polarized, grounded (but not really), duplex
socket with my VOM (battery powered) for voltage. I pushed one probe
into the short slot, the other into the long (left) slot.

When I put the probe into the left slot-Pow! A nice, blue arc from
the tip of it into the slot.
I tried it again and the same thing happened. I switched the
probes-no arc. I was surprised by that since I thought with AC, as
long as the VOM is set to AC, it doesn't matter which way the +-
probes go.

Since the arcing distracted me, I failed to get the voltage. I tried
my VOM once more.

This time, when I put the probe into the left slot there was a big
flash. My VOM went dead-is dead-- and so is the wall outlet. Now,
I have to go by a new VOM, new wall socket. Funny that the fuse
didn't blow in the VOM nor did a circuit breaker trip.

Ideas on what may have happened and how do I fix it?

Most importantly though, any damage being done to the computer?

--more threads on my old house wiring, coming.

Bob T

Others have addressed the meter issues and the probable outlet issues so
I'll stick with just the computer issue.

A laptop "line lump" power adapter does not care at all which of it's
input leads is hot and which is neutral. Further, most any new laptop
line lump is auto ranging and should list something like ~100-240V
50/60Hz as it's input rating.

You may well get a small spark when plugging the power adapter in as
it's going to have an initial surge on power up (regardless of whether
the laptop is on or connected since the power adapter is always on.

If the adapter is indeed auto ranging as noted, there is nothing you
house wiring can do to damage it since the worst your wiring can do is
provide 240V to a 120V outlet which is bad for many items, but the
laptop power adapter would happily auto range to and operate just fine.

Pete C.