On Mon, 1 Sep 2008 12:10:22 -0400, "TWayne"
wrote:

[snip]

However, some (for no apparent reason) have POLARIZED plugs. That
has the same effect as having a ground pin, for limiting the ways
they can be turned.

The "invisible" reason would be the type of cktry in the warts types.
To some styles, as it used to be with TV sets, the polarity of
hot/neutral was important. But if an item is fully Class II
designed, then it doesn't need polarization.

For the ones (wall wart power supplies) I've examined, the prongs of
the plug are connected directly to the ends of the transformer
primary. There seems to be nothing special about one or the other.
This doesn't stop some manufacturers from using polarized plugs.

True; many will use whatever is cheapest and already on the market.


They can also use polarity to meet
certain safety ratings,

Would these ratings be nonsense, or is there actually some benefit to
using polarization here?

It's a UL/CSA/ETL thing. To me it's nonsense, but that's what the specs
require for many of them. One reason I still recall is, due to the
weight of the warts, they do not want more than one hung on a vertical
outlet on the wall. I used to have to spec supplies for our telecom
equipment (R&D) which meant passing all the safety agencies.
I try when I can to get things with warts that have cords on both
sides; the primary and secondary both; more wire to hide, but more fit
to a power strip.
I haven't seen a polarized direct plug in in a long, long time though
IIRC.


such as having to cover more than one receptable
position.

Why would a low-power device be designed to prevent use of a
receptacle?

As I mentioned above, the weight of the wart/s on the receptable seemed
to be the main reason. They aren't really considered "low power"
because you have line power coming into it and processed to produce
whatever kind of output/s was/were required. IIRC too, there was some
magic weight where even a non-polarized wart had to extend far enough to
negate using any receptacle next to it. We accomodated that by adding a
lip to the far end that covered most, not all, of any receptacle in the
opposite side.

There was more to all of this, but I've been out of the business for a
long time. I know Ault used to have a great web site with all the
UL/CSA and MOU plain language requirements on it; don't know if they
still do.

Cheers,

Twayne


You don't find many polarized wall warts anymore though.