Hi Ed:
My question is, why does this appliance have a polarized blade power
connector? I am assuming that the input power pins go directly to the primary
of a transformer, so why should we worry about which side is "high" or
"return"? Could wallwarts be designed using identical power blades, allowing
the option of a 180-degree rotation installation?
1) My guess is that someone told the manufacturer
that the wall wart must be polarized. That
someone could have been an "expert" or a cert
house engineer. I don't know of any safety
standards that would require polarization.
2) For most products, both the live and neutral
are treated the same within the product, so
there is no advantage to polarization.
As has already been mentioned, for products
with Edison-base lamp sockets, the neutral is
connect to the screw part of the socket.
Another reason mentioned was with respect to
EMI filters on 2-wire products that return
current to the secondary. If the cap is
connected between neutral and the secondary,
then the leakage current to the secondary
is very much less than if connected to the
line.
3) Yes, wall warts can be designed without
polarization. I have a number of them in
my home. The charger for my Sears drill is
not polarized. Likewise for the power supply
for my Panasonic phone.
Best regards,
Rich
Richard Nute, CFEI
Product Safety Consultant
San Diego
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