Hi Ken:
> Thank you for your comprehensive answer. I am a little surprised that after
> all the discussion in this forum on specs relative to the width of the
> yellow stripe on the green wire that there is no rule on how or if things
> get a green wire in the first place!
The choice of whether to design any particular
product as double-insulated or grounded is the
manufacturer's choice.
The rules are:
If your product is grounded, it shall meet
these requirements...
If your product is double-insulated, it shall
meet these requirements...
We, HP, make both double-insulated and grounded
computer peripheral products. We waffle back and
forth between the two constructions, and are not
consistent in our choice.
Our primary motivation is cost. Two-wire seems
to be lower cost (one less wire, etc.). But, the
EMC filter seems more difficult to design.
Then, we are concerned with worldwide distribution.
The same two-wire plug can be used in many more
countries than the grounded plug (i.e., Denmark,
Switzerland, Italy). So, there are fewer power
cords to stock. But, we already stock all of the
grounded power cords.
Finally, there is customer convenience. Two-wire
works everywhere, grounded only works in a grounded
environment. Japan residences are 2-wire. Many
European residences have both grounded and 2-wire
outlets in various parts of the home. Many homes
in North America still have 2-wire outlets.
So, there seems to be some advantages to 2-wire.
On the other hand, grounded is a very familiar
construction, and is easy and straight-forward for
both design and manufacturing.
No rule. Manufacturer's choice, but biased by
competition and "inertia" of the product line.
Vacuum cleaners are 2-wire; washers are grounded.
Best regards,
Rich
ps: Yes, we do get hung up on issues such as the
width of the stripe on the grounding conductor
because this is a RULE. The choice of using a
grounding conductor is NOT a rule.
The only rule is that the product must be either
grounded or double-insulated.
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