Hi Manning:
Some comments in response to your assertions...
You pose the question: What is the purpose of the
"n" switch?
The "n" switch is provided for one of two purposes:
1) To represent a failure (open-circuit) of the
neutral conductor during leakage-current testing.
2) To facilitate leakage-current testing of non-
polarized products having a single-pole mains
disconnect switch.
There aren't any other purposes.
*****
With regard to switches:
For purpose 1:
The product's OFF-ON switch is relevant to the
results of the leakage current test (with the
"n" switch open) only when the switch is ON, in
which case the leakage current is about twice
that with the "n" switch closed.
Whether single-pole, double-pole, or absent is
irrelevant to the results. It is only relevant
if it is ON.
Likewise, the electrical location of the EMC
filter is irrelevant to the results.
For purpose 2:
The product's single-pole OFF-ON switch must be ON.
*****
With regard to purpose 1:
The issue is whether or not an open neutral is a
valid condition for the measurement of leakage
current.
An open neutral conductor results from a major
"trauma" to the product's power cord, plug,
receptacle, or the building wiring (within a wall
or within a conduit). (Remember, overcurrent
protection in the neutral conductor is forbidden,
so an open neutral is the result of some major
damage somewhere along the neutral path.)
The issue is whether or not the neutral conductor
is likely to be cut by some external force.
All we can say is that experience shows that such
physical damage sufficient to open the neutral
conductor while maintaining the phase conductor is
rather rare.
With regard to purpose 2:
No issue. Okay for facilitating testing of
specific products.
*****
My vote is no.
Best regards,
Rich
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