Hello from San Diego:
Terry Meck asks about connecting the PE conductor to
anodized aluminum. Terry is concerned whether the
construction will provide a reliable low-impedance
connection.
The first point to consider is whether or not the part
to which the connection is being made is the proper
part. The criterion is that the part is susceptible
of becoming live in the event of an insulation fault
(including a clearance distance).
Assuming that the anodized aluminum part is susceptible
of becoming live in the event of a fault, then not only
should the PE connection be considered, but also should
the other connections to other parts that need to be
grounded. So, the anodized aluminum part will probably
need to have at least TWO reliable, low-impedance
electrical connections to it.
The second point that needs to be considered is whether
the star washer will cut through the anodize with a
reliable and low-impedance connection.
A reliable connection is one that is gas-tight. I.e.,
once made, no oxygen can attack the points where the
connection is made. Supposedly, a star washer SHOULD
make a good, gas-tight connection.
A low-impedance connection is one providing a large
heat sink compared to the current. Usually, this means
large contact area. In the case of a connection to an
aluminum bar, the aluminum itself will provide a heat
sink, such that the contact area need not be large.
The standards only address electro-chemical potentials
and high-current impedance. So, for a connection to
anodized aluminum, the proof is in the 25- or 30-amp
grounding impedance test.
So, test the proposed construction and see if it passes
the high-current test. If it does, then it is as good
as a connection to ordinary aluminum.
Regards,
Rich
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|Richard Nute |Quality Department |
|Hewlett-Packard Company |Product Regulations Group |
|San Diego Division (SDD) |Tel : 619 655 3329 |
|16399 West Bernardo Drive |FAX : 619 655 4979 |
|San Diego, California 92127 |e-mail: [email protected] |
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