Rich
The obvious question I would have is... why couldn't you test at a higher
current for longer time meeting both requirements? For example 30A for two
minutes. I know the document indicates a maximum current, but does this make
sense?
OK I guess I know understand what you mean by Technical Requirement vs.
Technical Committee.
-----Original Message-----
From: Rich Nute [mailto:[email protected]]
Sent: Wednesday, August 25, 1999 2:37 PM
To: [email protected]
Cc: [email protected]; [email protected]
Subject: Re: Grounding Bond Test
Hi Carmen:
You ask how to resolve the difference between two,
different production-line (routine) test standards.
If your product is certified by CSA, then you test
to the 30-ampere value.
If your product is certified by a CB Certificate
and Test Report, and the issuing body invokes
EN 50116, then you test to the 25-ampere value.
If your product is certified by UL, then you test
to any current of your choosing.
So, the answer to your question is:
Whatever your certification house says.
In essence, the requirement is proprietary to the
certification house. The certification house can
invoke any production-line test it feels is
necessary. CSA uses 30 amps, 2 minutes. A
certification house that invokes EN 50116 uses
25 amps, 1 minute as a maximum test. UL does not
require a high-current test.
The CSA 30-amp requirement derives from the fact
that a CSA circuit-breaker rated 15 amperes (the
most common 120-volt circuit in Canada) is not
required to trip before 2 minutes at a current of
twice rating, 30 amperes. So, the equipment
grounding circuit must withstand 30-amperes for
2 minutes.
The CENELEC 25-ampere requirement history is not
at all clear. It has been in both European standards
and UL standards as a type test for many, many years.
It only appeared as a routine test when EN 50115 was
published a few years ago.
By the way, neither high-current test (as a
production-line test) will identify continuity
problems any better than a low-current test.
The presumption is that the high-current test will
identify a manufacturing defect in the grounding
circuit, while a low-current test will not.
In actuality, the grounding circuit, in order to pass
the type test, had to be properly designed to handle
the high current, no matter whether 25 amps or 30
amps. So, for the production-line, we need to be
assured, by test, that the high-current circuit has
been assembled correctly and with no defects.
The high-current test WILL NOT identify loose screws
if the conductors are making contact! The high-
current test WILL NOT identify cut strands of wire
if there are 3 or more strands in the circuit!
(Feel free to duplicate these tests or any other
grounding circuit defects you can imagine; the
circuit will pass the high-current test!)
The high-current test does not identify continuity
problems any better than a low-current test.
I did point this out to the EN 50116 committee when
they asked for comments before it was published.
Interesting that the committee ignored the data and
required the test anyway! I guess the lesson is:
don't confuse a technical committee with technical
facts.
Rich
-------------------------------------------------------------
Richard Nute Product Safety Engineer
Hewlett-Packard Company Product Regulations Group
AiO Division Tel : +1 858 655 3329
16399 West Bernardo Drive FAX : +1 858 655 4979
San Diego, California 92127 e-mail: [email protected]
-------------------------------------------------------------
ps: In high-volume production, both the 1-minute
and the 2-minute tests are unacceptable to the
manufacturer. It seems that most certification
houses will waive the long-term test in these
cases! This seems to admit that the high-current
test is not particularly valuable.
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