Hi Ron:
Two years ago, Jim Bacher presented my paper,
"Equipotentiality and Grounding -- Deriviation
of Grounding Resistance for Equipment"
at the IEEE EMC Symposium Product Safety Workshop.
This paper is available for download from the IEEE
PSTC Mindcruiser web site:
http://ieeepstc.mindcruiser.com/
On the left side, click on "Infopieces," then
"Latest postings." Scroll down to the bottom, and
click on the title. Then, click on "download."
This paper discusses the 0.1 ohm value for equipment
and how this value performs in terms of prevention of
electric shock.
You will see that values up to 0.5 ohm will also
provide the same degree of protection against
electric shock.
As for the 25-amp test current, I have no answer for
the rationale. We do know that a circuit-breaker
will operate for no more than 1 minute at twice rated
current. So, for a 15-amp branch circuit, 30 amps
would be a rational test current (and is the required
current under CSA standards).
I have conducted tests that show that the 25-amp test
current will not show any flaws or defects in the
current path that an ohmmeter will not show. The
test will not find a loose connection! And, a short
length of #22 AWG wire will pass the test. I believe
the 25-amp test is of no value.
The high-current circuit path must be visually
inspected for robust construction techniques. Wires
must be at least 18 AWG. Screwed connections must
use lock-washers that provide gas-tight connections
between metal parts. Crimp connections must be
according to crimp parts manufacturer's instructions.
Etc.
Best regards,
Rich
> From owner-emc-p...@majordomo.ieee.org Wed Jul 24 16:17:44 PDT 2002
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> From: ron_well...@agilent.com
> To: emc-p...@majordomo.ieee.org
> Subject: Bonding Impedance
> Date: Wed, 24 Jul 2002 14:57:33 -0600
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>
> Hello all,
>
> I recent issue has come up for me regarding why some safety standards
> specify 100 milliohms as the acceptable impedance for a protective earth
> ground bonding test. I am curious as to what the rationale is for this
> specific value and why 25 amps is chosen as the default test current.
>
> Regards,
> +=================================================================+
> |Ronald R. Wellman |Voice : 408-345-8229 |
> |Agilent Technologies |FAX : 408-553-2412 |
> |5301 Stevens Creek Blvd., |E-Mail: ron_well...@agilent.com|
> |Mailstop 54L-BB |WWW : http://www.agilent.com |
> |Santa Clara, California 95052 USA| |
> +=================================================================+
>
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