It is definitely not a requirement for EMC, regardless of the standard.
The ground connection has no function in EMC but for the extremely low
frequencies.
I believe that is a generic design principle to ALWAYS connect
protective ground first and disconnect last when connecting any connector
regardless the requirements of the standard. Even when using fixed
connections make a habit of placing the ground connector in such a place
that when pulling of the wires by force, the ground wire is pulled out last.
(many connectors for fixed wiring do have such a topology by default)
If that is impossible, wiring practice normally prescribe that the
ground wire be cut off slightly (0.5) longer then phase and return
wires of the cable, ensuring the proper disconnect order of the wires
even if forced.
A peoduct safety designer should not inquire if any
design rule is mandatory in a specific standard, but instead,
question himself if any extra safety measure can be included in
the design without exceeding the design specifications (might include
cost!).
The PE connect first disconnect last principle is so fundamental to safety,
that it should be honored in any design, even not mains related.
The ground connection is one of the 2 fundamental safety layers between
user/operator and parts at live voltage. As important as insulation. Would
you
ask the same question if it concerned internal wire insulation ?
The actual moment of connecting/disconnecting power plugs is precisely the
same moment
where users put one hand on the equipments cover and push-in/pull-out the
plug
with the other hand. At that same moment emc filter capacitors charge with a
high
peak current steered by a possible steep voltage (up to 320 Volts in
europe).
Equipment needs grounding most at exactly *that* moment.
Regards
Gert Gremmen
ce-test
-Original Message-
From: owner-emc-p...@majordomo.ieee.org
[mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Lou Aiken
Sent: maandag 1 juli 2002 17:27
To: Jon Jones; Emc-Pstc (E-mail)
Subject: Re: EN60950 functional earthing.
My recollection is (without reading the standard) that the make first /
break last requirement only applies to connectors operated by the user or
other non trained persons.
Then it should also seem reasonable that the requirement would not apply to
a product meeting ALL class II requirements.
However, protection preventing contact (by the test finger) with a live pin
of a partially inserted plug or connector WILL apply if the connector can be
used by non trained persons, regardless of the protection class.Rgds,
Lou Aiken, LaMer LLC
27109 Palmetto Drive
Orange Beach, AL
36561 USA
Tel 251 981 6786
Fax 251 981 3054
Mobile 251 979 4648
- Original Message -
From: Jon Jones jon.jo...@atltelecom.com
To: Emc-Pstc (E-mail) emc-p...@majordomo.ieee.org
Sent: Monday, July 01, 2002 11:40 AM
Subject: EN60950 functional earthing.
Group,
Regarding Functional earthing requirements for Class II equipment.
Is there a general requirement for the functional earth in an equipments
power connector to follow the make first break last rule with regards to
EMC
(EN55022) and Safety.
Thanks in advance
Jon Jones
ATL telecom.
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