Ron, et al,
Most product standards specify low levels of touch current
to protect users from injury - whether direct electric shock injury or even
getting caught up and not be able to let go of the electrical unit. Worse
is going into VF (Ventricular Fibrillation) which requires intervention to
avoid death.
There are two principle ways to provide protection for most
products. Provide adequate insulation (usually Double Insulation) or
provide a Single Insulation along with a ground/earth connexion (the second
protection) which will carry away the unwanted fault current and keep the
exposed conductive product at a low, safe potential.
It is well known that the ground/earth connexion is
problematic in many places in the world. In the US a full 3 wire grounded
installation was only required in the 1960s. By the turn of this century it
is estimated that only about 50% of all US installations are full 3 wire
grounded.
So, an expected abnormal operational condition for cord
connected equipment is that the grounding, which is a designed-in safety
feature, is not present so a Touch Current measurement is made to ensure
that the current from the product is below the hazardous level. Exceptions
are made for robust cord connexions; eg locking connectors which are used in
high current situations and require a licensed electrician installation.
Perhaps this is adeqate explanation to your question.
:>) br, Pete
Peter E Perkins, PE
Principal Product Safety Engineer
PO Box 23427
Tigard, ORe 97281-3427
503/452-1201 fone/fax
[email protected]
From: Ronald R. Wellman [mailto:[email protected]]
Sent: Wednesday, November 12, 2014 5:05 AM
To: [email protected]
Subject: Re: [PSES] Open Protective Earth Conductor Fault
I appreciate the responses to this but I want to emphasize that the
"standards" give you an out to open earth leakage current testing if the
mains connection means meets certain requirements. This has nothing to do
with internal product construction of the protective bonding circuit. That
is covered elsewhere in most standards. Therefore, what is the origin of
this requirement and why are you allowed to waive a touch current test if
your mains connection means meets certain plug type requirements?
Also, I am aware of the two-wire USA NEMA 1-15P versus the three wire NEMA
5-15P plug/socket connection issues. Is it because of this that we have the
plug type exemptions from touch current testing?
Best regards,
Ron Wellman
> As I recall, touch current is effectively measured with the ground pin
> lifted. The rationale is that there should be no hazard even if the
> safety ground is left floating.
>
>
>
> Joe Randolph
>
> Telecom Design Consultant
>
> Randolph Telecom, Inc.
>
> 781-721-2848 (USA)
>
> <mailto:[email protected]> [email protected]
>
> <http://www.randolph-telecom.com> http://www.randolph-telecom.com
>
>
>
>
From: Scott Aldous [mailto:[email protected]]
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