Maybe these Byzantine definitions are an attempt to reconcile
conflicting views on the subject. I agree that they are singularly
unhelpful.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK
On 2017-11-23 01:08, Richard Nute wrote:
For definitions of ELV, SELV, and PELV, I turn to IEC TC64, Electrical
installations and protection against electric shock, and its publication 61140,
Protection against electric shock – Common aspects for installation and
equipment. TC 64 is “to lay down basic safety requirements for protection
against electric shock for use by technical committees.” IEC 61140 is “… a
Basic Safety Publication intended for use by technical committees in the
preparation of standards in accordance with the principles of IEC Guide 104 and
ISO/IEC Guide 51.”
IEC 61140 defines ELV, SELV, and PELV:
3.26
extra-low-voltage (ELV)
any voltage not exceeding the relevant voltage limit specified in IEC 61201
3.26.1
SELV system
an electrical system in which the voltage cannot exceed ELV:
– under normal conditions; and
– under single-fault conditions, including earth faults in other circuits
3.26.2
PELV system
an electrical system in which the voltage cannot exceed ELV:
– under normal conditions, and
– under single-fault conditions, except earth faults in other circuits
Most product safety standards prohibit access to ELV on the assumption that ELV
is not adequately separated from a higher voltage.
I admit that I don't understand the statements about earth faults in other
circuits. I don't know how an earth fault in another circuit can increase the
voltage of SELV or PELV.
However, in my reading of 61140, I did not find any requirement that either
SELV or PELV could or could not be connected to earth.
Rich
-----Original Message-----
From: John Woodgate [mailto:[email protected]]
Sent: Wednesday, November 22, 2017 2:52 PM
To: [email protected]
Subject: Re: [PSES] Safe powering 12V doorlock
The definition of PELV that I have is, I think, from IEC 60364, and it says
'not electrically separated from earth', which I interpret as meaning
'connected to earth but not necessarily with a connection that can withstand a
large fault current'.
You must do as you see fit, but I think that if a potentially fatal fault,
however improbable, could exist undetected, but could be neutralized by a
simple earth connection, it would be good practice to provide the earth
connection.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk Rayleigh, Essex UK
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