> =3D OZ seems to think 50 V a.c. or 120 V ripple-free d.c. is the
> ticket =A0 =A0AS/AZS 3000:2007 definitions 1.4.98
>
> =3D The IEC appears to agree.

I think the above is an abomination and a stupidity that crept in
through human error some while ago.
I may be wrong - it may be an abomination and a stupidity that crept
in on purpose.

I seem to recall that I actually wrote to the authorities at the time
of the change and was ignored - but maybe I just planned to write and
didn't do so.

At one stage ELV was AFAIK 50 VDVC or 32 VAC.
The two are about the same in peak instantaneous voltage liable to be
encountered across a circuit.
You can full wave rectify the AC to more - but then it classes as DC
and is covered appropriately.

50 VDC allows telephone circuits to be covered by ELV regulations.

50 VDC with lowish impedance behind it will give you (usually) small
shocks and burns if (when) brushed againhst - as in eg telephone
exchange setting. . More so when hands are wet or atmosphere is damp.
Especially so running jumper wires where traditionally hands are
inserted through open jumper block fields with many solder tags whole
running wires.

50 VDC CAN kill you but you could probably grab the two bus bars on a
large communications battery and live - possibly feeling little or
nothing if hands and surface was dry. If you happened to die in the
process you shouldn't be surprised - BUT I am not aware of any telecom
techs being killed in this country by this.

120 VDC is lethal. Early Edison reticulation was DC at about this
level and linemen died from it. I would not consider open hand seizing
120 VDC conductors. (Nor 50 VDC but I'd be far more confident of the
result.)

There is no sensible reason (IMHOAE) to allow people to work with
voltages of this level without some form of training and/or
certification UNLESS you also free up electrical wiring work in
general as well as a "cost saving" or philosophical measure.

I suspect that the change from ? 32 VDC/ 50 VAC may have been due to a
series of erroneous technical interpretations OR to philosophical
decisions not based on safety or technical considerations. I may be
wrong.




       Russell

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