50 Volt SELV always has been based on Telephone exchanges,
The Positive pole of the supply is connected to Earth at the exchange so it is ELV and not SELV
50 Volt SELV always has been based on Telephone exchanges,
I have always assumed that the 50V limit of ELV presumably related to a perception of what voltage was 'fairly safe'. However, for someone with, say, wet hands, 50V can be more than enough to kill, so I'm not sure that it is all that 'safe' an approach!50 Volt SELV always has been based on Telephone exchanges, a nominal 48 Volt system, that when fully charged would have 56.x Volts on it, in recent years more testing and looking at automotive "Load dumps" has led to an increase to 63 Volts, I must have missed it creeping up again to 70! It is based on not being able to have a sustained arc in the dc circuit when a switch is opened.
As bernard has said, NO. SELV stands for Separated Extra Low Voltage.Safety Extra Low Volts ....
I personally find that hard to believe, for any variant of ELV.... has always been about not having to use a "contactor" to break the supply, it is seen as being unable to sustain an arc.
That's the very point I made. Nevertheless, in a number of contexts BS7671 appears to take the view that 'protection from electric shock' can be achieved by limiting "touch voltages" to 50V (AC).In extreme circumstances les than 6 volts can kill! dip each hand in a separate bowl of salty water, connect 6 volt bike battery across both bowls, could easily be fatal.
I think we are probably talking at cross-purposes.I stand corrected on the S bit, but I worked on a 50 V 500A battery charger many years ago and the belief then was that the ELV part was about being safe with a simple switch as much as about being non lethal.
Those correspond with the spirit of the BS7671 definitions.I understood the different types of ELV as.
SELV, separated from the mains and from mains earth by an isolation barrier that meets certain safety standards.
PELV, separated from the "live conductors" of the mains but not separated from mains earth.
In this case, the BS7671 definition is much more vague, so I don't think necessarily restricts FELV to only what you suggest ......FELV, not separated from the mains or seperated by an isolation barrier that is not safety rated..
BS7671:2018 said:Functional extra-low voltage (FELV). An extra-low voltage system in which not all of the protective measures
required for SELV or PELV have been applied.
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