on ESC Website

[ebee]

I sent a message to the ESF Website ref their take on the 13A twin socket rating meaning.

anyway I noticed this (unrelated piece) about ELV.

Everybody happy with it???

SELV is Safety Extra Low Voltage, PELV is Protective Extra Low Voltage and FELV is Functional Extra Low Voltage.​

Answered by Dave, Electrical Safety Expert​

• SELV is Safety Extra Low Voltage; its output voltage is in the Extra Low Voltage range (Generally <50VAC/120VDC or 25VAC/60VDC) it has a double or reinforced layer of insulation between the Extra low voltage output and the Low voltage (Mains input).
• PELV is Protective Extra Low Voltage; its output voltage is in the Extra Low Voltage range (Generally <50VAC/120VDC or 25VAC/60VDC) it has a double or reinforced layer of insulation between the Extra low voltage output and the Low voltage (Mains input), similar to SELV apart from it is not electrically separated from Earth.
• FELV is Functional Extra Low Voltage; its output voltage is in the Extra Low Voltage range (Generally <50VAC/120VDC or 25VAC/60VDC) However, it does not have a double or reinforced layer of insulation between the Extra low voltage output and the Low voltage (Mains input).

 

[JohnW2]

I sent a message to the ESF Website ref their take on the 13A twin socket rating meaning. ... anyway I noticed this (unrelated piece) about ELV. ... Everybody happy with it???

Your 'this' does not seem to have made it into your post

 

[ebee]

aw ok i`ll look again, thank you

 

[ebee]

PS I have since noticed other things on this website too

 

[JohnW2]

PS I have since noticed other things on this website too

In the past, we have noticed all sorts of very questionable things on their website - not the least some extraordinary 'statistics' (removed a long time ago' about the number of people experiencing electric shocks in the UK

Kind Regards, John

 

[ebee]

I was thinking along the lines of calling it Live instead of Line and similar . I mean so called experts using the incorrect names or even using wrong common ones with a brief mention of the correct ones .

however the initial piece I was noticing was SELV meaning "Safety" not "Separated" Extra low Voltage, it did stand for Safety but did change quite a while ago now.

One observation about shocks, a lot of folk get them and discount them as "it was only a shock it did not kill me!" LOL Oh ok then, my problem is that not only could a shock become electrocution but up a ladder over a staircase etc etc it could easily be fatal or bone breaking bad news

 

[ericmark]

I thought the S stands for separated, not safety? And being separated is important, it is not linked in any way to earth.

 

[bernardgreen]

And being separated is important, it is not linked in any way to earth.

I am not so sure about that being important. In fact I would say that in some applications there are good reasons to Earth the ELV supply.

 

[JohnW2]

I thought the S stands for separated, not safety?

I believe it does. That's certainly what BS7671 thinks

 

[JohnW2]

I was thinking along the lines of calling it Live instead of Line and similar . I mean so called experts using the incorrect names ...

As I often say/imply, 'clear and unambiguous communication' is often more important than 'strictly correct terminology'.

ESF is very much focussed on an audience of consumers/users/general public, a very high proportion of whom probably wouldn't have a clue what was meant (in this context) by "Line" (not to mention the fact that very few of them believe that,say, 230 V is "Low Voltage"!

Kind Regards, John

 

[bernardgreen]

Continuing from last post.

A transformer that is layer wound relies on a few layers of insulating tape. If the Live side of the mains is connected to P1 then capacitive coupling between the windings can lift the S2 side of the ELV up to mains voltage. Enough to cause a tingle from a damp door bell push button

In all cases a failure of the isolation between LV and ELV will connect the ELV circuit to to mains voltage. There will be no Earth current from the now hazardous ELV circuit which means the protective RCD supplying the transformer will not trip.

 

[flameport]

Mostly Safety, sometimes Separated depending on which standard you look in.

The good thing about standards is that there are so many different and conflicting ones to choose from. Ideal for every argument.

https://products.iec.ch/view/search/all?q=eyJxdWVyeSI6IlNFTFYiLCJtb2RlIjoiR0xPU1NBUlkiLCJzb3J0QnkiOiJ0ZXJtLS1hc2MiLCJsYW5ndWFnZSI6ImVuIn0%3D

 

[ericmark]

There will be no Earth current from the now hazardous ELV circuit which means the protective RCD supplying the transformer will not trip.

The mains RCD will not trip with any supply from an isolation transformer. This has been the argument over the use of reduced low voltage, it may mean only 64 volts to earth, but the RCD on the low voltage side of the supply, will not trip.

I read @flameport link, but we are not worried about "Normal conditions" the whole idea is to protect when the conditions are not normal.

 

[bernardgreen]

The mains RCD will not trip with any supply from an isolation transformer.

The mains RCD protecting the supply to the isolation transformer is likely to trip if the isolaton has failed and the ELV has a connection to Earth.

The mains RCD protecting the supply to the isolation transformer is un-likely to trip if the isolaton has failed and the ELV has no connection to Earth

 

[ericmark]

If the isolation has failed, it is not an isolation transformer.