SELV AND ISOLATION TRANSFOMER

[Dylboy]

Hello

Quick one, is a SELV device the same as an isolation transformer ?
i.e both isolate the secondary from the primary ?

So I can call an isolation transformer a SELV device if the isolation transformer goes from 230V to 12V ?

And if it goes from 230V to 230V then it is just an isolation transformer as not extra low voltage ?

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[GCE]

Hi

If you look at the definitions - It has more to do with not earthing the output of an isolating transformer which makes it a " Safety" supply

So on 230V - instead of having live and neutral at 230v you will actually have 2 lives at 230v - same as a 12v output , neither will be zero in relation to earth

Only when you earth one of the lives will it be a neutral , basically

Highlighted in red what I see as answering your question

Definitions from SANS 10142-1 pasted below

3.67
safety supply
supply of electricity that is obtained from
a) the unearthed secondary circuit of an isolating transformer with limited
output voltage, specified by the manufacturer, or
b) any other isolating device that provides equivalent safety and the same
degree of separation between the primary and secondary circuits, or
c) an isolated generator or a battery that provides a non-earthed supply



3.11.1
Protected Extra Low Voltage (PELV) circuit
extra low voltage (ELV) circuit with protective separation from other circuits
and which, for functional reasons, may be earthed or the exposed
conductive parts of which may be earthed (or both)
NOTE 1 PELV circuits are used where the circuits are earthed and SELV is not
required.
NOTE 2 See 7.14.2 for additional safety precautions when SELV and PELV circuits
are used in hazardous locations.

3.11.2
Safety Extra Low Voltage (SELV) circuit
extra low voltage (ELV) circuit with protective separation from other
circuits, and which has no provision for earthing of the circuit or of the
exposed conductive parts

[Dylboy]

Ahhh ok so it's the same thing as there is no earth reference thus safety.

The 2 lines as you said is correct as there is no neutral as no earth connection, I never realised that or at least said it in those terms so that is cool thank you.

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[Isetech]

Make sure you understand this information, the reason I say this, if you install a strip light around the lip of a swimming pool, it must be the correct type of transformer, not just any old LED driver/transformer, it must be a 12 V safety transformer. this has been discussed on this platform in the past. Meanwell do a 12 V safety transformer/driver for LED lights.

[Dylboy]

Yes I agree! Reason this came up is I know of Selv but now I was subbing for a guy and they using 230V lights in an ornamental pool and then they said as 230V no need for a driver. I had flags pop in my head. so read the regs and said needs to be fed from an isolating transformer and from there I wanted to dig deeper on the subject

What I have uncovered and also from here is that one item supplied by a SELV or isolationg transformer as if there is 2 can increase faults and this 2nd earth fault stuff. I.e 1st fault not noticed but 2nd fault deadly



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[Isetech]

You must be referring to this section.


7.2.4.5 Luminaires
7.2.4.5.1 A luminaire that is underwater, or within 2,5 m of the water surface,
or so situated that a person has to go into the water to service it, shall be fed
from a transformer that is out of arm's reach from zone 1 and
a) is a class II isolating transformer with a maximum output voltage of
1) 250 V, if the luminaire is used in an ornamental pool or fountain, or
2) 12 V, if the luminaire is used anywhere else, or
b) is an isolating transformer (see 3.83.3) (double-wound transformer)
1) with a maximum output voltage of 12 V, and
2) is protected by an earth leakage protection device that has a rated
earth leakage tripping current (rated residual current) IΔn not exceeding
30 mA.

[Dylboy]

Yes that's the exact one

Now as far as I understand a SELV or Iso. TX (Isolating transformer) can only serve one item.

Now this ornamental pond has 2 lights so then there should be an iso.TX for each ?

Am I correct ?

Edit: it also says luminarie and not the plural so Futher makes me think it can only supply one light

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[Alfred M]

The design involves using an insulation transformer, guaranteed minimum distances between conductors and insulation barriers. The SELV systems must have protective-separation such as reinforced insulation, double insulation or protective screening from all circuits carrying higher voltages. The SELV cables must be double insulated or pass through plastic conduits especially when they are likely to come into contact with other circuits

[GCE]

The design involves using an insulation transformer, guaranteed minimum distances between conductors and insulation barriers. The SELV systems must have protective-separation such as reinforced insulation, double insulation or protective screening from all circuits carrying higher voltages. The SELV cables must be double insulated or pass through plastic conduits especially when they are likely to come into contact with other circuits

A statement made above, that made no sense to me as to the context of the discussion - Looking at the article I have pasted below , in paragraph 3, I realized that nor did AlfredM fully understand why he made the statement as it belong to somebody else and was made in a different context

https://www.sunpower-uk.com/glossary/what-is-separated-extra-low-voltage-selv/