Systems for use with Renewable Energy
Relevant Regulations 1
Extra Low Voltage (E.L.V)a definition: A voltage that does not exceed 50V r.m.s., A.C., or 120V ripple free D.C., between conductors, or between conductors and earth.
These voltages are covered by I.E.E regulations (16th edition) under S.E.L.V
(safety extra low voltage) where the low voltage itself is used to prevent
shock, and under F.E.L.V (functional extra low voltage) which is more applicable
to site and show purposes. As a rule of thumb,
follow S.E.L.V where possible and when this is impractical adhere to F.E.L.V
regulations. The following are the applicable extracts from the regulations.
Protection against direct and indirect contact Using SELV is a means of providing
protection against direct and indirect contact; SELV must
not exceed 50V r.m.s. A.C. or 120V ripple free D.C.
411-02-01
SELV Sources
The extra low voltage shall be obtained from one of the following sources.
1. A safety isolating transformer having no connection between the secondary
winding and the core of the transformer, or the primary earthing circuit.
The transformer must also comply
with BS 3535, with no connection to earth on the secondary side.
2. A motor generator whose windings etc, provide the same degree of safety
as an isolating transformer made to BS 3535.
3. A battery or other source which is independent of higher voltages.
4. Electronic devices manufactured and tested to British standards, the output
terminal voltage of which cannot exceed extra low voltage, even with an internal
fault condition.
411-02-02
Where extra-low voltage is obtained from a higher voltage system, the device
reducing the higher voltage must have the necessary electrical separation
between the higher voltage and the extra-low voltage (as between the primary
and secondary windings of a BS3535 transformer).
Where extra-low voltage is provided from a higher voltage system through an
autotransformer, potentiometer, semiconductor device etc, it is not a SELV
system.
411-02-03
The regulations for Class II equipment, or for equivalent insulation shall
be used for the selection and erection of a mobile source for SELV.
411-02-04
Segregation of live and exposed parts
Live parts of SELV circuits must not be connected to earth, protective conductors,
or live parts of other circuits.
411-02-05
Exposed parts of SELV circuits must not be connected to earth, to an exposed
conductive part, or to the protective conductors or extraneous conductive
parts of another system.
411-02-07
Where equipment has to be connected to extraneous conductive parts, any voltage
that may appear on the extraneous conductive part must not exceed extra-low
voltage.
411-02-07
Live parts of SELV equipment shall be electrically separate from higher voltages.
The separation required is equivalent of that obtained between the primary
and secondary windings of a safety-isolating transformer. Additionally, a
live part of a SELV system must not be connected to a live part, or to a protective
conductor of another system, or to earth.
411-02-05
Segregation of Conductors
FELV (SELV) circuit conductors shall be kept physically separate from conductors
of other circuits (e.g. mains style inverter circuits). Where this cannot
be done then one of the following requirements shall be satisfied,
1. The conductors shall be insulated to the highest voltage present.
2. They shall be non-metallic sheathed cables, for instance cables installed
in plastic conduit or trunking, and this sheathing will protect them to the
highest voltage present.
3. They shall be separated by an EARTHED metallic screen or sheath (such as
a metal conduit or trunking or an armoured cable).
4. When grouped with other cables, or enclosed in multicore cable, they shall
either be insulated individually or collectively for the highest voltage present.
In 2 and 3, the basic insulation between conductor and screen need only be
sufficient for the voltage of the FELV or SELV circuit.
411-02-06
Plugs and Sockets
Plugs used on FELV and SELV circuits must not be capable of insertion into
sockets of higher voltages or of non-FELV/SELV circuits.
Sockets must not be capable of having plugs for other voltages used on the
same premises inserted into them.
411-02-10
Protection against touching live parts (direct contact)
Where the SELV exceeds 25V A.C. or 60 V ripple free D.C., one or more of the
following has to be adopted for protection against direct contact:
1. Protection by barriers or enclosures, giving protection against direct
contact by the insertion of a solid body more than 12mm diameter, and up to
80mm long, (IP2X).
2. The insulation shall be capable of withstanding 500v D.C., (r.m.s, A.C.)
for one minute.
411-02-09
If the nominal voltage does not exceed 25V r.m.s. A.C. or 60V ripple free
D.C. there is no need to insulate the cables, or to protect against direct
contact, unless the normal body resistance is reduced, in which case the voltages
of 25V A.C. and 60V D.C. must also be reduced. (Body resistance can be reduced
by a large portion of the body being in contact with earth, or in wet conditions).
411-02-09
Protection against indirect contact
If there is likely to be intentional or fortuitous contact between the exposed
conductive parts of an extra-low voltage system and exposed conductive parts
of any other system, that system shall be treated as a FELV system and the
FELV regulations shall be applied.
411-02-08
Other extra-low voltage systems
Where extra-low voltage is used, but not all the requirements for SELV are
complied with, additional measures shall be taken to protect against both
direct and indirect contact, as laid down in the regulations for FELV.
411-03