Safety
Fact Sheet 7
The following information was kindly provided and compiled by
Ken Lawrence - Electrical Safety Consultant
(Tel: 01564 777914
Mobile: 07802 577764 Email: ken.lawrence@btinternet.com)
The Low Voltage Directive – Key points
All electrical equipment supplied in the European Economic Area must comply with the Low Voltage Directive
(LVD). In UK law this is implemented through the Electrical Equipment (Safety) Regulations 1994 and it is a CE
Marking requirement. It is not essential that testing for the LVD is carried out by a third party test house if the
manufacturers are sufficiently confident of doing it themselves.
The safety standard covers equipment in normal use or in foreseeable misuse conditions and also applies to
equipment built for own use by the manufacturer. It also covers prevention of access to hazards without the
use of special tools or a key. The regulations do not apply to explosive atmospheres, medical equipment,
aircraft, ships, railways, lifts, electricity meters, domestic plugs and sockets or components. However, there are
other Directives or Regulations that apply to these items
Voltages covered by the LVD are 50 – 1000 Vac (rms) and 75 – 1500 Vdc. However, there is some discussion
at the moment about reducing the minimum to zero volts.
General requirements
Additionally the following should be considered
Voltages greater than 30 Vac or 60 Vdc are normally considered to be hazardous
Voltages greater than 2V with available power greater than 240VA are considered to be hazardous energy
levels.
It must not be possible, under normal or single fault conditions, to make contact with hazardous voltages or
hazardous energy levels.
Accessibility to Electrical Hazards
There must be two levels of protection between hazardous voltages and “safe” voltages. This can be made
up of one layer of insulation plus earth or two layers of insulation.
The first layer of insulation is known as Basic Insulation. There will be Basic Insulation between hazardous
voltages and earth or earthed parts.
If there is not an earth a second layer of insulation is required and this is known as Supplementary
Insulation.
A combination of Basic Insulation and Supplementary Insulation is known as Double Insulation.
Often there is a single layer of insulation between hazardous and “safe” voltages which has the same
insulation properties as Double Insulation, this is known as Reinforced Insulation.
Types of Insulation
Reinforced
Insulation
Basic
Insulation
Primary Circuit
(mains)
Supplementary
Insulation
Secondary Circuit
(ELV)
Operational
Insulation
Secondary Circuit
(SELV)
Earthed Metal
Case
page 1 of 3
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series of informative mini guides on related key topics – go to
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The small print: Every effort has been made to ensure the integrity of the information in this data sheet, which has been provided in good
faith and the authors do not accept liability for any loss or damage caused by omissions, errors or the interpretation of the reader.
Safety
Fact Sheet 7
Insulation Distances
Insulation distance through air is known as the Clearance Distance.
Insulation distance along a surface is known as the Creepage Distance.
Assuming the hazardous voltage is 230V single phase mains, the following table shows the normal
insulation distances:
Clearance
Creepage
Distance through insulation
Stress Voltage
Basic Insulation
2.0 mm
2.5 mm
Not Specified
1.5 kVac
(2.1 kVdc)
Double or reinforced
insulation
4.0 mm
5.0 mm
0.4 mm
3.0 kVac
(4.2 kVdc)
Examples of Creepage Distances and Clearances
Creepage Distances
and Clearances (2)
Creepage Distances
and Clearances (1)
<1mm
≥1mm
Clearance
Clearance
Creepage Distance
Creepage Distance
Creepage Distance (1)
L
R2
F1
L
C1
N
Creepage Distance (2)
R2
F1
C1
N
RL1
RL1
F2
F2
T1
+
D1
R1
OC1
D2
+
T1
+
D3
D4
+
+
D1
R1
+
OC1
C2
D2
+
+
D3
D4
+
+
C2
R3
R3
R4
L1
R4
L1
Basic insulation - creepage distance at least 2.5mm
between protective earth and hazardous circuitry.
Reinforced insulation - creepage distance at least 5mm
between hazardous circuitry and selv circuitry.
Basic insulation - creepage distance at least 2.5mm
between protective earth and hazardous circuitry.
Note:
There must still be a creepage distance of at least 5mm to maintain
reinforced insulation between hazardous circuitry and selv circuitry
even though the earth track separates the two circuits.
To see lots more fact sheets like this one, or to register for our
series of informative mini guides on related key topics – go to
www.reo.co.uk.
The small print: Every effort has been made to ensure the integrity of the information in this data sheet, which has been provided in good
faith and the authors do not accept liability for any loss or damage caused by omissions, errors or the interpretation of the reader.
Safety
Fact Sheet 7
Clearance Distance
Distance through
Insulation
Creepage
Distance
Mains
Mains
at least
4mm
selv circuits
SELV
T1
F1
R1
OC1
SELV
R4
Insulation in
thin layers
Distance through
Solid Insulation
hazardous circuitry
2 or 3 layers
of tape
Reinforced insulation - clearance distance at least 4mm
between selv circuitry and hazardous circuitry.
Other important considerations
Earthing
z Earth wiring must be green/yellow (bare or transparent covering is allowed
for earth braiding).
z The resistance between any point that requires to be earthed for safety
reasons and the earth terminal must be less than 0.1Ω.
z The primary earth connection must be marked
should be marked
.
Rating Plate
A rating plate must be affixed to the
equipment in a visible position
, subsequent earths
z The primary earth should preferably be connected to a separate terminal,
subsequent earths being taken from another terminal. If this is not possible
Primary
the primary earth should be connected first
To other
Earth
earth points
and held in place with a nut, subsequent
earths can then be added and held in place
with a second nut. The reason for this is to
prevent the main earth from being disturbed
during servicing.
®
SMITHEN
INPUT
OUTPUT
ACH-6X
AC 100 - 240 V
180 mA 50 - 60 Hz
DC 10 V, 740 mA
Indoor
use only
Made in Germany
SN 00074884/CD11/560
To see lots more fact sheets like this one, or to register for our
series of informative mini guides on related key topics – go to
www.reo.co.uk.
The small print: Every effort has been made to ensure the integrity of the information in this data sheet, which has been provided in good
faith and the authors do not accept liability for any loss or damage caused by omissions, errors or the interpretation of the reader.