IEC 950
CENELEC EN 60950
(UL 1950)
690-258B
IEC 950
CENELEC EN 60950
(UL 1950)
Contents
CENELEC EN 60950 (IEC 950)
Safety of information technology equipment
including electrical business equipment . . . . . . . . . . . . . . . . . . . . . 2
1 Shock hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Insulation and grounding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3 Electrical discharge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4 Leakage current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5 Switching and fusing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6 Flammability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7 Electrical ratings and testing for safety
a) Dielectric strength test (Hi Pot) . . . . . . . . . . . . . . . . . . . . . . . . . . 5
b) Overvoltage transient test (Surge) . . . . . . . . . . . . . . . . . . . . . . . 6
Abstract of IEC 950 (Table 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Applicable power distribution systmes (Table 2) . . . . . . . . . . . . . . . . . 8
Schaffner EMV AG
CH-4542 Luterbach/Switzerland
1
CENELEC* EN 60950 (IEC 950)
Safety of information technology equipment including
electrical business equipment
Equipment versus components
This new CENELEC standart, familiarly referred as “IEC 950”, is the primary
safety standard which must be met by electronic equipment if it is to be sold
into the European Union after December 31, 1992.The standard is intended to
control equipment and is not a component standard. Therefore, although a
power line EMI filter (such as made by Schaffner) can be designed and built in
accordance with IEC 950, it is not possible to have a formal IEC 950 approval
granted for such a filter. Underwriter’s lab standard UL 1950 is intended to be in
harmony with EN 60950, although at this time a few small differences still seem
to exist and approval by UL to UL 1950 does not automatically certify the equipment under EN 60950.
The following is an outline of the key parts of IEC 950. It is intended to help
Schaffner customers identify areas in which IEC 950 requirements differ from
past practices and is not a complete description of the entire regulation.
*CENELEC = Comité Européen de Normalisaion ELECtrotechnique
2
1
Shock hazards
Within IEC 950, equipments are classified according to their method of protection against electric shock.
IEC 950, like previous UL and VDE requirements, differentiates between equipment powered by voltage sources at levels dangerous to humans and which is
powered at a sufficiently low voltage to be inherently safe from shock perspective. In IEC 950 this voltage level (Safety Extra Low Level or SELV) is defined
as 60Vdc or 42.4V peak, which permits 48Vdc circuits (such as those powering
telephone systems from batteries) to be designed under more lenient SELV rules.
These SELV designs are called “Class III” insulation systems under IEC 950.
Class II equipment provides protection with additional insulation such as double
or reinforced insulation. There should be no provision for protective earthing or
reliance upon installation conditions.
Class I equipment provides protection by using basic insulation and providing a
means of connection to the protective earthing conductor in the building wiring.
Class I or Class II systems require careful mechanical and interlock design to
avoid shock hazards. Their insulation requirements are summarised in table 1
(page 7).
2
Insulation and grounding
Class I systems, which include almost all of the equipment designs likely to use
Schaffner filters, are controlled by the standard insulation practices of IEC 664
and require any accessible conducting material to be connected back to a
saftey ground or “earth” connection. Further, if the equipments is connected
to “ground” via the power line and the neutral conductor in the power line is
also tied back to ground, the system is considered a “TN” power system. A “TT”
power system has the equipment grounded independently of the power line but
the neutral wire in the power line still ties back to ground. Finally, an “IT” system
has the equipment grounded independently of the power line and the neutral
wire in the power line has, at best, a high impedance to ground. These three
basically different power distribution systems have their base schematic shown
in table 2 (page 8).
3
3
Electrical discharge
Even when a piece of equipment is not connected to the power system a shock
hazard can exist due to stored energy in capacitors. IEC 950 recommends that
these capacitors reach a safe level in a short time, either 1 second or 10 seconds
depending upon how the power is connected. In many cases this requires the
use of discharge resistors. Schaffner filters are designed to discharge in 1 second
or less to make them suitable for all IEC 950 applications.
The use of discharge resistors for this test however causes problems when an
equipment goes under hi pot testing for IEC 950. In such cases the resistor can
be subjected to over 2000 volts for 1 minute. This greately exceeds the resistors
power rating. To perform this test IEC 950 allows that discharge resistors be
removed. Schaffner will supply such filters for type testing; these filters are
designated with a “T” in their part number. For example:
required filter
FN 9675-3-06
4
for hi pot type test
FN 9675T-3-06
Leakage current
A piece of equipment can produce leakage current which can be a hazard if it is
allowed to become excessive. Because of this potential hazard IEC 950 limits the
amount of leakage current.
All Class II equipment may only produce a maximum of 0.25mA. The leakage
current for class I type equipment can vary from 0.75mA to maximum of 5% of
input current.
Power line filters are a source of leakage current. Schaffner filters for IEC 950
applications are designed to meet the requirements and leave sufficient safety
margin for other sources of leakage withih the equipment itself.
5
Switching and fusing
A major question raised by IEC 950 is whether switching and fusing elements
must disconnect one or two conductors in a single phase circuit. In multi-phase
circuits all “hot” phases must be disconnected by switches, circuit breakers and/
or fuses, and for “IT” circuits, the neutral line must also be disconnected. But, on
4
normal single phae circuits, if the grounded neutral line can be reliably identified,
only the “hot” phase line need be switched and fused. An argument can be
made that in the U.S., with NEMA 5-15 three-wire plugs and sockets, the neutral
wire is well identified. But this is not the case throughout Europe, especially
in places like Italy or Spain. Thus, for all practical purposes, IEC 950 requires
double contact switching and fusing for all equipment which might be used in
Europe. Schaffner recommends double fuse holders for all new designs using
power entry module filters, since it is possible to bypass one of the holders for
equipment to be solely used in North America single fusing is desired. Single pole switches may be used for strictly “ON/OFF” functions, as long as other means
exist for power line disconnect (IEC 320 plug, etc.).
6
Flammability
In accordance with IEC 950 flammability requirements all Schaffner components
for IEC 950 applications have class V2 flammability as a minimum, in most cases
the filters are class V0.
IEC 950 gives V0 better than V1, and V1 better than V2. For components IEC 950
recommends a minimum of V2.
7
Electrical ratings and testing for safety
a)
Dielectric strength tests (Hi Pot)
“Accross the line” components in a Class I system (like Schaffner filters) must
withstand 1500Vac or 2121Vdc (preferred when capacitors are under test) for one
minute from phase to phase or phase to neutral (X caps), as well as from phase/
neutral to ground (Y caps), as long as working voltages are below 250Vac.
With IT class system rated 220Vac (as in France), a phase to ground failure can
impose 400Vac to another phase, which may require Y caps in an IT system to
meet a 1875Vac or 2650Vdc one minute test (this requirement is still under
debate).
The above is a drscription of the ratings requirements. Detailed manufacturing
test conditions have not been fully specified as yet, but are anticipated to the 1
or 2 sec tests in production, this at 80% of the rated value.
5
b)
Overvoltage transient test (Surge)
Many safety testing agencies interpret IEC 950 to require that all accross-theline components conform to the “Insulation Coordination” limitations of IEC 664.
IEC 664, in turn, requires that appliances, computers and other such low voltage/line power devices (defined as “Installation Category II”) be capable of safely handling 2500V transients.
IEC 384-14 and in Europe the EN 132400 call up the following capacitor types
X1, X2, Y1 and Y2. Amendment A2 of IEC 950 (August 1993) defines the following
capacitor types which can be connected across the line:
X1 capacitors
X2 capacitors
X2 capacitors
tested as X1 but with 2.5kV surge
which meet endurance tests with the 220Ω resistor short
circuit
The X capacitors used in Schaffner filters are in general X2 capacitors, all with
SEV approval, which means a 3kV test has been carried out. These capacitors
comply then with the amendment A2 of IEC 950.
With the introduction of the EN component standards for capacitors and filters
there is a certain harmonisation between standards.
6
Abstract of IEC 950
Test voltage for electric strength tests-Table XV
For detailed applicable test conditions refer to IEC 950 or to a harmonised
standard.
Table 1
7
Applicable power distribution systems
Table 2
8
Corporate Headquarters
Schaffner EMV AG
Nordstrasse 11
CH-4542 Luterbach/Switzerland
Phone +41 (032) 68 16 626
www.schaffner.com
Subsidiary companies
Finland
Schaffner Electro Ferrum Oy
Phone +358 19 326 616
Fax
+358 19 326 610
United Kingdom
Schaffner EMC Ltd.
Phone +44 118 977 0070
Fax
+44 118 979 2969
France
Schaffner EMC S.A.S.
Phone +33 1 34 34 30 60
Fax
+33 1 39 47 02 28
China
Schaffner Beijing Liaison Office
Phone +86 10 6510 1761/62
Fax
+86 10 6510 1763
Germany
Schaffner EMV GmbH
Phone +49 721 569 10
Fax
+49 721 569 110
Japan
Schaffner EMC K.K.
Phone +81 3 3418 5822
Fax
+81 3 3418 3013
Italy
Schaffner EMC S.r.l.
Phone +39 02 66 04 30 45
Fax
+39 02 61 23 943
Singapore
Schaffner EMC Pte. Ltd.
Phone +65 6377 3283
Fax
+65 6377 3281
Sweden
Schaffner EMC AB
Phone +46 8 57 92 11 21
Fax
+46 8 92 96 90
USA
Schaffner EMC Inc.
Phone +1 732 225 9533
Fax
+1 732 225 4789
Switzerland
Schaffner EMV AG
Phone +41 32 68 16 626
Fax
+41 32 68 16 641
Printed in Switzerland in August 2002 · Albrecht, Obergerlafingen