Application Note IEC 950 e 4

7/29/2019 Application Note IEC 950 e 4

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I E C 9 5 0CENELEC EN 60950

(UL 1950)

690-258B


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I E C 9 5 0

CENELEC EN 60950(UL 1950)

Contents

CENELEC EN 60950 (IEC 950)Safety of information technology equipmentincluding 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 safetya) Dielectric strength test (Hi Pot) . . . . . . . . . . . . . . . . . . . . . . . . . . 5b) 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

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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 primarysafety standard which must be met by electronic equipment if it is to be soldinto the European Union after December 31, 1992.The standard is intended tocontrol equipment and is not a component standard. Therefore, although a

power line EMI filter (such as made by Schaffner) can be designed and built inaccordance with IEC 950, it is not possible to have a formal IEC 950 approvalgranted for such a filter. Underwriters lab standard UL 1950 is intended to be inharmony with EN 60950, although at this time a few small differences still seemto exist and approval by UL to UL 1950 does not automatically certify the equip-ment under EN 60950.

The following is an outline of the key parts of IEC 950. It is intended to helpSchaffner customers identify areas in which IEC 950 requirements differ from

past practices and is not a complete description of the entire regulation.

*CENELEC = Comit Europen de Normalisaion ELECtrotechnique

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1 Shock hazards

Within IEC 950, equipments are classified according to their method of protec-

tion against electric shock.

IEC 950, like previous UL and VDE requirements, differentiates between equip-ment powered by voltage sources at levels dangerous to humans and which ispowered at a sufficiently low voltage to be inherently safe from shock perspecti-ve. In IEC 950 this voltage level (Safety Extra Low Level or SELV) is definedas 60Vdc or 42.4V peak, which permits 48Vdc circuits (such as those poweringtelephone 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 doubleor reinforced insulation. There should be no provision for protective earthing orreliance upon installation conditions.

Class I equipment provides protection by using basic insulation and providing ameans 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 useSchaffner filters, are controlled by the standard insulation practices of IEC 664and require any accessible conducting material to be connected back to asaftey ground or earth connection. Further, if the equipments is connectedto ground via the power line and the neutral conductor in the power line isalso tied back to ground, the system is considered a TN power system. A TTpower system has the equipment grounded independently of the power line butthe neutral wire in the power line still ties back to ground. Finally, an IT systemhas the equipment grounded independently of the power line and the neutralwire in the power line has, at best, a high impedance to ground. These threebasically different power distribution systems have their base schematic shown

in table 2 (page 8).

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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 thatthese capacitors reach a safe level in a short time, either 1 second or 10 secondsdepending upon how the power is connected. In many cases this requires theuse of discharge resistors. Schaffner filters are designed to discharge in 1 secondor less to make them suitable for all IEC 950 applications.

The use of discharge resistors for this test however causes problems when anequipment goes under hi pot testing for IEC 950. In such cases the resistor canbe 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 beremoved. Schaffner will supply such filters for type testing; these filters aredesignated with a T in their part number. For example:

required filter for hi pot type testFN 9675-3-06 FN 9675T-3-06

4 Leakage current

A piece of equipment can produce leakage current which can be a hazard if it isallowed to become excessive. Because of this potential hazard IEC 950 limits theamount of leakage current.

All Class II equipment may only produce a maximum of 0.25mA. The leakagecurrent for class I type equipment can vary from 0.75mA to maximum of 5% ofinput current.

Power line filters are a source of leakage current. Schaffner filters for IEC 950applications are designed to meet the requirements and leave sufficient safetymargin 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-phasecircuits 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

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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 bemade 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, especiallyin places like Italy or Spain. Thus, for all practical purposes, IEC 950 requiresdouble contact switching and fusing for all equipment which might be used inEurope. Schaffner recommends double fuse holders for all new designs usingpower entry module filters, since it is possible to bypass one of the holders forequipment to be solely used in North America single fusing is desired. Single po-le switches may be used for strictly ON/OFF functions, as long as other meansexist for power line disconnect (IEC 320 plug, etc.).

6 Flammability

In accordance with IEC 950 flammability requirements all Schaffner componentsfor IEC 950 applications have class V2 flammability as a minimum, in most casesthe filters are class V0.

IEC 950 gives V0 better than V1, and V1 better than V2. For components IEC 950recommends 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) mustwithstand 1500Vac or 2121Vdc (preferred when capacitors are under test) for oneminute 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 canimpose 400Vac to another phase, which may require Y caps in an IT system tomeet a 1875Vac or 2650Vdc one minute test (this requirement is still underdebate).

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 1or 2 sec tests in production, this at 80% of the rated value.

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b) Overvoltage transient test (Surge)

Many safety testing agencies interpret IEC 950 to require that all accross-the-

line components conform to the Insulation Coordination limitations of IEC 664.IEC 664, in turn, requires that appliances, computers and other such low vol-tage/line power devices (defined as Installation Category II) be capable of safe-ly handling 2500V transients.

IEC 384-14 and in Europe the EN 132400 call up the following capacitor typesX1, X2, Y1 and Y2. Amendment A2 of IEC 950 (August 1993) defines the followingcapacitor types which can be connected across the line:

X1 capacitorsX2 capacitors tested as X1 but with 2.5kV surgeX2 capacitors which meet endurance tests with the 220 resistor short

circuit

The X capacitors used in Schaffner filters are in general X2 capacitors, all withSEV approval, which means a 3kV test has been carried out. These capacitorscomply then with the amendment A2 of IEC 950.

With the introduction of the EN component standards for capacitors and filtersthere is a certain harmonisation between standards.

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Abstract of IEC 950

Test voltage for electric strength tests-Table XV

For detailed applicable test conditions refer to IEC 950 or to a harmonisedstandard.

Table 1

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Applicable power distribution systems

Table 2


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Corporate Headquarters

Schaffner EMV AG

Nordstrasse 11CH-4542 Luterbach/SwitzerlandPhone +41 (032) 68 16 626www.schaffner.com

Subsidiary companies

FinlandSchaffner Electro Ferrum OyPhone +358 19 326 616Fax +358 19 326 610

FranceSchaffner EMC S.A.S.Phone +33 1 34 34 30 60Fax +33 1 39 47 02 28

GermanySchaffner EMV GmbHPhone +49 721 569 10Fax +49 721 569 110

ItalySchaffner EMC S.r.l.Phone +39 02 66 04 30 45Fax +39 02 61 23 943

SwedenSchaffner EMC ABPhone +46 8 57 92 11 21Fax +46 8 92 96 90

Switzerland

Schaffner EMV AGPhone +41 32 68 16 626Fax +41 32 68 16 641

United KingdomSchaffner EMC Ltd.Phone +44 118 977 0070Fax +44 118 979 2969

ChinaSchaffner Beijing Liaison OfficePhone +86 10 6510 1761/62Fax +86 10 6510 1763

JapanSchaffner EMC K.K.Phone +81 3 3418 5822Fax +81 3 3418 3013

SingaporeSchaffner EMC Pte. Ltd.Phone +65 6377 3283Fax +65 6377 3281

USASchaffner EMC Inc.Phone +1 732 225 9533Fax +1 732 225 4789

Printed in Switzerland in August 2002 Albrecht, Obergerlafingen

Documents

Application Note IEC 950 e 4