1、UL COPYRIGHTED MATERIAL NOT AUTHORIZED FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM ULNovember 15, 20061SUBJECT 508BOUTLINE OF INVESTIGATIONFORRELAYS USED IN INFORMATION TECHNOLOGY EQUIPMENTIssue Number: 2NOVEMBER 15, 2006Summary of TopicsThis new issue of SU 508B is being issued
2、through ULs electronicpublishing system to ensure format uniformity between the PDF andHTML versions of the document. No substantive changes have beenincorporated in the document.The UL Foreword is no longer located within the UL Standard. For informationconcerning the use and application of the req
3、uirements contained in thisStandard, the current version of the UL Foreword is located onULStandardsInfoNet at: http:/ 2006 UNDERWRITERS LABORATORIES INC.UL COPYRIGHTED MATERIAL NOT AUTHORIZED FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM ULNOVEMBER 15, 2006SUBJECT 508B2No Text on
4、This PageUL COPYRIGHTED MATERIAL NOT AUTHORIZED FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM ULCONTENTSINTRODUCTION1 Scope .42 Glossary .43 General 5CONSTRUCTION4 Spacings .65 Securement of Wiring and Parts 76 Flammability of Materials .7PERFORMANCE7 Electric Strength Test 78 Prim
5、ary Power Isolation (optional) .79 Safety Interlocks (optional) .8NOVEMBER 15, 2006 SUBJECT 508B 3UL COPYRIGHTED MATERIAL NOT AUTHORIZED FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM ULINTRODUCTION1 Scope1.1 This Outline of Investigation covers the requirements applicable to relays
6、 intended for use inaccordance with the Standard for Safety of Information Technology Equipment Including ElectricalBusiness Equipment, UL 1950.1.2 The relays covered are limited to those with air gap isolation or a barrier of solid insulation betweencoil and contacts (electromechanical types) or be
7、tween input and output circuits (solid state types). Thisseparation between coil and contacts or input and output circuits shall comply with the requirements forbasic, double, or reinforced insulation as specified in UL 1950.1.3 Limiting impedance, as described in the Standard for Industrial Control
8、 Equipment, UL 508, is notconsidered a suitable means of isolation between input and output circuits.1.4 An optical isolator may be used in solid state relays to comply with the air gap or solid insulationrequirement.2 Glossary2.1 For the purpose of this Outline of Investigation, the following defin
9、itions apply. See UL 1950 foradditional definitions.2.2 BASIC INSULATION Insulation that provides basic protection against the risk of electric shock.2.3 DOUBLE INSULATION Insulation comprising both basic insulation and supplementary insulation.2.4 EXTRA-LOW VOLTAGE (ELV) A voltage between conductor
10、s or between a conductor and earthground not exceeding 42.4 V peak, or 60 V dc, existing in a secondary circuit that is separated fromhazardous voltage by at least basic insulation, but does not meet the requirements for a SELV circuit ora limited current circuit as defined in UL 1950.2.5 HAZARDOUS
11、VOLTAGE A voltage exceeding 42.4 V peak, or 60 V dc, existing in a circuit thatdoes not meet the requirements for a limited current circuit as defined in UL 1950.2.6 OPERATIONAL INSULATION Insulation needed for the correct operation of the equipment.Operational insulation does not protect against ri
12、sk of electric shock. It may, however, provide a degreeof protection against the risk of ignition and exposure to fire.2.7 PRIMARY CIRCUIT An internal circuit that is directly connected to the external supply mains orother equivalent source (such as a motor-generator set) that supplies the electric
13、power. It includes theprimary windings of transformers, motors, other loading devices, and the means of connection to supplymains.2.8 REINFORCED INSULATION A single insulation that provides protection against risk of electricshock equivalent to double insulation under the conditions specified in UL
14、1950. Reinforced insulationdoes not need to be in one homogeneous piece. It may comprise several layers that cannot be testedas supplementary or basic insulation.NOVEMBER 15, 2006SUBJECT 508B4UL COPYRIGHTED MATERIAL NOT AUTHORIZED FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM UL2.9
15、 SAFETY EXTRA-LOW VOLTAGE (SELV) CIRCUIT A secondary circuit that is so designed andprotected that under normal and single fault conditions the voltage between any two accessible parts, orbetween one accessible part and the equipment protective earthing terminal for Class I equipment, doesnot exceed
16、 a safe value. Under normal conditions this limit is either 42.4 V peak, or 60 V dc. Underfault conditions, higher limits are specified in UL 1950 for transient deviation.2.10 SAFETY INTERLOCK A means either of reducing the likelihood of accessing a hazardous areauntil the hazard is removed or of au
17、tomatically removing the hazardous condition if access is gained.2.11 SECONDARY CIRCUIT A circuit that has no direct connection to primary power and derives itspower from a transformer, converter, or equivalent isolation device situated within the equipment. Somesolid state devices may provide equiv
18、alent isolation.2.12 SUPPLEMENTARY INSULATION Independent insulation applied in addition to basic insulationin order to reduce the risk of electric shock in the event of a failure of the basic insulation.3 General3.1 In addition to complying with the applicable requirements in UL 1950, the relays sh
19、all also comply withthe applicable requirements in the Standard for Industrial Control Equipment, UL 508. References to UL1950 are to the Second Edition of that standard, and references to UL 508 are to the Sixteenth Edition ofthat Standard.3.2 The following are two examples of typical relay constru
20、ctions covered by this Outline of Investigation.These examples specify the circuit construction and the corresponding insulation that would be requiredfor their end-product application.a) A relay containing hazardous voltage and SELV circuits. This relay construction requiresdouble or reinforced ins
21、ulation between hazardous voltage and SELV circuits; basic insulationbetween hazardous voltage circuits and dead metal parts; and operational insulation within eachindividual circuit;b) A relay containing hazardous voltage and ELV circuits. This relay construction requiresbasic insulation between ha
22、zardous voltage and ELV circuits; basic insulation betweenhazardous voltage circuits and dead metal parts; and operational insulation within eachindividual circuit.3.3 A construction other than as noted in 3.2 may also be covered by this Outline of Investigation if itcomplies with the insulation app
23、lication requirements in 2.2.6 of UL 1950.3.4 A relay that has been investigated in accordance with UL 508 and having basic insulation betweenthe coil and contacts and between input and output circuits (see 3.2(b) is considered to be in compliancewith UL 1950 without any additional investigation.NOV
24、EMBER 15, 2006 SUBJECT 508B 5UL COPYRIGHTED MATERIAL NOT AUTHORIZED FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM ULCONSTRUCTION4 Spacings4.1 Spacings for operational insulation (for example, within hazardous voltage, ELV, or SELV circuits)need not be subject to further evaluation.
25、4.2 Spacings for basic insulation (for example, between hazardous voltage and ELV circuits and betweenhazardous voltage circuits and dead metal parts) need not be subject to further evaluation.4.3 Spacings for double and reinforced insulation (for example, between hazardous voltage and SELVcircuits)
26、 shall comply with the applicable clearances noted in Tables 3 and 4, and the applicable creepagedistances noted in Table 6 of UL 1950. The applicable clearances and creepage distances shall be thoseassociated with a Pollution Degree 2 environment and Material Group IIIb.Exception No. 1: The clearan
27、ce and creepage distance associated with a Pollution Degree 1 environmentmay be employed in an encapsulated construction.Exception No. 2: The applicable creepage distances may be those associated with a higher material groupif a CTI rating higher than 175 is involved. See note 4 of Table 6 of UL 195
28、0.Exception No. 3: A printed wiring board having a coating that complies with Subclause 2.9.5 of UL 1950(such as a conformal coating that complies with the Standard for Polymeric Materials Use in ElectricalEquipment Evaluations, UL 746C), may have clearance and creepage distances in accordance with
29、Table6 of UL 1950.Exception No. 4: As specified in Subclause 2.9.7 of UL 1950, a relay that is epoxy encapsulated need onlycomply with the through insulation requirements specified in Subclause 2.9.4 of UL 1950. Creepage andclearance distance requirements need not be applied within the encapsulation
30、. The thermal cycling,humidity, and electric strength tests for compliance in Subclause 2.9.6 of UL 1950, and the visualinspection described in Subclause 2.9.7 of UL 1950 are to be conducted if the temperatures measuredwithin the encapsulation exceed the thermal index of the encapsulation.4.4 A barr
31、ier that is necessary to maintain isolation between the coil and contacts or between input andoutput circuits involving hazardous voltage and SELV circuits shall comply with the distance throughinsulation requirements for reinforced insulation as specified in Subclause 2.9.4 of UL 1950.Exception: An
32、 optical isolator that complies with the requirements for double-protection optical isolatorsin the Standard for Optical Isolators, UL 1577 and with a dielectric insulation voltage rating at leastequivalent to the minimum required by UL 1950 for the application is considered to be in compliance with
33、the requirement specified in 4.4.4.5 The requirements for enclosed or hermetically sealed constructions contained in Subclause 2.9.6 ofUL 1950 need not apply to relays.NOVEMBER 15, 2006SUBJECT 508B6UL COPYRIGHTED MATERIAL NOT AUTHORIZED FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM
34、 UL5 Securement of Wiring and Parts5.1 As specified in Subclause 2.3.8 of UL 1950, uninsulated wiring and parts at a hazardous voltage shallbe so located or guarded as to reduce the likelihood of accidental shorting to SELV circuits, for exampleby tools or test probes used by service personnel.5.2 A
35、s specified in Subclause 4.3.9 of UL 1950, equipment shall be so constructed that if any wire, screw,nut, washer, spring, or similar part becomes loose or falls out of position, it cannot in normal use becomeso disposed that creepage distances or clearances over supplementary insulation or reinforce
36、d insulationare reduced to less than the required values.5.3 Some examples of constructions that comply with 5.2 are mechanically securing and then solderingleads to printed wiring boards, or the use of double crimp type pressure wire connectors or spot welding.6 Flammability of Materials6.1 Polymer
37、ic materials used in a relay are considered to be in compliance with the flammabilityrequirements specified in Subclauses 4.4.3.1 4.4.3.3 of UL 1950.PERFORMANCE7 Electric Strength Test7.1 Insulation breakdown shall not occur when a relay is subjected to the applicable test voltage noted inTable 18 o
38、f UL 1950.Exception: Circuits involving operational or basic insulation are considered to be in compliance with thisrequirement.8 Primary Power Isolation (optional)8.1 If requested by the manufacturer, the contact separation of an electromechanical relay can beinvestigated for compliance with Subcla
39、use 2.6.2 of UL 1950. This option is applicable to relays that serveas a means to provide isolation from the incoming primary power source.NOVEMBER 15, 2006 SUBJECT 508B 7UL COPYRIGHTED MATERIAL NOT AUTHORIZED FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM UL9 Safety Interlocks (opt
40、ional)9.1 If requested by the manufacturer, an electromechanical or solid state relay can be investigated forcompliance with Subclauses 2.8.4 and 2.8.6 of UL 1950. This option is applicable to relays that serve assafety interlocks. This will require:a) Electromechanical relays to maintain the specified contact air gap as specified in Subclause2.8.6 of UL 1950 and to be subjected to a 10,000 cycle operation test as specified in Subclause2.8.4 of UL 1950; andb) Solid state relays to be subjected to an analysis as specified in Subclause 2.8.4 of UL1950.NOVEMBER 15, 2006SUBJECT 508B8
