Re: IEC 364 - Definition of SELV
Hi Kevin: Is IEC 536 the base document for the definition of SELV? (where it says that SELV means Safety Extra-Low Voltage)? Yes. IEC 536, Definitions, Sub-clause 2.6: Safety extra-low voltage (SELV) HISTORY LESSON == Prior to IEC 536, I believe SELV was not defined as such, but the concept of SELV, i.e., low voltage protected from higher voltages did indeed exist. CEE Publication 10, Electric Motor-Operated Appliances, October, 1964, has the following definition: Extra-low voltage denotes a nominal voltage not exceeding 42 V between conductors and between conductors and earth, the no-load voltage not exceeding 50 V. When extra-low voltage is obtained from the supply mains, it must be through a safety isolating transformer or a converter with separate windings. Due to its similarity with the definition from IEC 536, it appears this CEE 10 ELV definition evolved to SELV. CEE: International Commission on Rules for the Approval of Electrical Equipment. (I believe the CEE was absorbed by CEN and CENELEC.) CEE Members: Austria, Belgium, Czechoslovakia, Denmark, Germany (FR), Finalnd, France, Greece, Hungary, Italy, Netherlands, Norway, Poland, Spain, Sweden, Switzerland, United Kingdom, Yugoslavia. Best regards, Rich From owner-emc-p...@majordomo.ieee.org Tue Oct 26 23:44:11 PDT 1999 Received: from hpsdlo.sdd.hp.com (hpsdlo-sw.sdd.hp.com [15.80.36.40]) by hpsdlfsg.sdd.hp.com with ESMTP (8.7.6/8.7.3 TIS 5.0/sdd epg) id XAA23435 for ri...@hpsdlfsg.sdd.hp.com; Tue, 26 Oct 1999 23:44:11 -0700 (PDT) Received: from ruebert.ieee.org (ruebert.ieee.org [199.172.136.3]) by hpsdlo.sdd.hp.com (8.8.6 (PHNE_14041)/8.8.5btis+epg) with ESMTP id XAA04752 for ri...@sdd.hp.com; Tue, 26 Oct 1999 23:44:09 -0700 (PDT) Received: by ruebert.ieee.org (8.8.8+Sun/8.8.8) id CAA20446; Wed, 27 Oct 1999 02:19:26 -0400 (EDT) Date: Wed, 27 Oct 1999 02:18:15 -0400 From: Kevin Richardson k...@compuserve.com Subject: Re: IEC 364 - Definition of SELV To: Rich Nute ri...@sdd.hp.com Cc: [unknown] emc-p...@ieee.org Message-ID: 199910270218_mc2-8a97-1...@compuserve.com MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by ruebert.ieee.org id CAA20443 Sender: owner-emc-p...@majordomo.ieee.org Precedence: bulk Reply-To: Kevin Richardson k...@compuserve.com X-Resent-To: Multiple Recipients emc-p...@majordomo.ieee.org X-Listname: emc-pstc X-Info: Help requests to emc-pstc-requ...@majordomo.ieee.org X-Info: [Un]Subscribe requests to majord...@majordomo.ieee.org X-Moderator-Address: emc-pstc-appro...@majordomo.ieee.org Hi Rich, Thank you for devoting so much time to reply. This is just what I needed. I am familiar with IEC 60950 and I wanted to be able to compare the definitions. Thank you. One other question to Rich or anyone else that can help. Is IEC 536 the base document for the definition of SELV? In addition to how SELV is expressed in IEC 364 I am also trying to confirm the base standard in the IEC responsible for the SELV definition. Is it IEC 536 or some other document? In which standard or guide is the term SELV spelt out (where it says that SELV means Safety Extra-Low Voltage)? There must be a base IEC document somewhere that defines the term. Best regards, Kevin Hi Kevin: Can anyone please provide the SELV definition from IEC 364? I'm working from some old documents, but... SELV is not expressly defined in IEC 364-4-41. Instead, it specifies Protection by safety extra-low voltage. It says: Protection against electric shock in normal service and in case of a fault is deemed to be ensured when: - the nominal voltage cannot exceed the upper limit of Voltage Band I*, - the supply is from one of the safety sources listed in Sub-clause 411.1.2, and - the conditions of Sub-clause 411.1.3 are fulfilled. *See IEC Publication 449: Voltage Bands for Electrical Installations of Buildings. The safety sources are: - a safety isolating transformer, - a source of current providing a degree of safety equivalent to that of the safety isolating transformer (e.g., motor generators with windings providing equivalent isolation), - an electrochemical source (e.g., a battery) or another source independent of a higher-voltage circuit (e.g., a diesel-driven generator, - certain electronic devices complying with appropriate standards where measure have been taken to ensure
Re: IEC 364 - Definition of SELV
Hi Rich, Thank you for devoting so much time to reply. This is just what I needed. I am familiar with IEC 60950 and I wanted to be able to compare the definitions. Thank you. One other question to Rich or anyone else that can help. Is IEC 536 the base document for the definition of SELV? In addition to how SELV is expressed in IEC 364 I am also trying to confirm the base standard in the IEC responsible for the SELV definition. Is it IEC 536 or some other document? In which standard or guide is the term SELV spelt out (where it says that SELV means Safety Extra-Low Voltage)? There must be a base IEC document somewhere that defines the term. Best regards, Kevin Hi Kevin: Can anyone please provide the SELV definition from IEC 364? I'm working from some old documents, but... SELV is not expressly defined in IEC 364-4-41. Instead, it specifies Protection by safety extra-low voltage. It says: Protection against electric shock in normal service and in case of a fault is deemed to be ensured when: - the nominal voltage cannot exceed the upper limit of Voltage Band I*, - the supply is from one of the safety sources listed in Sub-clause 411.1.2, and - the conditions of Sub-clause 411.1.3 are fulfilled. *See IEC Publication 449: Voltage Bands for Electrical Installations of Buildings. The safety sources are: - a safety isolating transformer, - a source of current providing a degree of safety equivalent to that of the safety isolating transformer (e.g., motor generators with windings providing equivalent isolation), - an electrochemical source (e.g., a battery) or another source independent of a higher-voltage circuit (e.g., a diesel-driven generator, - certain electronic devices complying with appropriate standards where measure have been taken to ensure that, even in the case of aninternal fault, the voltage at the outgoing termainals cannot exceed the values specified in Sub-clause 411.1.1. The definition of SELV appears in IEC 536: A voltage which does not exceed 50 V ac rms between conductors, or between any conductor and earth, in a circuit which is isolated from the supply mains by means such as a safety isolating transformer or converter with separate windings. IEC 950 defines SELV CIRCUIT: A secondary circuit which is so designed and protected that under normal and single fault conditions, its voltages do not exceed a safe value. SELV is a special case of ELV, Extra Low Voltage. ELV is defined (or implied) as a maximum voltage value deemed not to cause an electric shock. SELV applies to an ELV where, in the absence of specific protective mechanisms, the ELV would exceed ELV under fault conditions. So, SELV implies ELV with some means to prevent the voltage from exceeding ELV limits in the event of a fault. A single-insulated transformer ELV secondary is ELV. A double-insulated transformer ELV secondary is SELV. An ELV battery is ELV. It may or may not be SELV, depending on your point of view. 1: Since the battery itself cannot exceed ELV under single- fault conditions, then it cannot be SELV. Or, 2: Since the battery itself cannot exceed ELV cannot exceed ELV under single-fault conditions, then it must be SELV. However, as defined, SELV implies an included protective mechanism to limit the voltage in the event of a fault. SELV also implies that the ELV is derived from a higher, non-ELV source. If you accept that a battery is ELV, then the safety standards require that the battery voltages cannot be touched! Best regards, Rich - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators). --- Internet Header Sender: owner-emc-p...@majordomo.ieee.org Received: from ruebert.ieee.org (ruebert.ieee.org [199.172.136.3]) by spdmgaaf.compuserve.com (8.9.3/8.9.3/SUN-1.7) with ESMTP id UAA01279; Tue, 26 Oct 1999 20:08:23 -0400 (EDT) Received: by ruebert.ieee.org (8.8.8+Sun/8.8.8) id UAA19661; Tue, 26 Oct 1999 20:07:41 -0400 (EDT) Date: Tue, 26 Oct 1999 17:06:45 -0700 (PDT) From: Rich Nute ri...@sdd.hp.com Message-Id: 199910270006.raa26...@epgc478.sdd.hp.com To: k...@compuserve.com Subject: Re: IEC 364 - Definition of SELV Cc: emc-p...@ieee.org In-Reply-To: 199910252120_mc2-8a6c-2...@compuserve.com from Kevin Richardson at Oct 25, 99 09:20:44 pm MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer
Re: IEC 364 - Definition of SELV
Hi Kevin: Can anyone please provide the SELV definition from IEC 364? I'm working from some old documents, but... SELV is not expressly defined in IEC 364-4-41. Instead, it specifies Protection by safety extra-low voltage. It says: Protection against electric shock in normal service and in case of a fault is deemed to be ensured when: - the nominal voltage cannot exceed the upper limit of Voltage Band I*, - the supply is from one of the safety sources listed in Sub-clause 411.1.2, and - the conditions of Sub-clause 411.1.3 are fulfilled. *See IEC Publication 449: Voltage Bands for Electrical Installations of Buildings. The safety sources are: - a safety isolating transformer, - a source of current providing a degree of safety equivalent to that of the safety isolating transformer (e.g., motor generators with windings providing equivalent isolation), - an electrochemical source (e.g., a battery) or another source independent of a higher-voltage circuit (e.g., a diesel-driven generator, - certain electronic devices complying with appropriate standards where measure have been taken to ensure that, even in the case of aninternal fault, the voltage at the outgoing termainals cannot exceed the values specified in Sub-clause 411.1.1. The definition of SELV appears in IEC 536: A voltage which does not exceed 50 V ac rms between conductors, or between any conductor and earth, in a circuit which is isolated from the supply mains by means such as a safety isolating transformer or converter with separate windings. IEC 950 defines SELV CIRCUIT: A secondary circuit which is so designed and protected that under normal and single fault conditions, its voltages do not exceed a safe value. SELV is a special case of ELV, Extra Low Voltage. ELV is defined (or implied) as a maximum voltage value deemed not to cause an electric shock. SELV applies to an ELV where, in the absence of specific protective mechanisms, the ELV would exceed ELV under fault conditions. So, SELV implies ELV with some means to prevent the voltage from exceeding ELV limits in the event of a fault. A single-insulated transformer ELV secondary is ELV. A double-insulated transformer ELV secondary is SELV. An ELV battery is ELV. It may or may not be SELV, depending on your point of view. 1: Since the battery itself cannot exceed ELV under single- fault conditions, then it cannot be SELV. Or, 2: Since the battery itself cannot exceed ELV cannot exceed ELV under single-fault conditions, then it must be SELV. However, as defined, SELV implies an included protective mechanism to limit the voltage in the event of a fault. SELV also implies that the ELV is derived from a higher, non-ELV source. If you accept that a battery is ELV, then the safety standards require that the battery voltages cannot be touched! Best regards, Rich - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
