Richard, I' m sure you're aware but to provide a basis for my interpretation of the requirement as it pertains to your situation, I'll first summarize a basic requirement of the 950 series of standards: Two levels of protection against electric shock are required. In a construction that employs exposed earthed conductive parts, hazardous voltages (I make no distinction between mains or secondary) must be separated from these parts by basic insulation in order to achieve the two levels of protection.
In the case of an earthed hazardous voltage secondary (as it is defined by the standard), the shock hazard is essentially equal to that of a mains circuit. Therefore, I believe it may be necessary to provide basic insulation between the unearthed conductor of the circuit in question and earthed conductive parts other than those directly related to the earthed conductor of the same circuit. Between the conductors of the hazardous voltage circuit I believe only operational insulation should be required just as it is for a mains circuit. I hope this point of view helped you. Rick Cooper MET Laboratories, Inc. 410-354-3323 Ext. 331 > -----Original Message----- > From: WOODS, RICHARD [SMTP:[email protected]] > Sent: Friday, January 08, 1999 09:03 > To: 'emc-pstc' > Subject: Spacings for Hazardous Secondary Voltages > > Would someone please explain the rationale for IEC 950 requiring basic > insulation between earthed secondary hazardous voltage circuits and > earthed > parts? Since the circuit may be bridged by ordinary electrical > components, > the need for anything beyond operational insulation appears to be > unwarranted. A safety agency is attempting to enforce the exact > wording of > the standard. Under what conditions could one argue that operational > insulation is sufficient, and that a hazard does not exist? > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to [email protected] > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to [email protected], > [email protected], [email protected], or > [email protected] (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
