Bob, At 01:31 PM 03/11/1998 -0500, you wrote: >Which brings up the question about whether central office DC supplies which in >some countries or circumstances run up to 70 volts should be considered SELV >circuits.
No, if they're over 60 V dc, they shouldn't. By definition, SELV must less than or equal to 60 V dc. >We do not treat the central office supplies as SELV at Motorola. Isolation is >provided in switching supplies as with ac mains circuits. I agree that this is a sound approach. If you provide reinforced insulation from input to output, then it really doesn't matter if the input is SELV or not. But the original question involved a 48 V dc circuit, which could be regarded as SELV, depending on the actual insulation to the output. If so, then IEC 320 connectors are not allowed. On the other hand, if this input is not considered to be SELV, then there is an exception in IEC 950, if the connector is only accessible by service personnel: Clause 4.3.17: "Within a manufacturer's unit or system, plugs and sockets likely to be used by the OPERATOR or by SERVICE PERSONNEL shall not be employed in a manner likely to create a hazard due to mismating. Keying, location or, in the case of connectors accessible only to SERVICE PERSONNEL, clear marking are permitted to meet the requirement." Please note, however, that IEC 320 connectors are clearly specified as being intended for ac applications only. Clause 4.3.17 may be used as an excuse, but it's still basically a poor design. I would strongly *recommend* another connector. Regards, Egon __________________________________________________________ Egon H. Varju, P.Eng. CSA Pacific Region Tel: 1-604-244-6640 HAVE MODEM - WILL TRAVEL Fax: 1-604-244-6600 E-mail: [email protected] [email protected] [email protected] __________________________________________________________ --------- 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).
