Richard: The insulation you describe below is indeed operational because, by definition, it does NOT protect against electric shock (see 1.2.9.1). Therefore, I believe the table 0.1 is, in the situation you describe, very questionable. However, this situation is never ending. If one begins to think about possible discontinuity of the exposed metal parts, and the possiblity of touching the surface of the insulation in question you can easily convince your self that insulation on a hazardous secondary circuit should be reinforced!
There is essentially no difference between the physical requirements between basic and operational insulation. So I recommend you forget the terminology. Just perform the fault testing, make sure it cannot be touched by the test finger, and move on to the next product Regards, Lou <---- Begin Forwarded Message ----> Return-Path: <[email protected]> From: "WOODS, RICHARD" <[email protected]> To: "'emc-pstc'" <[email protected]> Subject: Insulation for hazarous voltage circuits List-Post: [email protected] Date: Fri, 6 Nov 1998 15:22:26 -0500 Reply-To: "WOODS, RICHARD" <[email protected]> IEC 950 and its clones require basic insulation between earthed or unearthed secondary hazardous voltage circuits and earthed conductive parts (Clause 2.2.6 and Table 0.1). Can someone please explain why basic rather than operational insulation is required? Let's take a simple example. Assume a hazardous secondary winding with a bridge rectifier, filter capacitor and a load resistor where the negative side of the supply is earthed. Note that the positive side of the circuit must have basic insulation to earth, but the capacitor and resistor are bridging the insulation. Fault testing requires us to short the capacitor or resistor to ensure no hazards exist. And, indeed, no electrical shock hazard will exist even if the mains earthing connection is open. So why isn't operational insulation sufficient in this example? --------- 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).
