Richard...it seems to me that Edward has a point. Clause 5.4.4 allows one of three options for operational insulation; a) creepage and clearances, b) applicable dielectric withstand test of 5.3.2, or c) short circuit test demonstrating no shock or fire hazard. It seems to me that if the equipment is going to pass the clause 6.4 electrical strength test, then it seems to me it should pass the relevant test for your situation in clause 5.3.2 and 5.4.4, and you have therefor demonstrated that your OPERATIONAL INSULATION meets the relevant requirements.
Also, I believe your original question was asking for a minimum or clearance distance determined by experiment that would pass the applicable electrical strength test, not so much the minimum laid out by the standard. Regarding creepage distances I am not sure if this would be so straight forward as an (easy) formula (which I believe you also inquired about), as determination of the creepage distance is so dependent on the material one would use. Also the conditions the barrier was subjected to. You also mentioned that the underlying reason for creepage distances is long term reliability of the barrier. That is correct, and the reason that the option is given for operational insulation not to use the creepage distances, is that OPERATION INSULATION is not regarded as providing a level of protection (at least in the same manner as BASIC or SUPPLEMENTARY) from electrical shock. Also, as you are dealing with insulation between Secondary circuits, I would guess that conditions that may cause your creepage path to track over time may not be as prevalent as they would when dealing with a primary circuit. My advice is to try a few things out to see what minimum creepage you can get away with and still meet the dielectric requirements. I would imagine a body like the IPC would have some recommendations concerning this? just my $ 0.02, which myself or my employer cannot be held responsible for. Hope this is some help. Mel Pedersen Midcom, Inc. Homologations Engineer Phone: (605) 882-8535 [email protected] Fax: (605) 886-6752 ---------- From: Richard Steele[SMTP:[email protected]] Sent: Wednesday, September 24, 1997 5:40 AM To: [email protected] Subject: Re: Creepage and Clearances Edward, Edward H. Eszlari wrote: > > If this is truly OPERATIONAL insulation per EN 60950..........why don't you > do the short circuit test per 5.4.4?? But the equipment will have to be able to withstand the Electric Strength test of EN60950/A4 Clause 6.4. Operational is being used because the equipment will meet the conditions applicable to table 19 where Basic is not required and can be replaced with Operational. Regards Richard
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