Hello from Dayton, Ohio. I love this question! The periodicity of ice ages is about 50,000 years. The effects from glaciers is only periodic and not continuous. In fact, I am told that if you sit in one place, you can see Kudzu grow, but if your period of observation is continuous, the growth of Kudzu is hazardous to your well being. The effect of the TNV is defined as being safe, similar to SELV, since the ring voltage is intermittent, but I still would not like to be shocked by the 120V ring voltage. In this case the ring time is about one second in length. How long does the ring tone have to be to become hazardous? The GFCI will interrupt in about a 100th of a second and again, I would not want to get shocked by a voltage to have the GFCI to kick in. I am confident that the energy in the GFCI circuit is very high, so is this better than the clause 1.2.8.7 on Haz Energy. If the GFCI operated in one tenth of a second would this be hazardous?
There is a popular book with the title some what like coming into the light, where the author was struck by a continuous bolt of lightning and lived to tell all. There is a veiled relationship between the hazard severity and the length of the time for exposure. How short is short for being intermittent and how long is long for being continuous. The threshold of acceptability for the pain or physical reaction, blister, etc, and the rate of delivery of the energy to the person, hand, skin, etc. determines what is short and just too long. A similar pet peeve of mine is the frequency of occurrence versus the severity of the event or hazard. One pundit proposes that there is a zone of acceptability between the graph of these two, but I believe that hazard reduction is for safety and frequency reduction is the domain of insurance statisticians. So can we develop a graphical representation of the length of time of exposure versus the severity of the hazard and have a zone of safety? The continuous level is not an asymptote but a parallel to one axis of the coordinate system. So any point under the parallel must be safe. So I would ask Rich's question the other way around, when can we stop the test for a continuous application of a hazard? One hour; 2 weeks, etc.? To answer Rich's question, any point of time under the parallel is part of of the continuum, including ground zero, at the inception of the application of the hazard. Manning Rose NCR Corporation [email protected] ---------- >From: Rich Nute >To: emc-pstc >Subject: How long for continuous? >Date: Tuesday, November 12, 1996 4:46PM > >Hello from San Diego: > >With regard to IEC 950: >........................................................... >1.2.8.7 HAZARDOUS ENERGY LEVEL: A stored energy level of >20 J or more, or an available continuous power level of 240 >VA or more, at a potential of 2 V or more. >........................................................... >At what point in time after start of the measurement is the >available power considered "continuous"? > >In the application, a fuse is used to limit the continuous >power to less than 240 VA. At 240 VA, the fuse WILL operate -- >but it may take up to the maximum fuse operating time. > >Is this okay? > >If not, what is the time after which 240 VA is considered to >be continuous? > >Best regards, >Rich > > >------------------------------------------------------------- > Richard Nute Quality Department > Hewlett-Packard Company Product Regulations Group > San Diego Division (SDD) Tel : 619 655 3329 > 16399 West Bernardo Drive FAX : 619 655 4979 > San Diego, California 92127 e-mail: [email protected] >------------------------------------------------------------- > > > > >
