Hello Rich, Peter, and all distinguished colleagues: Couldn't resist...
I agree that it would certainly not be SELV, however. I am not sure if one would call this ELV or TNV however. (I lean toward TNV...) 1) You have stated the following Rich: The IEC 950 definitions for TNV, TNV-1, TNV-2, and TNV-3 do not imply in any way a circuit that is "exposed outdoors." In fact, TNV is defined as "...a circuit in the equipment..." However, if you read the definition of TNV-1 circuits in clause 1.2.8.9, it states that TNV-1 is a circuit on which "...overvoltages from the Telecommunications Network are possible." I believe that the "overvoltages" referred to imply the possibility of an "exposed outdoor" TNV circuit. Continue reading, as my next answer (concerning IEC 950 lightning considerations) gives more justification for this answer. 2) You both mention that lightning surges are not considered by IEC 950, however, I believe that they are. If one considers clause 6.4.1, and the testing options for compliance for isolation from the Telecommunications Network, the 6.4.2.1 impulse test option are the ITU K.17 lightning surge (see Annex N) testing recommendations. I believe that these were developed with the transmission line characteristics of a twisted pair copper wire in mind...so I am not sure if they would be exactly applicable to your situation anyway...something to look into. Maybe the IEC 65 impulses are typical of lightning strike transmitted down Coax (I do not know IEC 65...)? Anyway, the intent here is that the insulation not be damaged from an overvoltage from the TELECOMMUNICATIONS NETWORK, and I believe that the "overvoltages" in mind included lightning strikes. It will be interesting to hear answers on 3 & 4. Just my $0.02, I could be out to lunch on this one... Mel Pedersen Midcom, Inc. Homologations Engineer Phone: (605) 882-8535 mpeder...@midcom-inc.com Fax: (605) 882-8633 ---------- From: Rich Nute[SMTP:ri...@sdd.hp.com] Sent: Tuesday, December 01, 1998 10:49 AM To: pe...@itl.co.il Cc: Product Safety Technical Committee Subject: Re: TNV-1 vs SELV for unit with Outdoor Coaxial Cable Connection Hi Peter: > 1. The coaxial cable output is conductively connected to the input. > It carries the same voltage and an amperage of 1 A (limited to 3 A > max). Assuming the input supply tolerance not to exceed 60 Vdc, > does everyone agree that this is SELV? ELV, yes. SELV, I don't know because there is not enough information. SELV is defined as a voltage source that does not exceed the limits of ELV (i.e., 60 V dc) in the event of a single fault (usually a fault in Basic Insulation). This implies that SELV is derived from a hazardous voltage source. Since you did not describe the energy source, we cannot answer your question. > Some of you may argue > that it is TNV-1 since it is exposed outdoors! Based on the 950 > definition of TNV, to the best of my understanding, the circuit is not > a telecommunication network voltage circuit. The IEC 950 definitions for TNV, TNV-1, TNV-2, and TNV-3 do not imply in any way a circuit that is "exposed outdoors." In fact, TNV is defined as "...a circuit in the equipment..." The coax cable output you describe is nothing more than a secondary circuit. It is either SELV or ELV or a Secondary Circuit. It is not Hazardous Voltage. It is not a TNV circuit (however, the definitions of TNV are sufficiently vague that any circuit, including the one described here, meeting the limits of TNV-1, TNV-2, or TNV-3 could be a TNV circuit!). Many IT products include coax cable inputs and outputs. The fact of a coax cable means nothing special with regard to the safety of the product. > 2. 950 does not discuss protection of the equipment or user from > lightning. It should be noted that the unit also has user accessible > SELV interfaces. What type of tests or construction would you > recommend for the coaxial interface? I believe the Impulse Tests in > IEC 65 or in UL1492 should be highly recommended. Neither IEC 65 nor UL 1492 consider safety from lightning. Without an isolating barrier of some sort between the coax circuit and all other circuits, or some attentuators from both the shield and the center conductor to a good ground, it is unlikely you can provide any protection against lightning. > 3. Are there any requirements for the outdoor coaxial cable? > Should it be Listed cable for North America and if so, what type of > Listed cable? Should it be Approved for Europe and if so, what type > of Approved cable? If it is a SELV circuit, then the only requirements are those of the manufacturer. By definition, there is no shock hazard. (Some outdoors equipment standards specify one-half the ELV voltages for protection against electric shock.) > 4. Assuming the input tolerance now to be max 72 Vdc (a > secondary hazardous voltage circuit) which also makes the coaxial > output connection 72 Vdc, does anyone see a problem with this > type of circuit being transmitted through a coaxial cable to the > outdoor transmitter? A coax is an interesting construction from a safety point of view. Class I. The center conductor insulation is Basic Insulation. The shield braid is a ground to return the fault current in the event of failure of the Basic Insulation. End. Best wishes for the holiday season, Rich ------------------------------------------------------------- Richard Nute Product Safety Engineer Hewlett-Packard Company Product Regulations Group AiO Division Tel : +1 619 655 3329 16399 West Bernardo Drive FAX : +1 619 655 4979 San Diego, California 92127 e-mail: ri...@sdd.hp.com ------------------------------------------------------------- --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). 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