Peter, Please find answers to your query below.
Peter Merguerian wrote: > > Dear All, > > A CO equipment with a 48 Vdc nominal supply has coxial cable > connection to an outdoor transmitter. I have the following questions: > > 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? 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. In effect you are power feeding the external transmitting equipment. No doubt the coaxial cable from your equipment to the transmitter will also be carrying a data or voice signal which will float on the -48V DC level. As the cable is routed externally it is my opinion (and also that of the test houses that we use) that this is a TNV-1 circuit. > > 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. Clause 6.4 of EN60950 deals with "Protection of equipment users from overvoltages on telecomms networks". In order to prove that overvoltages will not propagate on to the user accessible interfaces the equipment must undergo either the impulse or electric strength tests described in that clause. Some equipment may be exempt from these tests, for example where both circuits have a permanent connection to protective earth. The coaxial interfaces should employ some form of protection such as GDT's so taking the transient overvoltage fault current to ground. > > 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? > Assuming the power output to the cable was limited in accordance > to UL1950/EN 60 950 (ie output was limited to Class 2), should the > cable still be Listed or Approved? I do not think this cable needs to be approved when used in the UK. Perhaps someone else can advise on this. > > 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? Test houses used by Fujitsu consider this level to be TNV-2 (internal), TNV-3 external. There is a draft document, EG 200 xxx V1.2.2 in existence which attempts to address these classifications. Annex B of this document lists -60V DC nominal supplies (ie max -72V DC) as TNV-2. Although not strictly TNV circuits in the true sense of the word this would appear to be a sensible approach as TNV2/3 circuits do have upper limits of 120V DC. (We have a product which power feeds external equipment at 117V DC along with a telecomms signal of 2V, it is considered to be TNV-3) No problem with this voltage being transmitted externally although you should note the requirements of Clause 6.5 of EN60950. Best Regards, Alan Booth. Equipment Engineering Group Fujitsu Telecommunications Europe Limited Solihull Parkway Birmingham Business Park Birmingham B37 7YU Telephone +44 121 717 6492 FAX +44 121 717 6014/6018 > > Thank you all. > PETER S. MERGUERIAN > MANAGING DIRECTOR > PRODUCT TESTING DIVISION > I.T.L. (PRODUCT TESTING) LTD. > HACHAROSHET 26, P.O.B. 211 > OR YEHUDA 60251, ISRAEL > > TEL: 972-3-5339022 > FAX: 972-3-5339019 > E-MAIL: [email protected] > Visit our Website: http://www.itl.co.il
