Hello Neven, setting safety and EMC aside for a moment, be careful not to overlook your video signal quality. Exceeding 750ft with RG59/U coax is not recommended in security video applications. The signal loss at 2,000ft would render the video unusable. Specifying coax with heavier gauge center conductor will allow you to run additional distance and help preserve your SI, but not by much and your cost will go up. This assumes a passive, straight connection between camera and head end (monitor, DVR, etc). You may want to consider UTP instead of coax. A good quality, active UTP video network can easily exceed 2,000ft with no appreciable signal distortion. The UTP video link is immune from the 'ground loop' issues that can plague long coaxial cable runs. Whether the camera is powered by a limited power circuit, as Ted explained, or by a.c. mains, the UTP link can help you avoid performance issues in the field. If the cable absolutely must be RG59/U, then connect a suitable isolation transformer to one end of the cable to help limit the common mode current flow on the braid. Use a good quality video amplifier in conjunction with the isolation transformer for the coax runs over 750ft. cordially, Chet Summers Sr. EMC Engineer Pelco [email protected] ________________________________
From: [email protected] [mailto:[email protected]] On Behalf Of Ted Eckert Sent: Tuesday, April 07, 2009 10:01 AM To: [email protected] Subject: RE: Security Camere Coax Grounding Take a look at Article 725 of the National Electrical Code (NEC) for requirements in the United States. If the circuit is a power limited circuit, the NEC will not require a safety ground. See NEC Tables 11(A) and 11(B) for the definition of these circuits. You will find the requirements to be basically the same as the IEC 60950-1 requirements for Limited Power Sources. For Europe, consider starting with IEC 60364. Many of the European electrical codes will have deviations from this standard, but the basic content should be similar. IEC 60364-4-411 allows SELV circuits to be ungrounded. Disclaimers: You will need to look at the power levels, isolation and circuit classifications of the signal in the cable. Information I have provided is for reference only; obtain copies of the standards and review them to make your own decision about the applicability of any clauses. Regards Ted Eckert Compliance Engineer Microsoft Corporation [email protected] The opinions expressed are my own and do not necessarily reflect those of my employer. From: Grasso, Charles [mailto:[email protected]] Sent: Tuesday, April 07, 2009 9:33 AM To: [email protected] Subject: Re: Security Camere Coax Grounding Neven – There *may* be building code requirements that you will have to meet. Not sure what those are. I suggest a review of the NEC2008. Chas ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Tuesday, March 24, 2009 3:32 PM To: [email protected] Subject: Security Camere Coax Grounding Can anyone help me understand what would be the requirement, preferably worldwide worst-case if possible, for connecting the outer conductor ("shield") of the coaxial cable (RG59) in a security-camera application? The cable can be up to 2000 ft (~ 600m) long, between the central unit (inside the building) and the remote camera (anywhere within the reach). The application can be anything from industrial to apartment buildings. Can I (or do I have to) connect the outer conductor to the safety ground (enclosure) on both ends? .. on one end (which?), etc. Alternatively, do I need to provide safety isolation from the outer conductor to the safety GND (enclosure?), how much, on which end, what kind of caps to GND can I use for EMI if I need safety isolation, etc.? I am asking strictly from the safety/regulatory hard requirement point of view, not trying to discuss which would be better for EMC. Is there an simple answer? Did I miss any key info or question? Thanks, Neven - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. 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