Surge Protection and Grounding Issues Presented to SCTE
Surge Protection and Grounding Issues Presented to SCTE Chicago Chapter January 21, 2004 By: Nisar Chaudhry VP Electrical Engineering, CTO Introduction Transients caused by disturbances on the power lines and by lightning strikes have been analyzed thoroughly for twisted pair transmission lines. It was assumed that the coaxial cable center conductor had not been affected by the transients on the coax cable. Considering multiple layers of outer conductor might provide adequate shielding and prevent any damage to the equipment connected to the coax cable. Reports from the field on damaged equipment suggest that the assumption of being protected is wrong. Many television sets, TV cable converters and other cable connected equipment have been damaged by transients. The degree of damage varies from large sections of a device being vaporized to simple degraded performance. Network Protection and Management
TII as a Surge Protection Provider TII has been in the forefront of providing quality surge protection devices to the telecommunications industry. TII at present has a number of high performance broadband coaxial surge protection devices just for 75 ohm coax cable surge protection at the customer premises. These surge protection devices have very minimal insertion loss up to the highest broadband frequencies used on CATV networks. Network Protection and Management Coax Protector Design Grounding Clip Ceramic Seal
SERVICE Connected To CATV Distribution Network Inner Electrode Ceramic Seal Ceramic Metal Seal Ceramic Metal Seal CUSTOMER Connected To Electronics To Be Protected Connector Clips Connector Clips F-Type Connector F-Type Connector Failshort Clip
Inert Gases Argon Hydrogen, Etc. Outer Electrode Firing Surface Network Protection and Management Theory of Operation 1 The body of the coax protector is a conductive nickel plated die cast zinc material. When grounded it forms the outer conductor of a coax line. The center conductor carries the RF signal. The 75 ohms impedance of the device is determined by the size of the center conductor, the air gap (or dielectric) and the inside diameter of the body. The coax gas tube consists of outer electrode, inner electrode and ceramic insulating discs. Network Protection and Management Theory of Operation 2
The two ceramic discs form a hermetically sealed space that contains a suitable gas mixture. This gas mixture is composed of argon, hydrogen and some other rare gasses. The inside surfaces of the ceramic discs have a carbon film coating that enable a high speed reaction to surges on the center conductor. The arc initiated by the fast reaction on the ceramic disc energizes the gas and sustains the electron path to the body or ground. There is a failshort clip pressed into the service end of the coax protector. The failshort clip is made of a spring metal that is in contact with the inside diameter of the gas tube body. In a power cross condition the thin plastic insulating sleeve melts and the failshort clip shorts the center conductor to ground protecting the electronics. Network Protection and Management TII Coax Protection Typical Voltage Breakdown Levels Device
Network Protection and Management TII 75 Ohm Coax Protector Typical Return Loss Frequency in MHz 5 0 77 150 225 SCTE Requirement 300 375 450 525
600 675 750 825 TELCORDIA Requirement 900 975 1005 -10 Return Loss in dB -20 -20dB
-24dB -30 -40 TII Performance -50 -60 Network Protection and Management TII Surge Characterization TII conducted a series of tests by impressing lightning surges to the outer conductor of various sizes and lengths of coaxial cables. Data and figures on the following pages show that high energy
lightning surges can be induced on the center conductor of a coax cable. The magnitude of voltage induced on the center conductor is proportional to the length and inversely proportional to the size of the coax cable. Network Protection and Management Experiment 1 Magnitude of Induced Surges Test Circuit Setup Network Protection and Management Experiment 1 Results 2KA, 10/250 s surge applied on outer conductor Monitored induced voltage and current on inner conductor for various
lengths of coax cable Cable Length (ft) 20 50 100 200 RG 59 RG 6 RG 11 Induced Current Voltage (A) (V) Induced
Current Voltage (A) (V) Induced Current Voltage (A) (V) 1.8 3.0 5.0 6.0 120 220 350 460 1.5 2.6
4.0 5.2 110 180 300 400 1.2 2.0 3.0 4.5 85 150 240 330 Network Protection and Management Experiment 2 Magnitude of Induced Surges (Inner Conductor Isolated) Test Circuit Setup
Network Protection and Management Experiment 2 Results Repeated Experiment 1 with inner conductor Completely isolated from outer conductor Monitored induced voltage and current on inner conductor for various lengths of coax cable Cable Length (ft) 20 50 100
200 RG 59 RG 6 RG 11 Induced Induced Induced Current (A) Voltage (V) Current (A)
Voltage (V) Current (A) Voltage (V) 1.0 1.4 1.5 1.75 750 1050 1150 1300 0.9 1.3 1.6 1.8
700 1050 1300 1500 0.7 1.6 1.7 2.0 650 1000 1300 1600 Network Protection and Management Experiment 3 Surge Testing of Network Interface Card Apply increasing current levels of 10/1000 surge to coax protector, monitor let through voltage. S U R GE GE N ER A T OR
10x 1000S S H OR T C I R C U I T CU RRENT P OS . T I I 210F F 75F 22521 C OA X P R OT E C T OR C OM P U T E R N E T WOR K CA RD N E G. OS C I L L OS C OP E V OL T A GE M E A S U R E M EN T Network Protection and Management Experiment 3 Results Surge Current
111.00 NIC Card With TII Protection (OK) Y Y Y Y Y Y Y Y Y Y NIC Card Without TII Protection (OK) Y Y Y Y Y
Y N N N N Network Protection and Management Experiment Summary Potentially damaging surge activity may be present on the center conductor of the coax cable Use of surge protection devices reduce damage to the connected equipment A surge protection device should be transparent to signal transmission for good reception
Network Protection and Management Field Lightning Damage Testimony Lightning Damage Lightning Lightning struck struckaacable cable coming comingdown down aatree. tree. Network Protection and Management Lightning Damage The
Thesurge surgewas was carried carriedon onthe the underground underground cable cableleading leading toward towardthe thehouse house Network Protection and Management Lightning Damage The Thesurge surgewas
was carried carriedinto intothe the coaxial coaxialcable cable enclosure. enclosure. Network Protection and Management Lightning Damage The Thesurge surgewas was suppressed suppressedby by
TII TII212 212 In-Line In-Line Coaxial CoaxialSurge Surge Protector Protector(circled). (circled). Network Protection and Management Grounding and Bonding Issues National Electrical Code (NEC) Article 800 Communication Circuits Article 810 Radio and Television Equipment
Article 820 Community Antenna Television (CATV) and Radio Distribution Systems Article 830 Network Powered Broadband Communication Systems Network Protection and Management NEC Article 820 Sections of Article 820 cover various aspects of CATV systems at the customer premises including: Point of Entrance Protection
Grounding Conductor Bonding of Electrodes Network Protection and Management NEC Article 830 Geared more toward network powered communication systems covers following: Power Limitations Electrical Protection
Grounding Methods Direct-Buried Cables & Raceways; Mechanical Protection Fault Protection Device Network Protection and Management Grounding 820.33 Grounding of Outer Conductive Shield of a Coaxial Cable The outer conductive shield of the coaxial cable shall be grounded at the building premises as close to the point of cable entrance or attachment as practicable. Network Protection and Management Grounding 820.40 Grounding of the Coaxial Cable Shield is specified as: Insulation. The grounding conductor shall be insulated and shall be
listed as suitable for the purpose. Material. The grounding conductor shall be copper or other corrosion-resistant conductive material, stranded or solid. Size. The grounding conductor shall not be smaller than 14 AWG Length. The grounding conductor shall be as short as practicable, not to exceed 6.0m (20ft) in length. Run In Straight-Line. The grounding conductor shall be run to the grounding electrode in as straight a line as practicable. Physical Protection where subject to physical damage. The grounding conductor shall be adequately protected where the grounding conductor is run in a metal raceway both ends of the raceway shall be bonded to the grounded conductor or the same terminal or electrode to which the grounding conductor is connected. Network Protection and Management Point of Entrance Network Protection and Management Support Network Protection and Management
Grounding Network Protection and Management Bonding Network Protection and Management Conclusion Proper grounding and bonding practices need to be followed for a reliable safe CATV service. Surges do cause damage to the equipment at the customer premises. A surge protection device, when properly installed, will provide necessary protection to the equipment and property.
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