Plant Power Fundamentals
Coax Plant Is Not RF-Only
Amplifier housings carry RF and plant power. In classic HFC, ferroresonant supplies put 60 VAC or 90 VAC (often a quasi-square waveform) onto the coax center conductor through a power inserter. Amplifier modules convert that plant voltage to internal DC for the gain blocks. Opening a housing without understanding power is how techs get shocked and modules get damaged.
Every trunk segment may carry plant voltage. RF meters show carriers — they do not prove a port is safe to touch. Treat housings, power pedestals, and power-passing taps as energized until verified de-energized per company procedure.
Plant power elements
- Power supply (PS)
- Utility/site AC in → plant 60/90 VAC out; often ferroresonant; pedestal or amp-related
- Power inserter (PI)
- Couples plant voltage onto trunk coax; keeps RF path per design
- Power-passing tap
- Passes plant power IN→OUT on trunk while feeding drop RF
- Amplifier module / PS
- Converts plant voltage to internal DC; lid interconnect often carries power
- Fuse / breaker
- Overcurrent protection — replace only with correct type/rating after finding the fault
- Bonding / ground
- Safety and RF reference — do not remove to “fix” signal
60/90 VAC plant power & ferroresonant supplies
Read the label on the supply you are servicing — 60 VAC and 90 VAC classes are both common. Higher plant voltage can mean lower current for the same power, but shock hazard remains serious. Neither is “safe to touch.”
Ferroresonant (constant-voltage) transformers hold plant output relatively stable as load changes — useful because amp draw varies with temperature and cascade load. Output may sag under heavy load or when many amps are offline. A dead short on trunk blows fuses — never bypass a fuse with jumper wire to “test.”
Power inserters & current path
Power inserters put plant voltage from the supply onto the trunk while keeping RF paths intact. Orientation matters — follow silkscreen IN/OUT. Reversing a PI can starve amps or feed power the wrong direction.
Not every tap passes power. Power-passing trunk taps carry center-conductor plant voltage IN→OUT. A non-power tap in a powered trunk darks downstream amps. Multi-port amps pass power only on designated ports — match the engineering diagram.
Center conductor can carry hazardous plant voltage relative to strand and ground. Unplug lid power interconnects when required, verify absence of voltage per procedure, use insulated tools, and avoid bridging energized conductor to housing/strand with your body or tools.