FAQ – Technology

I’ve heard of isolation systems before, but they were optical isolators. What is the underlying protection technology of Lightning Shield ?

Commercial power faults are detected by voltage comparators; lightning strikes and GPR are detected by an electrostatic field coupler. Both detection systems isolate the circuit by opening a contactor on the potential fault path.

Why does disconnecting the AC power protect the terminal from fault currents emanating from the ground system or telco lines ?

Fault current flows from high voltage to low voltage references over a closed circuit. Opening the AC power circuit assures that elevated voltage on the grounding system can not reference (seek) the lower voltage grounds on the commercial power service. Similarly, fault current induced on the telco lines can not reference the lower voltage power grounds across the protected equipment. The only remaining lower voltage reference is the grounding system.

The open circuit prevents the flow of fault current through the protected electronics. Instead all fault current is forced to the grounding system.

Why does the power neutral present the most attractive primary path for fault current ?

Of the alternative ground references (power and telco) the power service neutral offers the lowest impedance to the lowest ground potentials.  As a result the power neutral will carry most of the fault current.

Transients are fast – surge protectors must clamp within nanoseconds. Power Guard responds in milliseconds. Are the horses already out of the barn ?

Surge suppression technology is required to shunt the initial fast transients to ground. Lightning Shield responds to the let-though voltage and isolates the protected equipment from subsequent transients that may overcome surge suppression.

What power faults do you protect against ?

Lightning Shield protects against all power faults 20 milliseconds after first transient – the time required to activate circuit isolation. The Lightning Shield system is particularly effective against prolonged surges, capacitor bank switching, re-closure and power-up events that may overcome conventional surge suppression devices.

How does pre-emptive isolation augment TVSS and grounding systems ?

Surge suppression and grounding systems are designed to protect equipment from transients on the power and telecom lines.  If severe lightning saturates the grounding system the electronics are exposed to fault current.  Pre-emptive isolation detects the lightning threat and blocks the potential fault path.  Additionally, pre-emptive isolation providese a second line of defense against AC faults.

How does Lightning Shield protect against the fast transients produced by re-closures and power-up events ?

Both systems isolate upon detection of a power failure, which violates the sag threshold. Isolation is maintained until the power normalizes within the acceptable power window. Thus the protected equipment is not exposed to the power restoration or re-closure transients.

Power sag and recovery is protected by switch-mode power supplies.

Switch mode power supplies are typically designed to operate from 65 Vac to 265 Vac, allowing operation on power sags above 65 Vac. However as the voltage drops the current demand proportionately increases. At 65 Vac the current is approximately twice the current experienced at 120 Vac. The increased current and resulting heat may create a problem for sensitive circuits

Furthermore, power supplies are particularly susceptible to power recovery transients.  Lightning Shield assures AC power is not reconnected to the equipment until it normalizes within the user selectable parameters. .

How much voltage or fault current is necessary to damage remote terminal electronics ?

The severity will vary based on many factors, primarily fault duration and component sensitivity. High current for short time is typically less damaging than lower current for longer time. A long duration transient can apply sufficient current to overcome a TVSS device, exposing the protected equipment to subsequent faults.

How can a mechanical contactor protect against lighting, that happens much faster ?

The Lightning Shield system detects the developing potential of a lighting ground strike in sufficient time to open the AC power circuit before the strike occurs.

How do you detect lightning before it occurs ?

The lightning strike is the culmination of a series of events that discharges the electrostatic field between the cloud cell and the earth. The Lightning Shield system detects these developments in the immediate vicinity and detects the rising GPR produced by approaching thunderstorms.

Lightning Shield isolates on the power side; what prevents fault current flowing from the elevated ground system to the lower ground references on the telco copper ?

Fault current may flow to the subscriber, but this path does not threaten the protected equipment and the current will be distributed and substantially reduced by the multiple cable pairs and grounds along the path.

What is the false alarm potential of the Lightning Shield system?

Lightning Shield responds to the electrostatic field differential, so it will not false alarm on intra-cloud lightning which accounts for over 50% of all lightning activity. Also, the system will not respond to the electromagnetic energy of radio transmissions.