Originally Posted By: MolaKule
In our neighborhood, all powerlines are uderground with the center tap of the transformer secondary grounded at the transformer pit and an additional but buried ground rod at the house.
Irrelevant is if incoming wires are overhead or underground. Same type surge still seeks earth destructively via appliances. Same service entrance (secondary) protection is required. And primary protection is installed by the utility.
Only reason a 'whole house' protector might not provide sufficient protection: earthing only meets and does not exceed code requirements. For example, if the 6 AWG ground wire goes up over the foundation and down to earth, then protection has been compromised. Connection has sharp wire bends over the foundation. Induces surges on adjacent non-grounding wires. And is unnecessarily too long. Sufficient to meet code. Insufficient for superior protection. Protection means that wire is better routed through the foundation and down to single point earth ground.
Electronic design standards 40 years ago required 600 volts without damage. Today’s electronics will withstand higher voltages without damage. Properly earthing a ‘whole house’ protector means no such voltage should be anywhere inside the building. Protection inside appliances should be more than sufficient. But only if earthing is properly upgraded / installed.
E-M fields can induce high voltages on wires. For example, a 100+ foot long wire antenna was maybe 30 feet from a lightning strike. Thousands of voltage induced on a wire designed to maximize induced voltages. Connect an NE-2 neon glow lamp to that antenna lead. By conducting milliamps through the glow lamp, voltage drops from thousands to tens. Induced surges are that easily made irrelevant.
Induced surges are made irrelevant by protection that already exist inside electronics. A homeowner’s primary concern is a transient that might occur maybe once every seven years.
Destructive surges are current sources. As long as that current is diverted ‘low impedance’ (ie less than 10 feet’) to single point ground, then that current generates trivial voltages. Anything that might obstruct that current (ie long wires from receptacle to earth ground) results in significant voltages. Critical to keeping that voltage low is the low impedance (ie as short as possible 6 AWG wire) to single point ground. And earthing upgraded to exceed code requirements.
A typical 20,000 amp lightning strike is why a minimal ‘whole house’ protector starts at 50,000 amps. Why earthing must both meet and exceed post 1990 code requirements. And why every incoming wire (cable TV, telephone, satellite dish, Ham antenna leads) must connect short to the same earth ground at the service entrance.
