MOVs and surge suppressors

Have you read the illustration in the IEEE guide starting pdf page 40. The illustration has a surge coming in on a CATV cable. The 'ground' wire connecting the CATV entry block to the power service ground is 30 feet - far too long (not a "single point ground"). As a consequence, the CATV wiring is at 10,000V with respect to the power wiring.

The illustration shows that protection is provided by connecting the cable wire sheath (ground) the power ground wire at a plug?in suppressor and clamping the voltage on all the wires to the common ground at the suppressor. The voltages on the wires going to the TV are safe for the TV.

The illustration explains that the ?vast majority? of the earthing of the surge occurs through the 'ground' wire from the CATV entry block to the power service, as the NEC intended. Not much of the surge is earthed through the plug-in suppressor. But the suppressor protects the TV connected to it.

(In this case, a electric service panel surge protector will not help. The guide says in this case "the only effective way of protecting the equipment is to use a multiport protector".)

----------------- If a surge enters through the power service without a service panel suppressor, the surge energy entering on the neutral is earthed directly by the neutral-?ground? bond required in US service panels. For a large surge, the surge energy entering on the hot wires will cause arc-over from hot to ?ground? at the service panel (and receptacles) at about

6000V. Arc?over will dump most of the remaining surge energy to the earth and limits the voltage to something under 6000V. A service panel surge suppressor would be preferable. (In any case, a large surge current to earth will raise the voltage of the system ?ground? above ?absolute ground? by thousands of volts).

A plug--in suppressor in this case will still work by clamping the voltage on all wires to the common ground at the suppressor. Because the impedance of the branch circuit wires is high, not much of the surge energy left after arc-over will reach the plug-in suppressor (unless the branch circuit wiring to the panel is very short). Because a surge is a very fast event the inductance of the wire is much more important than the resistance.

------------------- Plug-in suppressors do *not* work primarily by earthing a surge. Earthing occurs elsewhere.