Brick Wall Series Mode AC Surge Suppressors/Powerline Filters 

The Consequences of Diverting Surge Current to Ground

Almost all manufacturers of shunt mode devices (those utilizing MOVís) design their products to divert surge current equally between the ground and neutral wires. A surge suppression device should not divert surge current to the ground wire.

Typical Ground Loop prevented by Brickwall AC surge protection


Our sales staff repeatedly hears this same story: It seems a company has experienced considerable surge damage to electronic equipment. The shunt mode surge suppression devices would appear to have done their job by protecting the loads from the front end (power line). The damage, in their estimation, resulted from surge current that traveled down the data lines. How do they know this? All the damage appears to have originated at the data ports, hence they conclude that the surge must have traveled this route. Their solution: They need data line protectors.

They are right in as much as the damaging current did propagate through the data lines. However, damaging surges do not originate in dataline circuits.

Their systems do not need data line surge protectors. Interconnected systems need powerline surge protectors that do not divert surge current to the ground wire.


Interconnected (networked) systems, so prevalent in todayís commercial/industrial world, have made shunt mode technology (origins 1972) inappropriate. Equipment sharing common power and data lines form circuits between themselves via the ground wire (both referenced at the load). What does current do in a closed circuit? It flows. A powerline surge diverted to the ground wire will make its way to the chassis, through the motherboard (which is also grounded at the chassis), onto and through the data lines (which use the powerline ground as a voltage reference and are also connected at the motherboard) and to the data ports of the rest of the connected system. This is how most data line surges originate.


Smaller surges diverted to ground wires may not immediately damage equipment (though the cumulative effect can eventually cause failures). On the other hand, low level surge current diverted to the data lines (via the ground wire) can immediately scramble data, slow down data transfer and cause mis-operations or lock-ups as a consequence of its effect as system noise (unwanted current on the data lines).

Brickwall AC surge protection outlet box


Brick Wall products are based on the current (hence voltage) limiting of a massive inductor. Residual energy that leaks through is captured by a series of electrolytic capacitors. There it is slowly leaked back to the neutral at a harmless level. Outside of trivial amounts of parasitic capacitance our Series Mode devices do not put any surge current on the ground of your systems. Engineers of an MOV based surge suppressor face the dilemma of what to do with potentially large amounts of surge current. They donít want to overload the neutral and want to prolong the life of the MOV. Using two of these elements and diverting equally between the ground and neutral wire prolongs MOV life and prevents overcurrent on the neutral. Series Mode technology presents no such dilemma.

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