Grounding - Part 8
How grounds affect Surge Suppressors
Presented by Todd Humphrey

Most surge suppressor does not suppress power surges. There are a few models that absorb the power and drain it to ground or the neutral line, but almost every common surge suppressor redirects power to the electrical outlet ground. If a surge suppressor is plugged into an ungrounded outlet, the unit will fail to provide proper protection. Surge suppressors use a metal oxide varistor, or MOV, which serve as gate keepers. Each MOV is connect to the line it is protecting (hot or neutral) and the electrical ground in the surge device. When the voltage on a protected line increases to more than 330 volts, the MOV opens the gate to allow the over voltage to pass to ground. 330 volts is a typical value and may not be the point at which every MOV opens the gate. The goal is have the power flow through the ground wires in your home to the electrical ground, were it is safely dissipated to earth.


Ungrounded Electrical Outlets

When a surge suppressor is plugged into an ungrounded outlet, the over voltage cannot be routed to the electrical ground. That is bad. The increased voltage can flow out the surge suppressor through the ground prong of a three-prong power plug. If the three-pong plug powers a device that is grounded though other means, the current can flow through that device to reach the other ground. With a satellite receiver, that other ground is often the coax ground on the exterior of the building. Satellite system installers may find themselves in tough situation. If they ground the satellite system as they are required, but the outlet used to power the satellite receiver is not a grounded outlet, the results of a power surge may cause more damage then if they did not ground the satellite system. Personally, I will not ground a satellite system if the home is not wired properly.


Ground and Protect Lights

Surge Suppressor Ground and Protect Lights

Many surge suppressors have lights to indicate the operating status of the device. Usually there is a Ground Light (sometimes labeled "Ground Fault") and a Protect Light (may also be labeled "Protection, or "Protected".

The ground light indicates the unit is plugged into a grounded outlet.

The protect light indicates the ability of the device to protect.



Surge Suppressor with ground light but no protect light

Overtime, the MOV's and other internal components can fail. The protect light indicates the MOV's, and other internal components are working, however, unless the unit is grounded, the internal components cannot work as intended. BOTH lights must be on for proper protection.



To determine if the surge suppressor is plugged into a grounded outlet, it senses continuity between the Neutral and Ground wires of the electrical system. In a properly wired home, the Neutral and Ground wires are connected to a common point in the breaker panel. Under normal conditions, continuity exist between the Neutral and Ground wires.



Surge Suppressor with no ground light


When an electrical outlet is ungrounded, there should NOT be continuity between those wires and the surge suppressor will not "sense" a grounded outlet and the Ground light will not light.




Tricking a Surge Suppressor

When a grounded coax is connected to a satellite receiver with a three-prong power plug which is powered from a surge suppressor, the Ground light on that surge protection device will light up. Even if the power receptacle is ungrounded, the surge suppressor will sense continuity between ground and neutral via the satellite receiver and NOT the power receptacle. This can trick the surge suppressor into indicating proper operation.


A Ground Bridge

A ground bridge occurs when two electrical devices connected by conductors other than the electrical lines share a common ground. Satellite receivers are connected together by the coax cables, which connect to a common point. In most cases a satellite dish, or a switch acts as a common point. When both satellite receivers are powered through a three-prong plug, both wall receptacles must be properly grounded. If one outlet is grounded and the other is not, the ungrounded outlet can appear to be grounded because the coax serves as a bridge to the distant grounded outlet. Even if the coax is ungrounded on the exterior, the coax ties the two receivers together. This condition can also exist if the two, or more receivers are in different buildings or served by different power panels. .



To test your receptacle, you can use a circuit tester, or plug in the surge suppressor with nothing plugged into it. If you have a surge suppressor, with a Ground light on, unplug your satellite receiver from the unit. If the ground light goes off, your surge suppressor is not protecting properly. Any power surge will take a path through your satellite receiver to reach the coax ground.

A surge suppressor can provide great protection to your electrical devices, if in good operating condition and plugged into a grounded receptacle. It is a good idea to regularly check the lights on your surge suppressor. I highly recommend checking after every power outage and thunder storm.





Return to Part 7 - Improper Grounding

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