Power surges and grounding

A power surge is an unexpected increase in voltage in an electrical system. Surges are typically caused by lightning, unstable power grid events, outage reconnections; or by a high-power internal appliance or device that inputs excess power back into the system instead of drawing it out e.g. when the AC or water heater starts/stops. When a large amount of electricity is released, it must find the easiest way out. This excess is either absorbed by other devices on the same circuit as heat or by neutral and ground wire connections into the earth.

So when lightning strikes an obstacle, the millions of volts find the nearest best conduits to the earth. The force of the strike also creates an electro-static discharge (ESD) wave that spreads in a large radius (kind of like an EMP). Any good conductor picks up the charge and these could be the copper cables in your house like power, coaxial, ethernet and HDMI. Any device connected to these cables are then hit with the excessive power surge and this is how sensitive electronics get damaged. The point is, that just installing SPDs on the main service panel and distribution and branch sub-panels may help protect against extreme grid surges, but not necessarily against a lightning “side” strike (think neighbors’ tree) that emits an electro-static discharge wave throughout your home. Because of the shear power of a direct strike, SPDs may help, but there is not much you can do, other than totally disconnect all your critical devices.

Another more common surge scenario happens when a large power draw (AC, range, water heater) suddenly connects or disconnects. This is also known as an Electrical Fast Transient burst (EFT). You may see the lights dim briefly as the power balance adjusts to the new demand. The same happens in the nano second of a disconnect e.g. AC or water heater switches off, the excess power must go somewhere and may affect other connections on the circuit. In most cases it dissipates through the neutral and ground wires.

The importance of proper grounding

The function of ground wires is to divert away excess electrical current from the house into the earth. Every power outlet should have copper ground wires installed that lead back to the mains panels and then through a much thicker copper wire connected to a 3–6-foot copper spike driven deep into the earth outside the house. There may be more than one and you will usually see them close to the main power boards or connected directly to outside appliances.

Ground wires are almost always green or yellow/green and come in different AWG (American Wire Gauge) sizes or thickness depending on the level of excess current to be supported. The smaller the AWG rating the thicker the copper or conductive alloy e.g. 14 AWG is used for typical 15-amp wall outlets, 12 AWG solid copper is used for 20-amp circuits and 10 AWG solid copper is used for high power 30-amp circuits e.g. dryers, ranges, washing machines, water heaters, AC etc. Most SPDs use either 14 AWG (coaxial, ethernet cable) or 16 AWG (HDMI cable) for their ground wires depending on the max current capability.

It is important that you get an electrician to test that the house and all power outlets are properly grounded. A good time to do this is when you install your type-1 and type-2 surge protectors. You can also safely test that your power outlets are properly wired and grounded by using a simple “outlet tester”. These are cheap and are available online.

All SPDs must be properly grounded. Some vendor SPD products do not have a ground wire connection and rely instead on resistors and varistors to absorb excess current as heat. These should be avoided. The simple rule is “no ground – no buy”.

How do you install a ground connection for a SPD?

A common question we get asked is how to connect a ground wire from the SPD. If one is not supplied with the SPD, you can purchase AWG 12 or 14 ground wire at most hardware stores or online. The ground wire should be long enough to reach the nearest wall outlet. The easiest way is to crimp on #10 ring terminal connectors on each end, connect one end to the ground screw or case of the SPD and thread the other end onto the ground prong of a plug which is inserted into the wall outlet. Use an outlet tester to make the wall socket is grounded.

Additional information:

Download our free Surge Protection PDF.

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