Surge Protection Devices and their usage

There are three categories or type of SPD device: type-1, type-2, and type-3. This section summarizes the different devices. Specific brands are used for examples, but you should do your own research and decide the best options that suit your own requirements. The following are the main categories of SPD:

Electrical Mains Panels

These are type-1 and type-2 SPDs that are installed in the mains, sub-panels (main breaker box, pool panel), AC compressor connections etc. These must be installed by a licensed electrician. Massive surges typically last only nanoseconds and so these Type-1/2 SPD devices contain resistor or varistor material that can absorb the excess current as heat as well as being grounded to redirect the excess current. In many extreme surge cases, they do their job and are destroyed in the process. It pays to have spares on hand so that they can be replaced quickly by an electrician to restore protection. 

We recommend Eaton Type-1 and Type-2 SPDs for the USA. You must use a qualified electrician to install Type-1/2 devices.

Eaton Whole House surge protector


Appliances such as refrigerators and freezers usually require up to 20 amps 2400 watts protected by a specialized fire-proof SPD plug that disconnects in nanoseconds when an over or under voltage event occurs and then automatically reconnects when the current is stable again. These types of SPD do not rely on resistor or varistor materials to absorb the excess current (joules) but act as trip switches to completely shut off power. 

Power strips and single smart plugs don’t support higher levels of power and should NOT be used in case of damage and fire.

Appliance Surge Protector

Coaxial Connections

Coaxial RG6 cable connections include cable modems, tuners, DVRs, set top boxes and TVs. These are especially important because street connections are buried in the earth and satellite dishes/aerials are mounted on roofs i.e. more exposed to lightning ESD surges. In most cases these SPDs are used to protect cable modems, DVRs and set top boxes. These devices use a gas discharge tube (GDT) that blows when a certain level of voltage passes through it e.g. 90V. 

The GDT should be replaceable and you should keep spares.

Coaxial Surge Protector


Ethernet Connections

Ethernet CAT cables are used to link networked devices together and are good conduits of electricity. All ethernet RJ45 connection points to routers, switches, patch panels, security cameras, VoIP devices, computers etc. contain sensitive electronics and should be protected. In the case of POE (powered over ethernet) applications, the CAT cables also carry an electric charge and require specialized POE/POE+/POE++ support by the SPD. 

Never use SPDs that are not grounded.

HDMI Connections

HDMI cables contain copper/alloy and are excellent conductors of electro-static discharge which can easily blow sensitive HDMI ports and connections. These SPDs are installed as close to the protected device as possible and are grounded to a nearby wall outlet or grounded appliance.

It is important to understand your HDMI application requirements e.g. 1.4, 2.x etc. and select the right SPD to support it. For example a HDMI 1.4 SPD supports a max bandwidth of 10.2Gb/s and if this is exceeded by a higher 2.x 8K bandwidth, signal loss or distortion will occur. It must also be properly grounded to avoid sparking and fire.

Power Strips

These are high quality fire retardant multi-outlet, multi-USB power strip SPDs used for low to medium power devices. They are plugged directly into grounded wall outlets in offices, entertainment centers, bedrooms, power tool benches etc. The key thing to look for in power strip SPDs is the level of amps, joules supported and LED power and protected indicators. For example: A 10-outlet 4-USB power strip should be 15 amp and 3,000+ joules to properly protect up to 14 connected devices in an office or entertainment center. A smaller 4-outlet 4-USB power strip may be used for smaller bedroom/travel devices and should be 10 amps and 150+ joules. When selecting power strips, carefully consider the devices and power requirements that are to be supported.

Beware of cheaper strips that don’t have the correct level of amps, joules (varistors) and fire protection. Only use surge protected power strips. Never plug household appliances such as refrigerators or freezers into power strips. Use a specialized appliance SPD instead. Always check that the wall socket is properly grounded. Good power strips have a “protected” LED indicator to show that the SPD is functioning.

Power Strip Surge Protector summary

 In some cases, you may use a UPS (uninterruptable power supply) in place of a power strip. This is usually to keep devices running during a power outage or to facilitate a graceful shutdown of computers and NAS to protect their hard drives and data. See the next section for more details.


A UPS  (Uninterruptible Power Supply) device is basically a large battery and surge protector that acts as a buffer protecting office equipment, entertainment centers and gaming rigs. They come in various sizes to support different voltage capacities. A 1000va unit is usually fine for most home applications but you may need a 1500va or 2000va unit for larger requirements e.g. home computer center.

A UPS "cleans" the current and has a battery to continue power for a limited amount of time depending on the power draw. It provides multiple outlet groups, one for essential devices to continue working for as long as possible on battery or another just for surge protected outlets.

Modems, routers, network switches, NAS devices, printers, TV's, AV's, computers, laptops, media servers plug into the UPS. The UPS status can also be automatically monitored by a dedicated USB connection or over the network. This is essential for computers, servers, and NAS devices to automatically detect outages and gracefully shut themselves down to avoid disk crashes and loss of data.

The main difference between a UPS and a power strip is that a UPS can absorb power surges and keep devices running during a prolonged power outage. This is useful for LAN network devices, NAS, media servers and PC’s. It is never good to abruptly switch off devices with data drives and a UPS allows these devices to shut themselves down gracefully if the outage exceeds a defined period or the battery power drops below a certain percentage.

UPS Surge Protector


Speaker Wires

Most speaker wires are threaded from a central amplifier through walls, ceilings or are external to the home. Speakers can also be very expensive and can be easily damaged by power surges. Most speaker wires can be protected by a 12-volt AC (alternating current) surge protector. These can be quite difficult to find but can be sourced from high end specialist audio stores. 

Be careful not to buy a 12V DC surge protector as used in cars and boats.

LED Transformers and Wires

There are an increasing number of LED systems being implemented in the home and externally in gardens. These use a transformer to step-down the voltage from 120V AC to 3-12V DC depending on the application. Most garden LED lighting set ups use 12V DC and you can use a car, marine or LED specific SPD for these connected in either a serial or parallel configuration. 

For external applications, put an SPD on each end of the wire run.

WiFi Smart Plugs, Hubs and IoT devices

These types of devices are easily protected using a basic single outlet low power SPD plug/socket. These plugs typically utilize varistors to absorb excess power surges and should operate at 1000+ joules and protect to at least 10,000 max surge amps. These are relatively in-expensive and easy to source online. Note that some of the WiFi Smart Plugs also operate as surge protectors and can notify you of power events or if they are disconnected for a period. 

Because of their low power rating, these plugs are not suited to protect appliances such as refrigerators, freezers, dishwashers, microwaves etc.

Additional information:

Download our free Surge Protection PDF.

< Back