Do surge protectors last forever?

No, they do not. Each time a surge protector reroutes a power surge away from your connected equipment, the internal structure of the protector takes a little bit of damage. Over time the parts of the surge protector that keep your connected equipment safe simply stop working. How long this takes depends on the frequency and strength of power surges.

Are the existing protections like MCB, ELCB etc. not sufficient to protect against surges?

All the existing protecting devices like MCB, ELCB etc. are current sensitive devices. They get activated based on a fault current. These devices are triggered when the fault current persists for duration of more than 3 to 20 milliseconds. However, the surge typically lasts for a few micro seconds only during which time it causes all the damage.

Hence the conventional devices like MCB, ELCB fuses etc. are not effective in protection against surges. In view of the above, special equipment called surge protection device which has a response time of two nanoseconds is required to be installed to protect against the surges.

What is a power surge?

A power surge is a spike in the electrical current flowing through the wires of your house. They can damage common appliances, sensitive AV electronics and computer equipment.

What are the different technologies used in SPDs?

Some of the popular technologies used in SPDs are the following:

i) Gas discharge tubes

ii) Metal oxide varistors

iii) Spark gap

iv) Zener diode

v) Silicon Avalanche diodes

Among these, gas discharge tubes, metal oxide varistors and spark gap are the most popular types of surge arresters.

What causes a power surge?

Most power surges stem from inside your home. Power surges are caused by many different factors, including severe weather, faulty or damaged electric wiring or the sudden turning on and off of a high power electrical device like an air conditioner or large electric motor.

Are the SPDs ratings to be selected depending on the line current?

Generally, the SPDs installed on the electrical Power circuit are connected in parallel and hence will be independent of load (line) current.

Why worry about power surges?

Strong power surges can wipe out your home equipment in an instant. In addition to surges caused by storms, the average home can experience multiple "hidden" surges a day from other various sources. These smaller surges cause cumulative damage to electronics, shortening their life and eventually causing them to fail.

How to determine what types of SPDs are to be installed at a given location?

The selection of SPDs at a given location depends on:

a) The topography of the location in terms of lightning strikes.

b) Susceptibility to switching surges in terms of proximity to large loads / connected to rural feeder etc.

c) Sensitivity of the equipment connected to the circuit.

Normally SPDs with Class-B & C are installed at the main panels and SPDs with Class-C rate are installed at the sub panels. The ratings for class-B, SPDs shall be a minimum of 12.5 KA Iimp.

For the Class-C (Imax. rating), it should be, a minimum of 40 kA at the sub panels.

For the Class-D SPDs which are installed near sensitive equipment, the criteria shall be the residual voltage or the protection level which should be lower than the temporary over voltage withstanding capacity of the protected equipment.

What does a surge protector do?

A surge protector safeguards electronics from the harmful effects of power surges and voltage spikes. Surge protectors can absorb and dissipate the power of a surge so that connected equipment is shielded from the surge.

How does one know the SPD installed is working?

Since the SPDs are always connected in parallel to the electrical circuit, during the normal course it is not possible to know whether they are in working condition or not. Hence it is necessary to have a local and remote indication using electrical contact in order to know and monitor the healthiness of the SPD.

Is it necessary for having separate grounding for SPDs?

It is not necessary to have a separate or dedicated grounding for SPDs. The SPDs should always be connected to the general earth grid.

Is a good earthing system necessary for efficient working of the SPD?

All SPDs work by diverting the excess energy to the ground. Hence it is imperative that the earthing system connected to the SPD must be in efficient working condition so that the surge current can flow to the earth without any hindrance.

Are SPDs available for applications other than the electrical circuit like telephone lines, data lines etc.?

SPDs are certainly available for every circuit like telephone lines, data lines, Ethernet lines, signal lines etc. In all these circuits SPDs are connected in series.

Are primary SPDs alone sufficient for equipment protection?

No, from a small facility to a large facility, it is usually necessary to adopt a cascaded or layered approach where primary protection is installed at the service entrance panel, and secondary protection at branch panels. Each facility requires individual analysis to determine the right protection to meet the needs of the equipment being used. It can even be necessary to include additional point-of-use SPDs if this equipment is located some distance from the supplying panel. A cascaded approach is recommended by the IEEE and this type of approach will provide the most effective surge protection throughout a facility. For more information on where to apply SPDs, select the type of environment you’re interested in: industrial, commercial, or residential.

Why do I need an SPD when I already have an isolation transformer?

Isolation transformers provide very good common mode rejection but do not provide good differential (normal) mode rejection. In other words, a surge superimposed equally on both the line (L) and neutral (N) conductors will see rejection by the isolation transformer, while a surge appearing differentially between the L and N conductors will pass through the transformer. Also, keep in mind the majority of transients are being generated by the loads within the facility, on the load side of these transformers. To minimize the effects of these internally generated transients from one piece of equipment to another an SPD should be placed.