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SIEMENS - Whole-House Protection Strategy
SIEMENS – Whole-House Protection Strategy

No single SPD (Surge Protection Strategy) can protect all the equipment in a residence from all causes of electrical surges. Instead, a whole-house protection strategy, consisting of point-of-entry and point-of-use SPDs, is necessary to help guard against disturbances from inside and outside the home.

A point-of-entry SPD is necessary to limit damage from electrical surges entering the home via service entrance conductors. As previously discussed, these electrical surges can come from a lightning strike on or near high-voltage transmission lines, switching of primary circuits by the local utility, or equipment operation in nearby commercial or industrial facilities.

Point-of Entry Protection
Point-of Entry Protection

Surges from Within the Home

Point-of-entry SPDs, however, cannot provide protection from surges developed within the home. For example, an air conditioner can cause a small electrical surge every time it cycles on or off. Surges caused by equipment within the home are usually weaker than surges caused by lightning; however, they occur more frequently. These surges are distributed throughout the home’s electrical system, possibly causing problems with other connected equipment.

Surges from Within The Home
Surges from Within The Home

Exterior Wiring

Additionally, many homes have some form of exterior electrical wiring. Security gates, outdoor lighting, electronic dog fences, and swimming pool filtration equipment are just a few examples of outdoor electrical devices in use today.

Exterior wiring
Exterior wiring

A cloud-to-earth lightning strike in close proximity to underground wiring can cause a voltage surge which has a direct path to the home distribution system.

Voltage surge which has a direct path to the home distribution system

Surges from Other Services

Most damage occurs from electrical surges that enter the home from outside services. We have already learned how lightning strikes can enter the home through the electrical utility. It is equally important to note that telephone lines and TV cables can also conduct electrical surges into the home causing damage to electronic equipment connected to these lines.

The National Electrical Code® requires services to be grounded and bonded together. The purpose is to reduce fire and shock hazard in the event electric utility power conductors come in contact with communication conductors.

However, this will not protect sensitive electrical and electronic equipment located within the house.

Surges from Other Services
Surges from Other Services

Type 3 SPDs

Type 3 SPDs, also called point-of-use SPDs, are essential to any surge protection strategy to provide household equipment with a degree of protection from surges created in the home. In addition, point-of-entry SPDs typically have a relatively high clamping voltage and this allows some let-through energy that can be absorbed by point-of use SPDs.


Type 3 SPDs
Type 3 SPDs

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About Author


Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry fascilities. Professional in AutoCAD programming. Present on


  1. Imtiaz Alam
    Aug 17, 2011

    This is a very informative article pertinent to Pakistan where there are outages & surges of unknown dimensions. How to protect oneself. Is there anything as a protector gadget available in the market. . .

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