In today‘s electronic world, electrical systems for the home or business just aren’t complete unless they incorporate surge protection. The most effective way to defend and safeguard this environment against damaging surges is by hardwiring surge protective devices (SPDs) throughout the electrical distribution system.

Government studies suggest that the most efficient way to surge protect an electrical system is by applying hardwired surge protective devices at the main incoming electrical and communications services. Additional hardwired suppressors were recommended to prevent backfed surges that could bypass the primary electrical service SPD. Also, localized equipment SPDs are recommended to protect against residual and internally generated surges.

Following these practices, 5 common SPD electrical systems installation points can be identified. Applying surge protection at these points will maximize a facility’s surge immunity. These locations can easily be remembered by using the following acronym, “The best surge protection installation is a S.O.L.I.D. one.” Where S.O.L.I.D. stands for the following:

• Service Entrance
• Outside Loads
• Lower Voltage Panels
• Individual Loads
• Data Lines

With SOLID installation points identified, we can use SurgCalc™ to select appropriate SPD surge current and modes of protection redundancy.

SurgCalc™ is a facility surge susceptibility profiling tool that uses the answers to the following survey questions to generate the facilities surge index. This index is then used to select either Super, Standard, or minimal redundancies for each SOLID location of your facility.

• Answer each question by selection the appropriate answer from the corresponding pull down menu that best represents your facilities characteristics.
• At the end of the questionnaire is an SPD Redundancy selection pull down menu. It is defaulted to Super Redundancy, which is recommended for mission critical or high profile locations. Click on submit to see the APT SPD recommendations.
• For Standard and Minimal redundancies, click on category pull down menu, and select the appropriate category. Once the new category is selected, click on submit, and the corresponding SPD part numbers will appear corresponding to these redundancies.

Most consultants will print out the results and include them with their project file.

With the help of SurgCalc™’s susceptibility profiling, consultants can quickly find a calculated recommendation instead of just guessing or relying on a manufacturer’s representative’s recommendation.

If you need further assistance, please contact the APT Technical support group at

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1. Geographic location of the facility.

This can be determined by consulting an Isokeuronic map and finding the location of the facility. Colored regions show increased number of lightning days experienced within the region. Each region corresponds to an IEEE exposure classification category.

High Medium Low



2. Facility location relative to other buildings.

If the facility is in a rural location isolated from other structures, or on a hilltop the probability of a lightning induced surges is much higher than in an urban environment.

Rural Suburban Urban

3. Adjacent Structures.

If the facility has a large antenna, water tower, or is the tallest building in the area it has a higher probability than a facility nestled among other structures.

Tallest Equal Smallest



4. Location of the facility on the utility service.

If the facility is at the end of the utility line surges will travel down the transmission line, or if there are other large industrial facilities on the same line surges could be introduced on the line by these nearby endusers.

End-of-Line Multiple Clients Dedicated Line



5. Utility history for an existing facility or for facilities being served by the same utility of a planned facility.

If there has been equipment disruption or equipment damage in an existing facility this is an indication of a high probability of surge activity. If this is a new facility, an inquiry to other facilities served by the same utility will give an indication of surge activity.

Damage Has Occured Restarts Required Few Disturbances



6. Consideration of the equipment being protected and the function this equipment performs as it applies to the facility mission.

If the equipment is supporting mission critical functions such as an on-line database, a continuous process control application, life support equipment, or other equipment that is essential for the operation of the facility it should have a high level of protection.

Must Not be Down Loss of Revenue Recoverable



7. Expense to repair equipment.

If there is equipment within the facility that is very expensive to repair if damaged, such as MRI equipment, network controllers, CNC machinery etc. the level of protection should be high to avoid expensive repair bills.

Expensive Moderate Inexpensive



IEEE C62.41 Category: Category C Category B Category A

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