St Andrews Lutheran College on Tallebudgera Creek Rd, Tallebudgera were having problems with sensitive electrical equipment being damaged. Here’s how we explained why and the solution we provided.

Following on from your inquiry in relation to the recent failure of sensitive electrical equipment including expensive LED floodlight fittings.

I’ll put this in layman’s terms so it is easier to understand. Basically, there are two ways surges can occur, through the front door (from the network via the main switchboard – Energex voltage regulation issue, loose neutral, lightning strike upstream) or via the back door (lightning strike that induces a high voltage into cabling beyond the main switchboard or as a result of a power system fault within your installation.

The distance from the surge protection in the MSB to the classroom DBs and to the light poles with LED luminaires influences the effect of these back door issues.

To give you an idea, a direct lightning strike would contain around 30KA  40KA of energy. The reality is a non-direct strike is more probable and would be in the order of around 3-5 KA.

Proposed surge protection locations, product links, and some notes for each location:

You currently have a 100KA surge diverter we installed at the main switchboard. This is a very good surge diverter which acts as the first line of defense against surges and transients coming in from the supply network. It will also give some protection to equipment in the MSB from surges and transients induced into the cables routed around the campus.

As mentioned above though it won’t deal with the back door issues. To deal with those we recommend installing a 50 KA device within any classroom or admin building DB with sensitive, critical, or expensive loads. This will act as the second stage of a cascading surge protection scheme and also protect the DB loads from surges and transients induced in the cabling between the MSB and DB.

To ensure LED Floodlights are protected we recommend installing a 40KA device across the power connections in the base of each light pole you wish to protect. In other words, we are treating each light pole as a DB with a sensitive load connected to it, so the explanation is the same as for the Classroom DBs above.

In the short version you will need a 50KA for the 3-phase DB of each classroom block that you wish to protect and or a 40 KA for each light pole that needs protection.

The existing surge protection that comes in the light fitting is extremely small (approx. 1.5KA), so we don’t expect it would offer a useful level of protection.

The surge diverters we recommended would handle approximately 100 typical non-direct strikes and would fail if they were to endure a direct strike but save your sensitive equipment.

Pricing to follow.

Kind regards

Dean Kenway

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