Causes of Transient Overvoltage

• Secondary effects of a Lightning strike up to a kilometer away.
• Inductive switching of large loads such as motors, transformers and electrical drives
• Capacitive loads such as power factor correction equipment

• Disruption of system operations [Down time], caused through data loss or corruption, system crash
• Premature ageing and increased maintenance of equipment due to stressing of electrical / electronic components
• Physical catastrophic damage of electrical / electronic equipment

• Lost or destroyed data
• Equipment damage
• Repair work / increased maintenance call outs
• Operational downtime
• Loss of services, i.e. security, fire, [Building Management services], BMS
• Health and safety hazards, plant instability, loss of control
• Fire risks, electric shock hazards

What needs to be protected
All conductive points of entry into sensitive equipment need to be protected, these include Power lines, Data, Signal and Telecommunications lines.

• All cables which enter or leave the Building [except fibre optic] ·
• Power supply to sensitive equipment
• Electronic equipment outside the building

Protect at Point of entry for incoming and outgoing electrical services
Indirect lightning strikes up to a kilometer away can induce transient overvoltages on to electrical cables which will then be conducted into sensitive electronic equipment connected to them. All cables that leave and enter the building must be protected, these will include,

• Mains Power supplies, incoming and outgoing
• Data communication and Local area Network cables
• Signal, control, instrumentation and alarm lines
• CCTV, satellite, TV and aerial cables
• Telephone and elementary lines

Protect local Data Lines
The largest risk to Data, Signal, Telecom and network equipment, ie external cables leaving and entering the building which should always be protected.

There is however a risk to data cables within the building from induced transient overvoltages, due to pick up from power lines and data cable looping /crossing over each other. A transient on a power line from a Lightning strike will be induced in to the data lines.

Elimination of Power cables and data lines loops and cross over, and good caballing practice should eliminate most of these problems. However if these practices have not been put in place, local protection of equipment is recommended.

Protect equipment external to the building
Equipment external to the building with incoming and outgoing power and data, signaling, telecom lines need to be protected. As with protecting equipment within the building, all incoming and outgoing cables should be protected.