Guidelines on Electrical Installation for Practising Contractors
(TNEIEA – Tamil Nadu Electrical Installation Engineers’ Association www.teiea.com; email@example.com) Chapter -5: SWITCHGEAR & POWER DISTRIBUTION 4.3.10 Lightning & Surge Protection Devices (SPD) – (pp. 69 & 70)
To avoid pre-mature failure of sensitive electronic equipment like Computers, Servers, UPS, Soft starter, PLC, CNC machines, CCTV. Communication devices etc., protection from conducted & radiated surges are required.
Radiated surges (in the form of LEMP- Lightning Electro Magnetic Pulses) are greatly attenuated by the use of Faraday cage type of External lightning protection system in the form of Air terminal, Down Conductors & Ring Earthing as per guide lines furnished below:
Type 1 LPS (Lightning Protection System) is needed for Major Hospitals having more than 1000 beds & I.T companies having large amount of PCs & servers.
Type 2 LPS is needed for Petrochemical plants, refineries & fertilizer plants.
Type 3 LPS is needed for Cement plants, power plants- i.e. all types of industries other than the above.
Type 4 LPS is needed for Independent villas, multistory apartments etc.
Conducted surges are reduced to great extent by the installation of SPDs- Surge Protection Devices
(SPDS)at the following entry points:
At the Main DB – Min. 25 kA (10/350 micro Seconds) SPD between each phase to neutral &Min. 50 kA SPD (10/350 micro Seconds) from Neutral to Earth.
At the sub DB - Phase to Neutral: Min. of 5 kA (10/350 micro Seconds) of lightning surge & 50 kA (8/20 micro seconds) of Maximum Surge current.
Neutral to Earth: Min. of 25 kA (10/350 micro Seconds) of lightning surge & 50 kA (8/20 microseconds) of Maximum Surge current.
At the equipment level :
Phase to Neutral: Min. 30 kA (8/20 micro seconds) of Maximum Surge current.
Neutral to Earth: Min. 40 kA (8/20 microseconds) of Maximum Surge current.
Power line SPDs are connected in parallel to the load & Data/Instrumentation SPDs are connected in series. Parallel connected SPDs need local & remote indication facilities for failure indication & should be plug in type for easy replacement.
Apart from the above, data line SPDs are needed depending upon the sensitivity of the equipment-
i.e. Server, routers, CCTV cameras, TV, RS 485 communication etc. For detailed & accurate determination of LPS & SPDs, Risk Assessment as per IEC 62305-2 has to be carried out.