Lightning surge protection for 3G/4G/5G Radio Cellular Masts

but please can you tell me what TT and TNC mean

It's a shorthand description for the Earthing arrangement for the (LV) supply - T = Earth (Terra), N=Neutral, C=combined, S=Separate, I=Isolated (or Impedance Earthed)

So TT - means the supply star point (and hence supply N) is earthed by its own Earth electrode and the consumer's equipment is also Earthed by it own electrode. So you end up with two (or more) separate electrodes. Traditionally seen on overhead rural supplies, but also seen where the supplier's earth facility is considered unsuitable for some reason.

TN - means again the supply star point (and hence supply N) is earthed by its own Earth electrode, but this time the consumer earth is connected to the same point (i.e. the supply N). There are a few different sub-options:

• TN-S - where the consumer-side earth is connected to the star point (N) of the supply by a separate PE conductor throughout
• TN-C - where the consumer-side earth uses the supply N coductor to connect to the star point (N) - i.e. a single conductor serves as a combined N and PE.
• TN-C-S - where the earth is partly combined and partly spearate in the same system - often TN-C in the DNO's cables and separate within the consumer's installation.

Where you have a local generator, it's usual to have a TN-S arrangement where it's Earthed (or a separated or IT system where the system isn't Earthed).

Each system has its pros and cons. TN-C and TN-C-S systems have a particular issue where a single break in the supply PEN conductor can result in exposed metalwork in the consumer's installation being made hazardous live, so it's avoided in certain situations such as the supply to caravans or boats. TT systems are typically totally reliant on RCDs for shock protections (rather MCBs or fuses) and RCDs have a notorious failure rate. TN-S systems can have a faulty PE connection without anyone noticing until it's too late.

TN and TT systems also have somewhat different requirements when it comes to SPDs.

   - Andy.

but please can you tell me what TT and TNC mean

It's a shorthand description for the Earthing arrangement for the (LV) supply - T = Earth (Terra), N=Neutral, C=combined, S=Separate, I=Isolated (or Impedance Earthed)

So TT - means the supply star point (and hence supply N) is earthed by its own Earth electrode and the consumer's equipment is also Earthed by it own electrode. So you end up with two (or more) separate electrodes. Traditionally seen on overhead rural supplies, but also seen where the supplier's earth facility is considered unsuitable for some reason.

TN - means again the supply star point (and hence supply N) is earthed by its own Earth electrode, but this time the consumer earth is connected to the same point (i.e. the supply N). There are a few different sub-options:

• TN-S - where the consumer-side earth is connected to the star point (N) of the supply by a separate PE conductor throughout
• TN-C - where the consumer-side earth uses the supply N coductor to connect to the star point (N) - i.e. a single conductor serves as a combined N and PE.
• TN-C-S - where the earth is partly combined and partly spearate in the same system - often TN-C in the DNO's cables and separate within the consumer's installation.

Where you have a local generator, it's usual to have a TN-S arrangement where it's Earthed (or a separated or IT system where the system isn't Earthed).

Each system has its pros and cons. TN-C and TN-C-S systems have a particular issue where a single break in the supply PEN conductor can result in exposed metalwork in the consumer's installation being made hazardous live, so it's avoided in certain situations such as the supply to caravans or boats. TT systems are typically totally reliant on RCDs for shock protections (rather MCBs or fuses) and RCDs have a notorious failure rate. TN-S systems can have a faulty PE connection without anyone noticing until it's too late.

TN and TT systems also have somewhat different requirements when it comes to SPDs.

   - Andy.