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Surge protection on an mcb on a TT

Hi guys, i fitted a replacement CU today on a TT system. I have used a main switch with double pole rcbo's. The pre installed surge device is protected by a 32amp mcb.  It basically has a loop of 6mm inside the unit aprox 5 inches long that loops from the breaker, behind the meter tails into the top of the surge device.   I was a bit concerned because of the circuit breaker, i was tempted to order another rcbo, but after reading through the manufacturers bumf it says its fine on a breaker or fuse on a TT system.  I presume this is because it is part of the assembly ? Or is it because the link is so short and it's pretty much impossible to cause a problem.  A bit like meter tails in the metal box if installed correctly. Any thoughts please.

Cheers  Gary

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  • I’ve questioned this before and then told myself that the SPD isn’t protected by an mcb, it’s just supplied via one. It seems to be the norm in many preloaded units though, iv fitted quite a few and round here there’s a lot of TT systems, from my point of view I’m using the good old get out of jail free card that is the manufacturers instructions.

    As it’s not part of a final circuit the risk has got to be fairly small, it’s all in a fire proof earthed box very close the origin of the installation after all.

  • What happens if the S.P.D. goes dead short L to E in a TT system?

    www.bing.com/.../search

    Z.

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