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TT or PME..best practice?

Evening all,


I’m currently looking into running a submain approx 100m buried from a PME supply to a small outbuilding (timber frame, metal sheet clad) that is being used next to a glamping tent as a place to cook and shower etc. The sub main will be a 16mm SWA..I was initially going to run a 3 core SWA or potentially a 2 core SWA with a seperate 10mm CPC (slight cost reduction) with the later option. I’ve since thought that perhaps a TT install would suffice, and, as possibly in the future I might be asked to extend the power into the tent, which, would require a TT setup. Any thoughts of this from a safety point or preference, also, if deciding on a TT and running a 2 core SWA as a submain which would obviosuly be a cost saver compared to a 3 core, however, would it be best practice to still have a CPC available seeing as a trench is now open...future proofing....? just as a side note, the metal sheets will be bonded to earth and any plumbing in the building is plastic pipes, also, this isn’t a question about cable selection i.e. the sub mains might be 16 or 25mm once I know exactly what the client wants, this question relates to the earthing setup. Thanks in advance!.

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  • I was thinking of this:Transient overvoltages caused by electrical switching events are very common and can be a source of considerable interference. Current flowing through a conductor creates a magnetic field in which energy is stored. When the current is interrupted or switched off, the energy in the magnetic field is suddenly released. In an attempt to dissipate itself it becomes a high voltage transient. The more stored energy, the larger the resulting transient. Higher currents and longer lengths of conductor, both contribute to more energy stored and subsequently released. This is why inductive loads such as motors, transformers and electrical drives are all common causes of switching transients. So would a buried steel wire armoured cable be at risk of ground strikes? Wouldn't the armouring protect the inner conductors somewhat?


    Z.


Reply
  • I was thinking of this:Transient overvoltages caused by electrical switching events are very common and can be a source of considerable interference. Current flowing through a conductor creates a magnetic field in which energy is stored. When the current is interrupted or switched off, the energy in the magnetic field is suddenly released. In an attempt to dissipate itself it becomes a high voltage transient. The more stored energy, the larger the resulting transient. Higher currents and longer lengths of conductor, both contribute to more energy stored and subsequently released. This is why inductive loads such as motors, transformers and electrical drives are all common causes of switching transients. So would a buried steel wire armoured cable be at risk of ground strikes? Wouldn't the armouring protect the inner conductors somewhat?


    Z.


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