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Probably a stupid question...

tonydon

Right...

We are on a site with 2 onsite substations providing our supplys.

Upon inspection the supply comes from the substation transformer room, into our switch room, as a TP&N feed to our section boards.

We cant see any earth other than the armour of the supply cable which is obviously attached to the section board.

A colleague and I have been debating whether this is a TNS or TNCS supply.???

Given that the transformer is just the other side of the wall in our switch room, and that the earth and neutral must be bonded at the star point of the transformer secondary.

Are we right in thinking the supply is TNS??? 

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    tonydon said:
    the earth and neutral must be bonded at the star point of the transformer secondary.

    Have you actually checked that this is the case? It is quite possible (even likely) that it is expected that the neutral earth links are intended to be in your switchboard, especially if it's a single split bus board.

    If you're on site I would talk to the designer of the LV system, who should be able to tell you, as they will have needed to know / decide.

    Note that the armour may be only bonded to the gland plate (and thereon to the transformer tank) and not the neutral in the spill box... or indeed it might be deliberately isolated at one end to prevent circulating current.

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  • 0
    tonydon said:
    the earth and neutral must be bonded at the star point of the transformer secondary.

    Have you actually checked that this is the case? It is quite possible (even likely) that it is expected that the neutral earth links are intended to be in your switchboard, especially if it's a single split bus board.

    If you're on site I would talk to the designer of the LV system, who should be able to tell you, as they will have needed to know / decide.

    Note that the armour may be only bonded to the gland plate (and thereon to the transformer tank) and not the neutral in the spill box... or indeed it might be deliberately isolated at one end to prevent circulating current.

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