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Sub Boards or Incomer??

tonydon

Hi

We have a large commercial site fed by 2 onsite substations…

The substations feed panel boards in our side of the subs  i.e. Incomer

The panel boards then feed sub boards within the site, some of which will feed other downstream boards

Our questions are (for condition reporting)

  1. section i… Is the supply characteristic always referring to the incoming supply
  2. when testing a board is the supply protective device the supply feeding this particular board i.e. potentially an mcb in another upstream board that supply's this board … or  is the supply protective device the device on the incoming supply to the site  i.e this will then be the device listed on each board (the same throughout the site)
  3. Is the supply characteristic the supply to the whole site or the supply to just this board
  4. the ZE cannot be reasonably ascertained by test,  but, we also cannot get our supplier to give us this reading by inquiry  What should we do?

 

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  • 0

    Don't be too hung up on the details of the model forms - they're really intended for smaller installations (e.g. up to 100A/phase) with a single source of (grid) supply. For larger or more complicated sites you may well need to amend them to suit the circumstances.

    I'm not sure from your description whether the two transformers are DNO owned or part of the consumer's installation (supply provided at HV). Nor whether the two transformers supply separate distinct areas of the site or can have their outputs combined or switched into a common supply - either normally or say if one transformer/HV supply fails. The latter can affect Ze and PSSC values significantly of course.

    Calculation is always an option if you can't measure (effectively enquiring of yourself rather than the DNO) - usually backed up with with some means (e.g. inspection or test) to ensure that there's no lurking fault that invalidates the calculated result.

       - Andy.

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  • 0

    Don't be too hung up on the details of the model forms - they're really intended for smaller installations (e.g. up to 100A/phase) with a single source of (grid) supply. For larger or more complicated sites you may well need to amend them to suit the circumstances.

    I'm not sure from your description whether the two transformers are DNO owned or part of the consumer's installation (supply provided at HV). Nor whether the two transformers supply separate distinct areas of the site or can have their outputs combined or switched into a common supply - either normally or say if one transformer/HV supply fails. The latter can affect Ze and PSSC values significantly of course.

    Calculation is always an option if you can't measure (effectively enquiring of yourself rather than the DNO) - usually backed up with with some means (e.g. inspection or test) to ensure that there's no lurking fault that invalidates the calculated result.

       - Andy.

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