Hi All, we have been asked to install tails from a new DNO 400A TPN cut-out to an existing panelboard. This new DNO supply appears to be TN-S (we are trying to source the quotation to confirm the DNO supply arrangement.) The building is of steel frame cons

Is it more likely to be 1No. PME and 1 No. TT?

Its not clear what the question is ?

Mike.

Hi, The new supply appears to include a separate earth cable connected to the cut-out earth terminal. We are seeking clarification. Thank you.

Hi Mike, We are considering if there is a risk of circulating and diverted neutral currents given the steel frame construction of the building. Thank you. 

The DNO is obliged to give you the information under R.28 of ESQCR 2002:

A distributor shall provide, in respect of any existing or proposed consumer’s installation which is connected or is to be connected to his network, to any person who can show a reasonable cause for requiring the information, a written statement of—

...

(d) the type of earthing system applicable to the connection;

I will rephrase that, should it be 1 No. PME and 1No. TT?

If the DNO supplies an earth terminal, it is your responsibility to determine if it should be used or not and make the final connection.