More than a little disappointed I haven't had any meaningful reply yet.
Really I should be demanding my money back as this guide isn't worth the paper it's printed on.

Dear Graham

The IET technical helpline is for enquiries relating to BS 7671. For enquiries relating to IET codes and Guidance publications and activities, the email address is ietstandardsenquiries@theiet.org.

I have searched the IET technical mailbox but unfortunately I am unable to locate your enquiry. Are you able to resend it or provide the date it was submitted please?

Many thanks

Michael

This seems like advice from an older version. I read some main requirements from BS 7671 : 2008+A3 : 2015. They say that metalwork in boats cannot be supplied from a PME supply and only TN-S can supply houseboats and pleasure craft. TN-C-S is allowed for marina buildings (like offices, homes, stores etc). Because many marinas are large and varied, installing a TN-S system may be feasible. This makes sense if the marina has its own transformer.

Can't be. This is the first issue of this particular guide.

Can't be. This is the first issue of this particular guide.

Sorry I didn’t mean that particular guide. Another document I read from around the time of  BS 7671 : 2008 : A1 has a different recommendation. It says that if the supply system is PME, you cannot connect the neutral to the metal parts of any caravan or boat, according to Regulation 9(4) of the Electricity Safety, Quality and Continuity Regulations 2002. You can use the PME supply for permanent buildings in the marina, but not for small vessels, recreational craft or houseboats. They need a separate earth system. You can use a TT system that has its own connection with Earth, not the same as the PME earthing system, to satisfy this recommendation.