Hi weevilward, As I understand it, your main question was: “
in the event of loss is supply neutral, everything connected to MET, including that lamppost, will rise to a voltage, anyone touches it may get a shock? ”
You can find all answers in IEC 60364-4-41 standard. There is “Protection under fault condition -
Protection against indirect contact” in TN-systems for your case. According to IEC60364 you must consider two events:
Case-1 (easy to verify). Dangerous voltage potential (touch voltage on a lamppost) occurs from the loss is supply neutral. According to IEC60364 protections are protective earthing and protective equipotential bonding.
The protective equipotential bonding must connect all extraneous conductive parts within the installation, including an outdoor lighting lamppost, as part of installation. It means you must connect metal lamppost with the main potential equalization bar by a separate potential equalization conductor. Additionally you may make an equipotential bonding ring around lamppost. (for example, radius=1m, depth=0,5m). All these techniques are sufficient, but they don’t prevent you from using additional protection (rcd).
Case -2 (not easy to verify). Dangerous voltage potential (touch voltage on a lamppost) occurs from a short-circuit in a metal lamppost. In this case you must check the circuit breaker or fuse of the lamppost supply cable. According to IEC60364, disconnection time of a circuit breaker or fuse should be less than 0,2s. To check disconnection time you must calculate the minimum (phase-to- earth) short-circuit current in the lamppost. You can’t calculate it accurately by manual calculations - it’s very time-consuming. You can use any software, for example
Ecodial Ecodial Advanced Calculation | Schneider Electric - https://www.schneider-electric.com/en/product-range-presentation/61013-ecodial-advanced-calculation/ . I use the
MeteorCalc software
MeteorCalc SL - https://meteorcalc.com/ . It’s specialized soft for outdoor lighting design.
After the finish of work, you must measure the short-circuit current in the lamppost and verify disconnection time again.