In my house I have five instantaneous water heaters. Each is has three wire connections. The three terminals from bottom to top are LINE, NEUTRAL and EARTH (GROUND)

Four units, connected and working have the wiring emerging from the wall conduit as LINE (White), NEUTRAL (Yellow) and Earth (Green).

The fifth unit was removed by a repairman several months ago and now that I come to reconnect it I see that the wires emerging from the wall conduit are LIVE (White), NEUTRAL (Red) and EARTH (Blue). In all five case the EARTH wire is slightly thinner than the Line and Neutral wires. The 'remover' failed to identify the connection. Although all five units were installed at house build it looks as if the house wiring electrician ran out of Green and Yellow and substituted Blue and Red! TIT!

So, just to say that I am a retired aircraft engineer and capable DIY man but always aware of the need for electrical safety. I could assume that the White wire is LINE and the Blue wire (because it is thinner) the EARTH leaving Red to be the NEUTRAL.

I have a Multimeter and intend shutting off mains power and checking that the Blue wire goes to earth (any tips) leaving an assumption that the Red is NEUTRAL.

I'm in no hurry as I am rebuilding the kitchen but advice is welcome.

Crossy is our best color commentator.

In the mean time, white should NEVER be used for LIVE (unless clearly marked as such) and ground should only be green or green/yellow striped. And, yes the ground is usually a smaller diameter than the L/N.

You might check in your CU (breaker box) and post a photo to see what color wires are going to what there.

NOTE: CORRECTION

My Post # 1 - Paragraph 3 is in error. It should simply state that there are three wires, White, Red and Blue emerging from the wall conduit. They are not identified as to which connection.

Since this IS Thailand and this house is 8 years old from build do not assume that it was wired to European standards. There may be Thai standards for wiring up to the domestic connection but are there written standards for in-house domestic wiring?

The heaters are 6000 W Stiebel Eltron. The CU has six 30 amp breakers and I assume five of these are one for each of the heaters. None are marked although over the years I have identified and labelled most others.