Originally Posted by granite

Standard for Electrical Wire Installation for Thailand 2545 (with Revision 1 2551). This is the Thai electrical code and it governs, among other things, all electrical wiring in the home.

If you, or anybody else, has ever seen this code or has a copy of it, please let me know.

To ground the (consumer unit) entire installation, the ground busbar must be connected to a ground rod (other grounding electrodes are allowed by regulation, but they’re almost never used in domestic installations). Regulation requires that the ground rod be at least 2.4 meters long, 5/8-inches in diameter (which is about 15 mm), and made of solid copper or copper-clad steel (electroplated, not a copper sheath pressed onto a steel rod). Electroplated earth electrodes are not recommended. A copper sheathed steel rod is recommended (copper sheath is at least 1mm thick). The size of the wire that connects the ground rod to the ground busbar in the consumer unit depends on the size of the service conductors (the mains), but for almost all domestic installations it must be not smaller than 10 mm2.

The last element for a properly-grounded appliance is this: the neutral service conductor (the neutral wire running from the meter to the consumer unit) must be grounded at the consumer unit. How? The neutral service conductor must connect to the ground busbar in the consumer unit. Then, a short wire the same size as the neutral service conductor must be run from the ground busbar to the neutral terminal of the main breaker. This is called the main bonding jumper in Thai- and USA-regulation parlance, and you can look it up on the internet to read more about its importance in grounding.

This is not always the case in Thailand. Many areas DO NOT have the "star point" (neutral) of the supply transformer solidly earthed. For example, in many locations around Pattaya, it is eveident that an M.E.N. (Multiple Earthed Neutral) connection is required whereas in other locations, the M.E.N. system doesn't exist & if an M.E.N. connection is made, it will be a safety hazard.

Note that grounding a water heater (or any appliance) by connecting it to its own ground rod, as is sometimes seen in Thailand, is dangerous and prohibited by regulation. All grounding wires for appliances, luminaires, and receptacle outlets must run back to the consumer unit and connect to the ground busbar.

The above is very good advice. Multiple ground/earth rods can be very dangerous.

Earth Leakage Breaker Instantaneous water heaters have a built-in earth leakage breaker (ELB), also referred to on some units as an earth leakage circuit breaker (ELCB) or residual current device (RCD). I’ll use the term RCD because that’s the term used in the Thai electrical code. The built-in RCD was required by the 2545 version of the electrical code. Revision 1 to the code, which is now in force, has a more a stringent requirement. It is no longer enough to have an RCD built into the water heater—now, the entire branch circuit must be protected by an RCD. This requirement pertains to whirlpool tubs also, incidentally. There are a few ways to do this. First, the entire consumer unit can be protected by an RCD either with an external RCD, an RCD built into the consumer unit, or an RCD main breaker. Second, an RCD circuit breaker can be installed for the water heater branch circuit. Third, an RCD can be installed in the water heater branch circuit wires outside the consumer unit. This is a bad idea. All common protective devices must be installed at the main switchboard/consumer unit.
By regulation, the RCD must have a trip current not greater than 30 milliamperes (mA). All RCDs marketed for domestic use in Thailand meet this requirement. However, better to use an RCD with a lower trip current if one is available. RCDs with lower trip currents are available from some manufacturers. Square D markets RCD circuit breakers with a 10 mA trip current, and Safe-T-Cut has RCD-protected consumer units with trip currents adjustable down to 5 mA, for example.

Adjustable RCD's are prohibited for domestic use in many countries. I would suggest that an adjustable RCD not be used for domestic installations.

Safety Breaker It is customary in Thailand to install a switch for the water heater outside the bathroom. The switch is usually a so-called safety breaker. This switch is not required by regulation.

Just to clarify, this is NOT a "safety breaker" purely because it is not a circuit breaker. It is simply an isolator...a switch.

Recommendations for Fixing an Installation In a house with significant wiring deficiencies, what can be done to make instantaneous water heaters more safe? The easiest way to reduce the electrical shock hazard from a water heater is to install an RCD to protect the water heater branch circuit. If there is currently a safety breaker installed outside the bathroom for the water heater, it will be easiest and cheapest just to swap it out for an RCD safety breaker. Haco markets RCD safety breakers under the name Earth Leakage Breakers. Use a 16-ampere circuit breaker for a 3500-watt water heater, a 25-ampere breaker for a 4500-watt heater, and a 32-ampere breaker for a 6000-watt heater. Alternatively, if you have a Square D consumer unit, you can replace the circuit breaker for the water heater with a Square D RCD circuit breaker with a 10 mA trip current. Bad idea. Most water heaters etc develop increasing "residual leakage" over time. Use a minimum 30mA unit, which must trip at 30mA or can trip at between 15mA & 30mA.