General
During a period this July with varying voltage and problems with grounding failures, there were done some measurements and safety considerations I like to share within this document. The electric installation system is similar to what we have in Norway from about year 2000, what we call TN-system. The 230 V is obtain between one of the three phases and the neutral point in the transformer. Between the phases there are 400 V, but this voltage is only available on transformer side. The main distributions are separated in different enclosures located in the common area in the local street. Each enclosure contain a main circuit breaker of 3-phase 400 A for distribution load of 6 - 12 houses. Each house's energy meter (kWh-meter) are also located in these enclosures. None of the enclosures are key-locked.Must be done issue #1
The meter was the reason for the unpredictable variation of the voltage, and the voltage drop to less than 140 V when starting air-condition. Some high impedance problem must have occurred in the meter itself. By replacing the meter with a new one solved the voltage problem. The old meter is recommended to be replaced with newer type/model.Safety consideration
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| Not to be used in Thailand |
A worry is that when you buy a household product in Thailand, it could be an imported product with Scandinavian plug! I have several products bought in Thailand which I now have replaced the grounding plugs with the correct types.
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| Flat-pin plug |
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| Grounding plug mounted |
Computers and chargers for mobile phones with Scandinavian grounding plugs is not considered as a safety risk. The problem which may occur is electrical noise problem which is not considered here in.
An alternative is to change only the power cable, if plug-able, with Thailand type power cable as shown in picture below.
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| Plug-able power cable |
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| wall-socket |
When replacing the grounding-plugs it is important that live (L), neutral (N) and earth (PE) is connected correctly. When looking to a wall socket (right picture) the live is upper-right, the neutral is upper-left and earth is lower and in the middle. The neutral wire will always have the blue color on the PVC-isolation. The live can be brown or black. PE-wire will often be yellow or combination green/yellow.
The problem in kitchen area are the main components which is a part of the fixed installation, and are within reach simultaneous. The main components are the ventilator, the gas oven and the sink. As the hot-water is electric generated the sink itself must have a grounding wire connected to the common PE-point in the distribution enclosure inside the house. In my house I measured voltage between these components higher than 50 VAC. Which means something must be done to avoid accidents by electric shocks.
None of the outgoing from the distribution panel has 2-pole circuit breaker, which makes the possibility of dangerous touching voltage when several ground failures from different phases and houses occurs. The circuit breaker only cut the live (L) when off. In a special grounding situation the apparatus may still have dangerous voltage, even when the breaker is off! The only way around this is to mount a ground failure relay. When this is mounted in the common line the whole house will be out of voltage when the ground failure relay is activated. But, the safety come first!
Insurance companies in Norway recommend to unplug apparatus when not in use. Reasons for that are some situations that apparatus have started a fire, even when it was turned off by the switch. This is possible in TN-system when using 1-pole switch.
News of 22. February 2014
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| http://cnx.org/content/m42416/latest/?collection=col11406/latest |
The illustration picture shows the important that both feeding current and return current are measured to detect any leakage to ground, as illustrated with the man. That means also that all PE-wirings and N-wirings must be divided the whole way to the distribution panel. The wiring colour is the US-standard and not the EU/Thailand type! The neutral (N) is always blue. The PE (Protective Earth) is always green/yellow. The L (Live) is black.
Must be done issue #2
There are several things to be done. Here is what I have put in order:- An earth rod must be driven in the ground. A length not less than 1,5 m. This must be connected to the common PE-connection/N-connection in the distribution panel and connected to the PEN-connection from transformers earth rod.
- A separate grounding wire to be connected to the sink and goes direct to the PE-connection bar in the distribution panel.
- Each wall-socket to be checked that neutral-wire goes direct to the neutral connection bar in the distribution panel and connected to the neutral bar.
- Each wall-socket to be checked that PE-wire goes direct to the PE-connection bar in the distribution panel.
- One connection in the distribution panel connecting together PE, N, PEN from transformer and the local earth rod
- All outgoing single-pole breakers to be replaced with combined breakers including ground failure relay. The ground current set-point not more than 30 mA with a breaking time less than 0,4 s.
This document will be updated if/when new issues occurs.
Please make comments if something is wrong or may be done in a better way. Remember, safety first!
