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Friday, April 21, 2023

Roof Steel Frame Earthing Prevents Electrocution

Lightweight steel roof trusses are currently very popular. Because they are easy to build, cheap, strong, and rust resistant. But if there is a leak in the electric power line, for example: being bitten by a mouse, and the wire touching  steel roof trusses. Then the electric current will spread throughout the trusses. Even the electric current flows to the metal roof tiles, if you use these tiles.

One way to minimize the risk if an electric current leak occurs in roof steel, is to discharge the electric current from the frame to the ground, which is called earthing or grounding.

Earthing is actually somewhat different from grounding. Earthing means that the circuit is physically connected to the Earth, i.e. the voltage is Zero Volts to Earth.

Grounding is not physically connected to Earth, but the voltage is Zero Volts to any other point on the circuit. But the term grounding is more popular. Grounding can be a connection to the device body.

If the steel frame is big enough, and the steel surface attached to the wall is large enough, then earthing is usually sufficient. But it will be better and safer, if the earthing is ensured by connecting the steel frame to the electrical conductor, which is embedded in the ground.

Good earthing usually uses copper rod that is planted in the ground. Concrete iron that is planted and cast in concrete pillars, can be used as earthing. In the photo below, you can see the protruding concrete iron at the top end of the concrete pillar. 

The concrete iron (rebar, reinforcing bar, reinforcement bar) that sticks out like in the photo is usually plenty at the top end of the wall. So it can be easily connected to the steel roof truss.

It should be noted that the rebar that will be used as earthing must be properly closed, not located in the bathroom or in other damp places that people often walk through. This is to prevent anyone from being electrocuted in the event of an electric leak.

In the bathroom, there is a risk that the electric current will flow to the wet body of the person in the bathroom, not to the ground. This can be very dangerous.

It is necessary to ascertain whether the rebar is good enough to be used as earthing. You do this by connecting a lamp with an electric cable from the electric grid. In the photo below the lamp used is a 9 watts LED lamp.

In the photo above, the lamp is only connected to a phase (voltage) wire from the electric grid, this wire is black. While the other yellow wire from the lamp is connected to the rebar. If the ground is good, then the lamp will glow brightly. Even though the red (neutral) wire from the grid is not connected to the lamp. The phase wire is an electrical wire that can power on the tester pen's lamp. The phase wire can cause electric shock if touched.

Usually the rebar is covered in dirt, cement, and a bit of surface rust. Clean it with a file, it can also be cleaned with sandpaper.

Connect the roof frame by attaching a wire to one of screws on the roof frame. As in the photo below, the yellow wire is connected to the roof frame.

That yellow wire is connected to the rebar, and secured with a steel plate clamp.

It is recommended that the connection on the rebar be covered with grease, may also be smeared with used oil, or painted with anti-rust paint.. So that it is not exposed to air to prevent oxidation which can cause rust on the rebar and clamp.

If the earthing connection is good. Then the lamp that is grounded on the roof frame can be turned on brightly, like the photo below.

It can be seen the black (voltage) wire from the electric grid connected to the lamp, and the yellow wire from the lamp is connected to the roof steel frame. While the red (neutral) wire from the electric grid is not connected.

This method of earthing with rebar can also be applied for earthing electronic devices such as: televisions (TV), computers, refrigerators, washing machines, amplifiers, air conditioners (AC), radio communications, and various other devices.

If an electric current leak has occurred, when the roof truss is properly grounded, then the electric current in the roof steel frame cannot be detected with a tester pen. If the MCB (Miniature Circuit Breaker) is sensitive, it can be tripped when current leaks into the roof steel frame, but that doesn't always happen.

One way tro test for current leakage is to turn off all electrical loads, such as lights, water pump, air conditioners, refrigerators, rice cookers, electric stoves, TVs, and others. And keep all MCB connected.

If the electric meter is still counting, it means there is a current leak. It would be more accurate to use a clampmeter to measure the electric current flowing in the main cable from the electric pole to the electric meter. There shall be no electric current in the main wire when all loads are off.

If indeed there is an indication of current leakage to the steel frame. Keep all electrical loads off. Then turn off the MCB one by one, while checking whether the electricity meter stops counting. When the electric meter stops counting after the MCB is turned off, then on that MCB line there is a wire that leaks and sticks to the roof steel frame.

Moist soil is usually good for earthing, so earthing conductors can be planted in watery soils such as drains. But drains are usually dirty and can damage the conductor.

Earthing may also be connected to metal water pipes (iron, galvanized steel, copper) embedded in the ground. But still should be kept away from areas that are often passed by people.

Because the roof is grounded, it will also help distribute electrical energy if the roof is struck by lightning.

Apart from earthing, as an effort to prevent electric shock, electrical installations must be kept away from light steel frames. Even if the electrical installation must be attached to steel frame, then the electric cable must be properly insulated, such as using: conduit pipes, twist-on wire connector, and others.

Avoid the main power cable from electric pole being attached to roof steel frame. If there is an electric leak, it will be difficult to cut off the electricity. Because the cable from the pole has not gone through the MCB or fuse. The main power cable must not be covered and hidden, so that it is easy to monitor, prevent damage, and prevent electricity theft.

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