Can save human lifes, electrical appliances and accessories by good earthing in electrical system?

[admin]

I am a group leader of M&E installation group at Myanmar. When we do electrical installation works, we do to get good earthing for the first. After that we connect the earthing cable with conductors near electrical cable and appliances such as metal frame for ceiling, metal trunking, etc. In the power distribution system we used 30mA ELCB before single pole MCBs. I like to know such arrangement can save the whole electrical system. How to do more save?

[Laurent]

I believe all you do is already very good in terms of safety, in particular the use of 30mA RCDs. Just be sure to use good quality products and recommend that the RCDs are regularly tested using the test button.

I don’t know what are the standards and rules for electrical installation in Myanmar: if they are close to IEC, you might take a look at the chapter “protection against electric shocks” included in a WIKI I found recently (it is dedicated to electrical installation guide according to IEC60364 and other related IEC standards). It covers all types of electric shocks and protection measures (direct contact, indirect contact …).

Knowing also that on average 30% of fires in buildings come from electrical problems, it is good to take this kind of measures, plus adequate maintenance … You might also look at the type of cables you are using, as if the fire comes from other sources, the electrical cables when burning can have very bad consequences, such has helping the fire to expand, a lot of smoke which can kill people and make firemen work almost impossible, destruction of goods (electronics in particular) due to corrosiveness …

regards

[admin]

Hello,

In Schneider Electric’s website, you will find a section fully dedicated to people’s safety and protection against electric schocks. Browsing this section you will get a complete review of the good practices, and animations explaining how the safety devices operate in various hazard conditions. Hoping this will help improve the safety level of your designs.

[electricalexpert65]

30mA ELCB is good enough. But, just in case you want to improvise, you may go for 10mA ELCBs at least for devices in wet areas.

[Tamakuwala]

Reasons For Earthing:There are four basic

reasons for earthing an electrical system:REDUCTION OF SHOCK HAZARDAn

earthed chassis will provide a low impedance path to ground for any

active voltage that appears on the case or metalwork.SAFE DISCONNECTION

OF SUPPLYIf the exposed metalwork of an appliance were connected by a

fault condition to an active conductor, the active current path needs to

be able to flow to ground via a low impedance path so an excessive

current will flow that will cause a protective device such as a fuse or

circuit breaker to open circuit, thus prenting an electric shock

situation.MINIMISE THE DANGER OF FIRE HAZARDThe earth wire should always

be in good contact with all metal parts of any appliance the user may

touch. Should the equipment become faulty by the active wire touching

the case, then current will rush to earth, smoke will rise from the

equipment, and if the current is very high the fuse in the active line

will blow, disconnecting mains power from the faulty appliance. Without

the earth wire, this fault would go undetected, allowing high current to

flow through the patient whenever the patient formed a circuit to

ground. Standards limiting current in any circuit are vital to prevent

excessive heating of the power supply wires leading to fires.VOLTAGE

STABILITYNeutral earthing : Star point of Wye connected transformers and

alternator windings are earthed primarily to provide voltage stability

to system on account of imbalance in loading resulting in neutral

current flow. Neutral point allows vector sum of three phase currents

displaced at 120 degrees nullifying it to zero. Secondary purpose served

is detection of earth faults or earth leakages and allow the protective

gear to operate in desired time.In the view of high harmonic contents

found in modern facilities, the zero sequence or triplen harmonic

currents overload the neutrals if not adequately sized. This is because

these are in phase and hence do not cancel out at neutral point. So

neutrals are required to be sized equal to or sometimes double the size

of line conductors to carry “algebraic sum” of triplen components in the

lines. Neutral earthing for applicable to low voltage distribution

systems upto 1000 V ac comprise of solid earthing with no intentional

resistance connected in the path. Visit following

website www.picearthingtech.com

[Author]

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