Earthing System: Dirty/Clean Earth

Very simply

1. normal protection earth (dirty) and signal earth (clean) are kept separate and linked only at one point to prevent noise on the main protection earth from causing interference in sensitive electronics connected to the clean earth.

2. Depends on local regulations and standards. As a general rule of thumb only, 30mA for residential protection, 100 or 300mA for industrial.

3. Depends on local regulations and standards. As a general rule of thumb only, 1 ELCB can protect multiple feeders. If the feeders are powering variable speed drives or other devices with high leakage current to earth then this may not physically be possible thou.

Check your local electrical regulations for the actual requirements relevant to your country.

Dear Khalid,

1. As commented by Jack->#1

2. 10mA for Medical Electronic Equipment, 30mA for Human protection (power outlet), 300mA for Fire protection (Lighting system).

3. Normally main is Circuit Breaker, branch is ELCB but depend on the category as no.2 above. You have to consider the discrimination aspects and material cost.

regards.

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2. 10mA for Medical Electronic Equipment,

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<50 μA for under-skin Monitoring: Highly-Isolated