2 minute read
Earth Leakage Q&A with Megger
DID YOU KNOW?
“Intentional” earth leakage is a consequence of the way equipment is designed.
EARTH LEAKAGE Q&A
Peter Wade from Megger, answers some of the most commonly asked questions about earth leakage.
Q: What is earth leakage?
A: Earth leakage current is an electrical current in equipment or an installation that finds its way to earth.
THERE ARE TWO CATEGORIES:
1: Unintentional earth leakage which usually results from faulty insulation or equipment, or 2: Intentional earth leakage, which is the unavoidable leakage current as a consequence of the way equipment is designed, e.g. input mains filters on electrical appliances.
Q: What are the best protective devices?
A: Either RCDs (residual current devices) or RCBOs (residual current circuit breakers with overcurrent protection).
Q: How do they work?
A: They monitor the current in the line and neutral conductors. Any small difference, or imbalance, can be detected and if the difference exceeds anything from 50% of the mA rating of the RCD or RCBO (depending on its sensitivity), it will trip and disconnect the supply.
Q: What is “nuisance tripping”?
A: This is when an RCD or RCBO keeps tripping for no apparent reason.
Q: How can this be tackled?
A: You will need an earth leakage clamp meter, such as the Megger DCM305E. Clamp this around the line and neutral conductors together (but NOT the protective conductor!). You can then measure the current imbalance, indicating the presence of earth leakage current.
DON'T FORGET!
The RCD or RCBO could be faulty. To check, carry out an RCD ramp test. If it’s a 30 mA device (the most common rating) it should trip somewhere between 15 and 30 mA. If it trips at a lower current, you’ll need to investigate further.
For more information about Megger, visit: www.megger.co.uk
