© Abb Control Ltd - 1 ABB Protection - Overload What do we mean by a fault? Overload Operating condition in an electrically undamaged circuit which causes an current to flow in excess of the full load current Example: Starting condition during DOL start If this type of fault continues indefinitely because of an anomolous operating condition., damage begins to occur creating……….

© Abb Control Ltd - 2 ABB Protection – Short Circuit What do we mean by a fault? Short Circuit Operating condition in an electrically damaged circuit where there is an accidental or intentional connection by a relatively low resistance between two points of a circuit which are normally at different voltages This type of fault can generate high current flows, arcing and fire if not cleared quickly

© ABB Control Ltd ABB BS EN standard for Industrial Switchgear & BS EN60898 for Domestic Circuit Breakera An explanation of the terms

© Abb Control Ltd - 4 ABB The British Standards BS EN ( Industrial switchgear ) BS EN ( Domestic circuit breakers )

© Abb Control Ltd - 5 ABB BS EN Which section ? EN for Circuit breakers EN for Switches EN for Motor protection EN for Auto changeover

© Abb Control Ltd - 6 ABB BS EN Icu - Ultimate Short Circuit breaking capacity O - 3 min - CO ALL at full fault level Breaker must be intact and be able to pass insulation resistance test at the end of the test Breaker does not need to able to carry full rated current continuously without overheating after test Ics - Rated duty Short Circuit Breaking capacity Often expressed as a % of Icu O - 3 min - CO - 3min - CO The test may be at fault level lower than Icu value Breaker must be intact and be able to pass insulation resistance test at the end of the test Breaker MUST be able to carry full rated current continuously without overheating after test Note: O test begins with breaker closed before current applied CO test requires breaker to close onto fault current

© Abb Control Ltd - 7 ABB BS EN Icw - Rated Short-time Withstand current Preferred rating - 1 sec Limits are 12x In or 5kA whichever is greater for In <= 2500A 30kA for In > 2500A Utilisation Category A type - Instantanous type B type - Selective short circuit B type MUST have withstand (Icw)rating defined Icm Rated duty Short Circuit Making Capacity

© Abb Control Ltd - 8 ABB BS EN It is recommended that circuit breakers are examined for contact and arc chute damage after every fault clearance Icu/Ics values mean breakers can be put back into temporary service after fault clearance

© Abb Control Ltd - 9 ABB Definitiions within BE EN In – Nominal current rating Iu – Rated uninterrupted current Ue – Operational Voltage

© Abb Control Ltd - 10 ABB AC/DC Distribution Which mcb curve? BS EN B type General purpose lighting & power Magnetic setting 3 - 5x In BS EN C type Industrial application with high surges Magnetic setting x In Different devices for DC applications above 60V