Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, about double-pole circuit breakers and what they protect, is answered by SELECT:
Answer: You are referring to a double-pole circuit breaker, generally used more in the UK for 110V circuits supplied via a centre tap transformer, which have two live poles that require to be isolated and/or protected. They are used more in Europe for 230V circuits, but are and relatively little used in the UK, though they are available.
As you mention, such circuit breakers provide isolation of both line and neutral conductors and also provide appropriate overcurrent protection. Under normal load conditions, the current in the line conductor will also flow in the neutral conductor. Overcurrent conditions result in a higher current flowing in the line conductor. Neutral current will be dependent upon the type of overcurrent conditions.
In BS7671:2008, there is generally no requirement to switch a final circuit neutral for a TN system.
To see many more Q & A in Voltimum UK's Experts Area, please click on the link:
www.voltimum.co.uk/consult.php?universe=consult.index.questions