first year apprentice question: protected/unprotected neutral

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Dez LMS

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was wanting someone to explain protected and unprotected neutrals on a switchboard please. Thaaaaaaaaaaaaaaaaaankyou.
 

broadgage

Senior Member
Location
London, England
Here in the UK terminology varies somwhat, but I have heard the term "protected neutrals" used in two different contexts.

Firstly protected or not against being touched, some would argue that since the neutral should be at or very close to earth/ground potential, there is no requirement to protect neutral conductors against touch. (remember that until recently the NEC permitted, under certain conditions, the grounding of large appliance frames to the neutral)

Alternativly I have heard the term used to mean that the neutral conductor feeding a switchboard is protected against overload. In the UK and I presume elswhere,3 phase service entrance cables and large feeders within buildings sometimes have a half sized or even smaller neutral. This leaves the risk, in theory, of overloading the neutral. To protect against this, special circuit breakers were used that measured the neutral current but opened the phase conductors if the neutral became overloaded.
Modern practice is to use full size neutrals in most circumstances.
 
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