DIY Doctor


Postby Garry4093 » Sun Mar 08, 2009 8:48 pm

Could someone explain to me, in laymans terms, the difference between single and double pole MCB's and am i right in saying that these are the modern equivelent to the old style fuses in a consumer unit? am i also correct in saying things like electric water heaters (tanks) and electric cookers require a double pole MCB


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Simply Build It

Postby sparx » Mon Mar 09, 2009 7:28 pm

Hi, Garry4093,
Single pole MCB's just disconnect the Line (live) conductor & are the normal type fitted in consumer units, they are the equivelent of a fuse.
Double pole MCB's are in fact rarely used, they isolate both Live & Neutral conductors & the most used place for them is on garage petrol pump supplies due to requirement of petroleum regs to give full isolation.
Double pole switches however are very common, used for cooker/shower/immersion circuits and in fused connection units(fused spurs) & increasingly in socket outlets.
The increased use of RCBO's (combined MCB/RCD) units which have both L&N connected through them has mislead many to think they are double pole devices but 99% of them are not, the N is solid connection through the unit and is only there to allow the RCD part to see the flow & return current,
hope this helps, regards SPARX
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