rmu

<...what is mean by ring main unit ? and how it work ?...>

The ring main is a style of wiring used primarily in the UK for 13A socket outlet circuits to BS1363. The circuit is usually arranged in a ring of 2.5mm² twin-and-earth cable that leaves the distribution board, passes around in a ring, and arrives back at it again from a different direction. Any number of 13A sockets can be attached to a ring circuit, though it shouldn't cover more than 100m² of building room area.

Each circuit will therefore have two live tails, two neutral tails and two earth conductors to be connected. A simple continuity test can be used to prove the integrity of all conductors in the ring.

The distribution board is sometimes referred to as a "ring-main unit", though this term, which derives from the time that homes were being re-wired with ring mains instead of traditional radial circuit wiring, is falling out of fashion.

The circuit is usually fed these days from a 32A type B breaker. Older installations with 30A fuse wire protection can still be found; these can be serviced and maintained, though not installed from new.

<...where i get catlogs for the same ?...>

Oh, any number of places, though they are available off-the-shelf from a number of major home improvement outlets. Please be aware that installation and testing, unless replacing like-for-like, may be subject to the Local Authority notification beforehand and qualified person testing afterwards under Part P of the Building Regulations. If in doubt, consult a professional electrical installer that has Part P accreditation. On completion of the installation, a copy of the installation test certificate needs to be lodged with the Local Authority before a Completion Certificate can be issued for the works, the absence of which will prevent the property from legally changing hands.

Hi,

In EHT systems, there will be one incoming feeder. There will be an alternative feeder also for the Substation which will give the necessary redundancy.

In simpler terms whichever Substation having the above is in Ring Main System.

N.Suresh