Domestic 3phase supply

[gtownspark]

Just been asked to do some work at a house with a 3phase supply. 1 phase supply's the main consumer unit for the house, and the other 2 phases go into an off peak meter then into an old contactor before supplying two separate single phase consumer units for storage heating. My question is should the whole system be isolated by 1 main 3phase switch? (At the moment it relys on the main switch in each CU to isolate each phase individually)

 

[trev]

Does it really need 3 phases mate? You could save your client a good bit of cash and earn massive amounts of brownie points here.
Ideally there would be isolation for each live conductor preferably in one unit so you didn't have to mess around looking for it

 

[gtownspark]

Well your probably right, but for the purpose of an EICR I wanted to know if it was compliant a it stands.

 

[pmanku]

Assuming there is no 3 phase machinery I cant see any additional requirement, although individual fuse switches wouldn't go amiss.

 

[Knobhead]

Now why would you sugest seperate fuse switches as opposed to a single isolation switch? There is no mention of long meter tails to warrant a fuse switch.

 

[Deleted member 26818]

To my mind, you have two meters, two supplies, two installations so should have two main switches.
One main switch for the single phase, and another for the two single phases supplying the storage heaters.

 

[gtownspark]

No long meter tails!

I always thought that if you have a 3phase supply you should be able to isolate it from one switch. If there is a main D B then the incomer would act as this or if you have a busbar you would require a main switch. In this case I have one phase each going to a seperate consumer unit albeit 2phases via a contactor so wasn't sure if it should be isolated by one main 3 phase switch, a 2 phase and a 1 phase switch or as it is now 3 seperate single phase switches.

On page 45 of OSG it says that in a TNCS 3phase system (which this is) an isolator must interrupt the line conductors at the origin of the installation.

Technically this has been achieved through 3 seperate isolators.....still not sure

 

[Deleted member 26818]

The requirement to provide a main switch relates to the installation, not to the number of phases.
537.1.4: "A main linked switch or linked circuit-breaker shall be provided as near as practicable to the origin of every installation as a means of switching the supply on load and as a means of isolation."...
What you have to my mind would be considered as two installations.
One installation for the peak side of things, and the other for the off peak.
Obviously whoever made the installation, considered it to be three installations.
What would be your thoughts for instance, if the building were split into three flats, with each flat being supplied by a single phase?