100 A mains isolater to Garage unit.

[Bathey]

If a want to spilt the tails after a 100A isolation switch does the 2nd DB ( a new garage unit ) have to have a 100 a main switch or is a 40a RCD OK ? I’m assuming because there is a 100a isolation switch then I don’t need a main switch in the garage unit. The garage unit will only be powering a ring main 32a and lighting 6A.

 

[Andy78]

I see you are a trainee. Have you asked your supervising electrician about this issue ?

 

[telectrix]

firstly you need a switch/fuse where you split the tails. the rating of this will depend on the load and size of cable feeding the sub.

 

[Bathey]

I see you are a trainee. Have you asked your supervising electrician about this issue ?

ive been told to spilt the tails after the main isolator. 1 feed of 25mm2 tails will feed the house and that is a 10 way board with an 100 amp main switch but then from the 2 feed off the Henley block where I will spilt it I can go to a garage board where an RCD is present as I won’t need an 100 amp main switch at that board as the 100 amp isolation switch before the henley blocks is fine. I have asked the guy I work with but as I’m OCD I check things 100 times and as lots of people.

 

[Andy78]

ive been told to spilt the tails after the main isolator. 1 feed of 25mm2 tails will feed the house and that is a 10 way board with an 100 amp main switch but then from the 2 feed off the Henley block where I will spilt it I can go to a garage board where an RCD is present as I won’t need an 100 amp main switch at that board as the 100 amp isolation switch before the henley blocks is fine. I have asked the guy I work with but as I’m OCD I check things 100 times and as lots of people.

As Tel says, overcurrent and fault protection should be provided for the garage circuit as for all circuits. The garage board should have a method of isolation within it such as a main isolator or RCD.

 

[telectrix]

yeah. for the anticipated load ( socket ring, and 1 lighting circuit.) the garage feed would ideally be 6.0mm, top of head , dependent on the run , installation method and VD. therefore you would need to fuse it at source at, say, 40A.this is where you'd use a switch fuse.

 

[Wilko]

Hi - my thought is the isolation switch rating should equal or exceed the nearest upstream overload protection. If the new switch fuse after the service connector block is 40A then the existing 40A double pole RCD should be ok as a local isolator in the downstream garage board.

 

[Bathey]

As Tel says, overcurrent and fault protection should be provided for the garage circuit as for all circuits. The garage board should have a method of isolation within it such as a main isolator or RCD.

Ok great - The garage unit has a 40A RCD this is the Method of isolation. So it’s fine then

 

[Andy78]

Ok great - The garage unit has a 40A RCD this is the Method of isolation. So it’s fine then

Just overcurrent and fault protection at the circuit origin to sort out then ?

 

[davesparks]

Ok great - The garage unit has a 40A RCD this is the Method of isolation. So it’s fine then

You need overcurrent and fault protection at the start of the circuit which feeds the garage.
What are you installing after the 100A isolator to protect the circuit which feeds the garage?
What type of cable are you using and how long is it?