garage install

[wannaspark]

Hello to all wondering if any one can help on the install i have just carried out.my garage is detached from the house so to put electric into it i have ran some 2.5mm swa (buried) to it and connected it to a volex garage cu with a 30ma rcd 1x 32a mcb for the socketsx4 and a 6a mcb for the lighting 3x flourescent tubes.back in the house it is connected from the upstairs ring main to a 13amp fused spur ie 2.5mm t&e going into fused spur and 2.5mm swa coming out leading to garage.the main cu has 100ma main switch/rcd and the upstairs ring is connected via a 32a mcb my question is would that be a safe configuration bearing in my its a old stlye house and the cu is a pain to get cables in/out of, any help greatly appreciated cheers:dozey:

 

[telectrix]

i would replace the fused spur with a 20A MCB in an enclosure. change the garage 32A MCB for a 16A and just have a radial in the garage . FCU at 5A off that for the lights. the connection in T/E in the house must not be buried in plaster without 30mA RCD protection, but it can go through the wall.

how are you providing the garage with earthing? and are there any extraneous metal parts, e.g. water pipes etc. in the garage?

 

[wannaspark]

thanks for that there are no water pipes etc in the garage earthing is via swa as stated before should i have a separate earth point? would or could these connections cause nuisance trips back at the cu the only thing left on overnight in the garage is the alarm hardwired and a floodlight pir activated:vanish:

 

[Richard Burns]

Your install seems OK but not ideal; in general as the easiest way to do it, but you are limited to max 13A in total for the garage because of the FCU from the ring.
Your 32A MCB in the garage will never trip as the 13A fuse would go first then the 32A MCB in the house.
telectrix has given a good and workable solution to give the max capability, though I would stick with the 6A MCB in the garage CU for the lights rather than FCU off the radial, just for convenience.
No separate earth required, as no bonding required.
Have you taken into account voltage drop (depending on where the garage is from the house and how long a cable is required?

Unlikely that there is sufficient discrimination between the 30mA RCD and 100mA RCD to avoid nuisance trips, but if your whole house is on the 100mA any fault will take out the whole house whether inside or out so no real change, but if there are no faults then no problem.

 

[wannaspark]

Thanks for that richard will try those suggestions some time over the weekend if other committments (and the wife) allow cheers

 

[telectrix]

yeah 13A is a bit limiting if you want , say, to use some form of heating in the winter. that's why i suggested beefing it up to 20A.

 

[wannaspark]

how or what would you suggest is the best course of action to take to stop the whole of the house being plunged into darkness when a trip does occur the cu layout is as follows (not forgetting garage is still on upstairs ring) cu is proteus not split load.
upstairs skts 32A mcb downstairs skts 32Amcb upstairs lights6A mcb downstairs lights6Amcb outside floodlight 6Amcb 100ma main switch/rcd the reason i ask is this week we have had 2 x trips 1 during the day with only tv on and 1 very early morning ie 3.30 when landing light is left on for disabled daughter none of mcb's have tripped but only main switch.

 

[Octopus]

Replace the CU??

 

[telectrix]

as above. dual RCD or RCBO board

 

[wannaspark]

no sooner had i just asked the question about trips and the main switch has just tripped again this time the main thing working was the dishwasher on further interrogation to the wife she informed me that the said dishwasher was on the last two times the trips occured

 

[Octopus]

no sooner had i just asked the question about trips and the main switch has just tripped again this time the main thing working was the dishwasher on further interrogation to the wife she informed me that the said dishwasher was on the last two times the trips occured

That at the very least gives you an idea where to start looking, or where the sparky needs to start looking!

Having a single RCD "protecting" the whole installation is not ideal, as you are now aware.

 

[malcolmsanford]

The problem is that you are now going down the road of fault finding on an RCD protected circuit, and though the logical path would be yes the D/washer was on each time, is it the dishwasher, you may have factors apart from the D/washer.

I noticed your OP name is wannaspark are you at all connected to the industry?, because there are several tests you can do on the RCD to make sure that it is healthy.

 

[telectrix]

i never plug my dishwasher in. she works perfectly well without electrickery.

 

[wannaspark]

what is the difference between putting garage sockets on a radial as opposed to its own ring(pardon the ignorrance but i am hoping to start doing a home study course as a spark just in case current job goes pop in current climate) thanks....

 

[Richard Burns]

If you are not a sparky nor a member of an approved Part P scheme then you should have informed building control before you started your install and they would assess the install at various points to ensure compliance with the regulations (and charge you a Building control fee) as the work you describe is notifiable work.

Rings and radials are different methods of achieving the same result. Various people have differing views on which is best. Ring circuits are a British invention and not usually used in other countries.
Ring circuits effectively use two cables to increase the current carrying capacity so that you can have 2.5mm2 cable with a 32A MCB even though the CCC of a single 2.5mm2 is only ~24A because you have twice the cross sectional area. They are more complicated to test for safety than ring circuits, because of the potential for one cable to be disconnected or to have links across the ring; the circuit would still work but may be overloading the cable.
Radial circuits only use one cable so in order to use a 32A MCB you would need to use 4mm2 cable. You would be limited to 20A for a 2.5mm2 cable.
Depending on the installation it may be best to use one or the other. For a true ring starting and finishing close to the CU you would you less cable and it would be cheaper. For a long circuit ending far away from the CU a radial may be best.