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Hi, I am a retired IT professional. In the past I have worked for some large companies and for the last 10 years of my working life I was providing IT support for private clients and small and medium sized enterprises.


Although I have no electricians qualifications, I have always undertaken domestic projects. I am mindful of the risks when working with electricity and take safety seriously.


I have a garage which was built in the 1980s and at that time was electrically connected to the house. The circuit is protected by a 30mA RCD and 20A MCB in the house CU. The incoming cable to the garage is T and E, the live and neutral wires are 2mm in diameter and the earth is 1mm in diameter. In the garage this connects to an old fuse box with one 30A ring and one 5A lighting circuit. The garage also has a water pipe and a gas pipe and meter although there are no gas services. There is no earth bonding to either the water or gas pipes. The existing wiring is old and needs to be replaced.


Ideally I wanted to replace the old fuse box with a CU and rewire the ring and lighting circuits to new sockets and lighting fixtures. The size and capacity of the incoming cable raises some issues causing me to re-think my approach. I have the following scenarios and I would be grateful for any views or suggestions on the best way forward.


Option 1


Leave existing fuse box and just replace the ring and lighting circuits.


Option 2


As option 1 but add equipotential bonding using 10mm2 cable to the incoming water and gas pipes.


Option 3


Replace old fuse box with new CU with RCD and two MCBs, one 6A for lights and one 20A for ring (downgraded because of the protection provided in the house CU). Replace ring and lighting circuits. Add equipotential bonding.


Many thanks for any thoughts and suggestions.
 

buzzlightyear

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Arms
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Option 1


Leave existing fuse box and just replace the ring and lighting circuits.


Option 2


As option 1 but add equipotential bonding using 10mm2 cable to the incoming water and gas pipes.


Option 3


Replace old fuse box with new CU with RCD and two MCBs, one 6A for lights and one 20A for ring (downgraded because of the protection provided in the house CU). Replace ring and lighting circuits. Add equipotential bonding.
option 4
or get a spark in to have look at it.
 

buzzlightyear

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Arms
Esteemed
I have a garage which was built in the 1980s and at that time was electrically connected to the house. The circuit is protected by a 30mA RCD and 20A MCB in the house CU. The incoming cable to the garage is T and E, the live and neutral wires are 2mm in diameter and the earth is 1mm in diameter. In the garage this connects to an old fuse box with one 30A ring and one 5A lighting circuit. The garage also has a water pipe and a gas pipe and meter although there are no gas services. There is no earth bonding to either the water or gas pipes. The existing wiring is old and needs to be replaced.
I assume the garage feed is micc .
 
firstly you need to identify the csa of the supply from the cu in the house. It may be necessary to replace it with a larger cable if you want a 32amp ring etc
 
Option 5. Get rid of the fuse box and wire the sockets direct as a radial. Run the lights via a switched FCU (which is also your switch) with a 5 amp fuse.

You don't need a second RCD in line. You don't need a second 20 amp fuse in line.
 

Spoon

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Mentor
Arms
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Option 5. Get rid of the fuse box and wire the sockets direct as a radial. Run the lights via a switched FCU (which is also your switch) with a 5 amp fuse.

You don't need a second RCD in line. You don't need a second 20 amp fuse in line.
What about the gas and water pipes?
 
  • Thread Starter Thread Starter
  • #7
I assume the garage feed is micc .
Not sure, the cable has been laid underground from the house to the garage and it is whatever would have been used in the 80s. I can see that it is an AEI cable rated at 600/1000 and is probably in a PVC sheath.
 

buzzlightyear

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Arms
Esteemed
Why do you assume that Buzz?
just a hunch Peat , no good spark would put tand e in a ground and think they would get away with it.
 

littlespark

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Arms
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just a hunch Peat , no good spark would put tand e in a ground and think they would get away with it.
No one mentioned a “good spark” put it in.

There is a number of jobs here that need professional help on site. The bonding may or may not be required considering the pipe material and the presence of RCDs.
Why wasn’t the pipes bonded originally? An older house like that, I would have thought it necessary back then.
Can you check the size of the cable? You gave us a diameter rather than the cross section area which we are used to. If you can’t find it printed on the sheath somewhere, take a photo.
We like photos.
 
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