New circuits for shed.

[rog_yorks]

Hi. I own a large shed, currently served by 1 single socket, so need to make power points more accessible. My plan is to run two radial circuits, one down each side of shed with 4 double sockets on each circuit. Idea is to use 4.0mm2 t&e on a 32A rcbo for each circuit. Cable length from CU to last socket will be approx 44 meters on one side of shed and 38 meters on the other side. Shed is for my own personal use and will only be used to run light power tools, extra lighting, industrial vacuum, small PA system etc. Does this sound OK? Could I do it in 2.5mm2 on a 20A rcbo instead - i.e. cheaper cable and easier to connect I guess than 4.0mm? Any advice appreciated. I have no electrical qualifications, only many years of DIY jobs, so feel confident in actually doing the work but not sure on some of the technical specs etc.

 

[Pete999]

What size, type of cable is feeding the shed, and what is it fed from??

 

[rog_yorks]

Thanks for reply. Mains supply enters into another shed. Tails split into two large switch boxes. One switch supplies CU in first shed and second switch supplies the CU in shed I want to re-wire. Cable is flat twin core 16mm2 with a seperate earth cable.

 

[Pete999]

Thanks for reply. Mains supply enters into another shed. Tails split into two large switch boxes. One switch supplies CU in first shed and second switch supplies the CU in shed I want to re-wire. Cable is flat twin core 16mm2 with a seperate earth cable.

OK whats the shed fed from in the house, I presume it's a house, any RCDs in the picture and why 4mm cable when 2.5 would be ok for a radial

 

[rog_yorks]

No house on site, this is on the small holding I have inherited, just some land and several buildings. The mains supply in is to the first shed I mentioned and that is where the meter is. CU in shed I am wanting to work on has 100A mains switch, light circuit on a 6Amcb and the 1 single socket on a 32Amcb in 2.5mm2 cable. I didn't particularly want to use 4.0mm cable but I have read so much stuff about voltage drop etc on certain lengths of cable, hence as the run would be 40 meters plus I thought I was playing safe with 4.0mm, would much rather use 2.5mm if I know that would be OK. I originally thought of doing a ring circuit, right round the shed which would use about 100 meters of cabling and would certainly cover more than the 100 sq meters of floor space that I believe is the limit for a domestic ring, but this is a bit of a diffent situation, so would the ring circuit be the better option?

 

[Pete999]

No house on site, this is on the small holding I have inherited, just some land and several buildings. The mains supply in is to the first shed I mentioned and that is where the meter is. CU in shed I am wanting to work on has 100A mains switch, light circuit on a 6Amcb and the 1 single socket on a 32Amcb in 2.5mm2 cable. I didn't particularly want to use 4.0mm cable but I have read so much stuff about voltage drop etc on certain lengths of cable, hence as the run would be 40 meters plus I thought I was playing safe with 4.0mm, would much rather use 2.5mm if I know that would be OK. I originally thought of doing a ring circuit, right round the shed which would use about 100 meters of cabling and would certainly cover more than the 100 sq meters of floor space that I believe is the limit for a domestic ring, but this is a bit of a diffent situation, so would the ring circuit be the better option?

Big Shed then? two radials on 2.5mm would be OK still no mention of RCDs

 

[rog_yorks]

Yes it is a fairly big shed, roughly 220 sq meters floor space. Sorry for not mentioning RCD's. First shed consumer unit on an RCD main switch protecting lighting circuit and ring main on 6A and 32A MCB's respectively. Big shed has no RCD protection, just 100A main switch on CU and 32A MCB for the current single socket radial and 6A MCB for the lighting circuit. Hence I thought I will remove the 32A MCB and replace with 2 RCBO's for the 2 new radial circuits. Would these need to be 20A rather than 32A?

 

[Pete999]

Yes it is a fairly big shed, roughly 220 sq meters floor space. Sorry for not mentioning RCD's. First shed consumer unit on an RCD main switch protecting lighting circuit and ring main on 6A and 32A MCB's respectively. Big shed has no RCD protection, just 100A main switch on CU and 32A MCB for the current single socket radial and 6A MCB for the lighting circuit. Hence I thought I will remove the 32A MCB and replace with 2 RCBO's for the 2 new radial circuits. Would these need to be 20A rather than 32A?

Mate this is a far to complicated to be undertaken on a DIY basis, with drip fed information, you need to get a professional Electrician to quote for the work. to many imponderables to form a basis for advice.
Advising any further would be unprofessional, you're dealing with something that you do not have sufficient knowledge to do it safely, please get a sparky involved, there would be work you could do under supervision to keep the cost down, I can't in all sincerity advise any further.

 

[rog_yorks]

Mate this is a far to complicated to be undertaken on a DIY basis, with drip fed information, you need to get a professional Electrician to quote for the work. to many imponderables to form a basis for advice.
Advising any further would be unprofessional, you're dealing with something that you do not have sufficient knowledge to do it safely, please get a sparky involved, there would be work you could do under supervision to keep the cost down, I can't in all sincerity advise any further.

OK, thanks for your help and I appreciate all your comments. Maybe I have not made myself clear, I thought it was fairly straightforward as in I have a functioning CU installed and just wanted to run new radial circuits with RCD protection in the form of RCBO's and my main query was regarding what cable to use regarding length of run etc. I don't mean any offence at all but just wondered why you have now said it is not safe to advise when before I posted regarding RCD's you said radials in 2.5mm would be OK.

 

[Pete999]

OK, thanks for your help and I appreciate all your comments. Maybe I have not made myself clear, I thought it was fairly straightforward as in I have a functioning CU installed and just wanted to run new radial circuits with RCD protection in the form of RCBO's and my main query was regarding what cable to use regarding length of run etc. I don't mean any offence at all but just wondered why you have now said it is not safe to advise when before I posted regarding RCD's you said radials in 2.5mm would be OK.

PMd you

 

[telectrix]

@OP. assume you run 2 radials using 20A MCB/RCBO for each, in 2.5mm, the worst length case being 44m. using the mV/A/m calculation for 2.5mm, your volt drop can be calculated roughly at (18 x 20 x 44)/1000 = 15.8V ( it will actually be less than this as the load will reduce from socket#1 progressively.still will be high though, so 4.0mm radials or a 2.5mm RFC would be the options i'd consider.

 

[rog_yorks]

@OP. assume you run 2 radials using 20A MCB/RCBO for each, in 2.5mm, the worst length case being 44m. using the mV/A/m calculation for 2.5mm, your volt drop can be calculated roughly at (18 x 20 x 44)/1000 = 15.8V ( it will actually be less than this as the load will reduce from socket#1 progressively.still will be high though, so 4.0mm radials or a 2.5mm RFC would be the options i'd consider.

Thanks telectrix. Well those were kind of my ideas too but I don't have the knowledge or training to understand or work out the calculations, hence the post on this forum. If I do radials in 4.0mm should the RCBO be 32A? And a RFC (I guess this is the correct term for what I call a ring circuit) would be ok even though it will cover a much bigger floorspace area than is recommended in domestic installations? Would either RFC or radial circuit be preferable over the other?

 

[Octopus]

Given how big these sheds are what are you going to be using them for. ie what is the design load?

 

[rog_yorks]

Given how big these sheds are what are you going to be using them for. ie what is the design load?

Hi Murdoch, thanks for the reply. The shed is for my own personal use. Hoping to build house and live on my small holding in the future (slight difference of opinion going on here between the idiots, oops sorry I mean officers in our local planning department), and this shed will be my workshop/garage. Never intend to run more than light power tools, extra lighting like inspection lamps etc, industrial vacuum, maybe my son's guitar amp and small pa system when he rehearses. So really no more than in a normal domestic garage I guess, but spread out over a much bigger area. Hope that makes sense, sorry if I am rambling.

 

[bigspark17]

Id be more concerned with the earthing arrangement and wether the sheds are for livestock.?

 

[telectrix]

consideration should also be given as to whether cabling requires mechanical protection. no good clipping T/E in to find that it's going to be damaged, also whether or not metalclad sockets would be required. it really is a job for a qualified electrician.

 

[rog_yorks]

Id be more concerned with the earthing arrangement and wether the sheds are for livestock.?

Thanks bigspark. Definitely no livestock involved. I appreciate everyone's comments and it seems basically I am heading for the 'emply a sparky' solution but would still like to do it myself if I am convinced the job is safe. So still open to any advice. May be a while before I check this again as my wife thinks there are more important things in life than reading this forum...... huh, what does she know!

 

[HappyHippyDad]

Thanks bigspark. Definitely no livestock involved. I appreciate everyone's comments and it seems basically I am heading for the 'emply a sparky' solution but would still like to do it myself if I am convinced the job is safe. So still open to any advice. May be a while before I check this again as my wife thinks there are more important things in life than reading this forum...... huh, what does she know!

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