4 Core SWA linking two legs of a ring circuit

[Chris Packet]

Hi folks, I'm recently qualified so be nice...

I'm preparing a quote for the wiring of a dozen up and over garages which are in two rows of 6 and face each other with an 11m gap. One double socket per garage and fcu for a single 1500 fluorescent fitting. I was planning to wire them all as one ring circuit and use swa 2.5mm 4 core to link the two rows. Singles and pvc conduit for the wiring in each row of garages and then wiska box for the connection to the swa.

The armour would be the cpc so it wouldn't be a ring as such. I couldn't find anything in the regs which says it's a no no but I'm open to anyone opinions on this. It's obviously cheaper than running 2x 2.5mm swa cables but would it still be classed as a ring circuit?
I was hoping to use this job for my part p assessment so it has to be a perfect job. Feedback welcome.

Thanks!

 

[Sintra]

I would be more inclined to install 2 radials.

 

[Plonker 3]

As Sintra said, if someone decideds to overllad the circuit at least you have the ability to still have the lights working rather than losing everything in the garages.

 

[telectrix]

as they both said. ^^^^^

 

[guest119]

What is an up and over garage?

 

[davesparks]

Probably a garage with an up and over door

 

[cornishboy]

Separate radial to each garage with a 2 way garage unit with rcd in each unit controlled from one board least that way if u ever have to meter each one separately u can , don't think I would really like to rely on the swa for coc if they are rented out if people fiddle all the other units may loose the earthing too, garage units no more than 25 to 30 quid now and control gear and bg do a good one

 

[ipf]

Who'd be paying for the juice ?

Area of more than 100m2, too, I'd imagine.

 

[Pete999]

who is going to pay the electricity bill???

 

[Knobhead]

Run two lollipop rings, one for each row of garages.

I was going to make a suggestion but at a guess this is a cheap job not quality so I’ll not bother.

 

[Octopus]

1 ring? 2 radials? 12 seperate garages - are they used by multiple owners?

 

[Knobhead]

The whole setup sounds cheap and nasty to me. it would be interesting to know where this is fed from.

 

[Engineer54]

As usual, far too little information about the installation to give any meaningful advice!! We don't even know the construction material of these garages (metal, prefab concrete, brick, etc) or the supply source and earthing system to be used??

At the moment rather than being perfect, it could well end up a perfect cock-up!! lol!!

 

[7029 dave]

All tapped off the local street lighting.

 

[Guest77]

Hi folks, I'm recently qualified so be nice...

I'm preparing a quote for the wiring of a dozen up and over garages which are in two rows of 6 and face each other with an 11m gap. One double socket per garage and fcu for a single 1500 fluorescent fitting. I was planning to wire them all as one ring circuit and use swa 2.5mm 4 core to link the two rows. Singles and pvc conduit for the wiring in each row of garages and then wiska box for the connection to the swa.

The armour would be the cpc so it wouldn't be a ring as such. I couldn't find anything in the regs which says it's a no no but I'm open to anyone opinions on this. It's obviously cheaper than running 2x 2.5mm swa cables but would it still be classed as a ring circuit?
I was hoping to use this job for my part p assessment so it has to be a perfect job. Feedback welcome.

Thanks!

Yes we can see that, how about some info then, amount of sockets, length of runs, OCPD, earth arrangement, calculations regarding volt drop etc etc etc.

 

[Chris Packet]

Thanks for your replies. I'll ignore the rude/uselesscomments and respond to the more constructive ones. The garages are 1970'sconcrete block construction. At themoment one row of garages is supplied with 4mm swa on a 32A RCBO put in by aprevious sparky which goes to a single outside socket. It's fed from a small dbin the electrical room at the base of the flats.

This does limit me as the client has asked for power andlighting in each garage plus 2x security lights outside. So that will be 12sockets, 12 fluorescent lights and two security lights minimum. Two radialcircuits seems to be the way to go, I just thought a ring circuit would giveeach garage a better choice for extra sockets in the future. I'll use fcu forthe lights in the garages and the security lights.
I'm planning to fit a meter box with a garage cu with rcdmain switch and wire a radial circuit for each row on a 20A. Or maybe RCBO eachrow of garages. I'd change the 32A feed rcbo to an mcb.
I've calculated volt drop with 2.5mm cable and it's ok witha load of 9A. That's with a cable run of 40m which is being generous. I can'tsee anyone plugging in anything larger than a 2kw heater.
It's a block of flats so all the residents will be payingfor this hence why only one socket per garage and it will be used occasionallyhopefully.
TNS earthing arrangement at the flats but I was planning toinstall an earth spike and make the garages a TT system. Don't shoot me down!Everyone seems to have a different opinion on this.

 

[Engineer54]

One thing i wouldn't do, and that's TT'ing this installation, that will achieve Nothing!! Keep with the far superior TN-S earthing system, unless you can guarantee TN Ra results that is...

I'll let others comment on the proposed installation itself!!

 

[davesparks]

Why on earth do you want to ditch the TNS??

Why did you calculate VD with a load of 9A? It's a socket circuit which could have any load up to its OCPD rating plugged in to it.
Did you include the existing supply cable in the VD calculation ? And what % VD did you use for compliance?

 

[VoltzElectrical]

Thanks for your replies. I'll ignore the rude/uselesscomments and respond to the more constructive ones. The garages are 1970'sconcrete block construction. At themoment one row of garages is supplied with 4mm swa on a 32A RCBO put in by aprevious sparky which goes to a single outside socket. It's fed from a small dbin the electrical room at the base of the flats.

This does limit me as the client has asked for power andlighting in each garage plus 2x security lights outside. So that will be 12sockets, 12 fluorescent lights and two security lights minimum. Two radialcircuits seems to be the way to go, I just thought a ring circuit would giveeach garage a better choice for extra sockets in the future. I'll use fcu forthe lights in the garages and the security lights.
I'm planning to fit a meter box with a garage cu with rcdmain switch and wire a radial circuit for each row on a 20A. Or maybe RCBO eachrow of garages. I'd change the 32A feed rcbo to an mcb.
I've calculated volt drop with 2.5mm cable and it's ok witha load of 9A. That's with a cable run of 40m which is being generous. I can'tsee anyone plugging in anything larger than a 2kw heater.
It's a block of flats so all the residents will be payingfor this hence why only one socket per garage and it will be used occasionallyhopefully.
TNS earthing arrangement at the flats but I was planning toinstall an earth spike and make the garages a TT system. Don't shoot me down!Everyone seems to have a different opinion on this.

This is totally unacceptable. What happens when someone sets up a growing room in their garage. Is everyone going to split the bill?

This is potentially a major source of conflict and I wouldn't touch it with a bargepole. The landlord is well out of order instructing this setup.

 

[Guest77]

Thanks for your replies. I'll ignore the rude/uselesscomments and respond to the more constructive ones. The garages are 1970'sconcrete block construction. At themoment one row of garages is supplied with 4mm swa on a 32A RCBO put in by aprevious sparky which goes to a single outside socket. It's fed from a small dbin the electrical room at the base of the flats.

This does limit me as the client has asked for power andlighting in each garage plus 2x security lights outside. So that will be 12sockets, 12 fluorescent lights and two security lights minimum. Two radialcircuits seems to be the way to go, I just thought a ring circuit would giveeach garage a better choice for extra sockets in the future. I'll use fcu forthe lights in the garages and the security lights.
I'm planning to fit a meter box with a garage cu with rcdmain switch and wire a radial circuit for each row on a 20A. Or maybe RCBO eachrow of garages. I'd change the 32A feed rcbo to an mcb.
I've calculated volt drop with 2.5mm cable and it's ok witha load of 9A. That's with a cable run of 40m which is being generous. I can'tsee anyone plugging in anything larger than a 2kw heater.
It's a block of flats so all the residents will be payingfor this hence why only one socket per garage and it will be used occasionallyhopefully.
TNS earthing arrangement at the flats but I was planning toinstall an earth spike and make the garages a TT system. Don't shoot me down!Everyone seems to have a different opinion on this.

2 mistakes IMO, that double socket in the garage will have 2 multi extention leads plugged into it, a heater, a lawnmower, freezer and wood working machine plugged in to start haha

 

[Chris Packet]

Hmmm good points about the bill being split and I'll have a look at the volt drop again. The main argument I keep hearing for an earth spike is that the loop readings will probably be too high without one and why wouldn't you put one in?

It's only a quote at the end of the day but one that could easily spiral into a right cluster hence why I thought I'd get some opinions!

 

[VoltzElectrical]

Hmmm good points about the bill being split and I'll have a look at the volt drop again. The main argument I keep hearing for an earth spike is that the loop readings will probably be too high without one and why wouldn't you put one in?

It's only a quote at the end of the day but one that could easily spiral into a right cluster hence why I thought I'd get some opinions!

Unless you are already on a TT system, an earth spike won't bring the readings down, and given my previous point, is the least of the concerns regarding the viability of this installation.

Note that I don't use 'your concerns' as what you have been asked to do has been very poorly thought through by the customer.

 

[Engineer54]

Just think about someone using a JetWash outside his garage, many of which are over 2 KW, and even most vacuum cleaners run at around 1.6 to over 2KW as well.... Then think about the guy that just uses his garage to park his car in, maybe uses the light now and again, he'll be paying a portion for all his neighbours annual car cleaning costs etc!! lol!!

 

[HandySparks]

The occasional-use appliances aren't such a big deal.

However, someone leaving a heater on over the winter to keep his car (or workshop) warm could get mighty expensive.

 

[davesparks]

Hmmm good points about the bill being split and I'll have a look at the volt drop again. The main argument I keep hearing for an earth spike is that the loop readings will probably be too high without one and why wouldn't you put one in?

It's only a quote at the end of the day but one that could easily spiral into a right cluster hence why I thought I'd get some opinions!

That's a pretty big earth nest you 're planning to install if it's going to have a low enough Ra to lower your loop impedances!

You wouldn't put one in because on a TNS supply it will have no effect unless you install multiple long rods well spaced apart. (Earth nest) and get a reliable and very low (below 1ohm) Ra.

If your Calculated Zs is too high then a bigger cpc will do more good than adding an earth rod.

 

[Engineer54]

The occasional-use appliances aren't such a big deal.

However, someone leaving a heater on over the winter to keep his car (or workshop) warm could get mighty expensive.

It is, when you are talking about/in annual costs!!

They will all soon know who's leaving a heater on over winter, it'll be the only garage where there isn't any snow sitting on the roof!! lol!!

 

[Octopus]

All in all its a pretty stupid idea!

 

[Chris Packet]

That's a pretty big earth nest you 're planning to install if it's going to have a low enough Ra to lower your loop impedances!

You wouldn't put one in because on a TNS supply it will have no effect unless you install multiple long rods well spaced apart. (Earth nest) and get a reliable and very low (below 1ohm) Ra.

If your Calculated Zs is too high then a bigger cpc will do more good than adding an earth rod.

Well that's an interesting point, would it also make no difference on a TNCS system? (Gaps in my earthing system knowledge showing here...) Although with an rcd protecting the circuit the max Zs could be up to 1667 ohms and still comply in theory. Not that anyone would find that acceptable!

 

[amckay]

Maybe an afterthought, but you said a row of 6 garages with another row of six about 11meters opposite? Has the client requested external lighting to illuminate the "yard"? Maybe a few extra quid in it there too for a pint!

 

[VoltzElectrical]

Maybe an afterthought, but you said a row of 6 garages with another row of six about 11meters opposite? Has the client requested external lighting to illuminate the "yard"? Maybe a few extra quid in it there too for a pint!

Did you just completely IGNORE all of the much more important points regarding the viability of the proposed installation, and if so, why?

 

[Lucien Nunes]

Quite apart from the billing issues, one circuit for all the separate occupiers? What happens if one tenant has a dehumidifer which occasionally trips the RCD when its water tank leaks, or the OCP trips when seven heaters happen to come on at once on their thermostats? How is the landlord going to trace / identify the problem? Doesn't meet basic design requirements by my book.

 

[VoltzElectrical]

Quite apart from the billing issues, one circuit for all the separate occupiers? What happens if one tenant has a dehumidifer which occasionally trips the RCD when its water tank leaks, or the OCP trips when seven heaters happen to come on at once on their thermostats? How is the landlord going to trace / identify the problem? Doesn't meet basic design requirements by my book.

Totally agree, well put.

 

[VoltzElectrical]

DNO supply to external street lighting type pillar, then radial to each garage each with it's own meter.

 

[Octopus]

Or what happens when one tennent decides to grow "things" in his garage!

 

[VoltzElectrical]

Or what happens when one tennent decides to grow "things" in his garage!

Not a problem if they are the only ones paying for all those UV lights, heaters, ventilation units.

Hang on, how come I know so much about it!

 

[ipf]

Or what happens when one tennent decides to grow "things" in his garage!

Pinocchio.....plenty tall tales around.

 

[amckay]

Maybe an afterthought, but you said a row of 6 garages with another row of six about 11meters opposite? Has the client requested external lighting to illuminate the "yard"? Maybe a few extra quid in it there too for a pint!

Did you just completely IGNORE all of the much more important points regarding the viability of the proposed installation, and if so, why?

Yes, I'm having problems with the forums phone app.
But I can now see Chris' post re, clients requests.

 

[urbanmonkey]

I'm not usually one to jump in with the rest of you keyboard warriors and jump on people but in this case if the OP by his own admission doesn't have much knowledge of Earthing systems (basics) then perhaps this job may not be suitable for him. No offence, but if I didn't know that putting in an Earth spike won't do anything to TN-S/TN-C-S Ze values then I wouldn't be attempting a can of worms like this one.

Personally I wouldn't touch it, far too many problems when joe public cotton on to the fact they aren't solely responsible for the bill... 11 tumble driers anyone?

 

[VoltzElectrical]

Earthing is the least of the problems of this proposed installation, but point taken.

 

[Chris Packet]

Yep a lot of fair comments about this job and I'm still learning but earthing at outbuildings seems to be one of the most disputed topics among sparks. I've seen a lot of earth spikes on outbuildings on TN earth systems and I've been told on more than one occasion if in doubt, put a spike in.

Extraneous conductive parts seems to be the deciding factor in whether to TT an outbuilding am I right?

 

[Octopus]

Matey, I'd walk away from this - it will turn into a pile of poo!

 

[urbanmonkey]

'If in doubt put a spike in' is a cop out used by too many sparks, if you are at the start of your career, please don't fall into this lazy mans trap. Caravans, long runs to buildings/structures with pipework etc in and agricultural buildings with a lot of metal stuff about are a different ball game, all have their different reasons for not extending the equipotential zone to them and each case should be considered on an individual basis, not just 'come on billy lets knock a rod in'

I know it's hard to find work when you first start out and you don't want to turn anything away but this job has all the hallmarks of a pain in the buttocks for you and not something you need when you are trying to get yourself off the ground. Not having a go chap, just offering some friendly words of advice.

 

[davesparks]

The point about faults above is quite important.

There will inevitably be a freezer in one or two of these garages. So when someone else uses something in their garage which trips the RCD on Saturday morning and the electrician comes out to investigate on Monday, who's going to pay for the contents of the freezers?

 

[davesparks]

Well that's an interesting point, would it also make no difference on a TNCS system? (Gaps in my earthing system knowledge showing here...) Although with an rcd protecting the circuit the max Zs could be up to 1667 ohms and still comply in theory. Not that anyone would find that acceptable!

Adding a decent earth rod/nest connected to the MET of a TNCS system has it's advantages and is advisable in some situations but still won't help the Zs values in the installation.