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!

 

[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.