New sockets in workshop

Fireblade · Mar 7, 2011

Hi All

First post, so hope it's in the right place and I've followed all the rules...!!

Been asked to quote on a job which in the workshop of a car dealership. Job is to provide x2 new socket outlets. Original installation has numerous three phase DB's, not to mention all the steel conduit throughout the workshop for all the obvious reasons.

My thoughts are to avoid having to fit new steel conduit but to run 2.5mm 2 core SWA (utilising armour as CPC) from an existing switched double socket to a new switched FCU and then feed x2 double sockets as a radial from the new FCU again in 2.5mm SWA with the amour utilised as the CPC.

Any thoughts/comments

Cheers

Adam W · Mar 7, 2011

Aren't we assuming that the sockets are going to be used for some kind of mechanical equipment and not for an office area in the corner, and therefore wouldn't need rcd protection as it's surface mounted, protected by earthed metallic sheath and being used by skilled or instructed operatives?
Unlikely, but it was unlikely the Titanic would sink.

Adam W · Mar 7, 2011

My money's on 'ring' as well, hence "then feed x2 double sockets as a radial from the new FCU".
If it was a radial anyway there would be no need to specify - you wouldn't add a ring to a radial.

flukey · Mar 7, 2011

im with novus

Hawk81 · Mar 7, 2011

NovusSparkus said:
My money's on 'ring' as well, hence "then feed x2 double sockets as a radial from the new FCU".
If it was a radial anyway there would be no need to specify - you wouldn't add a ring to a radial.

Exactly the point I was making.

Fireblade · Mar 7, 2011

Hi Guys....

Wow, didn't expect so much feedback and so quickly - only popped downstairs for my dinner!!

Yes, it's a final ring with RCD protection.
Client is not worried about esthetics and therefore SWA will be fine.
Loading is low, hence a 13A fuse will surfice - however, I think I will hard wire in equipment to prevent some "dumb dumb" plugging goodness knows what in the future!!!

Am very keen to know why the general feeling is that 3 core SWA is a the route to go - surely earthing the amour and then having the third core as earth is beyond what is required. More than happy to take your advise but am interested as to what the rationale behind it is?

Look forward to your comments.....

Cheers

keefy · Mar 7, 2011

Hi Fireblade,

3 core SWA is usually prefered as the armour cannot always guarantee sufficient CSA to withstand a fault current. For a 2.5 SWA, you need to calculate the minimum size of the CSA of the SWA (k1 over k2 x S) and you get 7.77mm. 2.5 has 17mm CSA of SWA so that is well in. Some cables (10mm 2 core for example) do not comply once calculated so many people are adverse to installing 2 core, especially on 230V where 3 core is easy to use instead. However, you try getting the stuff. I have just had to wait a week for 50M of 2 core 6mm!

Even if you do use 3 core you should still fit the earth tags, bolts and some cpc. And on sockets that can sometimes be tricky if you are going side entry or have a few cables in the one box. For short, straight runs steel conduit or bush & coupling would be better. I recently saw a job where there was 6 sockets lined up on a wall 1M apart, all had short runs of SWA between them. Ughh, Ugly and no doubt time consuming to make of so many ends.

Hope that clears things up... or muddies the water further.

Knobhead · Mar 7, 2011

Do it in conduit! It will fit in. Plus there’s pride in the job

malcolmsanford · Mar 8, 2011

Do it is conduit as Tony says it will be in keeping with the rest of the installation, ....................and use the conduit as your CPC if it is suitable.

If your determined to use SWA then for crying out loud use a 2 core and the SWA as the CPC. What will be the maximum size of the CSA 1.5mm off a FCU and if your going to use normal 70c type PVC then you need an SWA equivilent of approx 3.5mm to equate to a copper conductor, and the CSA will in fact give you 15mm

somersetsparks · Mar 8, 2011

I would use 2-core, if your gonna go to the trouble of banjos etc. might as well use the armour, scratch the paint off from behind the locknut and fit serrated washers is what I would do, rather then banjos, they are a right pain on metalclad sockets if you have more then one cable.
3- core is way OTT really, although cost difference is probably negligable.
I would also always use a CW type gland personally, they are much better quality generally, and then you get less condensation rusting the armouring especially in workshops!

Hawk81 · Mar 8, 2011

malcolmsanford said:
Do it is conduit as Tony says it will be in keeping with the rest of the installation, ....................and use the conduit as your CPC if it is suitable.

If your determined to use SWA then for crying out loud use a 2 core and the SWA as the CPC. What will be the maximum size of the CSA 1.5mm off a FCU and if your going to use normal 70c type PVC then you need an SWA equivilent of approx 3.5mm to equate to a copper conductor, and the CSA will in fact give you 15mm

I dont know if it is just me or if anyone thinks the wording in this reply is a bit ott. saying things like "if you are determined" and "for crying out loud" is not needed. espcially when you are saying it over something like the use of 2 core or 3 core. its not like using 3 core was going to make the job any less safe. also if the op wants to do it in swa that is their choice. This is a new member to the forum and talk like this might not encourage them to return with more questions. Well thats my opinion anyway.

Adam W · Mar 8, 2011

Hawk81 said:
I dont know if it is just me or if anyone thinks the wording in this reply is a bit ott. saying things like "if you are determined" and "for crying out loud" is not needed. espcially when you are saying it over something like the use of 2 core or 3 core. its not like using 3 core was going to make the job any less safe. also if the op wants to do it in swa that is their choice. This is a new member to the forum and talk like this might not encourage them to return with more questions. Well thats my opinion anyway.

Well I didn't agree with any of that post - I would use 3 core not 2 core, I wouldn't use the armour or conduit as the CPC (especially for a final cct) and Tony wasn't the first to suggest extending the installation in conduit.
... And yes the language could be considered harsh but of course everyone is entitled to their opinion regardless of how much I disagree with them.

There's some guy who comments on the stories in my local paper and always seems to feel the need to express his opinion as "completely" this, "totally" that and "absolutely" the other. I think it makes someone's view sound overly opinionated, but again that's just me. Maybe he's just gone "utterly" butterly.

flukey · Mar 9, 2011

if the cable complies, which 2 core does then that would be my choice if i was to use swa, but as previously said i would be more inclined to stick with conduit as per existing install

malcolmsanford · Mar 9, 2011

Hawk81 said:
I dont know if it is just me or if anyone thinks the wording in this reply is a bit ott. saying things like "if you are determined" and "for crying out loud" is not needed. espcially when you are saying it over something like the use of 2 core or 3 core. its not like using 3 core was going to make the job any less safe. also if the op wants to do it in swa that is their choice. This is a new member to the forum and talk like this might not encourage them to return with more questions. Well thats my opinion anyway.

I have to say to start this that if I caused any offence to the op then that was defrinately not my intention as in his original post he was wanting to use 2 core SWA for a 13amp sub circuit of a final circuit via a FCU. If he did think I was OTT to quote your reply I do appologise as he got the circuit design spot on.

The for "crying out loud" was meant at you and the 4 or 5 others trying to convince him that for a small SWA feeding 2 sockets required a dedicated conductor, and then we get the tome from another poster which had no bearing at all on this thread or question.

If people can not be bothered to design a circuit correctly using calculations, then that is fine if that is their choice., but the OP designed his correctly and then was advised that a 3 core would be better, my question is why? What advantage would a 3 core SWA give him in this scenario?

The remark about doing it in conduit still stands. Perhaps it was the elder members on here that advised him to do it in conduit as it would be keeping in the style of the existing installation. I still believe he as made the wrong choice in SWA, but that is his choice and that is that.

To the OP I sincerely hope I didn't offend you and if I did I appologise unreservedly, to the posters who were trying to persaude you from not installing to your perfectly acceptable design................I'll leave it there.

mogga · Mar 9, 2011

SWA into a metalclad socket (assuming m/C ) as Assumption is rife in this thread ) your best bet would be Bush n coupling as the gland encroaching into the socket depending on manufacturer will leave no room for face plate to fit

Hawk81 · Mar 9, 2011

malcolmsanford said:
I have to say to start this that if I caused any offence to the op then that was defrinately not my intention as in his original post he was wanting to use 2 core SWA for a 13amp sub circuit of a final circuit via a FCU. If he did think I was OTT to quote your reply I do appologise as he got the circuit design spot on.

The for "crying out loud" was meant at you and the 4 or 5 others trying to convince him that for a small SWA feeding 2 sockets required a dedicated conductor, and then we get the tome from another poster which had no bearing at all on this thread or question.

If people can not be bothered to design a circuit correctly using calculations, then that is fine if that is their choice., but the OP designed his correctly and then was advised that a 3 core would be better, my question is why? What advantage would a 3 core SWA give him in this scenario?

The remark about doing it in conduit still stands. Perhaps it was the elder members on here that advised him to do it in conduit as it would be keeping in the style of the existing installation. I still believe he as made the wrong choice in SWA, but that is his choice and that is that.

To the OP I sincerely hope I didn't offend you and if I did I appologise unreservedly, to the posters who were trying to persaude you from not installing to your perfectly acceptable design................I'll leave it there.

I think if you read my first reply again you will see I told the op his design was fine. It was only later that I said that I would use 3 core and I still stand by this. I do not understand why you are so against 3 core. Hardly any price difference and surely having a dedicated core is. Safer. I was in a workshop recently where the sockets were done in 2 core and the second socket on a 4mm. Radial had the gland broke out of the metal box and the other 5 sockets had no earth.