Interested in your thoughts....

E

Engineer54

Here's one for you... I've been going through submittal drawings for a staff canteen, i won't go into too much detail but the means of access to the service counter is via below a modular tiled raised floor system from the DB.

The part of the submittal that i'm going to refer to, is the two ring circuits for the power outlets on the service counter to supply the various hot and cold drinks, food heating and cooling appliances etc.
They are proposing a 3 core 6mm SWA to a wall JB and a FRC within counter stud construction to a surface mounted dado type PVC trunking system housing the socket outlets etc wired in 2.5mm 3 core building cable, connected to the SWA via that wall JB. The use of the SWA is to conform to the project specification of only mechanically protected cables being allowed below raised floor areas.

So what are the thoughts on this arrangement, i'd be interested to know what others may think here??
 
I have come across this sort of arrangement before...the only issue I can see is the possible future difficulty in carrying out RFC tests,as the point where the radial becomes a ring may not be easily accessible for splitting and testing. Beyond that I cant see a problem. That said a 4.0mm 30a radial would possibly be a better solution.
 
Lenny said:
Are you working to BS 7671 mate???
Click to expand...

Another bone of contention Lenny!! Yes and No ...lol!! BS 7671 is one of the approved standards in the contract specifications. But basically calls for the highest international standards.. Something that i have to nail down without prejudice to the contractors!!
 
Only reason I ask is the description of a ring final circuit in app 15........"A ring final circuit starts and finishes at the distribution board"

Take that as you will.:stooge_curly:
 
Lenny said:
Only reason I ask is the description of a ring final circuit in app 15........"A ring final circuit starts and finishes at the distribution board"

Take that as you will.:stooge_curly:
Click to expand...

My thoughts exactly ...lol!!!
 
Chr!s said:
So a single 32 amp protecting the SWA and the two ring circuits? cant see know issues other assessing loads.
Click to expand...

Sorry, some confusion here...lol!! No a single 6mm SWA with it's own RCBO, feeds each FRC via separate flush wall connection/JB box with DIN rail connectors... Hope that clears up any confusion in my OP. ..lol!!
 
Lol, i'm non the wiser now.

So A 32 amp RCBO protecting the SWA, which feeds the JB Box, there two ring circuits are connected, will there be any protection provided for the ring circuits at the JB Box or are they reliant upon the 32 RCBO which also protects the SWA? Lol
 
Chr!s said:
Lol, i'm non the wiser now.

So A 32 amp RCBO protecting the SWA, which feeds the JB Box, there two ring circuits are connected, will there be any protection provided for the ring circuits at the JB Box or are they reliant upon the 32 RCBO which also protects the SWA? Lol
Click to expand...

2 SWA Circuits, each protected by an RCBO, each going to it's own JB box, each supplying a FRC. Each FRC supplying half the service counter. It's a fairly long counter with an extensive amount of various appliances as described in the OP. Any clearer now ?? lol!!
 
Last edited by a moderator:
Appendix 15 refers to a ring starting and ending at the dist board,but it also says for domestic and simmillar premises, so maybe app 15 may not be appropriate for refering too in this case


433.1.1 (ii) brb
The rated current or setting of the protective device does not exceed the lowest of the current carrying capacities of any of the conductors of the circuit

Its not a standard circuit as we know it but it complies with the above,
 
434.2.1
"The part of the conductor between the point of reduction of CSA or other change and the position of the protective device shall... ... not exceed 3m in length..."

Does that help?

ie are you fusing it down after the SWA, or could you just use, say, a 4mm radial throughout?
 
Last edited by a moderator:
The definition in the BGB of a ring is a final circuit in the form of a ring with a single point of supply, and effectively this is what you have, the single point of supply being the end of the SWA.

Or perhaps if the ring is parallel cables running down the counter you could wire it as a radial circuit with two parallel conductors! though I hate to think of the problems that could cause later.
 
Adam W said:
434.2.1
"The part of the conductor between the point of reduction of CSA or other change and the position of the protective device shall... ... not exceed 3m in length..."

Does that help?

ie are you fusing it down after the SWA, or could you just use, say, a 4mm radial throughout?
Click to expand...

Are you being serious here, or is this another chicken joke?? lol!!
 
Could you not run two SWA’s to each of the JB’s and run it as a true ring from the point of origin?
 
couldnt you fit mcb 1way modular box inplace of the Joint box hence making your swa a distribution circuit then the FRC from there? this would also provide isolation ??

Iv seen counters with their own 8way DBs mounted within the counter to assist with this and it also means that if providing a large enough db in counter you could have seperate radial circuits due to sockets being used and probably overloading the ring Once you add up a bainmarie microwave till equipment toaster griddle heat lamps at serve over coffee machine coke machine ect ect you will keech tourself at the possible loads and Diversity shouldnt realy comeinto it as the canteen staff just see a plug n use it regardless of what else is on
 
Engineer54 said:
2 SWA Circuits, each protected by an RCBO, each going to it's own JB box, each supplying a FRC. Each FRC supplying half the service counter. It's a fairly long counter with an extensive amount of various appliances as described in the OP. Any clearer now ?? lol!!
Click to expand...

I see, providing the circuits meet the requirements of BS7671 i see no issues, its not standard but then we are allowed to design our own circuits.
 
This Submittal came across my desk on Monday. Like some others here stated, there is nothing particually wrong electrically, but to my mind not really an acceptable layout on what is, a prestige project. So the initial submittal was rejected, on this and a number of other issues. The submittal was back on my desk yesterday morning, now showing 2 X 3core 4mm SWA to the JB box's and 2 X 3 core 4mm building cables forming the Final Ring Circuits, along with the other revisions that were requested...

I didn't mention in my OP, that the project specification calls for minimum size of 4mm conductors for power circuits, as that would have confused matters, and wasn't anything to do with why i asked for your thoughts on what is commonly known as a ''lollipop ring''. Personally, i would always want to see ring circuits starting and finishing at the protective device at the supplying DB/CU. If nothing else it would be a little confusing for an electrician at a latter date, to see a single cable connected to a protective device labeled as a ''Ring Circuit''

Anyway thanks all, for your thoughts. As i guessed there were the fores and against's, and none in this case being right or wrong, as in my case, more to do with personal preference as this arrangement will comply with BS 7671...
 
mogga said:
couldnt you fit mcb 1way modular box inplace of the Joint box hence making your swa a distribution circuit then the FRC from there? this would also provide isolation ??

Iv seen counters with their own 8way DBs mounted within the counter to assist with this and it also means that if providing a large enough db in counter you could have seperate radial circuits due to sockets being used and probably overloading the ring Once you add up a bainmarie microwave till equipment toaster griddle heat lamps at serve over coffee machine coke machine ect ect you will keech tourself at the possible loads and Diversity shouldnt realy comeinto it as the canteen staff just see a plug n use it regardless of what else is on
Click to expand...

All the bigger floor standing and the bigger mobile stuff like the Brain Marie's, pukka espresso machines etc, are all supplied via dedicated floor outlets, similar to the Britmac floor outlets , some of which are 3 phase jobby's all on their own radial circuits... These ring circuits are for general loads on the service counter.
 
BTW E54, I did not post my conclusions, because I would have come up basically with your points, obviously bar the knowledge of the actual specs of the job.
A lollipop is "acceptable" but confusing.
I would not install one on a new install, but, I would be tempted to mod an install to one, if cost was a significant factor.
BTW why rings not radials?
Is it a load distribution/volt drop thing?
If so you had better ensure that the rings are wired "every other" as it were!
 
netblindpaul said:
BTW E54, I did not post my conclusions, because I would have come up basically with your points, obviously bar the knowledge of the actual specs of the job.
A lollipop is "acceptable" but confusing.
I would not install one on a new install, but, I would be tempted to mod an install to one, if cost was a significant factor.
BTW why rings not radials?
Is it a load distribution/volt drop thing?
If so you had better ensure that the rings are wired "every other" as it were!
Click to expand...

It's a pretty long service counter Paul, with more than just a few appliances being supplied. And yes, all ring circuits are wired in a ''staggered'' configuration on this project, that's one thing i always lay down at the very begining of a project, i don't accept long runs back to the DB/CU. I prefer to see radials on circuits where loads can be moved about, rather than loading them up on a permanent/semi permanent basis, if you know what i mean. ...lol!!
 
Engineer54 said:
Explain yourself then, ...cause everyone loves a smart arse!!
Click to expand...
Your thread, your problem.

I was only trying to help by contributing to it, eg suggesting you shouldn't reduce the csa of a cable over 3m without a protective device, as per BS7671.

Sorry if that came across as being "smart".
 
Adam W said:
Your thread, your problem.

I was only trying to help by contributing to it, eg suggesting you shouldn't reduce the csa of a cable over 3m without a protective device, as per BS7671.

Sorry if that came across as being "smart".
Click to expand...

Even when the cables sizes are fully protected by the supplying protective device??

I don't think so... There is nothing electrically wrong with lollipop arrangement, it's just not what you would expect or be appropriate in a new installation.

If you explained your remarks a little better, it wouldn't have been taken as being Smart!!
 
I think you would need to identify if the 6mm "lollipop" was a sub main or part of the RFC

543.2.9 Except where the circuit protective conductor is formed by a metal covering or enclosure containing all of the conductors of the ring, the circuit protective conductor of every ring final circuit shall also be run in the form of a ring having both ends connected to the earthing terminal at the origin of the circuit.

So I suppose mate that if the ring starts at the junction box it would comply, but if the RFC starts at the CU then it does not comply.

Bottom line as you say mate it is just really not a good way to have a circuit IMO
 
malcolmsanford said:
I think you would need to identify if the 6mm "lollipop" was a sub main or part of the RFC

543.2.9 Except where the circuit protective conductor is formed by a metal covering or enclosure containing all of the conductors of the ring, the circuit protective conductor of every ring final circuit shall also be run in the form of a ring having both ends connected to the earthing terminal at the origin of the circuit.
So I suppose mate that if the ring starts at the junction box it would comply, but if the RFC starts at the CU then it does not comply.

Bottom line as you say mate it is just really not a good way to have a circuit IMO
Click to expand...

Agree Malc, i've seen plenty of these circuits over the years, and all have been confusing when first encountered. ...But one things for sure, you don't need a protective device in this instance at the transition point, when all else, electrically complies.
 
I suppose by the letter of the regs you should as your reduction in CSA will exceed 3 metres, but has the protection is just 32amps for the entire circuit and your using 6mm radial and 4mm for the RFC then I would only be fitting the one OPD at the origin.

Reg 434.2.1 IMO is aimed a circuit where you have a 63amp Ring Main in 10mm and you want to tap off for <3 metre in say a 6mm for something.
 
malcolmsanford said:
I suppose by the letter of the regs you should as your reduction in CSA will exceed 3 metres, but has the protection is just 32amps for the entire circuit and your using 6mm radial and 4mm for the RFC then I would only be fitting the one OPD at the origin.

Reg 434.2.1 IMO is aimed a circuit where you have a 63amp Ring Main in 10mm and you want to tap off for <3 metre in say a 6mm for something.
Click to expand...

Exactly Malc, ....The 3 metre rule was never meant for cables that were still being fully protected by the OPD at the origin of the circuit!!
 

Similar threads

F
UK Acceptable ways to terminate SWA - standard practice question
Replies
29
Views
2K
ELECNEWT
ELECNEWT
T
SWA cable Terminating or not??
Replies
8
Views
993
westward10
westward10

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Green 2 Go Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses Heating 2 Go Electrician Workwear Supplier
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

Advert

YOUR Unread Posts

Daily, weekly or monthly email

Receive a daily, weekly, or monthly email containing a digest of new and recently updated threads.

Thread Information

Title
Interested in your thoughts....
Prefix
N/A
Forum
Electrical Wiring, Theories and Regulations
Start date
Last reply date
Replies
58

Thread Tags

Tags Tags
electricians' talk interested thoughts

Advert

Thread statistics

Created
Engineer54,
Last reply from
Adam,
Replies
58
Views
4,896

Advert

TrueNAS JBOD Storage Server

Tilers | UK Tiling Forum | Tilers Forums | Find a Tiler
UK Tiling Forum by Tilers Forums UK
Plumbers Forums | Plumbing Advice | Gas Forum
Outside Play
Back
Top