2.5mm2 Ring Final Circuit vs 4.0mm2 Radial

[Deleted member 26818]

Working in some flats at the mo, where they show on the circuit schedule a 4mm ring to feed Fan Coil Units and wardrobe supplies.
32A breaker and an expected load of 21A.
No idea why they want a ring.

 

[atm84]

Working in some flats at the mo, where they show on the circuit schedule a 4mm ring to feed Fan Coil Units and wardrobe supplies.
32A breaker and an expected load of 21A.
No idea why they want a ring.

What? they have even put the expected load on the DB Schedule?

Odd they would Fan Coil Units in a flat. I dabble in Mechanical Design and it would be a rare occasion that FCU would go in flats unless there weren't any openable windows?

 

[Deleted member 26818]

Other than some UFC in bath/shower rooms, the FCUs are the only method of heating.

 

[davesparks]

What? they have even put the expected load on the DB Schedule?

?

Have you never seen that before? It seems to have been common in years gone by.

 

[Deleted member 26818]

It's annoying, when as the installer, you can see from the expected load, that the circuit is over engineered.
It would be a lot easier to wire if it was a radial, rather than a ring.

 

[atm84]

Have you never seen that before? It seems to have been common in years gone by.

The issue that I would have of doing that as a designer is it is very difficult to ascertain 100% what the expected load is on a circuit other than Ib. In my opinion expected load is Ib taking into account diversity, which, you will be aware is not an exact science. Also, any changes to the circuit may change the expected load and I could put money on the fact that the DB Schedule would not be altered after every change to circuit loads rendering it useless.

Unfortunately in today's industry, it is about covering your --- and by putting the expected load on a DB schedule you are opening your self up for a good shafting.

 

[turnitonagain]

personally i think there easier to wire, and test, providing the loop and volt drop are not an issue. i would not discount a rfc on a larger installation. i use 20a b rated mcbs on socket circuts backed up by rcd protection, which is mandatory.

 

[turnitonagain]

also as a designer, if your loop values and volt drop for that circuit are within the values given by your o/l and s/c protection, you are covered. in ireland loop for b20 mcb is 2.3 ohms max, and max volt drop allowed is 4% of supply voltage. using this as as an example,

 

[7029 dave]

Ring, because Im competent to install, test and fault find them eliminating most of the fears about them

And given the ring circuit was originally conceived to deal with a shortage of copper and we are now in a period of really expensive copper I don't see them going anywhere soon

And because it's ALL ours.

 

[uksparks]

I do both, really depends on what its for, the house, or building structure etc, various factors, personally though, I like a ring, but then again, I quite a radial.

 

[Deleted member 9648]

There are some here that swear getting 3 X 4mm into socket outlets is no problem at all!! I'd hate to think what that connection would be like after pulling and moving those conductors about while getting the socket back into the back box!!

Funnily enough I took a branch off a 4.0mm radial this week for two additional sockets.The socket the branch came from was a legrand on a dado trunking outlet box. It was tight,but not excessivly so.But whatever the accessory in whatever box with however many cables I ALWAYS dress it back fully,then ease the accessory forward and recheck terminations before finally fixing back.
If more sparks did that,specially with tight jobs like 10mm cables in shower switches etc,then there wouldnt be any dodgy terminations.

 

[turnitonagain]

Still think you will struggle to get 2 x 4mm and 1 x 2.5mm into most sockets, especially the big shed crxp

Hi there, a 2.5 cable on a radial circuit max mcb size usually 20 amp , so ok if ring is controlled by it,

 

[Pete999]

Hi there, a 2.5 cable on a radial circuit max mcb size usually 20 amp , so ok if ring is controlled by it,

Sorry mate you lost me, what do you mean?

 

[turnitonagain]

Sorry this reply was for someone else

 

[jonny705]

I worked for a guy who owned Nightclubs and had a tax haven Villa in Majorca years ago (20+ years!),
Had to do some electrics and if I remember correctly first time I had seen an RCD and radials everywhere. (although well dodgy wiring otherwise! it would rain you could see open chock blocks connecting outside lights and sockets sparking in rain !)

I found out then that's how Europeans wired them , and (I think ) they have never used ring main circuits.

We apparently used them because of copper shortage after WW2, However, now I don't see why we use them , what with harmonisation with EEC etc.

When I first done my 2391 and had no clue what so ever about testing , it was abundantly clear when observing, that the most confusing aspect of testing for the guys that had tested was the ring main!

If there was any confusion it was always over that, and associated (R1+R2)/4 equation!

I have wired kitchens where its easier when the circuit has come horizontal along the length of wall to use 4mm Radial rather than have to loop a return in 2.5 mm as such.

Also, a common bodge I come across in houses, is where someone has fitted an additional socket , and simply cut the ring it half and has no clue its reduced the capacity to 20amp, and obviously never changed the breaker from original 32 AMP.(if it works it must be okay philosophy)

IMHO I think, that although you can legally spur off a ring main with a single 2.5 cable which would normally be rated at 20amp, the fact you could plug in x 2 13amp loads to equal potentially 26 amp (forgetting about diversity etc) surely cannot be right?, how does the 32amp breaker know you have done that?


I sometimes find it a bit of a mare' to stick 4mm in the sockets especially spurs , because they are probably designed for x2 2.5mm and not X2 4mm ? not sure, as I think in Europe its a single 2.5 with 20 amp MCB so only ever x2 2.5 mm wires going into it.


The only advantage I can think of is if you have 2 separate earth connections in back of socket and use them, at least if one leg of earth drops/falls out you still have another, and it confuses Europeans LOL.

 

[atm84]

I worked for a guy who owned Nightclubs and had a tax haven Villa in Majorca years ago (20+ years!),
Had to do some electrics and if I remember correctly first time I had seen an RCD and radials everywhere. (although well dodgy wiring otherwise! it would rain you could see open chock blocks connecting outside lights and sockets sparking in rain !)

I found out then that's how Europeans wired them , and (I think ) they have never used ring main circuits.

We apparently used them because of copper shortage after WW2, However, now I don't see why we use them , what with harmonisation with EEC etc.

When I first done my 2391 and had no clue what so ever about testing , it was abundantly clear when observing, that the most confusing aspect of testing for the guys that had tested was the ring main!

If there was any confusion it was always over that, and associated (R1+R2)/4 equation!

I have wired kitchens where its easier when the circuit has come horizontal along the length of wall to use 4mm Radial rather than have to loop a return in 2.5 mm as such.

Also, a common bodge I come across in houses, is where someone has fitted an additional socket , and simply cut the ring it half and has no clue its reduced the capacity to 20amp, and obviously never changed the breaker from original 32 AMP.(if it works it must be okay philosophy)

IMHO I think, that although you can legally spur off a ring main with a single 2.5 cable which would normally be rated at 20amp, the fact you could plug in x 2 13amp loads to equal potentially 26 amp (forgetting about diversity etc) surely cannot be right?, how does the 32amp breaker know you have done that?


I sometimes find it a bit of a mare' to stick 4mm in the sockets especially spurs , because they are probably designed for x2 2.5mm and not X2 4mm ? not sure, as I think in Europe its a single 2.5 with 20 amp MCB so only ever x2 2.5 mm wires going into it.


The only advantage I can think of is if you have 2 separate earth connections in back of socket and use them, at least if one leg of earth drops/falls out you still have another, and it confuses Europeans LOL.

Check the regs cos I'm fairly confident that a bit of 2.5mm2 can take more than 20amps.

 

[davesparks]

IMHO I think, that although you can legally spur off a ring main with a single 2.5 cable which would normally be rated at 20amp, the fact you could plug in x 2 13amp loads to equal potentially 26 amp (forgetting about diversity etc) surely cannot be right?, how does the 32amp breaker know you have done that?
.

Do you only fit single sockets to avoid the potential of someone plugging 2x13A loads in to a twin socket which is only rated for 20A not the 26A that would give you?
BS1363 requires that twin sockets can handle a load of 20A with the compliance test being 1x13A load and 1x7A load connected simultaneously.

 

[turnitonagain]

yes 2.5 can take technically 26 amps, under perfect conditions ,ambient temp etc. etc. but i would not recommend more than 20 amps in a radial or 32 in a ring.

 

[turnitonagain]

remember a 32a mcb will not be a good choice for a sustained overload on a radial spur from a ring circut [if the spur is not protected by a fused connection]

 

[turnitonagain]

excellent, my point a 32a mcb will not protect an unfused spur from a ring circuit in event of a sustained overload.