16a MCB ring main

[Traineeboy]

Hi all to start off I know a ring main is normally on a 32a MCB. Today I was at at house with one of guys and he changed a MCB at the board to a 32a MCB where there was a 16a MCB. He said it had to be a 32a on ring but from my understanding if the circuit has been OK and not overloaded then surely a 16a would have been fine to stay. 
 

OPCD protects the cable so if the 16a MCB was fine then was there really need to change it to a 32a ? Don’t see that in the regs. 
 

but yes I know normally 32a is used for a ring. 
 

your thoughts ? 

 

[Sharpend]

Did this guy check that it was actually a ring circuit and not a broken ring hence the 16A Mcb? 

 

[Traineeboy]

He said that it came back with end to end readings so that proved it was a ring. He said if there wasn’t a reading between end to end then it would be a broken ring ? That sound right ? 

 

[Murdoch]

3 possible causes:

1. Install by diyer ego didn't have enough 32a breakers

2. Ring has a section of 11.5mm mm cable

3. There are spurs off spurs

 

[Traineeboy]

Thanks Murdoch. Just wounded if you could Clarify. 

1. Even if it is a true ring then if it’s on a 16a MCB the apart from the overload current being reduced to 16a not 32a then it’s fine. That right ? 
 

2. When you say have a section of 11.5mm do you mean the CSA - it was 2.5mm cable. 
 

3. If they are spurs off spurs or two radial circuits that join and meet , then when testing would you test as a ring or test each radial separately. Or would you break the ring and it just be two radial circuits going into one breaker ? 

 

[Evans Electric]

1. Even if it is a true ring then if it’s on a 16a MCB the apart from the overload current being reduced to 16a not 32a then it’s fine. That right ? 
 

The reason for the 16A  could have been anything TBH,  original sparky didn't have a 32A  ...been like that  forever.     Possibly an upstairs ring  with no load on it so the sparky just left it . 

I'd have left it alone TBH  ...if it  'aint broke , don't fix it . 

When you say have a section of 11.5mm do you mean the CSA - it was 2.5mm

I think Murdo meant  1.5mm    . 

 

[Murdoch]

3 possible causes:

1. Install by diyer who didn't have enough 32a breakers

2. Ring has a section of 1.5mm mm cable

3. There are spurs off spurs

bloody predictive text

1. Even if it is a true ring then if it’s on a 16a MCB the apart from the overload current being reduced to 16a not 32a then it’s fine. That right ? 
 

no problem unless it serves the kitchen with lots of white goods

On rewires these days I do a 32A ring for the kitchen then 20A radials elsewhere ............

 

[Evans Electric]

These things are adaptable to the circumstances you know .

Years ago the NICEIC man picked us up on a job we were doing in an electronics factory .     There was a long work station  for about 10 people  who  used a bright  anglepoise light plugged in and a soldering iron  at each point .  

We'd fitted a row of 10 twin sockets  on a 2.5mm radial  from a 16A MCB   .        He thought it should be a 32A  ring main  ...we didn't .   It was a designed circuit for that bench  , end of story .   

He couldn't get past having 10 twin sockets on a radial  .   We'd designed for 10  X  soldering irons & 10 X 60W lamps  .   100W per station  X 10 = 1000W   = say 5A  . 

 

[Murdoch]

Years ago the NICEIC man picked us up on a job we were doing in an electronics factory .     There was a long work station  for about 10 people  who  used a bright  angle poise light plugged in and a soldering iron  at each point .  

Surely all he should be asking was why you decided to do what you did ............ they are no position to criticise

 

[Evans Electric]

This is a long time ago but I distinctly remember him opening  a bench socket  and  commenting  there was only a pair of Red & blacks  passing through  and he expected a ring .

He made a note and we moved on .   I wasn't even foreman on that one   but could see nothing wrong with it .  

We'd also been picked up on  a 4 X 4  steel trunking   with a 2 x2 flanged off it  .  The guys had drilled   something like an 40mm hole for the 2x2   and had actually made a grommet  strip to fit . .... it was lying in the empty trunking .         I can hear him now ..."Oh dear  no grommet strip in there"      Writes it down ...I'm saying  " There it is , you can see it "   " Yes but its not fitted is it "       

 

[ProDave]

I once found an entire ring wired in 3 core & earth 1.5mm  Yellow used as earth and CPC not used.  The only solution I could find, other than a rewire, was change the 32A mcb for 16.  I suspect that was "whoops" job, well 3c&e 1.5 does look very much line 2.5 t%e

I also found a house with a shiny new CU with no labels, so to isolate a ring I went through each MCB in turn and none turned the ring off.  Further investigation found the ring was fed by two 32A mcb's one feeding each end of the ring.

 

[Murdoch]

I also found a house with a shiny new CU with no labels, so to isolate a ring I went through each MCB in turn and none turned the ring off.  Further investigation found the ring was fed by two 32A mcb's one feeding each end of the ring.

Seen that so many times - if switching MCB's off and on  1 by 1 doesn't isolate a circuit I then simply switch them off and then work backwards .

Did an EICR a couple of years back and only 1 out of 5 rings had both legs in the correct MCB

 

[Tony S]

At the foundry I found umpteen circuits with the wrong protection, usually oversized. 800A fuses on a 16mm² was a good one. Labels and drawings were like reading a Jackanory storybook.

 

[ProDave]

At the foundry I found umpteen circuits with the wrong protection, usually oversized. 800A fuses on a 16mm² was a good one. Labels and drawings were like reading a Jackanory storybook.

I learned that lesson in an industrial unit where I had to change the hand dryer in the gents toilet.  I was a bit optimistic turning of the MCB labelled "Gents Toilet" only to hear a groan from along the corridor where it turned out I had shut down an office full of computers.

 

[Evans Electric]

Further investigation found the ring was fed by two 32A mcb's one feeding each end of the ring.

Thats more common than it should be . 

 

[kerching]

Customer of mine had a new boiler room built each time they put a new building up.....blown warm air and present units couldn't be increased.. when they finally shut down there were 7 'New Boiker Room" keys

 

[Evans Electric]

when they finally shut down there were 7 'New Boiker Room" keys

My favourite is always when you open a fuseboard door  to find  ...Ct 1    "  Plugs in  Mr Brown's office "       Which was correct back in 1952  .   

I get it at the printers I look after  ,   rooms & areas  have been changing  over the last 25 yrs  .    Machines have moved that often  there are  5 pin  X  16 A  & 32A  sockets everywhere.  Pot of Tipex  is part of the kit . 

 

[binky]

OPCD protects the cable so if the 16a MCB was fine then was there really need to change it to a 32a ? Don’t see that in the regs.

This is entirely correct, s log as the cable is correctly protected from overload, it matters not if it's wired as a ring or radial.

Far too many sparks can't think beyond the 'normal' and get confused by such things. I have encountered lighting wired as a ring, lots of radal sochet circuits (I prefer these also in domestic) , lollipop ccts, usually in kitchens hwre an old cooker cct has been re-puposed etc etc. Nothing wrong with any of it.

Locked to prevent being resurrected (again)