Ring main help

Ideally you should have seperate ring final circuits for ground & first floors.

Are you sure it's not a radial circuit,if ring final 16A mcb might have been fitted due to a underlying problem with the electrics, or downrated to 16A mcb for another reason.

 

Prehap of of our resident sparks can enlighten us.

Slightly off track, at a previous place I found the ring final split at the CU into seperate fuseway each protect by a 16A mcb, never understood why that was done.

 

I downgrade ring mains to 16A for various reasons, but if I do I tell the house owner why, I would not simply just put a 32A breaker over a 16A because there are two 2.5 cables and it appears to be a ring. It needs testing completely to verify it is a ring and not a ring within a ring which only correct ring final testing and a figure of eight test will produce, there may be spurs taken off spurs etc so 32A would overload the cable. Lots of reasons why this is how it is. It probably isn't the fact that the spark who did it only had a 16A breaker so put it in, if this where the case then I would expect him to have returned to swap it out. However that does happen. The best advice is get it checked correctly by a spark and he will tell you if it is a true ring that can be made back into a 32A ring. Don't just assume a ring because it continuity tests end to end.

 

If you have tested out and don't understand the readings you have obtained whether they are correct or not, I am sorry but I am not going to help you. I cannot advise you on this basis as how come you understand how to perform the correct tests but not the readings, therefore I am not willing to help nor will any spark. Sorry but you must understand that safety is paramount. A decent spark will only help to a point that once your understanding stops, then so does the help in a case like this. If I said yes that's fine go ahead and put a 32A breaker in and your house set fire as you tested incorrectly then I would be responsible. If you don't understand your readings then what are you testing for to begin with? Harsh but safe advice.

 

Totally agree.

You need a proper spark in, who can throughly test your system,plus you need to have seperate ring finals in house nowadays, the days of one ring final serving two floors of a house are long gone in my opinion.

Depending what your spark find, you might find it's better to have a part rewire,just adding seperate ring finals for ground & first floor, even going as far as a seperate ring final also for kitchen/utilty.

 

As above, you need to get a spark, good solid advice

 

My house is 1958, original wiring and has a single final ring for both ground and first floors, on a 32A. So in theory you should be OK *if* what you have really is a final ring.

As above - best get in some professional advice before changing, as the 16A fuse may have been put in for a reason.

 

Disgraceful.

 

It will get changed KIAB...possibly 4 final rings on the cards

 

Its a bloomin PITA having only one single socket in each bedroom at present though, and its not much better downstairs. Lots of extension leads upstairs...

 

Using calibrated test meters (17th edition), you would most likely got a totally different reading, hence the need for a proper spark to test it.

 

Andrew, not wanting to get into a ping pong slanging match with you, but I know what I am doing and for the advice I gave you was purely out of respect and safety for you and your family. I cannot understand how you could do testing on a ring main to ensure it is a ring and not interpret the readings which incidently is what a figure of eight test gives you, therefore I cannot give you the assurance you are seeking when you are obviously not confident in testing and inspection. You shouldn't be in your mains board or dabbling with electricity when you have no understanding of what you are looking for. Sorry but no spark will give you this advice from the question you have asked, it would be irresponsible and foolish as how on earth would i know if you have done these tests correctly. I would advise you to seek professional help from a spark. He will conduct the tests and interpret the readings he gets not what you get.

 

Poor guy, he is trying to figure it out and i know most here expertise is outstanding.

Ok Andrew here it is. Fuses burn out at a different current vs time to what a MCB will disconnect at, everything takes time nothing is instant. You have to look at the current curve for a fuse and that for an MCB. An MCB of Type B should disconnect at 3-5x the rated current in less than 5 seconds, preferably Milliseconds. That means that if a short circuit(and MCB's are really only good for circuit protection) is rated at 16Amp then if 16x3 = 48Amp was hit then the 16 Amp breaker would open circuit. For a 32Amp breaker this is 96Amp.
Ohms law is V/IxR so if you have 0.8Ohm then 230v/0.8 = 288Amps rounded up which will disconnect the breaker clearly. Lets say you measure 3 ohm on the circuit that is 230/3 = 76Amp which is well bellow the Type B curve for a 32Amp breaker and would not disconnect quick enough if a short fault occurred.
The difference is that when we look at a fuse compared to overload and not short circuit then things get very different. A 16Amp fuse may well be happy running at over 20Amps and run like that for quite some time before it melts. An MCB on the other hand has a thermal component that will disconnect in a given time based on how much over-current is drawn through it for nth amount of time. An MCB protects far closer to it's rated current compared to a fuse in fact a fuse will be happy for quite a long time with double it's rated current through it. This is why i get where you are coming from as yes a 32Amp circuit may well have been installed with a 16Amp fuse.
You should also not rule out that the 16Amp breaker maybe tripping far lower than it's rated current(faulty) and or one of your appliances has become faulty and is pulling too much juice so go read the appliance labels KW rating and work out their max current draw. Most power hungry appliances are around 2KW which is 8.6Amps so two of these running their heaters at the same time may not trip the breaker but if a third is added then yes it may well do that.
P=VxI so re-arrange the formula and you have P/V so example is for a 8.5Kw shower this is 8500/230 = ~36Amps

So yes the circuit could well handle a 32amp breaker but if you are changing it then you better make sure it is RCD protected as well. If you cant satisfy the RCD protection then i'd say leave it alone or get in a sparky.

I get the impression you want a quick cheap fix, buy or source a single breaker and just swap it but has it got RCD protection.

If you don't know if you have RCD protection post us a picture of the consumer unit so we can see what is going on.
My advice is unless you do a full test which means not only a resistance test and continuity check on the ring final(that by sound of it you have already done) but an insulation test, finding any spur if any as well. Are you certain that all spurs on the circuit are fused and if not what size cable is used for the spur etc. Again checking resistance is only a fraction of the job in calling it safe to a breakers rating and that can not be advised on a forum sorry. You yourself need to call that or get a spark in to fully take a look at the circuit.

Again if you do not have RCD protection for your socket ring final then it is a problem on that alone and needs correcting so the least of your worries would be a 16amp breaker tripping from overload.

Fuses and MCB's protect the circuit and cabling.
RCD's save you and your families life.

So now you have a better understanding of what you are doing or at least i hope you do, you can make a better educated decision on what to do.

 

Well hopefully that made it simpler for you Andrew, it would be foolish to tell you that your readings are good, what was you Zs readings for example? Your figure of eight test will verify whether or not you have a true ring and that your polarity is correct, So many other readings to verify your ok to uprate your existing 16A circuit to a 32A safely, as above you have not mentioned RCD protection either that will be an influence to the safety of what you want to do, you mentioned in your post that you have 3 children in the house. Be pretty irresponsible of someone to advise you to go ahead on both your limited Knowledge of testing and interpreting the readings and other factors that you have not even mentioned. Solid advice is if your unsure of what it is you want to do, then seek help from someone who can take responsibility of advising you. Not what you want to hear from a forum and with limited information you have given it would put your family at risk. I would not offer advice for you to either injure yourself or harm your children as I haven't actually seen or tested your installation to say with confidence yes. Now I have no problem helping you with any issues that you have an understanding of, but this is not the place to receive an answer to your question.

 

A standard ring uses a 30/32A protective device with cables and accessories rated at 20A or above.
It could be, that the installation methods used for the cables have de-rated them to below 20A.
Only way to determine if the cables have been de-rated, is to visually inspect and then calculate using appropriate correction factors.
The disparity between readings, could be that one of the sockets is a spur rather than part of the ring, or could be due to a high resistance joint?
High resistance joints can be caused by various reasons, corrosion or poor termination being the most common.

 

Correct, could be a ring within a ring or spurs off spurs, any number of problems or circumstance could downrate a circuit like this, testing, testing, testing.