Fault find RFC, next socket

[BackToSchool]

Hi all,

Hope you all had a nice Christmas!

I'm a college student, (I worked in an office, but I wanted a change so at 30, decided it was time to do something else).

I can't ask my lecturer as it's the holidays, but my brain can't figure this out so hopefully someone on here can help me.

If on a fault-finding mission (tripping sockets for example), while in a new build, or a place that has been rewired recently, it should be easy to work out the next socket in sequence of a ring final circuit, however when it comes to an older building, sometimes socket 1 might not be anywhere near socket 2. In that situation, how would you map out the next socket in sequence?

 

[ImpededLoop]

I'd link line and cpc on one leg of the ring final at the consumer unit and then do an R1+R2 test at each socket. The resistance value will increase as you go around the ring. Plotting the values on a plan can help you visualise how it's wired.

Watch out for spurs as they can confuse things. If needed, then link the other leg of the ring at the consumer unit (unlinking the first) and measure the values again which should identify any spurs.

 

[pc1966]

Also on older properties also watch out for dirty/tarnished switches and socket contacts on those outlets that are hardly used when doing your R1+R2. Inserting and removing the test plug a couple of times, and operating the socket's switch a couple of times, should get you back close enough to the true conductor values.

 

[telectrix]

similar method but quicker. I use a wander lead and measure from 1 end of the disconnected circuit's cpc and the 3.5mm faceplate screws. also saves taking the faceplates off unless an unexpected reading is obtained.

 

[BackToSchool]

Thank you all for your help there.

It's good to see there is more than one way to do the same thing, and get the same result.

Thank you for the advice on tarnished switches/sockets. It's something that I never thought about, but I guess all sorts of crud can get into the sockets over the years.

 

[PEG]

Another tip,is to expect,the unexpected. Take all information in to account,and do not ignore a reading or lack of one,just because it ruins what you hoped for

You WILL,sooner or later,get the cross links,bad joins,variations in cable size,type,material,and a lot of other surprises.

The problem with all the varieties encountered in an older installation,is you may get a correct reading,but for the wrong reasons....just factor that in,so any determination you make,is as accurate as can be,with room for a re-think.

Think of all the journeys you have been on,where you got lost or diverted,and find something surprising,which is either great or horrible....that's fault finding

 

[pc1966]

Thank you for the advice on tarnished switches/sockets. It's something that I never thought about, but I guess all sorts of crud can get into the sockets over the years.

Normal high current loads tend to simply blast it away, but on ~0.2A low R measurement you will see the effects of poor connections easily.

 

[BackToSchool]

Hi all, thanks for the advice on the above, although I have another question which is semi linked to the above. Not sure if I need to make a new thread or just use this one but if it needs to be moved, then that can be done.

I was clearing out the boiler cupboard earlier as I have a man coming in a couple of days to install a new boiler, (WHY does everything have to break at Christmas?!) and I noticed that the boiler is connected via a switched fuse spur to the RFC, but it got me thinking, that if I had to do an IR test on the RFC at the CU, how would I treat the boiler as it is still a connected load? Would removing the fuse from the holder be enough, or would it need to be completely disconnected from the fused switch? It’s not something we have covered in college yet, but it just got me thinking.

 

[ImpededLoop]

Good question. A switched fused spur is always double pole (it switches line and neutral), so you just have to ensure that the switch is off when you IR test.

Be wary of switched socket outlets as many are only single pole switched, so you need to physically remove anything that is plugged in.

If I'm in any doubt about possible connected loads, I do an IR test at 250v rather than 500v so that I don't damage anything. If it's clear, I then test at 500v.

 

[telectrix]

you would link L to N and IR test from there to E. you only need to do L-N on an initial install, beforel oads are connected.

 

[BackToSchool]

Thank you both for that. I had not realized that the SFS was DP, but it now makes more sense when thinking about it.

Thank you