CU Updated But No Rewire

[alamski]

Hi Guys,

Wanted to know your opinions on a situation I came across recently. Long story short customer wanted their old CU replaced to a modern updated one (RCD protected) but did not want a full rewire. The original CU was a Wylex 12 way rewireable fuse unit, instead of the usual ring main setup this was a radial circuit in 4 mm feeding each room with several sockets. Included were the usual cooker, shower circuits etc. Tested out the installation and it passed but some (IR) readings were on the low side. Did mention this to the customer but his response was that he simply does not have the money and the time to do a rewire of the house at this present time.

What would have been your response if you were in the above situation?

Many thanks.

Sayeed

 

[Sintra]

Personally I would have done a global IR prior to any works then I would have highlighted any anomalies. What where the IR readings?

 

[alamski]

If memory serves me right I tested each circuit and they were averaging around 40-70 Mohms, I know it says 1Mohm in the regs most circuits i've done just used to seeing >200.

 

[Deleted member 9648]

Remind me why it needs rewiring?I must be missing something.

 

[GMES]

At those readings the installation is good for years to come.

 

[Dave OCD]

I've had readings of 10-12 Megohms on various circuits and across all conductors when upgrading CUs , nothing to worry about as it's still a very high resistance !

 

[alamski]

@wirepuller
You've not missed anything, rather my misunderstanding, I'm so used to seeing >200Mohms on the tester, seeing around the 50Mohms mark just got me wondering if the installation was still of good quality.

Thanks guys for the input.

 

[DNS1]

It's not as good as new, but there's a good reason for that... it's not new!

It's way in excess of the requirements, so bobs yer uncle...

 

[Jimmyb]

OMG, 50mohms is 50000000ohm !!!!!!!!!!!!!!!!!!!!

 

[amlu]

nothing wrong with 4mm radials. 32A in right conditions, 20A to be on the safe side, more than enough for a room.

 

[alamski]

@Amlu
Yeah I have come across a few installs with that sort of arrangement, maintained it closely as possible, 20a mcb's. Just me ocd kicking in again.

 

[davesparks]

What type of cable is it?
Have you actually calculated the leakage current you will get from the IR results? Or do people not bother with things like that any more?

 

[Leesparkykent]

What type of cable is it?
Have you actually calculated the leakage current you will get from the IR results? Or do people not bother with things like that any more?

Why bother? The IR results are acceptable for the purpose of filling in a cert!

 

[davesparks]

Why bother? The IR results are acceptable for the purpose of filling in a cert!

I wouldn't, but he obviously thinks that the results are a cause for concern so I would have thought the first thing you'd do is work out what that IR will cause to happen.

 

[infinity]

The scary part is, if the guy had the money you would have rewired it! It would have been a rip off

 

[alamski]

@Davesparks cable was very old t&e, red and black with cpc. Did not calculate ir leak test.

 

[davesparks]

@Davesparks cable was very old t&e, red and black with cpc. Did not calculate ir leak test.

Very old T&E? That's not very descriptive! What material is the insulation and sheath made of, is it imperial or metric?

 

[telectrix]

to these young 'uns, anything older than 2008 is very old. imperial cable is positively ancient. not to mention coffin dodgers like me and pete999.

 

[alamski]

@Davesparks
Imperial, pvc sheathing

 

[telectrix]

stranded imperial cable was and still is better stuff than the crap we get now. bet if you return in 10 years time to do a routine test/inspect, the IR readings will still be close to what they are now. provided no plumbers have been messing with it.

 

[davesparks]

@Davesparks
Imperial, pvc sheathing

There's no problem then is there?

 

[alamski]

Thanks davesparks

 

[Deleted member 9648]

Just out of interest you state in post #1 that circuits are in 4.0mm radials. As we now know it is imperial are you certain that it is 4.0mm equivalent? It could be 2.5 equivalent which to the untrained eye might well appear to ne 4.0mm.

 

[shanky887614]

Just out of interest you state in post #1 that circuits are in 4.0mm radials. As we now know it is imperial are you certain that it is 4.0mm equivalent? It could be 2.5 equivalent which to the untrained eye might well appear to ne 4.0mm.

just to add to wire pullers comment.

if you cant visually tell the difference grab a set of calipers.

they come in very handy from time to time especially with small drill bits that you cant see the numbers on anyway even when new