Dead Tests - Board Change

[m4tty]

Hi,

As you most probably know Im changing my dads board for Elecsa Assessment and Ive been round there today to do the dead tests and the results are as follows. The old board is a BS3036 rewirable (pictures attached) and it has been wired up from 1970 onwards so theres a mixture of cables in there. Some are solid core and some are stranded and testing was grief as the stranded cables earths (cpc's) have all been twisted together so had to untwist them all to do the continuity tests.

Gas Bonding - 0.00 ohms (very short run 10mm)

Water Bond - 0.02 ohms (10mm)

Kitchen Ring

L-L - 0.35 ohms

N-N - 0.35 ohms

E-E - 0.89 ohms (this is very high but could not find loose connection anywhere*)

L-N Crossed

Socket 1 - 0.17 ohms

Socket 2 - 0.17 ohms

Socket 3 - 0.17 ohms

Socket 4 - 0.18 ohms

Socket 5 - 0.16 ohms

L-E Crossed

Socket 1 - 0.28 ohms

Socket 2 - 0.30 ohms

Socket 3 - 0.30 ohms

Socket 4 - 0.39 ohms

Socket 5 - 0.31 ohms

I understand these should be within 0.05? of eachother so are these ok other than socket 4 being a bit high (maybe loose connection?*)

When I had the legs hanging out of the board disconnected just before I was about to do IR test, the probes were connected to Line & Neutral and the meter was on continuity and I saw it reading continuity of 14.3 ohms. I did make sure I unplugged everything in sight but the washing machine & dishwasher must still have been plugged in as I couldnt get to these to unplug them, would this 14.3 ohms be them?

Also one last question on this post (as Ive got loads to ask but dont want to do a massive post as some questions may get missed) As i was reading continuity between Line & Neutral I didnt want to send 500V DC and blow something up (central heating has been wired up from ring too I believe with no FCU to isolate) so I IR tested 250V DC L&NtoE and I got a reading of 55.6MOhms which is a pass as above 1MOhm but the meter was creeping whilst doing this test. It was rising and rising?

Ill finish babbling now as Ive got loads of other questions so will start a new post.

Thanks in advance for any pointers/advice and maybe this post may help newbies as well.

Cheers

Matt

Where ive put * can you give me any guidance as to if this is ok or needs further investigation

ThanksGuinnessrayGuinness

 

[AndyD1]

M4tty,

The 0.05 relationship is between L-L and N-N & appears to be fine looking your readings.

Your L-E readings look to be ok too based on r1+rn/4.

The high earth reading may be a non-accessible joint?

The higher reading could be a worn earth pin at socket outlet no4?

Your IR readings may as you say be the connected appliances.

Sorry for the bullet point answers but I thought it would make it easier to follow.

 

[AndyD1]

Should have added that the relationship between L or N and CPC will be approximately L-L x 1.67 = E-E if you are using T+E as the wiring method.

 

[NozSpark]

Matty..

First off I guess that this kitchen ring is 2.5mm/1.0mm??

If so then your readings are correct..

For 2.5/1.5 then your r2 reading would be r1 * 1.66

For 2.5/1.0 then your r2 reading would be r1 * 2.5

as for the high readings on socket 4... I guess (again!) that you are taking your readings via a test plug.... in which case I'd say that the socket internals are worn (is a high load appliance normally plugged into this socket?)

 

[m4tty]

M4tty,The 0.05 relationship is between L-L and N-N & appears to be fine looking your readings.

Your L-E readings look to be ok too based on r1+rn/4.

The high earth reading may be a non-accessible joint?

I spoke to my dad and he said there was a socket where the radiator is now and the cables have been choccy blocked and tiled over so most probably is a non accessible joint.

The higher reading could be a worn earth pin at socket outlet no4?

Your IR readings may as you say be the connected appliances.

Sorry for the bullet point answers but I thought it would make it easier to follow.

Thanks for replying mate nice one. cheersGuinness

 

[m4tty]

Matty..First off I guess that this kitchen ring is 2.5mm/1.0mm??

Yeah Noz its wired in 2.5mm/1.0mm

If so then your readings are correct..

For 2.5/1.5 then your r2 reading would be r1 * 1.66

For 2.5/1.0 then your r2 reading would be r1 * 2.5

as for the high readings on socket 4... I guess (again!) that you are taking your readings via a test plug.... in which case I'd say that the socket internals are worn (is a high load appliance normally plugged into this socket?)

I was using a kewtech socket adapter and found that if you waggled it hard and put a little force to one side the reading came down. This is what Ive been doing at all the socket outlets to get the lowest reading. This socket has been used in past for kettle so your guesses are spot on. Thanks mate

 

[Barx]

The ring will be 2.5 with a 1.0mm earth (alot were done like this back in day) and the high reading will be worn socket as above.

 

[Lee321]

gas bonding cannot be 0ohms

 

[Zeespark]

Well it could be that if there is no gas main to bond to or is within a foot or so of the MET.

AndyGuinness

 

[Lee321]

Well it could be that if there is no gas main to bond to or is within a foot or so of the MET.AndyGuinness

assuming there is a gas main bond as he has listed it

there must be some ohms even if its a inch long

on his sheet or notes he should note that the reading was lower than his meter could read and state what that value is

 

[m4tty]

Well it could be that if there is no gas main to bond to or is within a foot or so of the MET.AndyGuinness

Yeah andy your correct its about 2 foot away so suppose under 0.005 but over 0.00 so meter is reading 0.

 

[Zeespark]

Lost I agree with you that there would be resistance in any cable, but if its of a short length, the continuity tester may not be able to pick up such a miniscual reading of resistance. This would show up as 0.00 ohms on a standard Con/IR tester.

AndyGuinness

 

[Lee321]

all agreed then Guinness

 

[Zeespark]

Must be

AndyGuinness

 

[initforthemoney]

IR results will creep as the cable is being charged.

 

[m4tty]

Hi,

Ive been back round today and changed the board over and whilst trying to re-do the IR tests for the kitchen ring theres still something connected. Ive unplugged the microwave, cooker (timer), washing machine, dishwasher, fridge & freezer. All which had to be slid out you know the type all integrated. After all this I meggered at 250V just to make sure it was clear and it read 0.37Mohm Line to Neutral, so the central heating timer is the only thing left which can be on the circuit. It has been wired in direct from Kitchen Ring and I know this aint ideal but has been fine for the past 30 years and me dad not going to want to change this. As I am only changing the board (for assessment) I wouldnt have to sort this problem out or would I?

Can I disconnect either line or neutral at the ch programmer for the test to ensure the wiring is >299MOhm.

Thanks in advance for any replies.

Mattut the kettle on

 

[sparkytim]

The heating programmer should have a means of isolation and 3 Amp fuse protection.

If its wired directly off the Ring Main then this is NOT OK, never mind how long it has been like that.

Wire in a FCU with 3 amp fuse and then you will be able to isolate for testing and provide adequate protection.

 

[PC Electrics]

Hi,Ive been back round today and changed the board over and whilst trying to re-do the IR tests for the kitchen ring theres still something connected. Ive unplugged the microwave, cooker (timer), washing machine, dishwasher, fridge & freezer. All which had to be slid out you know the type all integrated. After all this I meggered at 250V just to make sure it was clear and it read 0.37Mohm Line to Neutral, so the central heating timer is the only thing left which can be on the circuit. It has been wired in direct from Kitchen Ring and I know this aint ideal but has been fine for the past 30 years and me dad not going to want to change this. As I am only changing the board (for assessment) I wouldnt have to sort this problem out or would I?

Can I disconnect either line or neutral at the ch programmer for the test to ensure the wiring is >299MOhm.

Thanks in advance for any replies.

Mattut the kettle on

I'm guessing then that your Dad has never had the boiler serviced?

This is contrary to the gas regs (and has been for 'donkeys'). The boiler and controls must have an FCU fitted with a 3A fuse. If there is no FCU any CORGI registered engineer can refuse to touch it.

it has been normal practice for 40+ years to use an FCU with a 3A fuse, so if this was wired direct into a 30A ring, then it was a bodge when it was done.

 

[PC Electrics]

Hi,As you most probably know Im changing my dads board for Elecsa Assessment and Ive been round there today to do the dead tests and the results are as follows. The old board is a BS3036 rewirable (pictures attached) and it has been wired up from 1970 onwards so theres a mixture of cables in there. Some are solid core these will be metric cables and some are stranded probably imperial cables, see the downloads section for my sheet containing imperial cable ratings and testing was grief as the stranded cables earths (cpc's) have all been twisted together yeah, this can be a proper pain on board changes, but careful how you go, it's easy to break the strands if you're heavy handed untwisting - you could always untwist at a socket to test the ring continuity so had to untwist them all to do the continuity tests.

Gas Bonding - 0.00 ohms (very short run 10mm)

Water Bond - 0.02 ohms (10mm)

Kitchen Ring

L-L - 0.35 ohms

N-N - 0.35 ohms

E-E - 0.89 ohms (this is very high but could not find loose connection anywhere*) can you confirm the size of this cables cpc? it could be some of that old 2.5/1.0 stuff that was around for a little while in the 70's. That's not a problem if you're putting it on a 32A MCB, but you'll want to quote the correct size on your EIC. And your assessor will want to see you can identify cables properly.

L-N Crossed

Socket 1 - 0.17 ohms

Socket 2 - 0.17 ohms

Socket 3 - 0.17 ohms

Socket 4 - 0.18 ohms

Socket 5 - 0.16 ohms

L-E Crossed

Socket 1 - 0.28 ohms

Socket 2 - 0.30 ohms

Socket 3 - 0.30 ohms

Socket 4 - 0.39 ohms something amiss at the socket eg. loose conn / corrosion / worn socket pins / worn switch

Socket 5 - 0.31 ohms

I understand these should be within 0.05? of eachother so are these ok other than socket 4 being a bit high (maybe loose connection?*)

When I had the legs hanging out of the board disconnected just before I was about to do IR test, the probes were connected to Line & Neutral and the meter was on continuity and I saw it reading continuity of 14.3 ohms. I did make sure I unplugged everything in sight but the washing machine & dishwasher must still have been plugged in as I couldnt get to these to unplug them, would this 14.3 ohms be them? could be - 14ohms would be about a 4kW load

Also one last question on this post (as Ive got loads to ask but dont want to do a massive post as some questions may get missed) As i was reading continuity between Line & Neutral I didnt want to send 500V DC and blow something up (central heating has been wired up from ring too I believe with no FCU to isolate) BAD BAD BAD so I IR tested 250V DC L&NtoE and I got a reading of 55.6MOhms which is a pass as above 1MOhm but the meter was creeping whilst doing this test. It was rising and rising? dodgy conn / damp

Ill finish babbling now as Ive got loads of other questions so will start a new post.

Thanks in advance for any pointers/advice and maybe this post may help newbies as well.

Cheers

Matt

Where ive put * can you give me any guidance as to if this is ok or needs further investigation

ThanksGuinnessrayGuinness

***************

 

[spinlondon]

I like to drop socket/switch plates when testing.

Gives a better reading, I can see if earth sleeving is present and can show up loose terminations.