Old circuit, low insulation resistance readings - REPLACE?

[Tony13579]

How old is your house?
Aluminium wiring was used around 1960-70 when copper prices went extremely high.
How high off the floor are your sockets? Are any in the skirting board?

 

[essexmick]

How old is your house?
Aluminium wiring was used around 1960-70 when copper prices went extremely high.
How high off the floor are your sockets? Are any in the skirting board?

6-8 inches, there are no plugs in the skirting boards.

What are you thinking?

The house is 1930s with a 1980s extension.

 

[Tony13579]

If your sockets are in the skirting board they are very old and at risk of damage. Wiring this old almost always need a full rewire. It's cheaper than trying to bring the old stuff up to standard.

If it was built or rewired after 1970's it can usually be brought up to standard without a full rewire. (Assuming I t hasn't had a load of botches)

 

[ericmark]

The house is 1930s with a 1980s extension.

It is unlikely it's 1930's wiring. At that time normal would be 15A socket up stairs and down stairs i.e. just two sockets for whole house and lighting would have no earth wires.

Around 1960's the rules on earths on lights changed so since there are no codes raised for no earth on lights likely it was re-wired after 1960.

If the electrician even considered changing the consumer unit first then we must assume the insulation resistance problem is very minor. 16 kΩ is the point where a RCD will be likely to trip and normally 1000 kΩ is considered as pass mark. Even at 1000 kΩ or 1MΩ we would normally be still looking for faults.

I have read some reports which as one reads one start to get suspicious and one realises the guy had just plugged in meter and pressed the button sorry to say some firms pay their guys per inspection and allow them that little time they can't investigate further it is really an insurance scam where the building owner needs a certificate for insurance and is not really worried about real state of building so employs the cheapest. The inspection firm often have very high turn over of staff as their get out method is always to blame electrician who they then sack saying it would happen again then employ another who also is forced to take short cuts.

So although if we assume the original electrician was doing a good job we would not change the consumer unit first if we assume the original electrician did a very poor test then assuming tests to not replicate the original electricians results then to change consumer unit and see what happens may be a good plan. However I would use all RCBO's and be ready to swap to MCB if fault does show its self.

However with my father house pre-2008 when rules changed he was having a wet room fitted and the electrician offered to swap the consumer unit for £100 extra rather than fit a sub consumer unit for the wet room. We said yes seemed a very good price. However when it came to commissioning he could not get the RCD to hold. As a temporary measure he swapped the RCD for an isolator promising to return the next day. In hind sight we should have realised as the guy had no test gear with him other than a multi-meter and he was never seen again.

There are still circuits in that house with no RCD protection but in 2006 when it was done it was not required for all circuits.

 

[essexmick]

The house is 1930s with a 1980s extension.

It is unlikely it's 1930's wiring. At that time normal would be 15A socket up stairs and down stairs i.e. just two sockets for whole house and lighting would have no earth wires.

Around 1960's the rules on earths on lights changed so since there are no codes raised for no earth on lights likely it was re-wired after 1960.

If the electrician even considered changing the consumer unit first then we must assume the insulation resistance problem is very minor. 16 kΩ is the point where a RCD will be likely to trip and normally 1000 kΩ is considered as pass mark. Even at 1000 kΩ or 1MΩ we would normally be still looking for faults.

I have read some reports which as one reads one start to get suspicious and one realises the guy had just plugged in meter and pressed the button sorry to say some firms pay their guys per inspection and allow them that little time they can't investigate further it is really an insurance scam where the building owner needs a certificate for insurance and is not really worried about real state of building so employs the cheapest. The inspection firm often have very high turn over of staff as their get out method is always to blame electrician who they then sack saying it would happen again then employ another who also is forced to take short cuts.

So although if we assume the original electrician was doing a good job we would not change the consumer unit first if we assume the original electrician did a very poor test then assuming tests to not replicate the original electricians results then to change consumer unit and see what happens may be a good plan. However I would use all RCBO's and be ready to swap to MCB if fault does show its self.

However with my father house pre-2008 when rules changed he was having a wet room fitted and the electrician offered to swap the consumer unit for £100 extra rather than fit a sub consumer unit for the wet room. We said yes seemed a very good price. However when it came to commissioning he could not get the RCD to hold. As a temporary measure he swapped the RCD for an isolator promising to return the next day. In hind sight we should have realised as the guy had no test gear with him other than a multi-meter and he was never seen again.

There are still circuits in that house with no RCD protection but in 2006 when it was done it was not required for all circuits.

RCBO?
MCB?

 

[essexmick]

1. Need to wait for exact figures from electrician.
2. Low insulation resistance (assuming it's low enough to worry about) probably should at least be investigated (and rectified as necessary)
3. Aluminium and rubber cables need to be taken out and rewired.

 

[JohnW2]

RCBO?
MCB?

MCB = Minature Circuit Breaker - the 'trip switches' which are the modern equivalents of fuses.

RCBO = combination of MCB and RCD-like-functionality for one circuit. By providing 'RCD'-type protection separately for each circuit, it means that a fault on one circuit does not take out several other circuits (which is the case if several circuits share a common RCD). However, they are much more expensive than MCBs.


Kind Regards, John

 

[JohnW2]

1. Need to wait for exact figures from electrician.
2. Low insulation resistance (assuming it's low enough to worry about) probably should at least be investigated (and rectified as necessary)
3. Aluminium and rubber cables need to be taken out and rewired.

I wouldn't argue with any of those, for starters. (1) and (2) obviously overlap to some extent.

Kind Regards, John