Commercial EICR - Your opinion?

[HomeCert ltd]

Hi All,

Being doing a commercial EICR over night (7-7) for the past week, still got a good few nights to go.

The installation is most likely 40-50 years old, was originally done well. About 5 years ago they had another contractor redo a lot of the electrics to accommodate the current owner. The previous electricains work is unreal, he has completely ruined the installation.

I'm not 100% sure how to approach this. There's a lot a minor things which need doing which I will report back, but the lighting in some of the areas is unreal. The previous contractor had used SY cable everywhere, not correctly terminated at any point, which I found out is carrying a healthy 157v on the braiding. Basically every earth has been cut out throughout the lighting, mainly class 2 fittings, but due to the fact a lot of he circuits are new and all the existing work has an earth, would that be a C2. As it should comply with when he installed it.

Also getting 287v back down a neutral when not connected via a circuit fed by a Seperate DB on the other side. Earths used as feeds in some cases, some lighting circuits supplied via 2/3 circuits, all with no CPC and low IR. Due to the fact it's suspended ceilings everywhere etc... I was thinking it might just be easy to just redo a lot of the lighting instead of trying to break it down and see what's salvageable.

What would any of you do?

 

[Risteard]

Then why do the model forms provide individual boxes to record IR for each circuit? If they had intended us to measure and record global tests then surely the model forms would reflect this?

My understanding is that the boxes were intended to look nice. Hard to believe but apparently true. You could ask the same of the RCD test boxes. If the RCD is an RCCB it is likely to be protecting numerous circuits.

 

[Risteard]

That’s why we are tought the 1/Rt method of calculating the total resistance in parallel.
Scientific calculator at the ready

But that will give you an equally poor result than measuring the DB in parallel.

 

[davesparks]

My understanding is that the boxes were intended to look nice. Hard to believe but apparently true. You could ask the same of the RCD test boxes. If the RCD is an RCCB it is likely to be protecting numerous circuits.

But for RCBOs it is necessary to have individual results, which covers the majority of installations outside of domestics.
Where does this understanding come from because it is quite hard to believe?

 

[Ian1981]

The insulation resistance of a conductor is inversely proportional to its length that is, its insulation resistance decreases as the conductor’s length increases and vice versa. It follows that the insulation resistance of a complete electrical installation, or a section of it, will be less than that of a single circuit of that installation.
Global testing a large installation will mostly give you relatively low IR readings.
There’s no format to insulation resistance testing other than the overall resistance of the db circuits and any distribution circuit applicable to said DB is 1M ohm or greater.
The method you test it is down to the individual.

 

[DPG]

The insulation resistance of a conductor is inversely proportional to its length that is, its insulation resistance decreases as the conductor’s length increases and vice versa. .

To a point. But in practice, any length of new cable will have an IR of pretty much infinity, at least as far as any normal test equipment goes.

 

[Ian1981]

To a point. But in practice, any length of new cable will have an IR of pretty much infinity, at least as far as any normal test equipment goes.

It was more to do with carrying the test out during a eicr on larger 3 phase DBs.

 

[ipf]

Lets say that you measure 20 circuits at 10 Megohms each. The fact is these resistances are in parallel so would you wrongly consider that to be OK in spite of the fact that the requirement in BS7671 is for an installation/distribution circuit with all final circuits connected and not for any one circuit?

That depends on how far you want, or need in some instances, to break things down. As the thread indicates, 'your opinion'. There's an argument to every opinion... we can all pick straws.

 

[Risteard]

Where does this understanding come from because it is quite hard to believe?

From someone who was senior with the NICEIC at the time, as quoted on the IET forum on numerous occasions. (I don't know him personally.)