Tragic IR fail on EICR

[putalightuponce]

Hello all,
I could use some help here:
I was recently asked to do an EICR at a small warehouse/office unit.
The installation was, to put it mildly, less than satisfactory; with multiple C1 and C2 conditions. However, of greatest concern to me were the insulation resistance readings I was getting. I left the job, trying to explain the severity of the condition to the client, but still feel under the circumstances, he is unlikely to take any further action, despite his report been top to bottom in 'further investigation's.
Whereas I'm sure everybody on here has had this at some point (if not daily), it is the specifically the IR fails I am still scratching my head over.
2xsockets in floor boxes, 3xsockets in dado trunking, 3xlighting circuits, and 2xhand dryer spurs were all returning 0Mohms IR L-E, yet none of the associated breakers were tripping or had been problematic in any way. Breakers and board were old (maybe late 70s early 80s), no markings on breakers except obvious ratings, but I'm assuming wiring can't have been of same period unless floor boxes and dado trunking wre popular back then?? The decor and fittings were certainly more recent.
I was pleasently suprised to find a single A4 schedule of circuits reinforced with several layers of tipex and the board had a Ze and PFC reading written in it from 2002, but that was it for records.

Any thoughts???

 

[CockneyReject]

As per usual, no actual figures.

I was under the impression that if a reading was <1MΩ the meter gave a reading in KΩ. I must be mistaken.

What I find annoying is the OP seems willing to condemn a system when he clearly hasn’t tested correctly.

Depends on the meter, on the 1720's we use if it's <1Mohm it shows 0.00 then you have to change the setting to continuity to measure the resistance

Loads of "sparks" are the same now though tony they just record whatever the meter tells them and move on, get the report out and condem an install which is still most likely in a serviceable condition

 

[shanky887614]

Depends on the meter, on the 1720's we use if it's


not me i passed

 

[Knobhead]

Loads of "sparks" are the same now though tony they just record whatever the meter tells them and move on, get the report out and condem an install which is still most likely in a serviceable condition

What are the chances of them knowing how to calculate the minimum IR value?

 

[shanky887614]

What are the chances of them knowing how to calculate the minimum IR value?

no need it tells you in the reg book what the minimum valve should be for the supply voltage.

i bet a lot of people fail circuits for 1.5Mohm when actually it complies for that voltage

 

[Knobhead]

1MΩ is a convenient figure dreamed up by the IET. It’s not the calculated value.

I’ll give you a scenario:
If you were to test a 50 year old 75HP 433V 3Ph motor, what would you accept for the supply cable minimum IR for L→L and L→E?

 

[telectrix]

1MΩ is a convenient figure dreamed up by the IET. It’s not the calculated value.

I’ll give you a scenario:
If you were to test a 50 year old 75HP 433V 3Ph motor, what would you accept for the supply cable minimum IR for L→L and L→E?

is there a RCD on the circuit? :iamwithstupid:

 

[Knobhead]

It’s a rotten question.

I’ll tell you when I get back home.

 

[Knobhead]

is there a RCD on the circuit? :iamwithstupid:

It’s a motor in a plant, no E/L protection what so ever other than OCPD.

Keep out of this tel, let the youngsters have a go.

 

[shanky887614]

1MΩ is a convenient figure dreamed up by the IET. It’s not the calculated value.

I’ll give you a scenario:
If you were to test a 50 year old 75HP 433V 3Ph motor, what would you accept for the supply cable minimum IR for L→L and L→E?

depends on the age of the cable but i would accept a low ir figure as long as it hasnt degraded a lot from last ir test. if last ir test a year ago was say 10Mohm and this year was 1Mohm i would fail it for example

i have no idea tony

 

[telectrix]

It’s a motor in a plant, no E/L protection what so ever other than OCPD.

Keep out of this tel, let the youngsters have a go.

i was being facetious, tony. whoever heard of a RCD on a motor that size. :38:

 

[Knobhead]

This is from a genuine case, a plant with 250+ motors in a damp, dusty and cold environment. The motors ranged from ½ to 800HP.

The calculation is based on a maximum of 1/10000[SUP]th[/SUP] leakage of the circuit FLC.

2 x the Ph→Ph or Ph→E DC voltage is used for the tests.
For 433V you would use 1000V DC Ph→Ph or 500V Ph→E.

I said it was a rotten question, you need the FLC from the scant information I gave.

You need to calculate the motor FLC taking in to account efficiency and power factor. It’s an old motor so 92% efficiency could be a start 0.87 PF maybe?

But we’ll base this on 75HP 92% Ef 0.87 PF where 1 HP = 764W
There could be another way though.

Anyone care to carry it on?

 

[davesparks]

There are a couple of different calculations which have been used over the years.
For complete installations there was a calculation based on the number of circuits in the installation, I'll look it up when I get home later.
The other method I know is the one Tony posted above using 1/10000th FLC as the maximum leakage.

 

[Knobhead]

It is Saturday night so I’ll leave this until tomorrow evening.

As Dave said it’s an old method but in a large installation it’s invaluable.

I said earlier, 1MΩ was a global figure adopted by the IET for ease, it has no real foundation.

 

[sparksburnout]

No, no, no - job was in London :smile5:
Off topic, but I got asked about an outside light in Chester a while back; I said I could do it but I wasn't gas safe.

Not safe at all if you ask me.

 

[davesparks]

Here we go, IR testing according to the 13th edition.