Low IR readings....

[sythai]

Just wondering what sort of IR reading it would normally take to trip a 30mA rcd?

Been testing today and ring is showing approx 5 Mohms on each leg?

Lighting is showing:

L-N 12.4 Mohms
N-E 5.4 Mohms
L--E 3.94 Mohms

Everything was definately unplugged, lamps out etc..

Cant energise supply until next week, will find out then I suppose.

Install is about 30 years old, would these sort of readings normally just be due to age and deteroation of cables?

Not had to do much fault finding before so bare with me just trying to learn.

Thanks,

Sy

 

[stef]

Hi Sythai,

I personally would disconnect the circuit from the RCD. Is it a type with an earth lead on?
You will get a funny reading as it compares incoming-outgoing to earth.

 

[sythai]

Nop it's not connected, got all the ends sticking out at CU....

 

[stef]

OK. If the trip current is 30mA @ 230 V then it is 7.6 KOhm , minimum allowed is 1MOhm so you are OK anyway

 

[sythai]

I understand the min allowed no prob with that.... just wondered if when I do come to energise there may be a chance it will trip with those low IR readings ?

 

[stef]

Hi again,

no it won't trip 'cos you are well above the 7.6 KOhm trip margin. You readings for a 30 year old install
are quite normal.

 

[sythai]

Thats good thankyou...........

 

[Johno]

To be honest I wouldn't be happy with them readings, even though they are allowed but I suppose all you can do is explain to customer and see if he wants you to look into it further or not.

 

[lloyd1980]

mate even lower than that wont trip an rcd

Had it today on a mains change, flicked rcds on temporarily just to see if they would hold
everything held thought, great no faults to sort out
turned it off, came to IR and on the lighting it was 0.45 M Ohms
dead low, cables out of the rcbo out the board and both RCBOs were holding

was at a cieling rose with a screw that had clipped a cable

 

[sythai]

Yeah customer understands no prob, he was there helping me test and I fully explained what is acceptable, what is not etc.

Well all being well then when come to energise on Tue should all stay in

Not so sure about when he turns on the cooker though,it's the orginal 60's one and same goes for immersion, older than me

Thanks chaps,

Sy