funny readings

[paul b b]

hello gents,

doing a bit of second fixing today, i sorted my strappers out (thanks chaps!) and a ring circuit, did a few tests on the ring, all seem fine, turn breaker on, check voltage, megger reads 244v, do a Zs 110ohms.....eh, try another socket, plug megger in it reads 2v....eh turn it on megger says reverse polarity...wtf is going on??? take all sockets off, all wired correctly.

try again, plug megger in, reading 245v polarity fine, Zs 0.79ohms.

could this be down to damp plaster? or is it because the customer is getting me to use rubbish sockets?

thanks

paul

 

[ianmacd]

Could be both. Also check the terminals are all actually in the same place as I seem to remember one manufacturer that swapped L & N over and if you had some out of each batch, it was a PITA.

 

[paul b b]

i double checked that after getting funny readings

 

[ianmacd]

So how many sockets had dodgy readings and when did you last change the batts in your megger?

 

[paul b b]

i tested about 6

changed the batts about 2 months ago

i just thought it was odd that when everything was unscrewd it tested ok

 

[ianmacd]

Ahh ok so only when they are on the wall do you get strange readings? Did you not get them when doing dead tests too?

 

[paul b b]

i did the dead tests when they were off the wall

 

[ianmacd]

ahh. OK. With sockets, there is no need for them to be off the wall when dead testing assuming you have a plug in adaptor (which I assume you do with the megger). I would also have switches fixed when testing otherwise you will not know that a wire has popped out the back before you energise the circuit.

 

[paul b b]

i understand that, but i thought i saw a post about damp plaster causing funny readings, just to to clarify this before i start ripping everything apart

 

[ianmacd]

It most likely will be damp plaster and you would have got weird readings at dead test stage if they plates had been in place. Has the room recently been plastered then?

 

[paul b b]

yes, and cold house, so taking ages to dry, i told the builder to get a space heater in there for a day, but you know what builders are like

 

[ianmacd]

Probably take more than a day. The thing that slightly worries me about performing the dead tests without all the plates in place is that when the circuit was energised there could have been an accident. Electrickery and wet plaster do not mix.

 

[gselectrical]

i tested about 6changed the batts about 2 months ago

i just thought it was odd that when everything was unscrewd it tested ok

Damp house. Damp plaster. J

 

[paul b b]

yeah, i just wanted to 'screwup' as the customer is back on the weekend and wanted it to look good. i would have redone the dead tests when i screwd up. just keen to get it looking good

 

[tom1]

prob not this but what batteries did u put in. I was told that you can only use alkaline

 

[tom1]

using other types can give dodgy readings. So I am told

 

[paul b b]

using other types can give dodgy readings. So I am told

think it was duracel

 

[tom1]

prob alkaline

R9 I think

 

[Lurch]

using other types can give dodgy readings. So I am told

Possibly due to the lower voltages, 1.2V on rechargeables versus 1.5V on alkalines. So going on the basis most use around 6 batteries it'll be running about 1.8V lower, which is enough to give low battery readings on a lot of equipment.

I've seen similar symptoms on non electrical equipment with rechargeable versus alkalines.

 

[SPECIAL LOCATION]

hello gents,doing a bit of second fixing today, i sorted my strappers out (thanks chaps!) and a ring circuit, did a few tests on the ring, all seem fine, turn breaker on, check voltage, megger reads 244v, do a Zs 110ohms.....eh, try another socket, plug megger in it reads 2v....eh turn it on megger says reverse polarity...wtf is going on??? take all sockets off, all wired correctly.

try again, plug megger in, reading 245v polarity fine, Zs 0.79ohms.

could this be down to damp plaster? or is it because the customer is getting me to use rubbish sockets?

thanks

paul

Switched Sockets?

Did you rock the switch off & on a few times...

I have had a higher resistance reading through switch contacts before now...

I always tend to rock the switch off & On three or fours times just to help clean the switch contacts a bit!