Risteard
Senior Member
The >50V warning should flash and the meter should beep intermittently.
Rcd Test Problem
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sparkytim
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Sounds like Faulty MeterHi again,I've just ran some RCD tests with my Megger.
The touch voltage is shown on a bar graph above the trip time - on each of my tests the graph didn't move, but I am testing on TN-C-S.
I must admit, I've never had a case where the set touch voltage (25v or 50v) has been exceeded on my megger, so I can't say for sure what it would display if this were to happen.
As someone mentioned earlier, though, I can't see how the touch voltage can be exceeded with a Ze of 320 ohms when the calculation for a 50v touch voltage gives us 1667 ohms at 30ma
Bit of a puzzler:C
3 Year warranty, they are pretty good at sorting them quickly.
Just been thinking a bit more about this today and I definately think that you have a N_E fault on another (lightly loaded) circuit.
Assuming that your socket circuit is ok but that you have a 100ohms N-E fault on another circuit and a Ra of 300ohms,, then when you meter sticks 30mA down to earth then the prefered path for that test current is back up the faulty circuit (earth) and onto it's N conductor and then back through the RCD .. in the case as I have stated above then the ratio of this current will be 3:1 i.e. 22.5mA through the faulty circuit N-E fault and only 7.5mA straight to earth... the imbalance on the RCD will only be 7.5mA and will therefore allow the touch voltage to exceed the 50v limit.
HTH.... do full IR cecks on all circuits!
Assuming that your socket circuit is ok but that you have a 100ohms N-E fault on another circuit and a Ra of 300ohms,, then when you meter sticks 30mA down to earth then the prefered path for that test current is back up the faulty circuit (earth) and onto it's N conductor and then back through the RCD .. in the case as I have stated above then the ratio of this current will be 3:1 i.e. 22.5mA through the faulty circuit N-E fault and only 7.5mA straight to earth... the imbalance on the RCD will only be 7.5mA and will therefore allow the touch voltage to exceed the 50v limit.
HTH.... do full IR cecks on all circuits!
No mate, I wasn't implying that my meter was wrong - I was comparing things to the Ops problem with his meter.
I wouldn't have thought anything would register on the touch voltage read-out with Ze readings below 33 ohms - ( I delta n X Ze ) 0.03A X 33 = 1volt
In the OPs case, his touch voltage should read 0.03A X 300 ohms = 9 Volts, although I think this reading would also depend on how fast the RCD tripped.
In the OPs case, of course, it didn't.
Has anyone considered that he could just have a faulty RCD?
Unless, of course, I'm missing the obvious
Thanks for all your replies it is a bit of a brain teaser.
The polariry is fine. Well its been there for 20+ years.
The meter is fine works everywhere else.
I could be a faulty RCD i suppose.
Doesn't it only put 15mA through on the
test?
I guess the best way to test for a N - E fault would be to test continuity between all the N seperately at the CU and the MET.
I'm just wondering if the RCD in question is a time delay? But why would they put a time delay main switch/rccb if it was the only RCD on the installation?
I might turn the touch voltage off on the tester and see what happensheadbang
The polariry is fine. Well its been there for 20+ years.
The meter is fine works everywhere else.
I could be a faulty RCD i suppose.
Doesn't it only put 15mA through on the
I guess the best way to test for a N - E fault would be to test continuity between all the N seperately at the CU and the MET.
I'm just wondering if the RCD in question is a time delay? But why would they put a time delay main switch/rccb if it was the only RCD on the installation?
I might turn the touch voltage off on the tester and see what happensheadbang
Just do a global N-E IR test
I'll try that first then.
Just pinched this off a test instrument website.
"This is known as touch voltage. It is requirement of the regulations that a measuring instrument cannot create a situation whereby 50v or greater could be passed into the earth system. The tester will check the mains supply in all configurations, it the result shows that the 50v rule could be breached further tests are inhibited. If this occurs check appliances are not connected to the supply under test as leakage currents from these could be causing the problem."
There could be a hidden appliance lurking somewhere that i missed
Just pinched this off a test instrument website.
"This is known as touch voltage. It is requirement of the regulations that a measuring instrument cannot create a situation whereby 50v or greater could be passed into the earth system. The tester will check the mains supply in all configurations, it the result shows that the 50v rule could be breached further tests are inhibited. If this occurs check appliances are not connected to the supply under test as leakage currents from these could be causing the problem."
There could be a hidden appliance lurking somewhere that i missed
paul b b
Well-known member
silly question but have you tested a rcd since? it maybe a dodgy lead
Yeah mate i came home and tested it, worked fine.
I think on Monday i'm going to:
1) Have a damn good look around and make sure all the load are disconnected because it was Friday afternoon and i was being called Guinness
Test again
2)N - E IR Test as mentioned and if fails further investigate to find suspect circuit.
Cant think of anything else to do really apart from break it down into sections and test everything!
Thanks for all your help guys its nice to be on a forum were people want to help you and dont just take the p**s
I think on Monday i'm going to:
1) Have a damn good look around and make sure all the load are disconnected because it was Friday afternoon and i was being called Guinness
Test again
2)N - E IR Test as mentioned and if fails further investigate to find suspect circuit.
Cant think of anything else to do really apart from break it down into sections and test everything!
Thanks for all your help guys its nice to be on a forum were people want to help you and dont just take the p**s
