RCD x 5 touch voltage too high

[Sintra]

A ramp test basically is used to confirm that an RCD trips out at a current greater than 1/2 the rated current and up to 1 x the rated current of the device.

So for a 30mA RCD the ramp test values should be >15mA and <30mA

 

[brucelee]

Hi Sintra clear and precise mate as always

 

[pushrod]

marcusone when you say all loads off do you mean nothing pluged into sockets or am i missing the point when i test my rcds ie ring main sockets there is nothing plugged into them hence i then carry out my secuence of rcd test with my tester cant understand were this 25v touch voltage is from is the tster detecting this interesd to find out as i have never came across this before

If for example you have 1 rcd protecting 4 mcbs then if you want to test the rcd, switch of the other 3 mcbs and remove all loads from the one remaining mcb then test the the rcd through that circuit.

The reason is that if you have the other mcbs on they could be contributing small earth fault currents as well as the one your rcd tester is introducing to the circuit so you can get wrong results.

 

[Just]

Don't understand why your meter is indicating a touch voltage >25V as this would be acceptable.

Touch voltage has to be <50V

I think high end test kit has the option to select a touch voltage error of >25V or >50V( although I am not sure why you would need two options) I agree Sintra, >50V warning makes sense but >25V is annoying as it has no relevance and should be an accurate result to the nearest volt that you could accept if necessary, and it won't complete the trip test. You get what you pay for..

 

[pushrod]

I think high end test kit has the option to select a touch voltage error of >25V or >50V( although I am not sure why you would need two options) I agree Sintra, >50V warning makes sense but >25V is annoying as it has no relevance and should be an accurate result to the nearest volt that you could accept if necessary, and it won't complete the trip test. You get what you pay for..

Certain special locations used to (not certain if they still do) limit touch voltages to 25V

 

[Sintra]

Yes they do but the meter should still be able to test for the standard 50V scenario unless the op has the instruement on the wrong setting. Not sure as I have had no experience of that meter.

 

[pushrod]

TBH i didn't even know that socket and see did proper test meters

 

[Sintra]

TBH neither did I.

 

[pushrod]

Great minds ... equally vacant eh? lol

 

[malcolmsanford]

The Fluke 1653B we use over here in Saudi is from Europe and it is set up for 25v touch voltage but you can change it to 50v which I did.

The 25v touch voltage as been forwarded to be included into the next amendment of the BS 7671-2008 in the medical location sections. The man to ask probably will be IQ

 

[Farmelectrics]

cheers pushrod i no were your coming from i personally dont test the rcd i just do the indiviual circuts and if it takes the rcd out as it should with the x1 x5 tests job done as far as im concerned

 

[Farmelectrics]

im sorry still dont understand this 25v touch voltage please explain is the meter detecting this why cant you continue with your rcd test anyway

 

[pushrod]

cheers pushrod i no were your coming from i personally dont test the rcd i just do the indiviual circuts and if it takes the rcd out as it should with the x1 x5 tests job done as far as im concerned

Hi farmelectrics, if you are not actually switching off all the the other relevant mcbs, and loads on that individual circuit then you can not be certain that you are getting the correct test currents of 15mA, 30mA and 150mA (for 30mA rcd) going through your rcd because the other circuits/loads could be contributing some earth leakage which will be added to the test current the meter supplies. So you can not be confident the disconnection times are correct. When you have tested the rcd properly once, there is no need to test it through the other circuits.

 

[Farmelectrics]

ok pusrod i understand just thinking of were im working on rcbos not the domestic boards your on about were does this touch voltage come from though

 

[pushrod]

ok pusrod i understand just thinking of were im working on rcbos not the domestic boards your on about were does this touch voltage come from though

Yes if you are working with rcbos then they all need individual testing.

TBH i am not familar with meters that can signal about touch voltage, mine doesn't.

As i understand it an rcd should limit the voltage on any exposed-conductive-part to a max of 50V(the touch voltage).

We check that the Zs on a 30mA rcd protected circuit is < 1667 ohms.

If that is the case you know from V = IxR when a current of 30mA flows that in the worst case of a 1667Ω Zs then 1667 x 0.030 = 50volts for < 300mS (BS EN61008/9) ie the rcd trips preventing the voltage on metal parts rising above 50V.

If you were wanting to limit touch voltage to 25V you would effectively be halving the max Zs of 1667 to 834Ω for a test current of 30mA, or you could have a 1667 max and then the current would be 15mA that would cause the rcd to operate.
I don't however know the precise details.
Hope that is of some help.