Ramp testing a rcd

[Apache]

But it can also be used as a diagnostic aid to help see how much standing leakage there is on appliances that are plugged in.

So you'd do the test with everything disconnected and repeated under load and compare the difference?

 

[NozSpark]

So you'd do the test with everything disconnected and repeated under load and compare the difference?

Normally you'd turn up to a tripping RCD and maybe do a ramp test to see if there is any leakage, if it trips at a low value then you'd investigate it by disconnecting loads and IR tests

 

[Guy]

Because AC current is 50hz (thats back and forwards 50 times a second, if you test it for 40 milli seconds you wont have tested through the full 50 Hertz, I think

I am starting to think I am missing something obvious here...........I am unsure to why the hertz are revelent, I think its whether the line current is in its pos or neg cycle that matters, but whatever number of degree's the line current is in the neutral is the complete opposite, mmmm my brain is aching now!

 

[Doc Hudson]

Because AC current is 50hz (thats back and forwards 50 times a second, if you test it for 40 milli seconds you wont have tested through the full 50 Hertz, I think

I think I need to correct you calculations there John. 50hz = 1 second/50 = 0.02seconds = 20ms per cycle or 10ms per half cycle, 40ms would allow two full cycles to pass during the test no?

Doc H.

 

[Guy]

I found this statement on the web, can someone please confirm that this is correct/incorrect if they are completely sure.

By definition, AC current comprises of positive and negative half cycles with respect to a zero reference point, and an AC fault current can start to flow to earth at any point during either half cycle. An AC Type RCD will only trip in response to either the positive or negative half cycles of the AC earth fault current, whereas an A Type RCD will respond to both half cycles. As the AC Type RCD is blind to either the positive or negative half cycles of an AC fault current, the fault current could flow for up to 10mS before the RCD will see the fault current. This 10mS will be added to the response time of the device. RCD testers are usually provided with a switch to enable the user to start the flow of the test current at 0 degrees or 180 degrees, i.e. starting on a positive going or a negative going half cycle respectively. By starting the testing of the RCD at both settings of the test current conduction angle, the user will be able to determine the maximum trip time of the RCD. This can be done at different test current levels.

 

[SPECIAL LOCATION]

I found this statement on the web, can someone please confirm that this is correct/incorrect if they are completely sure.By definition, AC current comprises of positive and negative half cycles with respect to a zero reference point, and an AC fault current can start to flow to earth at any point during either half cycle. An AC Type RCD will only trip in response to either the positive or negative half cycles of the AC earth fault current, whereas an A Type RCD will respond to both half cycles. As the AC Type RCD is blind to either the positive or negative half cycles of an AC fault current, the fault current could flow for up to 10mS before the RCD will see the fault current. This 10mS will be added to the response time of the device. RCD testers are usually provided with a switch to enable the user to start the flow of the test current at 0 degrees or 180 degrees, i.e. starting on a positive going or a negative going half cycle respectively. By starting the testing of the RCD at both settings of the test current conduction angle, the user will be able to determine the maximum trip time of the RCD. This can be done at different test current levels.

Not sure about some of that definitions of the type AC & A..

The one is more to do with problems associted with pulsating DC currents

From Wiki..

Type

Standard IEC 60755 (General requirements for residual current operated protective devices) defines three types of RCD depending on the characteristics of the fault current.Type AC: RCD for which tripping is ensured for residual sinusoidal alternating currents

Type A: RCD for which tripping is ensured for residual sinusoidal alternating currents

for residual pulsating direct currents

for residual pulsating direct currents superimposed by a smooth direct current of 0.006 A, with or without phase-angle control, independent of the polarity

Type B: RCD for which tripping is ensured as for type A

for residual sinusoidal currents up to 1000 Hz

for residual sinusoidal currents superposed by a pure direct current

for pulsating direct currents superposed by a pure direct current

for residual currents which may result from rectifying circuits three pulse star connection or six pulse bridge connection

two pulse bridge connection line-to-line with or without phase-angle monitoring, independently of the polarity

This page..

Residual-current device - Wikipedia, the free encyclopedia

---------- Post Auto-Merged at 17:57 ---------- Previous post was made at 17:55 ----------

Bottom line is that as magnetic fields are involved and strength of leakage current and the relative potential of the path that the leakage is travelling down..

e.g. earth via a body may be at a different potential than true earth (ov)

so one half cycle may have greater fault current than the other IMHO..

Thus magnetic fields differ on the trip coil & operating times..

If you don

 

[Guy]

so the RCD can only recognise electron flow in one direction within the coil, correct?

 

[SPECIAL LOCATION]

so the RCD can only recognise electron flow in one direction within the coil, correct?

No..

The imbalance current will create and induce current into the trip coil.. (pic on page 105) yes?

The direction of that induced current will affect the polarity of the induce magnetic field in the windings of the trip coil yes?

Unless you can categorically say that:-

The potential from the positive half and negative half are equal with respect to the fault path to earth

AND

the induced current in the trip coil is alway equal on both halves of the cycle

AND

the magnetic flux is equal in strength to move whatever mechanical bit it moves to trip the RCD

AND

therefore the physical RCD always produces the same characteristic on both halves of the cycle..

and operate in the time frame on both halves of the cycle (which reality says they DONT!)

Then you MUST test both halves to ensure in a worst case the RCD will trip in the desired timeframe.

 

[Guy]

No..The imbalance current will create and induce current into the trip coil.. (pic on page 105) yes?

The direction of that induced current will affect the polarity of the induce magnetic field in the windings of the trip coil yes?

Unless you can categorically say that:-

The potential from the positive half and negative half are equal with respect to the fault path to earth

AND

the induced current in the trip coil is alway equal on both halves of the cycle

AND

the magnetic flux is equal in strength to move whatever mechanical bit it moves to trip the RCD

AND

therefore the physical RCD always produces the same characteristic on both halves of the cycle..

and operate in the time frame on both halves of the cycle (which reality says they DONT!)

Then you MUST test both halves to ensure in a worst case the RCD will trip in the desired timeframe.

Its still foggy but I can definately see some sunlight shining through, your time and patience are appreciated.................but dont pat yourself on the back just yet as I am not convinced I can tick the 'understand' box yet and might well be back