rcd not tripping

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went to a pre-fit for a kitchen company i do work for

recent c/u change, no paperwork, 16th board but done in may so no drama, 5+5 split load wylex. 16mm main earth

tns, ze = 0.15, socket outlet zs = 0.44-0.56(spur) l1-l1 = 0.4 n1-n1 = 0.5 r1-r1 = 0.75

rcd trips pressing test button but doesnt trip with meter on rcd test although with trip function disabled on loop test the rcd trips before giving a reading as it should

replaced rcd to no avail.

all neutrals look to be correct,

feel i have missed something obvious but had one of those days so if anyone has any thoughts they will be much appreciated before i contact original spark

 
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Is there a possibility of an insulation issue between N/E ?

If they are *almost* short, the RCD can`t differentiate the loss; therefore won`t trip. Can you do an ins. test?

What are the other 4 ccts? What happens if you disconnect them ( phase + neutral)?

If safe to do, try a ramp test for 100mA.

More info, methinks m8

 
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yes an insulation test will obviously have to be done either way but not possible today as it was just a pre-fit, the house was like a cluttered bomb site and i didnt want to run around trying to unplug everything.

i understand what you're saying about the *almost* short, makes sense however the house only has up and down lighting circuits on non rcd side and up and down ringmains,

the upstairs ringmain gave a loop reading but again didnt trip on rcd test which threw me to the point of doubting my meter, however i've since tried it at home and it was faultless

 
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But both rings are on the SAME rcd; so a fault with either one; or one of the three other circuits, could cause the problem............

And the problem will occur on ALL circuits, because they`re all in parallel at the point where they meet the RCD - yes?

 

seajayess

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Why dont you just do L/CPC then N/CPC insulation tests no need to unplug everything as long as you dont do L/N. The RCD will not trip with L/N fault anyhow and if in doubt do the test at 250 volts first CJS

 

mike spark

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Why dont you just do L/CPC then N/CPC insulation tests no need to unplug everything as long as you dont do L/N.
Thats a good little tip that mateApplaud Smiley, i never connected the dots on that one myself but it seems obvious when you think about it:8}.

The RCD will not trip with L/N fault anyhow and if in doubt do the test at 250 volts first CJS
Why wont the RCD trip, for instance i was lead to believe that a lighting circuit with no CPC will still trip a RCD, and shouldnt the MCB trip if there is a L-N fault.

Or is it just that i have had to much to drinkGuiness Drink and am talking nonsense.

 

mike spark

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Sorry for my stupidity steptoe but i am a little confusedBlushing

it will still have a leakage to earth through the fabric of the building
So is that why an RCD will still work on a light circuit with no CPC? Or will ot fullstop.

RCD only detects an imbalance between L-N.
Which you need an CPC to do?

 

Mr Sworld

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Sorry for my stupidity steptoe but i am a little confusedBlushingSo is that why an RCD will still work on a light circuit with no CPC? Or will ot fullstop.

Which you need an CPC to do?
However if you are providing the path to earth by touching a live wire you will create an imbalance as the current is passing through you.

 
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Which you need an CPC to do?
RCD does NOT need a CPC!

Main RCD switch only has 2 terminations Live(or 'Line') & neutral...

the imbalance between these two causes the trip..

e.g. person grab hold of the live wire with bare foot onto the ground..

NO cpc..

or your two wire double insulated lawn mower..

No cpc.. RCD breaker still functions quite happily! ;) :)

 

mike spark

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Yeah thats what i was taught that an RCD will still operate on circuit with no CPC but i got myself a little confused during this thread.

I understood it that a circuit with no CPC will trip if contact is made with phase or neutral, and that any short between phase and neutral will trip the MCB. Also that if the RCD has tripped and the circuit with no CPC has passed contnuity/IR then that circuit is not tripping the RCD.

Would i be right for thinking such terrible thoughts;) :^O ?

 
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Also that if the RCD has tripped and the circuit with no CPC has passed contnuity/IR then that circuit is not tripping the RCD.Would i be right for thinking such terrible thoughts;) :^O ?
Take a hypothetical situation

Light circuit NO cpc.. but connected via RCD (say TT inst)

some idjut sticks their finger in a live lamp holder while changing the bulb & resting across the metal central heating radiator..

30mm could flow through body.. trip RCD...

but then the fault path is moved, (persons takes their hand out of lamp holder),

so NO CPC circuit did trip RCD, when reset RCD all resets no problem..

IF RCD still tripping when try to reset, more likely a permanent fault somewhere..

less likely to be non-CPC circuit.. but still possible???

 

mike spark

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Take a hypothetical situationLight circuit NO cpc.. but connected via RCD (say TT inst)

some idjut sticks their finger in a live lamp holder while changing the bulb & resting across the metal central heating radiator..

30mm could flow through body.. trip RCD...

but then the fault path is moved, (persons takes their hand out of lamp holder),

so NO CPC circuit did trip RCD, when reset RCD all resets no problem..

IF RCD still tripping when try to reset, more likely a permanent fault somewhere..

less likely to be non-CPC circuit.. but still possible???
Thanks mateApplaud Smiley:D, that makes perfect sense.

In your hypothetical situation could the fault that is less likely to be on non-CPC circuit be something along the lines of, drill through phase conductor so RCD trips, so reset RCD but still trips because of open circuit fault on phase conductor.

Or am i way off the mark?

 
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Thanks mateApplaud Smiley:D, that makes perfect sense.In your hypothetical situation could the fault that is less likely to be on non-CPC circuit be something along the lines of, drill through phase conductor so RCD trips, so reset RCD but still trips because of open circuit fault on phase conductor.

Or am i way off the mark?
Open circuit wouldn't cause RCD fault..

If open circuit.. NO current flow.

If NO current flow... No imbalance between L&N

cuz both L&N have zero current flow!

If drilled though & live conductor still touching drill

or person grabs hold of drill bit & touching an earth? re-trip

 

mike spark

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Open circuit wouldn't cause RCD fault..If open circuit.. NO current flow.

If NO current flow... No imbalance between L&N

cuz both L&N have zero current flow!

If drilled though & live conductor still touching drill

or person grabs hold of drill bit & touching an earth? re-trip
Ok i see, so it would be more along the lines of the drilled conductor being damaged but not broken affecting current flow causeing RCD to trip? or maybe drilling the conductor could cause a loose connection affecting the current flow causeing the RCD to trip?

Or from your example of touching the conductor when changing the bulb causeing a loose connection?

 
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thanks for the responses the problem has been sorted apparently, no idea what that was, as i said in op it was just a pre-check before confirming prices and starting work next week on the kitchen, the original wylex consumer unit had been replaced by another contractor who, so im told, has been back and rectified the problem.

 

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