RCD tripping more since route of supply changed!

[Robin Spark]

If you wanted to read if there is any natural leakage occurring when appliances are in normal use, you would need to read the current flowing down the earth, CPC, But a normal clamp meter would not typically be able to read milliamp values..so you would need to put a meter on a milliamp scale in series with the earth conductor.. (cuz as we all know... voltages read in parallel, Current read in series)

Easiest place to do this is at the MET (Main earth connection.).

Turn installation Off

Disconnect main earth connection, put your meter probes on your two ends of the earth, (MET, and Earth conductor).

Re-energise installtion...

see what current if any is flowing down the Earth conductor....

If there is zero Milliamp flowing...

Its may imply there is one single fault event somewhere that is occurring & causing the trip..

If there is already a few miliamps... e.g. 10ma - 20ma,

could be a combination of various appliances each leaking a bit..

then one final one tips the balance!

Hi Specs,

is this method safe? didnt think it was a recommended method thats all and I am sure that I have read somewhere about not doing this.

I can appreciate in an ideal world we all would have one of those milliamp earth leakage clamp meters but we dont.

 

[SPECIAL LOCATION]

Hi Specs, is this method safe? didnt think it was a recommended method thats all and I am sure that I have read somewhere about not doing this.

I can appreciate in an ideal world we all would have one of those milliamp earth leakage clamp meters but we dont.

IMHO assuming you are a "Competent Person" its about as safe as doing a Ze test....Earth disconnected from installation!

Or

Doing a Zs on a live installation deliberately putting a voltage down the Earth/CPC!

Or

Opening up any live equipment to get you meter probes on to take some readings!

How else could you find out any leakage current value?

(other than Two clamp meters around each of the L & n tails! & minus any difference.)

If I were doing this, I would be at the CU, turn individual circuits on one at a time... whilst watching my meter to see if any readings appear...

Don't forget we are only talking milliamps.....

If you'd of had 1 amp or more flowing down the earth wire Your RCD would never set in the first place...

Most typical Clamp on Ampmeters dont get much good accuracy below 0.5amps!

 

[Robin Spark]

Gonna have to think where I read about this which was only over the last couple of days, I thought it was on the ECA website but just really quickly checked and couldnt find it.

However the article was recommending about not using a multimeter to measure earth leakage in the cpc as there was a good chance of it blowing up in your hand if not adequately internally fused and a large fault current occurred.

But now as per normal you've got me thinking cos my test leads are fused (not sure of fuse rating and too late now to check) and just so long as your method is followed ie isolate supply before putting mulitmeter in series with MET and earthing conductor and ensuring good connections with crocs then this should be ok.

 

[monkey5]

Other one to look at if it is every half hour or so is fridge/freezer, could be a fault on the compressor maybe ?

hi it was one of the first things i checked hoping it would be this but unfortunatly it still tripped when disconnected. thanks anyway

 

[monkey5]

My money would be on something along the lines of what the others have said... dodgy appliance... typically one permanently switched on OR one involving water, or damp external conditions..

Fridge..

Freezer..

Washing machine..

Dishwasher..

Central heating system..

Outside wiring..

Kettles..

Steam irons..

etc..

have tried most of these except the washing machine and dishwasher, they'll be the first thing im checkin morning. thanks

just re read the post and i think your meaning it could be a few of these all with small amounts of earth leakage so all added together eventually gives me the 30mA needed to trip RCD.

 

[monkey5]

If you wanted to read if there is any natural leakage occurring when appliances are in normal use, you would need to read the current flowing down the earth, CPC, But a normal clamp meter would not typically be able to read milliamp values...

which meter would recommend to use special. do you mean a multi meter with fused leads on milliamp setting

 

[Andy™]

Hi Specs, is this method safe? didnt think it was a recommended method thats all and I am sure that I have read somewhere about not doing this.

I can appreciate in an ideal world we all would have one of those milliamp earth leakage clamp meters but we dont.

its safer than it sounds. although your ammeter probably wont be able to take a full fault current to trip an MCB, it should be able to handle enough current to trip RCD. the ammeter wont really add much resistance to the main earth, so as long as power is turned off whilst you put meter into place/remove it, you should be safe

 

[monkey5]

its safer than it sounds. although your ammeter probably wont be able to take a full fault current to trip an MCB, it should be able to handle enough current to trip RCD. the ammeter wont really add much resistance to the main earth, so as long as power is turned off whilst you put meter into place/remove it, you should be safe

would you just use a multi meter with fused leads and clips. and i assume need to disconnect the main earth and earth/cpc from the circuit then connect to each end then energise the circuit? sorry just want to make sure i get it right.

Blushing

 

[SPECIAL LOCATION]

Gonna have to think where I read about this which was only over the last couple of days, I thought it was on the ECA website but just really quickly checked and couldnt find it.However the article was recommending about not using a multimeter to measure earth leakage in the cpc as there was a good chance of it blowing up in your hand if not adequately internally fused and a large fault current occurred.

But now as per normal you've got me thinking cos my test leads are fused (not sure of fuse rating and too late now to check) and just so long as your method is followed ie isolate supply before putting multimeter in series with MET and earthing conductor and ensuring good connections with crocs then this should be ok.

OK Robin, ermm.. :| yes..Blushing going in blind and just sticking a

 

[SPECIAL LOCATION]

would you just use a multi meter with fused leads and clips. and i assume need to disconnect the main earth and earth/cpc from the circuit then connect to each end then energise the circuit? sorry just want to make sure i get it right.Blushing

Hi Monkey

This is where Knowledge of the layout of the particular installation comes in to its own...

Basic concept:

1/

Any Residual earth fault current MUST by its very nature be flowing to earth.

2/

Hopefully this earth path is down though the main earth terminal..

e.g.

Incoming Cable sheath {TNS}

Strapped Earth+N at supply head {TN-C-S}

Down the rod {TT}

BUT... there could possibly be parallel paths down water / Gas metal pipes!

3/

You need to find an accessible point between

(a) the earth bar in CU where all the circuit CPC's terminate and

(B) the main earth terminal/Rod/Sheath/PME joint/Parallel path.

4/

If all of your earth bonding cables come onto the main earth bar in CU

this could be the place to do the biz.

5/

If you have an accessible external earth block adjacent to the CU & head,

this would be an easier point IMHO!

6/

On some really badly designed & laid-out installations, it may not have any suitable practical place to access or get your meter in to get any readings.

7/

But if you can do it you need to break in-between the point(s) where current can get to physical earth and the common connection where all circuit CPC's terminate!

HTH

; )Guiness DrinkGuiness Drink

 

[Robin Spark]

Thanks Specs, that was really good of you to explain that lot in detail and to make sure that everyone understands the safety aspects.

I'll pay for those drinks you got mate Guiness DrinkGuiness Drink

Just some extra info if anyone cares to read about multimeters

http://fluke.informationstore.net/efulfillment.asp?publication=10046-eng