Possible Job For Tomorrow

[Andrewr3]

Reported as occasional trip of an RCD. Leakage current noted 2.5A when cooker switched on (which is on a 30mA RCD). Could be interesting.

 

[Darkwood]

Are you asking for hints/tips or just informing us of your working day ahead?

 

[Pete999]

Whats the photo about Andy?

 

[uksparks]

If the cooker is on and it's leaking >30mA why has it not tripped then?

2,500,000 / 1000 gives milliamps

mA = 2500mA

IR = 230 / 2500

IR = 0.092 Ohms

if I'm correct in my calculation you have a almost a dead short somewhere? Either this is correct or I'm going to look like a right plonker.

working it the other way just to check...

R = IR x 1,000,000

R = 92,000

I = 230 / R

mA Leakage = I x 1000

mA = 2.5A

 

[uksparks]

That's based on 2.5A sorry, not 2.35A

 

[Marvo]

The 'occasional trip' and the 2.5A leakage current don't really go well together. 'Won't reset' would be better.
Measuring the leakage down the CPC or main earth doesn't show you what's being lost down parallel paths so it's not the most accurate way of testing..

 

[uksparks]

The oven must have an element on its way out or something.

 

[uksparks]

The 'occasional trip' and the 2.5A leakage current don't really go well together. 'Won't reset' would be better.
Measuring the leakage down the CPC or main earth doesn't show you what's being lost down parallel paths so it's not the most accurate way of testing..

I can't see how the RCD would hold if it 'is' leaking that much.

 

[uksparks]

If my calculation is incorrect please could someone with a little more understanding correct me.

 

[Octopus]

I can't see how the RCD would hold if it 'is' leaking that much.

Is it a single RCD or dual RCD board?

 

[Marvo]

You can't use the current in mA, you need to use 2.5 Amps instead.

 

[uksparks]

Is it a single RCD or dual RCD board?

It may be accumulated unless everything else is disconnected but still, I would expect to have to use an elastic band or a lock out device to hold the RCD on.

 

[Andrewr3]

Are you asking for hints/tips or just informing us of your working day ahead?

It has got me thinking and cannot work on it further until landlord gives permission. Thought it might give a few of you a puzzle to think about on your sunny Sunday afternoon. I am puzzled as to why the RCD has not tripped because outwardly it looks like a Neutral Earth fault, but I have not checked yet to find out more specifically where the the problem is. The lighting and smokes are not on the RCD. Also as someone, has mentioned here already, the occasional RCD trip could be unrelated to this high residual current. Hopefully I'll get the job and will be able to satisfy my curiosity.

 

[uksparks]

You can't use the current in mA, you need to use 2.5 Amps instead.

can you expand on that please.

 

[Andrewr3]

Oh, and I quickly checked the RCD was working fine on x0.5, x1, and x5 etc.

 

[MDJ]

The Rcd is faulty and there is a dodgy ring on the hob, test the rcd as per usual, at times half, one and five on 0 and 180 degrees, that will sort that bit out, then you can look at whats going on with the oven.

 

[Marvo]

If the cooker is on and it's leaking >30mA why has it not tripped then?

2,500,000 / 1000 gives milliamps Leave I in Amps, not Milliamps

A = 2.50A

IR = 230 / 2.50

IR = 92 Ohms

if I'm correct in my calculation you have a almost a dead short somewhere?

Not a dead short at 92 Ohms

 

[uksparks]

The Rcd is faulty and there is a dodgy ring on the hob, test the rcd as per usual, at times half, one and five on 0 and 180 degrees, that will sort that bit out, then you can look at whats going on with the oven.

It might be a gas hob ;-)

 

[guest119]

Is the leakage coming in or going out?

Boydy

 

[uksparks]

Not a dead short at 92 Ohms

I didn't think it looked quite right, thanks for that!

 

[guest119]

Dead short? We got slaughtered for saying that on the 2391.
Its a joint of negligible impedance that exists, acording to the lecturer!

Boydy

 

[SPARTYKUS]

Dead short? We got slaughtered for saying that on the 2391.
Its a joint of negligible impedance that exists, acording to the lecturer!

Boydy

Was that in the days when the 2391 was mentioned in hushed tones, as one wistfully looked into the distance and told of the 20 years it took and several attempts......over weeks at night school....

or, now, pay £800, cram it all in in 4 days and spew it out quick before you forget!!!!!

 

[guest119]

5 days in July 1997, September half day one to one in the workshop with lecturer, final exam in December 1997. A lot to remember for 5 months! (spew it out quick before you forget? no!)

Boydy

 

[HandySparks]

It has got me thinking and cannot work on it further until landlord gives permission. Thought it might give a few of you a puzzle to think about on your sunny Sunday afternoon. I am puzzled as to why the RCD has not tripped because outwardly it looks like a Neutral Earth fault, but I have not checked yet to find out more specifically where the the problem is. The lighting and smokes are not on the RCD. Also as someone, has mentioned here already, the occasional RCD trip could be unrelated to this high residual current. Hopefully I'll get the job and will be able to satisfy my curiosity.

The current in the earthing cable might be 'interesting', but to measure the leakage current you really need to be clamping around both the tails (and not the earthing conductor) as Marvo alludes to in post 6.

 

[Andrewr3]

The 'occasional trip' and the 2.5A leakage current don't really go well together. 'Won't reset' would be better.
Measuring the leakage down the CPC or main earth doesn't show you what's being lost down parallel paths so it's not the most accurate way of testing..

Ah yes, the current in Earthing Conductor is just part of the story. In this case it is in a block of flats so the services main bonding paths in the flat could be nicely carrying a proportion of any earth leakage current. The RCD "occasional" trip could be something else and may not even happen again. The tenant's brand new very basic cooker IR is OK, the install of this was the reason for being there in the first place.

 

[Andrewr3]

Is it a single RCD or dual RCD board?

RCD on Cooker and Ring Circuit only.

 

[GLENNSPARK]

Not a dead short at 92 Ohms

not a `dead short` anyway...as its earth fault...

 

[GLENNSPARK]

Ah yes, the current in Earthing Conductor is just part of the story. In this case it is in a block of flats so the services main bonding paths in the flat could be nicely carrying a proportion of any earth leakage current. The RCD "occasional" trip could be something else and may not even happen again. The tenant's brand new very basic cooker IR is OK, the install of this was the reason for being there in the first place.

hot?...or just measured cold?

 

[GLENNSPARK]

It may be accumulated unless everything else is disconnected but still, I would expect to have to use an elastic band or a lock out device to hold the RCD on.

do you think this would do the trick?

 

[spark 68]

As others have already said, clamp the tails to see the true leakage of the install, you always have a good few 100 mA or so of circulating earth currents sloshing about the system on a TNC-S earthing conductor from the supply side. This is external to your installation.

 

[Simonslimline]

I live in a flat (TN-C-S), just measured with an EL clamp meter, on the main earth it shows 247ma... and clamped on both tails shows 2.93ma. i imagine the leakage is coming from the computer. Interesting as this thread has just answered my question aswell.

As others have already said, clamp the tails to see the true leakage of the install, you always have a good few 100 mA or so of circulating earth currents sloshing about the system on a TNC-S earthing conductor from the supply side. This is external to your installation.

 

[Andrewr3]

hot?...or just measured cold?

Cold. Good point about it being hot because the customer stated it tripped after it had been used for a while.

 

[GLENNSPARK]

Cold. Good point about it being hot because the customer stated it tripped after it had been used for a while.

well.....there you goes then..

always listen to the operator...as they are at point of use and are a mine of info..before you go in there...

get it warmed up...IR....see what you get....try all rings as well....the lot...

 

[GLENNSPARK]

if you suspect other stuff as well (accumilated leakage) then ramp RCD with no load....ramp again with loads connected....the difference is the leakage....

 

[uksparks]

not a `dead short` anyway...as its earth fault...

Valid point, what was I thinking eh! Obviously an earth fault as it's the rcd that's tripping.

- - - Updated - - -

do you think this would do the trick?

Who knows, I'd rather not try! I'm sure someone has though.

 

[GLENNSPARK]

Valid point, what was I thinking eh! Obviously an earth fault as it's the rcd that's tripping.

- - - Updated - - -



Who knows, I'd rather not try! I'm sure someone has though.

on an MCB or an RCD the tripping mechanism `rides over` the button/lever...so that theres no possibility that the unskilled/uninstructed can `jam` it shut....

 

[MDJ]

Oh God this is getting a little Embarrassing now, surely UK sparks knew that and was just pulling your leg, dear God surely.

 

[GLENNSPARK]

Oh God this is getting a little Embarrassing now, surely UK sparks knew that and was just pulling your leg, dear God surely.

sorry Mike....lol..

 

[shanky887614]

I live in a flat (TN-C-S), just measured with an EL clamp meter, on the main earth it shows 247ma... and clamped on both tails shows 2.93ma. i imagine the leakage is coming from the computer. Interesting as this thread has just answered my question aswell.

Thats what you get for buying a cheap one. The ones withet better psu dont leak as much

 

[uksparks]

I suspected you wouldn't be able to, personally I don't like holding my finger on them when MCBs pop, makes me jump when your not expecting it.