Intermittently Tripping RCD

[m4tty]

Hi,

Ive been to investigate why customers rcd is tripping intermittantly. It was part of a long list of work. I completed the rest early and had some time to spare so I thought id do a full test of the installation (for practice).

Here are some of the results

TNS with Ze of 0.11/PEFC 2.1kA/PSCC 3.8kA

Main fuse 100A BS1361 Type IIB

1) CU Light & Bell (B10 1.0/1.0)

2) Lights up (B10 1.5/1.0)

3) Lights down (B10 1.5/1.0)

4) BLANK

5) BLANK

6) RCD 80A 30mA

7) Shower (B32 6/2.5)

8) Ring (Whole House) (B32 2.5/1.0)

9) Water Heater (B20 2.5/1.0)

10) Garage (B20 2.5/1.0)

11) Kitchen Sockets (B32 4.0/1.5)

R1's & R2's

1) R2 = 0.32 ohms

2) R2 = 1.26 ohms

3) R2 = 1.37 ohms

4) BLANK

5) BLANK

6) RCD

7) R1+R2 = 0.17 ohms

8) R1+R2 = 0.59 but readings varied from 0.37 to 0.59 ohms?

9) R2 = 0.74 ohms

10) R1+R2 = 0.40 ohms

11) R1+R2 = 0.11 ohms

Global Insulation Resistance

L-E >299MOhms

L-N>299MOhms

N-E 38.2MOhms

Earth Fault Loop Impedance (Zs)

1) 0.14 ohms

2) 0.53 ohms

3) 0.32 ohms

4) BLANK

5) BLANK

6) RCD

7) 0.16 ohms

8) 0.51 ohms

10) 0.55 ohms

11) 0.22 ohms

RCD Test

NO TRIP

(0 Degrees) 80.2ms

(180 Degrees) 39.9ms

(0 Degrees) 6.6ms

(180 Degrees) 12.0ms

10mm Earthing Conductor

6mm Main Protective Bonding Conductors

I didnt have to do the full test but had some tim to spare and need practice so i dont what I could.

Still dont really know why the RCD is tripping but PAT tested a few items as there were quite a few extension leads, multi way adaptors etc.

The 10m extension leads earth continuity was 2.48 ohms / Passed IR test but thats a fail for earth continuity?

Would this be one of the reasons why the RCD is trpping apart from acculmulative earth leakage of 3 laptops and the whole house being on one ring?

Any pointers or advice greatfully received ?

Thanksx five delta n

Matt ut the kettle on

1)

 

[ianmacd]

100A cutout fuse so guessing tails are 25mm? Any reson you haven't upgraded the Earth and Main bonding conductors before starting work?

 

[Revved Up Sparky]

The test results look fine to me. The R1+R2 for the ring will indeed vary with the highest reading occuring when you get to sockets near/ at the middle of the ring and the lowest readings near the ring ends. The R1+R2 should match up fairly well with your end to end ring continuity readings L-L + E-E divided by 4.

The insulation resistance results look fine even with 38megohms N-E.

I would conclude from the results taken that the installation is fine, therefore the logical step for me would be to disconnect all loads, ie, unplug every portable appliance and switch off every isolator before slowly and systematically switching loads back into each circuit whilst looking for the RCD to trip again.

 

[ianmacd]

The test results look fine to me. The R1+R2 for the ring will indeed vary with the highest reading occuring when you get to sockets near/ at the middle of the ring and the lowest readings near the ring ends. The R1+R2 should match up fairly well with your end to end ring continuity readings L-L + E-E divided by 4.

Depends how you have connected it up. If you have hooked leg1 R1 to leg2 R2 and leg2 R1 to leg1 R2 then the R1+R2 should be very similar at all points apart from on spurs.

 

[Revved Up Sparky]

Depends how you have connected it up. If you have hooked leg1 R1 to leg2 R2 and leg2 R1 to leg1 R2 then the R1+R2 should be very similar at all points apart from on spurs.

Yes you are referring to the cross connected method (step 3) of the ring continuity tests whilst I was talking about the end to end (step 1) method where the R1+R2 will be approximately equal to r1 + r2/ 4. (OSG sect 10).

 

[ianmacd]

Yes you are referring to the cross connected method (step 3) of the ring continuity tests whilst I was talking about the end to end (step 1) method where the R1+R2 will be approximately equal to r1 + r2/ 4. (OSG sect 10).

Thats not for rings. 10.3.1 says see 10.3.2 for rings.

 

[Revved Up Sparky]

Thats not for rings. 10.3.1 says see 10.3.2 for rings.

Whatever ! :Applaud , it's the section that covers initial testing of installations ! it's not difficult to miss the part about testing rings as there are only six pages !.

 

[binky]

How intermittent, daily, weekly, monthly, every full moon ?:| ? :| ?:|

 

[ADS]

Depends how you have connected it up. If you have hooked leg1 R1 to leg2 R2 and leg2 R1 to leg1 R2 then the R1+R2 should be very similar at all points apart from on spurs.

I agree - R1 + R2 same reading at all points on ring (within 0.05 of each other) - otherwise your looking at a spur or interconnect

.

.

.

.

Hey Ian, we agreed on something

 

[ADS]

How intermittent, daily, weekly, monthly, every full moon ?:| ? :| ?:|

Yes, and also, have you not been able to recreate the circumstances under which it trips? - this would be the most helpful

 

[m4tty]

100A cutout fuse so guessing tails are 25mm? Any reson you haven't upgraded the Earth and Main bonding conductors before starting work?

Hi,

It was sealed and thats what it said on the outside of the fuse carrier, i thought they all said 100A but majority of the time it would be a 60A or 80A and the tails were 16mm.

Should I have upgraded them before I started as im going back there so will do it then?

What if theres laminate floor throughout and the customer wont agree to it?

Thanks for replying everyone

Cheersut the kettle on

 

[m4tty]

How intermittent, daily, weekly, monthly, every full moon

Twice last week when they putting on laptop..... she thinks

Yes, and also, have you not been able to recreate the circumstances under which it trips? - this would be the most helpful

Havent been able to do this as they take laptop to work with them.

Thanks for replies

 

[SPECIAL LOCATION]

How intermittent, daily, weekly, monthly, every full moon Twice last week when they putting on laptop..... she thinks

Yes, and also, have you not been able to recreate the circumstances under which it trips? - this would be the most helpful

Havent been able to do this as they take laptop to work with them.

Thanks for replies

Have a look at the laptop PSU's ...

some of them only use 'L' & 'N' the 'E' pin is a plastic stud..

in which case the Laptop is probably NOT a potential culprit..

Was the washing machine, dishwasher or tumble drier running?

e.g.

reaches certain part of cycle something gets damp or overheats and trips!

appliances with water are often a prime suspect..

But also had problem with excessive build up of fluff & dust inside a tumble dryer, (filters not cleaned out regularly), bridging across some contacts.

 

[binky]

How intermittent, daily, weekly, monthly, every full moon Twice last week when they putting on laptop..... she thinks

Yes, and also, have you not been able to recreate the circumstances under which it trips? - this would be the most helpful

Havent been able to do this as they take laptop to work with them.

Thanks for replies

Run through what else they do at the same time ie come home from work, boil kettle, put dinner in oven, goes to work on laptop. Check socket used to power laptop. But nature of tripping sounds like appliance(s) rather than circuits, unless it coincides with weather ie every time it rains etc etc

You could also possibly suggest RCBO for power or kitchen circuit, if you have easily modified CU/ room to shuffle MCBs, or temporary fit RCD outside of CU for an individual circuit, it might remove problem of help identify which circuit (set of appliances) has an issue

 

[m4tty]

Hi,It was sealed and thats what it said on the outside of the fuse carrier, i thought they all said 100A but majority of the time it would be a 60A or 80A and the tails were 16mm.

Should I have upgraded them before I started as im going back there so will do it then?

What if theres laminate floor throughout and the customer wont agree to it?

Thanks for replying everyone

Cheersut the kettle on

Anyone got any pointers on the underlined

Thanks :Y

 

[ianmacd]

TBH it should have been the first job and if the cmr refused you shoul dnot have done any other work.

 

[TonyCE]

Any Neighbours (with RCD protected installations) reporting anything similar problems.

I've had a similar experience recently: One of the two RCD's tripping, no MCB's tripping, happens at night (between 11pm and 4am). Moved the Fridge and Freezer to another RCd, does not follow, ramp test showed 27Ma for both RCD's, and the one that was tripping was fine on 1/2 times, 1x, and 5X. Recent (10year old house) on TNCS. Have good IR on all circuits, rings all check out fine. No shared Neutrals. Neighbour said their alarm was occasionally resetting, and they'd had something done to prevent this. There is some heavy industry in the area. Still at a bit of a loss, but have swapped the two RCD's around to see if the fault follows. The rate of tripping has reduced from almost daily to "not for the last 5 days".

 

[Chr!s]

Stick a clamp around the line and neutral and what leakage exists, carry out a ramp test, it may be that the leakage is very close to trip current of the rcd.

Fridges are a common culprit, the list is quite long though.

 

[ADS]

This thread is nearly a year old, chaps:^O