TT tripping issues

[itchy]

System has had a new 16mm earth upgrade whilst the existing box was relocated. Ze (or Ra) has a new reading of 35ohms. (well within the parameters).

The issue the system is now having is, despite not having any circuits connected except one radial to one double socket to provide power whilst works are carried out on the home, as soon as power is drawn, the system trips out.

We've had the mcbs tested but the 63a rcds trip either at 35ms and 45ms (split board).

Didn't have time to have any more tests provided, but it stumped me...

Any ideas before we return to this on monday?!!

 

[telectrix]

faulty RCD. faulty wiring, faulty tools, one thing to note is if 110v transformers are being used on a 16A type MCB< that MCB will trip through surge. you need c or even a d type MCB.

 

[itchy]

The RCD's were fine prior to moving. No transformers were plugged in. The tail to the socket was initially on a 16a mcb, but the 63a rcd for that side of the board tripped. So the radio was replaced with a DIY'ers socket and see to check for polarity, all fine. Plugged in a battery charger, again tripped.
Removed from the 16a, and temporarily attached to a 32 mcb. Tripped again.
Started running tests, checked earth rod connection, re-tested Ra, still around 35.

fluke tester on 1xIdeltaN @ - & + = 35/45ms on either side of the split board. from my recollection tt's are allowed up to 200ms disconnection time?

Literally had the cable stripped that was used for the supply to the double socket, no damage anywhere, still, had it replaced and still had tripping on all circuits!

 

[telectrix]

sounds like a N/E reversal.

 

[itchy]

there were only 3 wires coming out of the board to one socket. All were correctly positioned.

if the socket was connected (to any mcb) it would only trip once it was under load.

Would the type of rcd on the system have any relevance? I don't think that was checked, but the main issue is that the board worked fine prior to the move. (same supply cable used as it was moved closer to the inlet), but new 16mm earth cable as the old 10mm was not long enough.

 

[Sav]

Hi,
Is it a dual board (2 x RCD'S) ? If yes, then could it be possible that the neutrals in the board are mixed up on the neutral bar in the consumer unit ?

Sav

 

[itchy]

hi thanks for the replies so far by the way.

It's a hager split board. 2x 63a rcd with an abundance of 16/20/32 mcbs on either side... but none connected to any other circuit.

The board was powering a couple of sockets prior to the move. and all the board connections were left in place as before.

All cables in the box were checked numerous times.... I can only think it's a fault to do with the new earth as hypothetically, it's the only part of the system that has changed!... but it seems to test fine!

 

[Iddy]

Hi mate

I am no expert in the field but if i remember correctly i once read some power tools do have a small amount of earth leakage on start up...

has anyone else heard of this>? or have i got my wires wrong Lol

 

[Richard Burns]

From what you describe of the fault I would say that somewhere there is a link between the neutral bar for the RCD that is tripping and another neutral bar.
If you have both RCDs tripping on use of power then there is a link across all neutral bars or between the RCD neutral bars; if there is only one RCD tripping then there is a link from that RCDs neutral bar to the main neutral.

This link could be either directly in the CU or via circuits with line in one side and neutral in the other.

Is this CU wired up in any way apart from the described sockets, i.e. are there any other circuits or are there just the unconnected breakers?

 

[itchy]

The rcds trip individually depending on which side of the board the feed is taken from.
The mcbs are empty, apart from the one feeding the one socket.
No other cables are present. Literally moved the box 8' and all lines were left as they were previously installed when working!
Wish I'd taken a photo of it before we left yesterday!

 

[itchy]

When I say other lines, I mean the links to the bars from the rcds etc.

 

[telectrix]

if all other things are as was and the only difference is the repositioning of the rod, then it's got to be something to do with the rod, though how eludes me. try moving the rod.

 

[Des 56]

The way I see it.
Concentrating on what changes to the earth or rod will sidetrack you with the problem

Back to basics,the Rcd will trip with an imbalance of Live-neutral,that is if the Rcd is operating correctly

I was going to list all the tests I would do, but you seem to have covered everything
I haven't, however, seen mention of the actual accessories being tested
I cant see anything about the earth cable or electrode being part the problem

 

[rich.250]

Sounds like a N/E fault somehow.
Ramp test Rcd, and insulation test all cables connected.

 

[RogertheBodger]

Is it a metal panel, could it be that in re-fixing it, you have drilled a neutral buried in the wall?

 

[rich.250]

Or there was a fault there all the time, and now you have an earth path..... LOL

 

[itchy]

The inlet comes through the floor And the wall the box is now on is a bare stud with all new cables for te rewire just hanging around and not connected to anything.
My tester doesn't ramp unfortunately... But I'm wondering if the sockets at fault as the chargers and radio are used daily and were operating ironically from the board that's been moved.
Will have to wait til Monday to have a proper look. But just thought it such an oddity that I'd post the issue to see if anyone had encountered it before!!

 

[tony mc]

Hi Itchy.

I am a little confused It is the RCD that is tripping with only one radial cct installed as you mention changing a 16A mcb for a 32 A .

So to confirm its the RCD not the MCB tripping.

If it is the RCD the ROD IMO will have nothing to do with it as long as upstream you line neutral and earth are seperate.

I take it on you radial cct the dead tests are all good especially the IR tests making sure the RCD will hold.

 

[itchy]

Yeah the mcbs don't trip, just the rcds. The only reason we moved the radial from 16 to 32 was to quickly eliminate the mcb. (tut tut!!).
The cable came straight out the box to a socket approximately 2' away. Cable not through walls or clipped at the time.
Didn't get a far as an ir test. Nobody living there and it was a Friday afternoon... You can guess the rest!
I'm pretty certain it's a simple problem, although as we've had everything tested pretty much, it would appear at the moment it's not.
If there was a l/n imbalance it would have had the issue before though?

 

[tony mc]

It is going to be either a L/E or N/E imbalance as that is what the RCD coil is detecting.

Once you IR the cct i would imagine you will locate your fault if you test between the above with your continuity meter I guess you will see a reading less than 7666 ohms !

 

[itchy]

Yeah true. I'll report the findings on Monday!!

 

[Engineer54]

IR tests would have been my first test to perform, even before energizing this temporary power outlet!! ...lol!!

 

[Deleted member 9648]

Cant believe a single socket radial tripping an RCD with nothing else connected would need an electrician to contact a forum for advise....5 minutes to sort with a tea break in the middle.

 

[topquark]

Dumb question, are you sure what you are using to draw current (extension/tool combo) doesn't have an earth fault and the RCDs are just doing their job? If so then I'd say you've got the neutral bars connected arse about face!

 

[Deleted member 9648]

Cant believe a single socket radial tripping an RCD with nothing else connected would need an electrician to contact a forum for advise....5 minutes to sort with a tea break in the middle.

Sorry...sarcasm not really called for...(it's been a rubbish day)....getting my coat now.

 

[itchy]

I don't mind sarcasm! I'm recently qualified and not really dealt with tt systems before. I'm not making excuses for not having a wealth of experience... Forgive me or not, no shame in asking questions on a forum?! Whether I was concentrating on something that I thought was a problem else where instead of just doing what I 'should' have been doing is just a learning curve for me surely?!
Thanks for the advice anyway, constructive criticism never goes amiss ;-)

 

[rich.250]

It is going to be either a L/E or N/E imbalance as that is what the RCD coil is detecting.

Once you IR the cct i would imagine you will locate your fault if you test between the above with your continuity meter I guess you will see a reading less than 7666 ohms !

I would go with neutral/earth as it doesn't trip until a load is applied

 

[tony mc]

I don't mind sarcasm! I'm recently qualified and not really dealt with tt systems before. I'm not making excuses for not having a wealth of experience... Forgive me or not, no shame in asking questions on a forum?! Whether I was concentrating on something that I thought was a problem else where instead of just doing what I 'should' have been doing is just a learning curve for me surely?!
Thanks for the advice anyway, constructive criticism never goes amiss ;-)

IMO I would not worry to much re TT systems once your Ra and RCD protection is in place.

Once you start testing its the same as TN systems with higher live ZS values depending on Ra and bonding paths.

Sometimes on 5 X RCD testing depending how high your Ra is the tester can abort the test when the touch voltage reaches 50v. (Something to be aware of) also many have tested with the test instrument set up at 25v for touch voltage which again can abort on 5 X RCD test.