Rcd Trips In Farm House

[Dave4718]

Hi Guru's

I am rewiring my first farm house and have a problem with tripping rcd, It is powered from overhead and i have changed the board for a wylex dual rcd one, i have a Ze at board of 7.02 and at sockets of 7.52. my tester is a megger 1730 and if i plug anything in apart from the tester the rcd trips. Am i correct in thinking i need to change the rcds for 100mA ones. Also when i try to test the trip times on Auto it wont trip, if i set the tester to 5x it trips ok. Any help not ridicule would be very much appriciated.

 

[SLIPSHOD & SLAPDASH]

Firstly, i would try to get that Ze down (or Ra or what ever you want to call it) Is it the old rod ? You may need to put one or more extra ones in.

Next, have you got the neutrals mixed on the wrong bars in the board ?

Nothing wrong with having 2, 30ma Rcd's, probably neede to conform to the 17th edition anyhow. Hope its an insulated board

 

[Steve3948]

The Megger MFT 1730 will not carry out RCD test if the touch voltage is >50V

What was in place before you changed board, did you test circuits prior to change.

 

[Dave4718]

No the circuits were all ripped out so didnt test, all cable was lead covered and the board was an old wire fuse type, i might add this is on a farm supply and is 3 phase one of which runs the domestic farm house. I have simply used the tails from the meter ( recently installed by east midlands elec) to the new board.

 

[ProDave]

No the circuits were all ripped out so didnt test, all cable was lead covered and the board was an old wire fuse type, i might add this is on a farm supply and is 3 phase one of which runs the domestic farm house. I have simply used the tails from the meter ( recently installed by east midlands elec) to the new board.

So if ALL the circuits are new, there are really only 2 possibilities:

A N-E short somewhere

Or neutrals of one (or more) circuits into the wrong neutral bar.

What testing have you done?

 

[Riggy]

Another one!

 

[M107]

Firstly, i would try to get that Ze down (or Ra or what ever you want to call it)

7.02 ohms slips did you not see the decimal point :innocent

 

[Revved Up Sparky]

An Ra of 7.02 ohms is an excellent reading for a TT system IMHO.

As stated above it sounds like an issue with a neutral. I would be tempted to do insulation tests N-E, then perhaps systematically disconnect each neutral (with MCB for that circuit off) , each time plugging an applicance in to see if there is a change.

 

[M107]

I am of course assuming TT from overhead....

 

[NozSpark]

I'd love a Ze of 7ohms on a TT,,, I think the closest that I got was 15ohms with a single 3/8 rod!!!

Anyway, back to the fault,,,, could it be a Neutral link within the board??

Or could you have mixed up your N ins and outs when you rebuilt the board?? (I'm ashamed to say that I have done this myself)

 

[SLIPSHOD & SLAPDASH]

7.02 ohms slips did you not see the decimal point :innocent

An Ra of 7.02 ohms is an excellent reading for a TT system IMHO.

As stated above it sounds like an issue with a neutral. I would be tempted to do insulation tests N-E, then perhaps systematically disconnect each neutral (with MCB for that circuit off) , each time plugging an applicance in to see if there is a change.

Woops, shall i spank myself after i go to specsavers O)

 

[Dave4718]

you guys are brilliant, i will try all of the above in the morning. i thought i had all the neutrals in the right place but i will double check. many thanks for your replies. watch this space.

 

[Dave4718]

Many thanks for the advice, It was a neutral fault. I had moved an mcb to the other rcd but didnt do the neutral durrrr.

thanks again

 

[ProDave]

Glad you got it sorted and thanks for letting us know and finishing the thread.

 

[Evans Electric]

That makes a nice change ....to get the fault reported back when sorted ...helps others out .

And , yes , I've done that too , suddenly decide to swop a circuit across and forget the neutral .

I'm somewhat saddened though that Dave 4716 needed to add " Any help not ridicule would be appreciated" TBH

 

[SLIPSHOD & SLAPDASH]

Thanks for reporting back.

 

[M107]

I'm somewhat saddened though that Dave 4716 needed to add " Any help not ridicule would be appreciated" TBH

Agree, but has to be said there was nothing but helpful replies.................a new look forum & new attitudes to helping rather than ridiculing.

Well done everyone keep it up.

 

[Steve3948]

It only takes a minute to update, we'll done.

 

[batty]

Not ridiculing but generally best to test before installing circuits that way you find the faults and can put them right.