Hi all,

I done a c/unit change last week, a bit of a rats-nest of a job as lot's of stuff had been added since the 70's looking installation had been done.
All went ok, all tested out ok and just as I was getting all my stuff together to leave one of the rcd's tripped, Asking the customer what she'd switched on & it was the microwave, great I thought must be a leaky microwave. No such luck as I then found whatever I switched on on that circuit (ring) the rcd would trip!
After a little bit of interrogation she then told me she'd plugged in her table lamp in the lounge, it turned out that the N-E was twisted together in the lampholder, obviously never caused a problem before I installed rcd's! So it appears that linking N-E won't necessarily trip an rcd unless there's a load on it, I had wondered about this a few times in the past as sometimes when i'm working on a circuit with the mcb switched off if I inadvertently touch N-E rcd's will trip and sometimes not, worth keeping this in mind I reckon,

Dave.

Draw the circuit out Dave - it's just a divider circuit.

With no load, the neutral voltage is "low" and no current is flowing. As you add load, some current goes down the N-E path and some back through the RCD in the relative ratios of resistance until you reach the imbalance tripping threshold.

It's a classic symptom of a N-E fault when any random load starts to cause tripping.

Be interesting if your RCD tester would have failed on disconnection time if the table lamp had been plugged in !!

Regards

OMS

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Failure is always an option

Oms

Come on you know your meant to test the rcd at the load termials with no load applied.

That's exactly what I did do, everything was working fine until unbeknown to me she plugged her bl**dy table lamp in!

Dave.

Better than than later after you had left.

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Norman

I've had similar situations in the past; the most glaring was when I moved house from one with rewireables, to one with an RCD. I had to dump a grill and an iron due to instant trips! Others after having changed a D.B., without the customer having agreed to a P.I.R. beforehand, and neutral to earth faults. Then the meter starts runnng, for repairs at stated daywork rates! (On the estimate, I spell out the possible consequences of not having a report carried out beforehand!)

Regards

That's true Norman, at least I knew what was plugged in. (except for the offending lamp!) If a day or two had gone by she'd have plugged everything back in and i'd have been starting from scratch!

Dave.

Has anyone done this - a bit moddy but it should work: -

I was once asked to work a circuit (adding extra lights, changing lights for new models) but the cilent refused to pay for a PIR on the house prior to works as suggested. I explained that I would have to install an RCD. Anyways she didn't want to know. So to save any arguments prior, I installed a temporary RCD prior to works to see if it'll hold.

Anyone else done this....just me....I'll get my coat. Looks like rain.

wouldn't it have been easier to IR the lighting circuit before you started. or did you just bang a front end RCD on the lot.

Gary

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Specialised Subject. The Bleedin Obvious. John Cleese

Gary, yea - really.

What happend there had been a board change over some time prior - a shoddy one of that - from the mains fuse the tails went into a Henly block and split. One into the new board and one into a little old black isolator unit which contained the rewirables for the lights. He had though linked the earthing of the his board back to the new board's MET which was connected to the means of earthing. So I just removed the tails and put in a front in RCD just so I knew what I was heading into. The board was in awful position and didn't really wanted to mucking about with the cables within and getting such a tight space. The RCD seemed to be a much more easier means in pactical terms. I then ran out a long lead from there main earth to the lights which were eaily access to see if the earth was continious.

Can't remember if I kept the arrangement or decided to drop the tails and have the board fed from the new board.... Though it was handy at the time because you could isolate the power yet still have the lights on.

Can't beat N-E faults & people who can't wire a 13A plug properly......

In a former life, we used to look after the power generation & distro for a furniture exhibition held in a clear span tent in the grounds of a local castle. Around 60 odd stands, each with a 16A or 32A feed, pair of synced 250kVA sets, catering feeds, posh porta-potties etc etc.The deal was that on openning day there would be a sparks on call to deal with any last min. changes/problems, but the following days would be handled on a call out basis.... if the problem was down to the 'fixed' wiring or distro then no charge otherwise call-out charge & time billed to whoever tripped the supply. Each stand was supplied via an RCBO..... two days in call out to a bedding stand.... RCD tripped. Came along, reset it, immediatley tripped. Investigations revealed that the stand holder had brought along a bedside lamp to add some ambience...every time this was plugged in, the RCD tripped. It tripped because her son had wired it between L & E ... 'but its fine at home, been fine for years' she protested. I rewired the plug, demonstrated that it now worked fine & releaved her of the requiste fee & thought no more of it....... until the following year when she did the same thing again!