Thread: Ocassional RCD Trip

My guess is that its a motor being brought on by a time-clock, or more likely a thermostat. Starting a motors causes a high in-rush current to the windings, and this can cause neutral circuit spikes, which can cause RCD devices to trip out.

Look for a correspondence with the activation of things like pool and spa pumps, reverse cycle air-conditioners, and of course fridges and freezers. Why doesn't this happen every time the motor starts? That has to do with the load on the motor, which will increase the in-rush current, and the impedance of the other loads on the same circuit at the time ... This means it may be more likely to happen more in hot weather, or cold weather etc.

I'm not an electrician ... but the solution is often to isolate the offender to its own circuit ... once you've found it.

Good luck.

Originally Posted by spartan

Any likely culprits?

Most like culprits are mineral insulated heating elements, these are the type of heating elements commonly found on electric stoves. Moisture can make the mineral insulation partly conductive and can trip a RCD. The fix is fairly simple - turn the element on to drive out the moisture.

Do you have an electric stove or oven? And if so, are they on the RCD?

Originally Posted by spartan

Any simple ways of testing?

Without the appropriate equipment, the easiest way is to progressively isolate appliances and note whether the tripping ceases. It can be difficult to work out - especially if the tripping only occurs once every couple of months.

I'd suggest that you concentrate on "earthed" appliances first (double insulated appliances shouldn't trip a RCD), especially anything that has anything to do with water.

I had some "nuisance tripping" on one power circuit that I thought was our dishwasher, but later the gas stove had a solenoid fail and it was the cause of the tripping.

I wont comment on wiring in Mexico (sth of the border) but in NSW electric stoves & ovens must be on a separate circuit to GPOs (read power points) and lights. Gas stoves may be connected to a GPO due to low current consumption.

If the device is a dedicated RCD not an MCB/RCD (minature circuit breaker/residual current device) then it won't be tripping out on an overload either. They cannot respond to loads, only to a connection fault - Active to earth or neutral to earth.

Generally RCD's that trip for no apparent reason are quite often connected to water handling pumps for pools/spas/pet hydrobaths or similar, or refridgeration devices such as A/Cs, freezers and fridges. In all instances the humidity of the surrounding air causes an increase in surface conductivity causing the active to earth or a cross connection between neutral and earth. Modern (last few years) wiring has a separate circuit for fridges and the like. As for pools etc I'd rather turn the unit off for a few days and let it dry out rather than risk it without an RCD.

In all cases call a sparkie. He has the equipment to check your appliances. If the device connected to your house GPO's is live and causing an intermittant trip it might also bite you whilst trying to locate it. RCDs are NOT guarenteed to work everytime - active to neutral without earth wont trip an RCD.

Originally Posted by Markw

I wont comment on wiring in Mexico (sth of the border) but in NSW electric stoves & ovens must be on a separate circuit to GPOs (read power points) and lights. Gas stoves may be connected to a GPO due to low current consumption.

Mark,

We, south of the boarder, also wire to AS3000, but wiring rules are in a constant state of change. Several years ago, in Victoria at least, a whole industry sprang up offering to install a "safety switch" for about $150 complete. But they only installed one RCD that covered the entire house. Talk about recipe for "nuisance tripping".

Chris

We had the same cowboys here too. Some would get it right with just the GPOs covered and some would include lighting. But to do a whole house :eek::eek::eek: that must be some RCD - size of a house brick. I'm running 100A mains with 3 seperate RCDs for house, and a sub board in garage with RCD for GPOs. To run all that with one unit - 100A, I don't think they make one.

Well I have checked a few things regarding my setup.

I had my board upgraded about 2 years ago, when we installed 3 phase - they used the old RCD, so it has the whole house on it. It is 40A., 4 pole 415V.

I purchased from Jaycar a powerpoint and EL Tester. I went around and checked all of the power points....all seemed good until I came to my bar.

I plugged it in and noticed that with the switch off it was showing live and earth wrongly connected.

When I turned the powerpoint on it was showing, Live and Neutral wrongly connected. There are two power points surface mounted in my bar, both gave me the same result. I went to check the powerpoint where my fridge is connected and noticed that the these wrongly wired points ran from this point - not an issue until I noticed that they had normal plugs connecting to the powerpoint - wow I thought, someone had basically cut the ends of two extension cords and connected them to powerpoints.

At least it was easy to disconnect them.

Normally I have had a stero connected to these powerpoint and the fridge connected to the master powerpoint - which is correctly wired.

With the 'cords' disconnected I could see that Brown was connected to N, and Blue was connect to Active - obviously wrong. So could this have something to do with my occasional RCD trips?

This is where for legal reason I step out. You have found a problem in the hard wiring of your house and I cannot advocate you fix it as I would conclude that you're not an electrician.

I know what I would do but I cannot provide this advice - sorry.

Absolutely no intention of fixing anything myself. Rather I was after an indication of if this could be the reason for the problem I was experiencing, or if there was still another problem. Did, I or do I have a safety problem.

I might also add the information I've asked here was an attempt to supplement any information from one of the two electricians I've called to have a look at the problem, neither of which have turned up at the agreed time (read at all).

Spartan,

An Active-Neutral transposition shouldn't effect the operation of the RCD. An RCD simply detect imbalance between the Active and Neutral currents, which usually occur due to a fault to Earth.

I take it that the bar power points are basically a home-made power board that plugs into another power point? If so, this is not strictly illegal but it would be a good idea to fix this up, or call an electrician to wire in a real power point. If the bar power points are wired in to the fixed wiring behind the other power point, then this would be illegal and should be attend to by an electrician.

Chris

Chrisp,

the bar power points are flat surface mounted power points, rather than power boards. They are on the top of the bench so by shinning a light under the bench I could see where the wires were going, so I didn't need to touch them after my tester said they were incorrectly wired, my quick visual inspection confirmed that.

I was able to safely disconnect them by pull out the three pin plug from the 'legit' power point that is under the bar. The fixed wiring appears to be simply extension cords with the ends cut off them.

I'm now attempting to get our electrician from work to come out on a weekend, as I can't seem to get a local sparky :mad: . But he hasn't been available to answer my question yet either...

Essentially, based on the advice given I'll get him to re-wire the bar.
And put in at least two new RCD, probably three - throwing the original out.

I was thinking of - Lights.
Internal GPO.
External GPO, this would be all the external GPO because I am pretty sure that some of these come from circuits that are from inside the house. The important one I want on a separate RCD is the pool, and my SPA, heater.

What would be a reasonable cost for the RCD and the labour to do this?

Originally Posted by spartan

I was thinking of - Lights.
Internal GPO.
External GPO, this would be all the external GPO because I am pretty sure that some of these come from circuits that are from inside the house. The important one I want on a separate RCD is the pool, and my SPA, heater.

What would be a reasonable cost for the RCD and the labour to do this?

Spartan,

It is probably best to ask your work electrician about the cost and the RCD configuration. If I were you, I'd get him to have a look first and work it out from there.

Chris

Spartan RCD's also have a limited life, and it sounds as if yours is quite old. Having said this It also appears you may have some conflict with your wireing, so if after resolving your wireing problems and the problem persists I would suggest a new RCD.

Rgds

Ok guys, it now seems very certain that it is my reverse cycle air con. Which is about 3 years old. It has tripped multiple times now over that last few days, in fact I now can't turn it on without the lights going out...

Is this a sign that the motor is on the way out?

Is this the kind of thing would be covered by the warranty? (5 year warranty)

I would think so , ring up the service reps explain the problem and get them to have a look.

Rgds