RCD tripping.

12 months or so ago I had my old fuse box replaced with a modern CU.
I have problems with the RCD tripping whenever I first switch on my pressure washer - and occasionally when I turn on the waste disposal unit in the kitchen sink.
Strangely - with both, once the RCD has been reset, I can restart both without problem.
I am assuming that it is the electrical spike caused by these motors suddenly demanding power that is causing the trip - but is there anything I can do about it?
--
Kev


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Added to uk.d-i-y.
As your CU is less that 12 months old I would expect it to have two RCDs. Is it the same RCD that trips with both the pressure washer and the waste disposal unit?
--
Adam



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ARWadsworth wrote:

Yes - ground floor ring main.
--
Kev

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OK. Is it possible to try either of the two appliances out via a circuit from the other RCD to see what happens? eg extension lead from upstairs. Note that the circuit MUST be fed from a different RCD than the one that feeds the ground floor ring not just a different circuit.
I strongly suspect that you have a live-neutral or live-earth low resistance on one of the circuits protected by the RCD that covers the ground floor sockets.
There is no reason why either of the appliances should trip an RCD unless there is a fault somewhere.
--
Adam



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I strongly suspect that you have a live-neutral or live-earth low resistance on one of the circuits protected by the RCD that covers the ground floor sockets.
There is no reason why either of the appliances should trip an RCD unless there is a fault somewhere.
---------------------------------------
RCD's can appear to be over-sensitive. I have a garden fountain pump that trips the RCD when it is turned off! Changed the pump - still the same. Has worked fine for years, but the RCD needs to be reset before it can be used again.
Chris R
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On 11/01/2011 18:29, Chris R wrote:

The fault may be not directly related to the appliance that apparently causes the trip.
--
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John.

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On 11/01/11 18:39, John Rumm wrote:

Tomorrow I'm going to cut a one meter extension lead in half and insert a 10ma RCD in it, so I can use it on as a sort of RCD leak current tester, and use it when using tools etc on extension leads, so it will trip rather than the main 30ma RCD in the consumer unit.
You could use it on your 2 bits of equipment and see if they trip it.
http://cpcireland.farnell.com/pro-elec/inlinercd/rcd-in-line/dp/PL10474
[g]
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The fault may be not directly related to the appliance that apparently causes the trip.
----------------------------------------- The other thing that occurred to me is that the problem could be at the switch. The two pumps are controlled by a light switch (though not off a lighting circuit), one of a panel of switches. As the RCD only protects the garden circuit it isn't a major issue if it trips.
Chris R
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On 11/01/2011 18:02, Ret. wrote:

The thing that your waste disposal and pressure washer possibly have in common is they typically have induction motors. These have quite high inrush current when first turned on (can be anything from 5 to 9 times their operational current). If your RCD is operating close to its trip current anyway, this inrush can be enough to push it over the edge.
See the sensitising RCD section here:
http://wiki.diyfaq.org.uk/index.php?title=RCD#Nuisance_trips
Fixing this can be tricky, since it may not actually be the result of a true fault (having said that, its worth working through some of the suggested tests, just in case it is). It could just be too many circuits sharing the same RCD and the small leakages from various appliances adding up. If this is the case, you may be able to reduce the effects by swapping which RCD the problem circuit is on, or possibly installing a dedicated RCBO for that circuit to give it its "own" leakage budget that does not need to be shared with other circuits.
--
Cheers,

John.

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John Rumm wrote:

Thanks for the advice and the link John. I'm not sure that I have the necessary expertise to sort this out for myself. The electrician who installed my CU lives on the same estate as me - just around the corner, so if I can't resolve it myself I may ask him to come and take a look.
--
Kev


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On 11/01/2011 19:49, Ret. wrote:

You may be able to do some preliminary stuff to help him track it down. Stuff like unplugging all the other appliances from the circuits that are protected by the RCD that trips, and then seeing if you can still get it to trip with just the pressure washer or waste disposal. If you can, then that would point to a neutral to earth short somewhere in the wiring.
--
Cheers,

John.

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John Rumm wrote:

Okey doke -I'll give that a try. The waste disposal trip is infrequent and so I don't think I can do much with that - but the pressure washer trips it every time I first switch it on. Can't quite understand why it should do it the first time I turn the washer on - but not the second time after resetting the RCD.
--
Kev


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BTW,
My email address works.
Send me an email. I have a pdf file (not a massive one) that I can send you that may help you with RCDs.
--
Adam



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Your waste disposal will have metal bits and is fastened to the sink so will be earth bonded. It could be the electrical filter on the input to the motor causing leakage. Don't understand why the unit is run through the RCD anyway as it is equipotentially (earth) bonded to and by the sink, assuming the sink is SS.
On the other hand your pressure washer should be double insulated - it has the square within a square symbol and a plastic earth pin on the plug. If that is so and is causing a trip then it is likely a faulty RCD - it is more common than you might expect. If the washer does have a proper earth pin then it may be that the filter there is causing the same problem.
I would have a look at the RCD and make sure it is 30mA. If it does not say 30mA trip on it then it may be marked something like 63/1/0.03. If it is less than 30mA then it has been wrongly supplied; if it is 100mA then it is the wrong type.
Finally, as someone else has said, run the washer from a different RCD. That may be your upstairs ring main or it may be your garage which should be separately supplied through a 16A MCB. If you cannot find the cause then a work around is to feed the washer from a non-protected outlet and use a plug-in RCD.
--
Woody

harrogate three at ntlworld dot com
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The 17th edition of the wiring regs requires most domestic circuits to be protected by a 30mA RCD.
There is no reason why a kitchen sink should be "earth bonded" and any waste disposal unit that requires an earth will get it's earth from the electrical suppy to the unit and not from the sink.
--
Adam



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ARWadsworth wrote:

Waste disposers I've fitted all had a grooved rubber ring with a clamp to fit the disposer to the sink waste. So there wasn't any electrical link between the sink and the disposer body (other than moisture). It may be that not all disposers are mounted like this but many are.
Edgar
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ARWadsworth wrote:

Spot on. My SS sink is not earth bonded - and the waste disposal unit is simply plugged into a ring main socket that is beneath the sink.
As my entire house is now RCD protected I don't have a socket that is not. Obviously this is only a problem since I had the CU unit fitted because before that I didn't have all the sockets protected by RCD.
My garage is attached to the house and has never had a separate mini CU.
I use the pressure washer at the front of the house via a socket in the garage - and at the rear of the house (cleaning the patio for example) via an external waterproof socket that is simply a spur from inside the house. Switching on the pressure washer for the first time from either of these sockets will trip the RCD.
I do have a mini CU in my garden shed and, thinking about it, when I clean the patio in the spring I may use an extension lead from the shed and plug the pressure washer into that. Hopefully, if the washer still trips the RCD - it will only be the RCD in the shed that trips, rather than the ground-floor ringmain RCD in the house.
I wonder if, when using the pressure washer at the front of the house, I used a 'plug-in' RCD in the garage socket, whether that RCD would trip rather than the 'house' RCD - saving me having to reset all the various cooker clocks etc? Perhaps worth a try. I presume there is no problem with using a plug-in RCD with a ring main already protected via RCD?
--
Kev


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I suspect that the house RCD will still trip.
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Adam



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On 12/01/2011 08:30, Ret. wrote:

There is no problem with using a plug in RCD on a RCD protected socket, however there is no real advantage either, since cascaded RCDs typically have no mechanism to discriminate - once the trip threshold is reached - one or both can trip.
If you sneak up on it with the ramp test on a RCD tester - i.e. gradually increase the leakage until you get a trip, you my find that one always goes before the other (although there is no way in advance of predicting which if they both have the same trip threshold). However if you simply apply a leakage that is over their trip threshold, then its anyone's guess as to what combination of trips you get.
Chances are however that assuming there is not a particular fault on the pressure washer itself, then the house CU RCD will trip before the plug in one, this that is seeing the combined leakage of all the house appliances as well as whatever the pressure washer introduces, whereas its dedicated one will only be seeing its leakage.
--
Cheers,

John.

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John Rumm wrote:

OK - I'll just try it and see! I'll probably be using the pressure washer in the next week or so to wash all the accumulated salt out from underneath the car.
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