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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> Advice on RCD problems https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1082992319 Message started by Learner Turner on Apr 26^th, 2004, 4:11pm

Title: Advice on RCD problems
Post by Learner Turner on Apr 26^th, 2004, 4:11pm

Can anyone shed any light on a problem I am having at the moment?

At Christmas time I upgraded my lathe to a Record CL4 (variable speed with inverter drive).

Everything was fine for a couple of months, but then the lathe started knocking out the RCD feeding my workshop as soon as the main power switch was switched on (before the thing had even been set to run).

Record Power replaced the inverter, and everything was fine for a while, but then the problem came back. Record sent an engineer out this time, and they have taken the motor (750W) and inverter (Telemecanique) away for testing. I had a phone call on Saturday to say that they couldn't find a problem, and that it must be a fault on my RCD. I run a 1500W table saw and an 1800W router off the same supply with no problems (albeit they are not inverter driven).

Does anyone have any suggestions as to how I can get around this (I would prefer not to have to send the lathe back!!).

Thanks

Title: Re: Advice on RCD problems
Post by plugwash on Apr 26^th, 2004, 4:59pm

sounds like a filter sending a large surge to ground on startup

you could try replaceing the rcd different rcds of the same type do trip at slightly different levels due to manufacturing tolerance but it's a bit of a long shot

your other option is something like this <link dident work and was altering the apperance of the forum ::)>

Title: Re: Advice on RCD problems
Post by supersparky on Apr 26^th, 2004, 5:33pm

wrote on Apr 26^th, 2004, 4:59pm:

you could try replaceing the rcd different rcds of the same type do trip at slightly different levels due to manufacturing tolerance but it's a bit of a long shot

if that was so id fail em all!!!

where abouts are ya mate? what ya need to do is test the rcd with an rcd tester(very expensive piece of kit) as sometimes rcds trip Too low(or too high) and are over sensitive. it maybe that each of your appliances are contributing to the earth fault current that is tripping the (possibly) oversensitive rcd.

there may also be earth leakage due to water in the cables/ damp sockets/ damp enclosures.

all can be found easly and im sure someone will be in your area, if not it shouldent cos too much!

ss

Title: Re: Advice on RCD problems
Post by L.Spark on Apr 26^th, 2004, 7:55pm

definatly, i would suggest getting it checked out, anything can go wrong or malfunction, so a RCD test would reveal this, and if the RCD is ok then it must be some other fault, but what your using shouldnt be causing you any problems.

Title: Re: Advice on RCD problems
Post by HandyMac on Apr 26^th, 2004, 9:25pm

wrote on Apr 26^th, 2004, 4:59pm:

your other option is something like this<Removed>

For very long URL's which spill over multiple lines I recommend using the service available at:

http://www.tinyurl.com

That long URL posted above becomes:

http://tinyurl.com/29cpl

which incidentally won't work now because the RS components web site posts the session ID into the address querystring (that's the bit BV_SessionID=@@@@2090375017.1082994738@@@@). You can't unfortunately link into a product page on the RS web site :(

Try clicking on the above URLs and you will see what I mean.

Andrew

Title: Re: Advice on RCD problems
Post by Learner Turner on Apr 29^th, 2004, 11:39am

Thanks for the help guys.

I have now had the motor / inverter back, and it runs fine iif I plug it ino one of the house sockets. As soon as I try it in the workshop, out goes the RCD again.

I should mention that there is an RCD on the main house circuit, which hardly ever trips (it trips OK when I press the test button), but not for spurious reasons.

All the outside electrics (including my workshop) are fed through an additional RCD (which preumably is in series with the main one??). This one trips at the slightest provocation (thunderstorms nearby are enough to make it go). The "outside" RCD is physically much smaller that the "main" one, although I am unable to read the data plate giving trip current etc.

I think I read somewhere that RCDs come in different sensitivities - 25mA and 50mA rings a bell. Is it possible that I need to change the one causing problems for a higher rated one?

From what you are saying though, it sounds as if I need a pro - I am just ouside Cardiff if anyone wants a job?

Cheers

Gary

Title: Re: Advice on RCD problems
Post by rabbit_rabbit on Apr 29^th, 2004, 1:59pm

OK so -

(a) it trips the RCD in ya shed and

(b) it does not trip the main RCD in ya house.

So -

I would guess that the shed RCD is a 30mA trip device and the one in the house is probably 100mA trip. It's also highly likely that the one in the house is a Type S time delayed RCD.

It may be that the inverter has a virtual earth point (2 capacitors one end of each being connected together ) and the start up causes an imbalance between phase or neutral and real earth.

I stand to be shot down but maybe the lathe with inverter best be conncted to an S type RCD.

RR

Title: Re: Advice on RCD problems
Post by Learner Turner on Apr 29^th, 2004, 4:16pm

Cheers RR,

That sounds reasonable, but one point springs to mind - surely the whole point of an RCD is that it is supposed to trip before sufficient current has had chance to flow to do any damage to the poor s*d who is unfortunate enough tb creating the connection from live to earth?

Would the type of RCD you describe provide a lower level of safety than the one that is there at the moment, or would the difference be trivial, as I realise we are talking about pretty low currents here?

On the other hand, it doesn't seem as if I have much choice, as I can't use the lathe at all at the moment. :P

Title: Re: Advice on RCD problems
Post by Dewy on Apr 29^th, 2004, 4:29pm

wrote on Apr 29^th, 2004, 1:59pm:

It may be that the inverter has a virtual earth point (2 capacitors one end of each being connected together ) and the start up causes an imbalance between phase or neutral and real earth.

RR

Getting off this problem but you just reminded me of something RR. I used to connect 2 - 100 microfarad capacitors together pos to pos or neg to neg & connect them across speaker terminals. They greatly reduced the background hiss. Over 20 years ago some bright spark enclosed them in plastic & sold them in CB shops for �5 and people bought them up as fast as they could find them. I went to an electrical components shop & paid a few pence for the same thing minus the plastic box. :D

Title: Re: Advice on RCD problems
Post by rabbit_rabbit on Apr 29^th, 2004, 5:33pm

Well yes LearnerTurner to be 'safe' then you would ultimately want a 10mA RCD, it would spend the whole time tripping but ya wud be safe for sure!!

I once worked inmedical electronics and as part of my 'training' I was shown what happended to a patient when a sensor failed on ECG equipment, the burns were horrific - 5mA at 50 volts that's all. After a major skin graft she was OK apparently.

I agree it's far from ideal but then... how many people actually test their RCD's at the specified intervals? I have yet to meet one, including myself. So, if we are all so safety paranoid then how come no-one test their RCD's- indeed I bet the only time they are tested is when some sparky does a PIR.

I suspect the inverter, have it checked - do you have access to an Insulation tester for starters? Just about evertime I have been called out due to RCD's tripping it has been caused by weak insulation and it don't have to be that 'weak' either.

Ray

Title: Re: Advice on RCD problems
Post by tidy on May 15^th, 2004, 12:31am

:oDon't use the insulation tester without disconnecting the inverter!! :o

Title: Re: Advice on RCD problems
Post by FWL_Engineer on May 18^th, 2004, 12:38am

I hate to be the bearer of bad news, but Inverters and RCDs are not actually compatible..especially if the RCD is DC sensing.

Title: Re: Advice on RCD problems
Post by Learner Turner on May 18^th, 2004, 9:22am

So does this mean that I have to get the RCD removed altogether?

Why does the thing run OK if I plug it into one of the house sockets, which is also covered by an RCD, albeit of a higher rating (I think)?

Title: Re: Advice on RCD problems
Post by plugwash on Jun 19^th, 2004, 5:08pm

is this much smaller rcd you speak of in your CU ?

if so it sounds like a rcbo and all rcbos are dc sensing (no i don't know why its some stupid standard i think)

with the lid off the CU a rcbo should be obviously different from a normal mcb as it will generally be muc taller and the neutral will be connected via it

i would just replace the rcbo with a mcb and make sure it is on the rcd side of the CU

Title: Re: Advice on RCD problems
Post by L.Spark on Jun 19^th, 2004, 5:15pm

and if there is a fault, thats the wrong way of going about it, the neutral wont be visable until removal of Consumer Unit cover, this applies to the lenthg of RCBO, as from the front they will all look the same, the RCBO can seen differently because of the test button which the MCB does not have.