RCBO timing too high

[shocked]

Hi All
just done a c/u change fitted with 8 RCBO's and when testing the trip times 2 of the RCBO times were too high (40a 30ma =40.8 ms . 32a 30ma = >40 ms )on X5 ? changed the 2 x trips and retest exactly the same times ?! disconnect the circuits and retest trip times perfect, ok so retest circuits all ok ??! phone control gear and speak to tech it could be the cooker hood (double insulated ) or the w/machine, they don't like them. in my case it was the (40a) electronic shower (32a) combi boiler .
just letting you know
John

 

[Pete999]

are you testing at the rcbo or at the end of the circuit, what bs number is the rcbo please

 

[R G]

I would always recommend testing RCDs without the loads connected , both live and neutral removed , with all the electronic equipment nowadays its a risk we all take leaving things in , the readings vary so much with connected loads ...

 

[Dizzy_Maskell]

I would always recommend testing RCDs without the loads connected , both live and neutral removed , with all the electronic equipment nowadays its a risk we all take leaving things in , the readings vary so much with connected loads ...

Yes that's great and by the book but if the device fails to operate in intended use (cables connected) then what's the point for me I like to make sure that with or without load connected the device operates in time or else it's effectively redundant.

If you tested a socket circuit protected by an RCBO 61009 and the unit tested correctly with the cables removed but then tested it at a socket using a socket tester lead and it failed would you be happy with this ????

 

[Silly Sausage]

You're testing the device, not it and the circuit together.
The circuit needs validating separately.

 

[R G]

The Problem is that many of the appliances are inductive and have capacitors etc that react with the RCD testing , but in case you are unsure if all appliances are isolated , or there may be items difficult to unplug then isolating at the board may be the best way ,

 

[Engineer54]

Seeing as you are testing, or should be testing the RCBO and not the rest of the circuit, ....Yes, it has tested out correctly and has proven to be within specifications!! So something other than the RCBO itself, is causing the long time delay!!

 

[MDJ]

Yes that's great and by the book but if the device fails to operate in intended use (cables connected) then what's the point for me I like to make sure that with or without load connected the device operates in time or else it's effectively redundant.

If you tested a socket circuit protected by an RCBO 61009 and the unit tested correctly with the cables removed but then tested it at a socket using a socket tester lead and it failed would you be happy with this ????

Okay great, what was the question again??

 

[MDJ]

Hi All
just done a c/u change fitted with 8 RCBO's and when testing the trip times 2 of the RCBO times were too high (40a 30ma =40.8 ms . 32a 30ma = >40 ms )on X5 ? changed the 2 x trips and retest exactly the same times ?! disconnect the circuits and retest trip times perfect, ok so retest circuits all ok ??! phone control gear and speak to tech it could be the cooker hood (double insulated ) or the w/machine, they don't like them. in my case it was the (40a) electronic shower (32a) combi boiler .
just letting you know
John

Congratulations, now your turn to buy the cakes.

 

[Pete999]

Congratulations, now your turn to buy the cakes.

Short and too the point

 

[Geoffsd]

Am I right in thinking that the appliances do not actually affect the tripping times of the RCDs when in normal use; they just affect the meter readings?

 

[Flanders]

Am I right in thinking that the appliances do not actually affect the tripping times of the RCDs when in normal use; they just affect the meter readings?

Yes you are correct

 

[shocked]

Hi Pete999
I was testing at the RCBO end and it was manufactured by controlgear (lewden) Bs61009
John

 

[southsea1201]

I wouldn't be losing a lot of sleep over the 5 times test. It's not always necessary anyway. As long as the 1 x is ok I'd be happy.

edit: I never bother with the 5 x on BS4293 as experience has shown you're almost doomed to failure everytime.

 

[Richard Burns]

I wouldn't be losing a lot of sleep over the 5 times test. It's not always necessary anyway. As long as the 1 x is ok I'd be happy.

edit: I never bother with the 5 x on BS4293 as experience has shown you're almost doomed to failure everytime.

And yet the 40ms at 5 x Idn is the only test that is specified by BS7671 to ensure compliance.
The other tests are only recommended in GN3 (or tangentially referred to in BS7671, which does require the RCD to be operational))

 

[Silly Sausage]

I wouldn't be losing a lot of sleep over the 5 times test. It's not always necessary anyway. As long as the 1 x is ok I'd be happy.

edit: I never bother with the 5 x on BS4293 as experience has shown you're almost doomed to failure everytime.

That could well be the most bizarre post I've ever seen!
Please enlighten us all with your reasoning.
Many thanks in advance.

 

[uksparks]

I have to say, I am a little concerned by you saying 5x is not necessary and you don't bother with it....

 

[southsea1201]

OK first of all let me say that that the most important protection on any supply is ADS and not RCD protection. I live in a city that does not have TT supplies. An RCD is recognized as Additional protection 415.1.1. It is very good for clearing minor faults to earth quickly and thus preventing that circuit(s) from causing damage to people/livestock.

Firstly I would say that an RCD is not the lifesaver many of you think. I have twice had a belt from an RCD protected circuit and the damn thing did not trip. (I'm old dry skin etc). Body resistance can be as high as 100kOhms or as low as 1kOhms when wet. So do any of you believe that wet and barefoot an RCD would save your lives?...less than 10mA would probably be fatal if wet or sweating.
OK when I ramp test an RCD at 30mA i usually get a value of 20-25 ms. I have misled you somewhat and I apologise (for the words "I don't bother"). What I meant to say is I am not concerned. As I'm testing 1x I always test to 5x anyway but what I'm trying to say is I'm not going to lose sleep over a few milliseconds out on the result.

For instance say you get the following results 1x = 70 ms and 5x = 46 ms what are the implications? Well the 70 ms complies with the recommendations of OSG. But what about 46 ms? Seriously now what difference would 6 thousandths of a second make? Would it save a life?

Even if the 5x test came in at 100ms that is still 1 tenth of a second, less than the time between a heartbeat.

Now I will say that every BS 61008 I have ever tested complies with the requirements of the BGB, and yes I always did the 5x test and recorded it. However, I have experienced a problem with a number of BS 4293's and also 1 BS61009. I had to make a judgement call and I am prepared to stick by my decision. Let me explain:

The BS 4293: At 5x test I got a reading of 54 ms. I had altered a circuit and was doing the testing. So dutifully I spent the next 10 days trying to acquire a replacement (not easy) as it was specific to that particular board. Anyway I got one...fitted it and tested it and it came in at 48ms. So what do I say to my client? "Change the board because it failed the 5x test". Sorry but I had to make a judgement call....and in my view the 8ms difference was acceptable. Subsequently I found that very few BS 4293's actually pass the 5x test.
Do any of you truly believe that the the 8ms (yes 8 thousandths of a second) rendered this installation any less safe than if it had been 40ms?

The BS61009: I had to add a socket to an existing circuit protected by an RCBO. It complied with OSG for 1x test but came in at 83 ms at 5x. I approached the customer and explained the result of the test and he retorted that he was not prepared to fork out another 50 quid to replace the RCBO. I recorded the result on the certificate. But seriously now is this RCBO any more of a lifesaver than one that trips in 40ms. I was going to lose sleep over that one.

OK I am well aware that many of you on the forum will attempt to rip me to pieces...please have fun I have thick dry old skin!!! Do remember though that BS7671 is guidance only and someone has to prove to me that the difference of 43 ms would actually save a life. Sometimes you have to make a call on site and I am prepared to stand by my decisions. For me the most important thing is a well constructed installation with good EFLI readings...for me an RCD does only provide additional protection and is not the primary importance.

What we have to try and imagine for instance, is how critical is 40ms compared to say 78ms...Can we actually perceive that sort of difference?...and will that difference actually save a life?

 

[derek]

I could be wrong but I seem to remember our lecturer at college telling us the reason 40ms was chosen was because medical research done by the Nazis suggested more than 2 cycles of ac current at 50hz meant increased risk of stopping the heart.

 

[southsea1201]

One of the shocks I received I estimate lasted for between 0.5 and 1sec...it's very difficult to estimate a duration of a shock, I initially didn't realise what was happening before I eventually removed my finger from the wire. If I'd had a cut or peeled skin on my finger it could have been a lot worse. Luckily my fingers were very dry and dusty. as I said previously the RCD did not trip.