RCBO passes 30mA but fails 150mA but in a strange way. Any ideas?

[slipnduck]

Morning everyone, this is my first post - although i had an account years before that seems to have been lost.

Can any of you shed some light onto a situation I've come across.
I have a newly installed RCBO which is failing the x5 test with a reaction greater than 40 mS.

Now, I don't have a problem with that as some devices do fail straight from the box but.... it's the manner in which it fails that I find perplexing.

It's a Type A b curve CP Fusebox RCBO at 40A - so admittedly budget kit.
When tested on the testers AC setting it tests fine - 30mA and 150mA both causing sub 40mS activation at 0 and 180 deg.
However on the type A setting it activates at greater than 40mS on x5 BUT it activates at 36mS on x1 at both 0 and 180.

How can it be that it can activate at the lower fault level in a time that would satisfy the higher fault level test but then go on to fail the higher fault level test?

I'm not sure exactly what the tester does for the Type A tests but I assume it just introduces a DC current whilst the test is in progress along side the simulated AC fault current. I thought then that the AC current is increased for the x5 test whilst the DC component stays the same. If this is the case then the result seems very confusing.

Mybe the DC component of the test is also increased by the tester for the x5 test but I wouldn't have thought that would be the case as they are for up to 6mA DC and you'd think that is the current used by the tester for both x1 and x5 tests.

I don't mind swapping the device out but I'd just like to understand why it's happening.
Any ideas?

It's a new tester BTW - Metrel MI3152 - which I'm still getting to know. But the settings used in the tests are the standard ones for a 30mA General use RCD on both type A and AC.

Thanks

 

[Baddegg]

I use a lot of fusebox stuff and the type A s always have greater trip times, never had one fail though, have you got another to try?

 

[grumpyjohn01]

Morning everyone, this is my first post - although i had an account years before that seems to have been lost.

Can any of you shed some light onto a situation I've come across.
I have a newly installed RCBO which is failing the x5 test with a reaction greater than 40 mS.

Now, I don't have a problem with that as some devices do fail straight from the box but.... it's the manner in which it fails that I find perplexing.

It's a Type A b curve CP Fusebox RCBO at 40A - so admittedly budget kit.
When tested on the testers AC setting it tests fine - 30mA and 150mA both causing sub 40mS activation at 0 and 180 deg.
However on the type A setting it activates at greater than 40mS on x5 BUT it activates at 36mS on x1 at both 0 and 180.

How can it be that it can activate at the lower fault level in a time that would satisfy the higher fault level test but then go on to fail the higher fault level test?

I'm not sure exactly what the tester does for the Type A tests but I assume it just introduces a DC current whilst the test is in progress along side the simulated AC fault current. I thought then that the AC current is increased for the x5 test whilst the DC component stays the same. If this is the case then the result seems very confusing.

Mybe the DC component of the test is also increased by the tester for the x5 test but I wouldn't have thought that would be the case as they are for up to 6mA DC and you'd think that is the current used by the tester for both x1 and x5 tests.

I don't mind swapping the device out but I'd just like to understand why it's happening.
Any ideas?

It's a new tester BTW - Metrel MI3152 - which I'm still getting to know. But the settings used in the tests are the standard ones for a 30mA General use RCD on both type A and AC.

Thanks

I have recently had a similar problem with a couple of Lewden Control Gear Type A RCBOs although they failed on the 1 x and passed the 5 x ....but were perfectly normal on the AC test, tbh I let it go , putting it down to a tester anomaly of some kind, also availability of Type As is a bit patchy atm where I am so there was a mix in the board anyway...

 

[slipnduck]

I have others in the CU that test ok - their A times are higher than the AC times but all less than 40mS.

The strange anomaly is that this on passes x1 in a time that would satisfy the x 5 test but then goes on to fail the x5 tests.

Just got me to thinking about how the testers work - but you'd assume, or at least I would, that the same level of DC would be introduced for both x1 and x5.

 

[Strima]

What do the manufacturers state about testing?

 

[Andy B]

When you say passes 30mA, how you testing it (i.e. @ 25mA, 30mA, & then 35mA). Also, are you using a tester that does both positive and negative part of cycle? Oops, just seen rest of your post. My question maybe irrelevant. Not familiar with tester specified.

 

[Andy B]

I just researched tester you quoted. There three versions, which you using?

 

[slipnduck]

I just researched tester you quoted. There three versions, which you using?

MI3152 EurotestXC. I think it was the standard kit - came with a set of earth spikes and leads for Ra testing.
I'd imagine they all have the same function for type A rcd testing though.
Still getting to know it as its new and has a lot of options with regards RCD testing - B, B+, F
But I was just using it on the preset Type A settings for a 30mA G RCD. It goes through an auto sequence like most other testers x1/2 at 0 and 180 x1 ...x5...ramp.

I don't mind it being a duff RCBO it's just the not understanding how it can activate at 30mA within 40mS yet can't at 150mA that is annoying me.
I've got a load of Hager Type A here for a job on Tuesday that I could have a play with, only trouble is I've never got around to rigging up a non RCD protected socket in my house to test them off.

 

[slipnduck]

What do the manufacturers state about testing?

The manual is on a CD I'm going to have a read of it now. I haven't until now as I know how to navigate the touch screen to the tests I want to do and how to do them which is pretty much same as before, I haven't had any need of some of the more exotic things it does yet.

 

[slipnduck]

BTW
Thanks all for considering this. I only bought it up because it was niggling me as I was trying to get to sleep last night.

 

[Andy B]

I know what you mean. I'm the same. Once I know why, I'm happy. Cause fixing a problem usually pretty straight forward. It the not knowing why that bugs the hell out of me. Sometimes it comes to me next day when wake up. Must be the "little grey brain cells" working their magic when asleep as Hercule Poirot would say. Lol. However, as you say, it a strange one. To pass the 5x but fail the 1x makes absolutely no sense.

Just a thought, but do you have access to another Tester to compare results? Just in case it the Tester, seeing as it new. I've known new test kit to be faulty too, not just protective devices.

 

[loz2754]

Are you testing the RCD with no load connected?

 

[pc1966]

It almost sounds like an AC type being tested with a A waveform and the sense transformer saturating!

 

[UNG]

Have you ramp tested the RCBO in question?. I've had quite a few RCD's / RCBO's where the trip current has exceeded the 30mA level fresh out of the box
While it is not a requirement I always ramp test RCD's and RCBO's now when I install them and also on EICR's, I started doing it after I was asked to do some other work at a property 6 months after I had replaced a CU, when doing the testing on the work I noticed the readings from the RCD tests were a bit different to 6 months earlier dug a bit deeper and found that on a ramp test the RCD tripped at 36mA. Since then I have found quite a few that would pass the prescribed tests but fall short when ramp tested

 

[Strima]

The manual is on a CD I'm going to have a read of it now. I haven't until now as I know how to navigate the touch screen to the tests I want to do and how to do them which is pretty much same as before, I haven't had any need of some of the more exotic things it does yet.

I meant the RCBO manufacturers.