RCBO Query...

[TopDog73]

Hiya Guys,

I hope there is someone out there who can answer my problem. I'll do my best to explain my situation.
Right then - I have been given the task by my employer to test/inspect some Distribution boxes.
(Here is a link from a random web site I found showing the boxes - Electrical Distribution Hire | Gofer Ltd - Event Power )
Before I go any further, I'd like to point out that I'm not actually fully qualified but in training at adult classes during the evening at my local college.
I work along side two fully qualified sparks, who are suppossed to aid me, but they'd much rather laugh at my efforts and fails. Hence me asking in here, and saving myself being patronised or critisised.:banghead:
So I'm doing the continuity test, R2 to R2 etc, L1 to L1 etc. Testing the sockets one by one. When I test my first socket from incomer L1 to outgoing L1 it passes with an expected 0.00 ohms (or there abouts) but when I come to test my second socket, from incoming Line to outgoing line, my RCBO trips. It'll even trip when testing continuity on the neutral.
Can someone please explaing why some breakers will trip, and others will be OK. Bearing in mind that most of the boards I test are 63A Single Phase incomer with the outlets being a mix of 16A and 32A Single Phase.
Other boards I test are 3 Phase incomers with 16A single phase outlets and 32A Single Phase outlets.
I just can't seem to get my head round it.

Also - just to add - Conntinuity is good from the incomer, to the bottom of the RCBO, and is also good from the top of the RCBO to the outlet. But to go from the incomer to the outlet, going through the breaker is a no no as it trips (on some but not all). Gutted.

Also like to add that these are all new RCBO's. Fresh out of the box.
Thanks Guys!!

 

[Rockingit]

Before I comment, they're not Dave's rubber boxes, are they? Someone else's, yes?

 

[Plonker 3]

Sorry I think I understand what you are doing, but just clarify please what test instrument/s you are using and what you are trying achieve by these continuity tests please.

 

[Richard Burns]

I am sorry that the people who are there to help are not helping, this is a foolish approach for them to take, but stick with it you have the capability to exceed them!
Always good to catch them out at a later date when you know you are right!

RCBOs tripping on continuity testing, hmm this is slightly odd, I would not expect a type AC (normal RCD) to trip from a continuity test.
In general I assume that any RCBO will be type AC.

However for distro boxes they may be designed to higher specification and may have type A or type B RCBOs protecting the box (if they exist) . Since type A and type B RCDs can react to direct current imbalances (pulsed DC current for type A and fluctuating DC current for type B) then it is possible that they are reacting to the DC current that will be injected by the continuity test (usually approximately 200mA so easily enough to trip a 30mA device).
Have a look on the RCBO and see if they have the different symbols as shown below on them, if so then this may be the reason.


Because you are not getting consistent tripping then if they were type A it may be they are only tripping if you have slightly poor contact on the probes and the current is jumping a bit as you test.

I assume you are testing continuity from supply inlet to each part of the circuit to ensure that there are no loose connections that may introduce a high resistance, however you may find it easier to make up a test plug (labelled as such) that can link poles together (obviously not for mains connection!) then you could keep the tester on the supply inlet terminals (perhaps after the RCBO if it is still tripping, and if you can get to those terminals) and simply move the plug around the sockets.
This would test two conductors simultaneously depending on your interconnection, but if all were OK then you would only need two tests ( or three for three phase) on each socket.

All this is supposition though and I am sure someone else will come up with a better answer soon!

 

[davesparks]

Before I comment, they're not Dave's rubber boxes, are they? Someone else's, yes?

You leave my rubber boxes out of this! They are all fully compliant with standard industry practice of bypassing that annoying trippy thingy that spoils the show

Funnily enough my job over the weekend is building a new 32A 3ph distro.

 

[davesparks]

It is perfectly normal for a 30mA RCD to trip when a continuity test is carried out through one of its poles, they trip at a 30mA imbalance and a continuity test passes 200mA through one pole and nothing through the other.
If you do a regular R1+R2 test with your test link before an RCD it will trip out when you test (puzzled me a bit the first time it happened to me)

The RCBO's that didn't trip out may well be faulty, have you carried out any tripping time tests on them yet to see if they are ok?

 

[trev]

If you're testing a ring final why are you using the method you appear to be using?
Test at the CU with the load side disconnected, this will tell you if the conductors on the ring are continuous. When you have a satisfactory result then you can move on through the test sequence

 

[Rockingit]

You leave my rubber boxes out of this! They are all fully compliant with standard industry practice of bypassing that annoying trippy thingy that spoils the show

Funnily enough my job over the weekend is building a new 32A 3ph distro.

Different Dave! "Dave Gofer", if you know him.

 

[davesparks]

Different Dave! "Dave Gofer", if you know him.

Excuse me while I just go and stand in the corner for a while

 

[davesparks]

If you're testing a ring final why are you using the method you appear to be using?
Test at the CU with the load side disconnected, this will tell you if the conductors on the ring are continuous. When you have a satisfactory result then you can move on through the test sequence

He's not testing Ring finals, he's testing rubber box type distribution boxes used in temporary power and events, have a look at his link for pictures.
When he says he is testing L1 to L1 what he means is L1 of the inlet connection to L1 of one of the socket outlets.

 

[Rockingit]

If you're testing a ring final why are you using the method you appear to be using?
Test at the CU with the load side disconnected, this will tell you if the conductors on the ring are continuous. When you have a satisfactory result then you can move on through the test sequence

Wont be a RFC - it's a radial of daisy chained ceeforms via splits (either made or pre-fab). And there's nothing that I can think of in an events environment that would warrant doing what the OP describes, tbh. If all cables are individually tested and certified then you're good to go. Test the actual RCD's in the box once every few months and inspect the box for damage along with maybe some R1R2 and IR tests between the I/P and O/P's and that's about it.

The box will have a 3PNE 63 or 125 ceeform as an input, then split it all out internally into various 1ph and 3ph things that make sense. So, say you had a 63A input, you might then have 2 x 32A 3ph outlets, 1 x 2x32A 1ph, 4 x 16A 1ph and maybe six 16's off the other phase with OCPD as appropriate at various stages along the way. All depends on what it's been designed to do.

 

[davesparks]

Wont be a RFC - it's a radial of daisy chained ceeforms via splits (either made or pre-fab). And there's nothing that I can think of in an events environment that would warrant doing what the OP describes, tbh. If all cables are individually tested and certified then you're good to go. Test the actual RCD's in the box once every few months and inspect the box for damage along with maybe some R1R2 and IR tests between the I/P and O/P's and that's about it.

The box will have a 3PNE 63 or 125 ceeform as an input, then split it all out internally into various 1ph and 3ph things that make sense. So, say you had a 63A input, you might then have 2 x 32A 3ph outlets, 1 x 2x32A 1ph, 4 x 16A 1ph and maybe six 16's off the other phase with OCPD as appropriate at various stages along the way. All depends on what it's been designed to do.

The way I read it he's just testing the distro's themselves in the warehouse rather than a whole site.

 

[Engineer54]

You shouldn't be conducting any IR, Continuity, etc tests ''through'' any RCD devices. The only test that any RCD device should be subject to, is the normal RCD testing and that is generally with the load side disconnected.... conduct continuity tests too and from these RCBO's, never through them....

 

[Rockingit]

You shouldn't be conducting any IR, Continuity, etc tests ''through'' any RCD devices. The only test that any RCD device should be subject to, is the normal RCD testing and that is generally with the load side disconnected.... conduct continuity tests too and from these RCBO's, never through them....

I was thinking about this thread earlier as I was driving around, and it occurred to me that we'd all overlooked that simple fact!

 

[trev]

Sorry guys, I wasn't thinking last night. I was doing something that rhymes with it.
Beer in, brains out.

 

[TopDog73]

Thanks kindly for all your responses.
It's looking like DaveSparks is spot on with my problem and the way I'm doing it. You explained it better than me Dave! lol.
Just some more info for you to look at so as to clarify at bit more.
- Yes, I'm testing in the workshop
- Yes, testing continuity L1 from the inlet plug to the L1 outlet socket (same for N and E and other lines if testing on 3 phase)
- outlet sockets vary in sizes. For example if it were a 16A socket, my RCBO would be a type C16.
and for a 32A socket, it would be a C32 RCBO. We don't tend to use type A's and very rarely use type B's.
- The tester I'm using is a Mettrel.
- 30mA operating current is the norm for these particular RCBO's
- The tests I have to carry out are continuity, Insulation Resistance, RCD operating times and obviously the general visual checks.

When doing the RCD operating times the Mettrel tester shows it a 'pass' with a green light and a 'tick' therefor giving me assurance that it's capable of doing what it's supposed to.

So it's baffling to see that it passes the RCBO's that trip out during my continuity test.
Even my IR readings are good.

Maybe you're right Dave - my tester is just giving out a bit too much 'umpf' to a slightly sensitive RCBO....

 

[davesparks]

Your tester isn't giving out too much, it is required to test with a nominal current of 200mA and the RCD is required to trip at a nominal 30mA imbalance so the RCD should operate in this situation.

You should be doing more than watching for a green light on the tester. You need to be keeping a record of all test results and comparing them everytime it is tested to see if anything has changed.

 

[Richard Burns]

Just to be clear about my post the tripping curve of an MCB e.g. B, C or D is a different thing from the sensitivity of an RCD to DC currents with the type A, AC, B.
This is a picture of two type A RCBOs but one is a C32 and the other is a B6 MCB.