RCBO problem

[SPECIAL LOCATION]

No, no, no, no, noooooooooooo!!!!!!NEVER do this. Never.

I am shocked and dismayed that three of you think this is acceptable practice.

Now some may say 'Dude, you're getting well confused'.

but I couldn't possibly comment.

In view of the fact that out in the real world there are numerous Earth Loop Impedance testers that either

1) have no anti-trip facility or

2) only perform anti-trip on certain type of RCD / RCBO...

AND

there are still loads of split load boards with several non RCD protected MCB's

or RCBO slots that could temporary be replaced with an MCB....

Then to disconnect the circuit conductors, Live & Neutral (which are probably off while doing other dead tests)

from an RCD protected MCB or RCBO ....

and temporarily reconnect back onto a NON-RCD protected MCB, (of suitable value)

such that it can be said.... "The RCD or RCBO is bypassed".

This posses less risk or danger.... IMHO than say disconnecting the main earth connection to take a Ze reading.....

Or do you frown upon this practice as well ??? ?:| :|

If you can't measure Zs directly (and why would you want to on a new installation?) then calculate in accordance with Appendix 14.

Possibly to verify maximum ZS values.. say in accordance with the information given in Guidance Note 3 around page 50ish???

also not ALL installations are new... some of us actually work on existing installations as well.

These are fairly basic tests that some may expect 'every spark to understand'.

Hope that helps.

 

[Andy™]

No, no, no, no, noooooooooooo!!!!!!NEVER do this. Never.

I am shocked and dismayed that three of you think this is acceptable practice.

If you can't measure Zs directly (and why would you want to on a new installation?) then calculate in accordance with Appendix 14.

maybe skip the RCD in controlled situations to safely carry out the testing... similar to how you can skip an RCD on socket outlets in controlled situations.... not ideal, but its not that much of a danger

im guessing that youve never done work on a real installation.

 

[Battersby]

Out in the real world, Special Locations?

That's where I live.

Real installations, andyc?

All the time, day in, day out.

Establishing a value for Zs?

You always have both options (calculation or measurement) for a new installation, so why take the one most likely to breach Regulation 14 of the EAW Regs?

Not so long ago some colleges used to teach you to bridge out 6A circuit breakers because loop testing tripped them, but that doesn't mean they were correct to do so. Even back then, the option to calculate was both valid and preferred.

Testing Zs requires that the installation be energised and involves creating a temorary fault, which, in turn, involves a fault potential appearing on all exposed and extraneous conductive parts.

Testing Ze, on the other hand is comparitively safe and is a necessary verification before energising an installation. (Even safer still with a two-lead tester.)

For PIRs, it is often more convenient to measure Zs directly, and it is safe to do so with socket-outlet circuits and a plug-in iec lead, but you should never bridge out any protective devices to do so. You will never be so advised by anybody who knows what they are doing.

If your test equipment is an issue then upgrade it, (and if you do PIRs you really should be bang up to date in all respects) but please don't tell people on a public forum to engage in a practice which has been deprecated for years and may be in breach of HSWA.

 

[Andy™]

a good reason to do a Zs on new install after you have done Ze and R1R2 would be to make sure that you have connected everything again properly after the testing. but that theory doesnt really work if you have to short/alter something to be able to do the test...

few years ago at a previous company, it was common practice to bypass an RCD (normally just move phase to a non-rcd breaker) then test. but defiantly much better a tester which doesnt trip

 

[Battersby]

a good reason to do a Zs on new install after you have done Ze and R1R2 would be to make sure that you have connected everything again properly after the testing. but that theory doesnt really work if you have to short/alter something to be able to do the test...

Unless you have an ancient tester, which generates a very high test current, that doesn't really hold true anyway - that's a hark back to the days of the Clare Tester, which used to reveal defective joints in conduit/trunking.

(But why not just do (R1 + R2) again... the proper way, without disconnecting anything?)

few years ago at a previous company, it was common practice to bypass an RCD (normally just move phase to a non-rcd breaker) then test. but defiantly much better a tester which doesnt trip

But, quite often, 'common practice' is not correct and can be just the preference of a single person with a big enough voice.

We have a big problem in this industry, which has never been very well regulated. The problem is keeping current and it occurs across the board, from domestic to industrial, from trainee to senior engineer. And it is often at its worst in long-served, apprentice-trained industry sparks, who have never picked up a regs book or read a guidance note in their lives, relying on advice from above.

When querying such advice, the response is usually "it's a reg", or "good practice, son", to which the reply should be, "Where can I read that, Boss?"

 

[Andy™]

Unless you have an ancient tester, which generates a very high test current, that doesn't really hold true anyway - that's a hark back to the days of the Clare Tester, which used to reveal defective joints in conduit/trunking.

(But why not just do (R1 + R2) again... the proper way, without disconnecting anything?)

even with a non-trip, it can still pick up if someone hasnt tightened a terminal properly. R1R2 again without disconnecting would also show that, but R1R2 again isnt 'the proper way'

But, quite often, 'common practice' is not correct and can be just the preference of a single person with a big enough voice.

you will never get rid of common practice... how many of you use side cutters to strip T&E?

We have a big problem in this industry, which has never been very well regulated. The problem is keeping current and it occurs across the board, from domestic to industrial, from trainee to senior engineer. And it is often at its worst in long-served, apprentice-trained industry sparks, who have never picked up a regs book or read a guidance note in their lives, relying on advice from above.

probably never been well regulated because most sparks were trusted to complete a job and managed that in a safe way. even if there were some times where parts were temporarily bypassed to do something

When querying such advice, the response is usually "it's a reg", or "good practice, son", to which the reply should be, "Where can I read that, Boss?"

'probably under that floor your about to crawl under with this cable'

my red above

 

[Battersby]

(But why not just do (R1 + R2) again... the proper way, without disconnecting anything?)even with a non-trip, it can still pick up if someone hasnt tightened a terminal properly. R1R2 again without disconnecting would also show that, but R1R2 again isnt 'the proper way'

I was being flippant about measuring (R1 + R2) twice - as you'd already acknowledged, making and re-making connections is prone to introducing faults. I was suggesting that, in the majority of installs, you can actually carry out (R1 + R2) testing without disconnecting anything.

I don't agree that Zs testing should be suggested as a way to reveal poor connections - the purpose of Zs testing is to verify that the loop impedance is sufficiently low to ensure sufficient earth fault current to operate the overcurrent device. You can always do this by calculation.

As regards sparks being trusted to do a safe job - the evidence is all around you that this wasn't always the case. Their being trusted simply meant that nobody checked. And since the advent of the fifteenth and a more complex set of requirements, I'd stick my neck out to say the majority of electricians appear to have been paddling way out of their depth. For a great example, witness the universally appallingly ignorant implementation of supplementary bonding!

Not to tar everyone with the same brush I will say I have encountered sparks with a good grasp of basic principles and a good understanding of the requirements... but not many of them are still on the tools.

'probably under that floor your about to crawl under with this cable'

Ha, ha! Good one, but it rather makes my point about passing on the knowledge.

 

[binky]

If its a 6A RCBO chances are it may trip as per 6A MCBs depending on make. Have fitted a few Steeple units without problem, from what I re-call they are the double pole type so should test same as RCD. Have you connected it correctly???

 

[batty]

The reason the Robin type with d-lok trip Rcbo's is because they put 25 amps down circuit for a very short time and because the neutral is solid Rcbo will sense this as a fault and trip this is also why they can trip 6 amp Mcb's. RCD'S on the other hand are double pole and what the d-lok does is freezes RCD while test is performed. Other testers put a much smaller current down circuit and hence do not trip both Rcbo's and RCD'S. I think this is correct if my memory serves me correctly.

Batty

 

[Evans Electric]

Thanks for that Batts. Deke.

 

[Evans Electric]

If its a 6A RCBO chances are it may trip as per 6A MCBs depending on make. Have fitted a few Steeple units without problem, from what I re-call they are the double pole type so should test same as RCD. Have you connected it correctly???

These were Steeple Binky ( made by Crabtree I'm told) Yes connected right, 32 amp RCBO trips as well .

I will continue to test through an MCB unfortunatly, certainly won't be buying yet another tester.

Deke

 

[batty]

Deke

Steeple used to be GE have they changed.

Batty

 

[Evans Electric]

Yes ,thats what Denmans told me anyway. Their new Steeple range CUs are made for them by Crabtree. Lately I've heard a few bad reports on Crabtree, returning stuff, RCDs packing up etc. I know its not made in England now (factory used to be about 4 mile away, houses now). Had no problem myself though.

Deke

 

[binky]

These were Steeple Binky ( made by Crabtree I'm told) Yes connected right, 32 amp RCBO trips as well . I will continue to test through an MCB unfortunatly, certainly won't be buying yet another tester.

Deke

Sounds like duff RCBO then, but strange to have 32A tripping aswell.