Consumer unit breakers

[bernardgreen]

Second hand but still in use and likely to have been checked / inspected when the house changed hands.

Why would used MCBs be on the market. why were they taken out of the house. Could have been a simple up-grade or replacement of a defective installation.

 

[ban-all-sheds]

Second hand but still in use and likely to have been checked / inspected when the house changed hands.

Yes, but MCBs are never tested.

 

[sparkiemike]

Not with an instrument, but the functional testing should take place, see reg 612.13.2

 

[OwainDIYer]

What cheaper than fully loaded £60 at screfix ?

Yeah, 'cos they can get it at Electricfix (trade only)

 

[ban-all-sheds]

Not with an instrument, but the functional testing should take place, see reg 612.13.2

I know that MCBs can be tested, i.e. there is equipment available to do it.

612.13.2 does not mention MCBs, but in the context of anything in Part 6 how do you do functional testing of an MCB? Even with an instrument, let alone without.

Just checking that it disconnects when you manually operate the lever is not a functional check of a protective device.

 

[sparkiemike]

Agreed you can't economically test all the functionality of MCBs.

I would say MCBs are switchgear, and the Inspection Schedule for ECIR would suggest the same, see item 4.8.


MCB can be used for isolation, so checking their operation would be advisable

 

[JohnW2]

Agreed you can't economically test all the functionality of MCBs.

Quite. In reality, testing of the primary (over-current protection) functionality of an MCB just doesn't happen, certainly not in relation to domestic or commercial installations.

MCB can be used for isolation, so checking their operation would be advisable

Fair enough - but that obviously falls far short of being able to test the functionality which most matters.

Kind Regards, John

 

[sparkiemike]

I think it depends on your definition of functional testing.

Both BS7671 (612.13.2 and the Inspection Schedule for an ECIR) and GN3 (table 3.3) advocate the manual operation of Circuit Breakers to prove the device disconnects the supply.

So MCBs are tested, but not the full extent of their functionality.

 

[JohnW2]

I think it depends on your definition of functional testing. ... Both BS7671 (612.13.2 and the Inspection Schedule for an ECIR) and GN3 (table 3.3) advocate the manual operation of Circuit Breakers to prove the device disconnects the supply. ... So MCBs are tested, but not the full extent of their functionality.

Yes, but is not this discussion a little silly, in as much as we all know what is the primary function of an OPD, and hence the aspect of functionality that would be most important to test (if we could)? Sure, if an MCB fails to disconnect the supply when operated manually, it probably wouldn't when confronted with an over-current - but that test is probably not going to catch many MCBs which are faulty in the sense that they would not operate (at all, or at the right current and within the right time) in response to over-current. The point obviously is that there is, in practice, essentially no way that one can check that an MCB (particular an old one) will still do 'what it says on the tin' if/when the occasion ever arises.

Since there is obviously much more testing one can do with an RCD, you obviously would not consider that an RCD had been 'functionally tested' simply because it disconnected the supply when you operated it manually (nor, really, if it had disconnected in response to pressing the test button).

Kind Regards, John

 

[ban-all-sheds]

I think it depends on your definition of functional testing.

A test to show whether the item functions as it should.

 

[SimonH2]

A test to show whether the item functions as it should.

As already pointed out, since the primary function of an MCB is to protect the circuit in the event of a fault or overload, merely checking that it "switches off" by operating the lever isn't really enough - it's only testing a secondary function.

I was thinking that a test jig could be made with the welder and a variac - but few would have the items required or the skills to use them (and testing the "fast" disconnect times would be quite tricky.) I wouldn't have thought there is any practical way to testing them in-situ.

 

[JohnW2]

As already pointed out, since the primary function of an MCB is to protect the circuit in the event of a fault or overload, merely checking that it "switches off" by operating the lever isn't really enough - it's only testing a secondary function.

Quite so - it shouldn't really even need saying!

I was thinking that a test jig could be made with the welder and a variac - but few would have the items required or the skills to use them (and testing the "fast" disconnect times would be quite tricky.) I wouldn't have thought there is any practical way to testing them in-situ.

I feel sure there's not. Furthermore, there is the added complication that deliberately subjecting an MCB to a very high overload current (and causing it to disconnect that very high current) to check the functioning of its magnetic trip mechanism might actually do harm to the device under test, thereby making it less likely to work satisfactorily 'next time'!

Kind Regards, John

 

[sparkiemike]

Testing MCBs as John and BAS suggest is just not practical. It would seem sensible to follow the guidance in BS7671 and GN3.

So for ECIRs, 621.1 uses the words "so far as reasonable practicable", I would think for testing MCBs this phase would apply.

 

[RF Lighting]

I see no one else has yet mentioned that in 2 1\2 months the OP's fusebox will also not comply with regs due to being plastic.

 

[JohnW2]

Testing MCBs as John and BAS suggest is just not practical. It would seem sensible to follow the guidance in BS7671 and GN3. ... So for ECIRs, 621.1 uses the words "so far as reasonable practicable", I would think for testing MCBs this phase would apply.

You keep talking about EICRs and, in that context, you have got to be right - since (as agreed) there's nothing more/else that one can do.

However, that's not how this discussion started. It was more a question as to how much faith one should have in an old, secondhand, MCB, probably with an unknown history, given that it's essentially impossible to test the aspects of functionality which most matter.

Kind Regards, John