RCBO/MCB swops & certification

[Cremeegg]

I read in page 9 of Chris Kitchers book “Practical Guide to Inspection Testing & Certification of Electrical Installations” that an Electrical Installation Certificate – required for –“……when a circuit is altered and the alteration requires the changing of the protective device”.

Much the same is repeated on page 11 “The EIC must be issued for a completely new installation or new circuit; this would include alterations to a circuit which would result in changing of a protective device or the renewal of a distribution board.”

I see no reference in BS7671:2008 to this.

The notes to the EIC on p 334 state EIC only used for addition alteration where new circuits are introduced.

A “circuit” using the BS7671:2008 definition …to paraphrase horribly….“a collection of bits protected by same protective device”. I take that to be everything downstream of the protective device. Correct ? Or does it include the protective device?


So last week I replaced a 8.5kW shower, straight swop, like for like, use the same 6mm2 cable but with an eye on good practice and BS7671 I swop the original undersized 32A MCB for a 40A RCBO. Thankfully it’s only a 5m run and clipped direct all the way with no insulation so 6mm2 is adequate with Table 4D2A quoting 46A. No new circuit. The circuit isn’t altered as I used the same cable but the protective device is altered for the better.

Later this week I’ll put a spur on an existing ring that is not protected by an RCD – chase the cable in <50mm deep – change the 32A MCB for a 32A RCBO. Not a new circuit but again the protective device is changed for the better.

Last example – say I reuse an old spur for an immersion heater for a lighting circuit but re-use the cable from the CU to the FCU. I swop the old 16A MCB for a 6A RCBO – again the protective device is changed for the better but only an altered circuit.

So an EIC or a MEIWC?

 

[Spark123]

I'd have thought the protective device has got to be part of the circuit. In the definition of electrical equipment it includes protective device.

As far as I know, replacing a protective device on a non like for like basis is not an acceptable use for a minor works certificate, new circuit rules apply.

You can use table 4D5 for flat twin and earth.

 

[securespark]

Egg, are you NAPIT registered?

 

[Pensdown]

IMO a Minor works cert is fine.

Part 1 is a description of the works.

Part 2 covers the details of the installation which would include the existing/new protective device(s) for the circuit.

Part 3 covers the testing of the circuit which would be after the new protected device(s) had been fitted.

Part 4 is your declaration that the works detailed in Part 1 will not impair the safety of the existing installation and that the works have been designed, constructed, inspected and verified in accordance with 7671

What other information would be relevant?

 

[Spark123]

Maximum demand, characteristics of supply, supply fuse type and size etc.

NICIEC book on I, T & C (16th ed regs) has a table of what is acceptable and what is not, in their eyes the replacement of a protective device not on a like for like basis is not an acceptable use of a MWC.

 

[Pensdown]

That does surprise me. We've been changing B's for C's and some cases C's for D's for years on a MW cert. Not once has this come up during an audit.

Why would you fill out an EIC if you changed a 32 to a 20?

IMO that's why Part 4 is on the MW cert.

 

[Spark123]

I have always understood changing a protective device is altering the protective characteristics of the circuit so the MWC isn't suitable. There is no space on the MWC to record the necessary i.e. Ze, R1+R2 etc which you would to do anyway before deciding it is suitable to energize the circuit. I can understand the reason why when you are making it conditions more onerous i.e. if you are changing from B to C or increasing the size, fwiw I think it is daft that a full EIC should need to be done for down sizing an MCB.
Maybe worth consulting with your scheme to see there stance.

 

[Pensdown]

The NIC MWC is more comprehensive than the 7671 sample and includes R1+R2 etc.

Untitled

• Pensdown
• 3 Sep 2008
• 2

 

[Spark123]

It doesn't include Ze or maximum demand
If you have the NICEIC Inspection, Testing and Certification book (I have the 4th ed) the table I referred to before is in chapter 4.

 

[ban-all-sheds]

I see no reference in BS7671:2008 to this.

Not even the part where it says that an MWC would not be appropriate, and therefore by implication all that's left is an EIC?

Later this week I’ll put a spur on an existing ring that is not protected by an RCD – chase the cable in <50mm deep – change the 32A MCB for a 32A RCBO. Not a new circuit but again the protective device is changed for the better.

How do you know that a 32A Type B device was appropriate in the first place? Where do you record the results of your testing to confirm it is? Where do you record the results of your RCD testing?

Yes, you can attach a schedule of results to an MWC, but the lack of any text on the certificate referring to attachments makes me think that an MWC is not the expected form for you to use.

Oh - and changing MCBs is notifiable, BTW....

 

[Pensdown]

It doesn't include Ze or maximum demand
If you have the NICEIC Inspection, Testing and Certification book (I have the 4th ed) the table I referred to before is in chapter 4.

I have a copy of that great book but I do think some of their recommendations assume a lack of “electrical common sense”.

For a straight forward final sub-circuit protective device change I would still use the NIC MWC.

As long as the circuit Zs is measured and conforms I can’t see the need to record Ze, bearing in mind that for most commercial installations it's normally "by enquiry" anyway.

I would also argue that if the circuit being modified had a detrimental effect on the total load/maximum demand of the building then it shouldn’t be done as it would make Part 4 invalid.

But if for example I was changing an MCCB on a sub-main that’s a different matter.

 

[Spark123]

Even if Ze is by enquiry you need to measure it anyway.
I still don't think that altering the protective device of a circuit is minor work as it is altering the protective characteristic for the whole circuit.

 

[Pensdown]

I'm still not convinced and it's a real treat when we actually get a chance to measure Ze.

 

[Spark123]

I know the feeling, proper Ze might be a limitation! But given the opportunity you have got to measure Ze to ensure that there is a connection.

 

[ban-all-sheds]

I have a copy of that great book but I do think some of their recommendations assume a lack of “electrical common sense”.

That'll be because it's written for NICEIC members.

Anyway...

As long as the circuit Zs is measured and conforms

Where do you record the measurement, and in the case of an RCBO the operating time?