Boiler circuit 16A MCB

[Michaelwgroves]

I'm following a spark who used an existing Panel Heater circuit, for new gas boiler circuit 6 months ago. The panel heaters were removed, so it's now a dedicated boiler circuit. I'm doing an EICR.
I've found a number of faults;
1. No grommet in Consumer unit knock out, used for gas bonding (It's a recessed consumer unit)
2. Stranded cable does not have ferrules
3. Unfused Boiler switch
4. 16A MCB (2.5mm T&E)
5. Gas not bonded, bonding taken to central heating pipe only

Most of these are black and white very poor work. I've had to fix all of these so the EICR is a pass, but I have a dilemma.
#4, the MCB is way too big for a boiler. I now have a switched fuse with 3A fuse, so the boiler is now protected. It's a 2.5mm T&E cable so the 16A MCB is protecting the cable. Nothing is unsafe. If it were a new circuit, I'm sure he would have purchased a 6A MCB, but as it's not he's just used existing 16A. I'm going to need to do 16 EICR's following these guys. I'm sure this will be a theme. Is there a reg I can quote for wrong sized MCB, or is this just poor workmanship ?

 

[Michaelwgroves]

Explain a bit more - cable for what, terminated where and how?

Its a 1mm cable from FCU to boiler. 526.9.1 requires suitable terminals. I'm now curious on the definition of fine wire & very fine wire. I'd say 1mm would come under this regulation. Any multiwire cable below 2.5mm I put a feral on. But I'm not aware of the physical difference.

 

[Michaelwgroves]

A rubber blind grommet wont stop any sort of fire, and regardless this is outside the scope of an EICR.

You are pulling up things that relate to workmanship (gas bond excluded) and adherence to BS7671. An EICR is solely to give an engineering view on whether an installation is safe for continued use.

For clarity, I am referring to 'Wylex Fire Retardant Membrane Cable Entry'

 

[davesparks]

For clarity, I am referring to 'Wylex Fire Retardant Membrane Cable Entry'

That still won't stop the spread of fire!

Fire retardent does not mean the same thing as fire proof!

 

[Michaelwgroves]

It's not the wrong size MCB and it's not poor workmanship.

16A 2.5mm radial has been the generally accepted standard supply for any small appliance such as a boiler for a long time.

Using a smaller MCB would be unusual and would be unlikely to give any selectivity with the 3A fuse for the boiler.

I'd not thought about, Selectivity, this is a good point. Saving myself doing the maths, what size MCB do you put on boiler circuit to achieve selectivity?

 

[Michaelwgroves]

Coarse stranded conductors do not need ferrules, fine stranded conductors do need ferrules or other suitable treatment at the end.

It is important to remember that the regulations do not require the use of ferrules, they require fine stranded cables to be suitably treated at their terminations. This can be achieved by using ferrules but this is not the only way.

I agree with your comments, but what is fine wire and very fine wire ?

 

[Michaelwgroves]

That still won't stop the spread of fire!

Fire retardent does not mean the same thing as fire proof!

So how would you prevent the spread of fire for a knockout?

 

[davesparks]

I'd not thought about, Selectivity, this is a good point. Saving myself doing the maths, what size MCB do you put on boiler circuit to achieve selectivity?

I would install a 16A 2.5mm radial by default.

 

[davesparks]

So how would you prevent the spread of fire for a knockout?

If it ever becomes a requirement of the regulations I will worry about it then.

Currently any fire sealing that is needed on a job I would get a specialist fire sealing contractor in to deal with it.

 

[loz2754]

I agree with your comments, but what is fine wire and very fine wire ?

Have a look at these:

ferrules - how to use, tips and colour codes

German and French ferrule crimp colour codes, how to use ferrules and where to use ferrules. Handy ferrule downloads and electrical tutorial videos.

www.efixx.co.uk

 

[Lucien Nunes]

I'm now curious on the definition of fine wire & very fine wire.

Generally copper conductors will be stranded to one of a number of classes within IEC 60228.
Class 1 = solid conductor.
Class 2 = stranded conductor (e.g. larger T+E, normal 6491x conduit cables) for which terminals in electrical fittings are normally suitable without ferrules or other treatment.
Class 5 = fine stranded / flexible and Class 6 = very fine stranded / highly flexible (e.g. tri-rated BS6231, BS6500 flexibles) may require ferrules or similar treatment when used with terminals that are not designed for class 5/6 conductors.

Post crossed with @loz2754

 

[timhoward]

I'd not thought about, Selectivity, this is a good point. Saving myself doing the maths, what size MCB do you put on boiler circuit to achieve selectivity?

My hunch was a B16.... and I was curious enough to do a bit of scribbling. This is a BS1362 3A fuse time/current curve roughly superimposed onto the type B MCB graph:

Without more accurate manufacturer's let-through data of the device in question, the lowest MCB that I would bet my supper on not tripping before the fuse is in fact a B16. A B10 is probably too close to call!

 

[Michaelwgroves]

My hunch was a B16.... and I was curious enough to do a bit of scribbling. This is a BS1362 3A fuse time/current curve roughly superimposed onto the type B MCB graph:
View attachment 107210
Without more accurate manufacturer's let-through data of the device in question, the lowest MCB that I would bet my supper on not tripping before the fuse is in fact a B16. A B10 is probably too close to call!

Excellent post, thanks for taking the time to put this together

 

[Michaelwgroves]

Have a look at these:

ferrules - how to use, tips and colour codes

German and French ferrule crimp colour codes, how to use ferrules and where to use ferrules. Handy ferrule downloads and electrical tutorial videos.

www.efixx.co.uk

Thanks mate, really good link. Learnt a bit about flexible cables.

 

[ERFspark]

Respectfully - if you don't know and understand what you're inspecting, should you be inspecting?

Could not agree more
A painful read that

 

[Michaelwgroves]

If it ever becomes a requirement of the regulations I will worry about it then.

Currently any fire sealing that is needed on a job I would get a specialist fire sealing contractor in to deal with it.

I would argue it is a requirement from 17th edition.
Guidance Note 4 (17th Edition) - Protection Against Fire advises
3.8.1 Consumer Units & Similar Assemblies in domestic premises
'The Installer must seal all openings into the non-combustible enclosure or cabinet for cables, conduits, trunking or ducting that remain after the installation of cables. Good workmanship and proper materials must be used and account must be taken of the manufacturer's relevant instructions, if any.'

I was pulled up on this by Stroma during an assessment.

I've not had a good reason to get latest Guidance Note 4 until now, so just ordered 18th edition A2. It arrives tomorrow. I'll give a further update once it arrives, unless someone beats me to it.