running a heavy load on a fused spur

[Taylortwocities]

No, it will not cause any problems.

in fact, a 2.5mm radial on a 32A MCB is not correct. The maximum standard protection device for that radial would be 20amp.

So retaining the 32A MCB and making the circuit into a ring would be an improvement!

I'm assuming the 32A MCB is protected by an RCD?

 

[toadhall]

No, there is no RCD. It is an old CU where the fuses have been replaced by clip in MCBs.

 

[Taylortwocities]

New electrical work should comply with the current wiring regulations.
Those sockets should be protected by a 30mA RCD.

Regulation 411.3.3.
States that additional protection by means of a 30mA RCD is to be provided for all socket outlets with a rated current not exceeding 20A for use by ordinary persons. The only exceptions allowed are for socket outlets for use under the supervision of “skilled” or “instructed persons” e.g. some commercial / industrial locations, or a specific labelled socket provided for connection of a particular item of equipment, e.g. a freezer circuit.

 

[AndyPRK]

I don't think you need to move the machines.

You don't need to worry about ballancing a ring with 3 sockets in effectivly one area.

 

[EFLImpudence]

Nor, indeed, have a ring.

 

[AndyPRK]

well with the load you probably need to fit a 4mm or 6mm radial , so it may as well be easier to have a ring if the OP only has 2.5mm.

 

[toadhall]

here's the irony. Tell me if I'm reading it wrong.

If I do nothing, then I have a potentially dangerous setup but legal.

If I improve the radial 2.5mm with a ring, but no RCD, the setup is illegal.

talk about perverse incentives

 

[plugwash]

The rule of thumb with ring balance is that the center third of the ring is your "safe" area. Loads in the end thirds cause dispropotionate currents in one leg and if a ring is fully loaded and the bulk of a ring is grouped in one of the two end thirds then overloading of the cable is likely

This applies regardless of how short or long the ring as a whole is.

Having said that the combination of cables being rated fairly conservatively and the intermittent nature of most large domestic loads means that it's rare for these overloads to actually cause problems in a domestic setting.

 

[Taylortwocities]

here's the irony. Tell me if I'm reading it wrong.

If I do nothing, then I have a potentially dangerous setup but legal.

If I improve the radial 2.5mm with a ring, but no RCD, the setup is illegal.

talk about perverse incentives

It depends on your understanding of "legal"

BS7671, the wiring regulations, are not a Statutory Document.

HOWEVER, Building Regulation Part P, that dictates that electrical installations must be safe, is a statutory document (i.e. law) and it refers to BS7671 as a way to meet the requirements of Part P.
BS7671 is not retrospective so there is no requirement to bring installations (like yours) up to today's standards. New work does need to meet todays regulations.

So, as an electrician I would always comply with BS7671 because, if there were a legal case against me, I would contest that I had fully complied with BS7671. If I had not installed an RCD in a new socket circuit, for instance, then the widow of my dead customer would take me to the cleaners.

You, as a DIYer have a choice:

1. ignore the guidance of experienced experts and the history of fatal electrical accidents that have concluded (over time) that in a domestic situation it is better and safer for all sockets to be RCD protected.

2.. Accept that the advice you are being given is in your best interest.

 

[AdamCH]

If you put an RCD on the circuit then you'd probably want the freezer on its own circuit. If other appliances sharing the circuit trip the RCD then the freezer contents would spoil.

 

[Bluehair]

Or use 4 mm for the leg from the CU to the new sockets. Then however "un-balanced" the load was that leg would not be over loaded by a load to the maximum of the MCB.

Considerable care will be needed in the terminals where the 4 mm meets the 2.5 mm to ensure the joint is secure.

A 4mm spur from a 2.5mm standard ring final? I'm not sure if that is best practise. Better to provide a separate 32A MCB and create a new 4mm radial circuit.

Was Bernard suggesting a 4mm spur from a ring final circuit?

 

[Taylortwocities]

I believe so, but I think that particular solution has been superseded?

 

[toadhall]

I'm not sure as a dIyer, it makes any difference.

If I conduct any work on the circuit without an RCB, my insurance could be invalid or worse, if the new owner of the house fries, then I am toast.
If I leave it alone, I claim complete lack of knowledge and blame the previous sparky/owner.

Really what you are saying is spank a few hundred quid on a new CU and installation costs (as I really would not be able to do this) for what is not even agreed as particularly dangerous.

Dont get me wrong, I appreciate the advice but the new regs are pushing me to do nothing.

 

[AdamCH]

infamy, infamy, they've all got it in for me!

Calm down dear.

 

[ban-all-sheds]

here's the irony. Tell me if I'm reading it wrong.

You are reading it wrong.

If I do nothing, then I have a potentially dangerous setup but legal.

If I improve the radial 2.5mm with a ring, but no RCD, the setup is illegal.

talk about perverse incentives

Would you rather be compelled to bring all of your installation up to the requirements of the latest regulations every time there's a change?

Not doing that but requiring that any new work complies with the regulations at the time it's done seems perfectly sensible.

What would be perverse would be to exempt people from complying with the current regulations because they were extending an installation which was already non-compliant.