Changes to connect a 16A (hardwired) oven to 13A socket

[EFLImpudence]

Let's start again and be pragmatic and pedantic.

am a bit puzzled why you can't take a 16A spur from a 32A ring

If by 16A spur, you mean connect a 16A oven to a spur from a ring final circuit, then it could be considered a 27A spur as that is the current carrying capacity of 2.5mm² cable and it would not necessarily require fusing down because the oven will not draw more than its 16A load.

However, this goes against the regulations governing ring final circuits, good workmanship and proper design.
Only accessories, not appliances, should be connected on a ring.
It would (only) be unsafe with regard to the loading of the ring - both balance and total.
The spur itself would be fine.

as long as the cable to the spur is big enough to carry 32A.

It doesn't need to carry 32A for a 16A oven; it just has to comply regarding fault current for a 32A MCB.

What am I missing?

The basics.

It is just wrong.

 

[ban-all-sheds]

Allowed to use for protection of the circuit with a suitable fuse holder installed in a suitable manner by a competent installer.

And that would be a fuseholder which complies with BS 1363, will it?

Might not be ideal but most customers would rather have a 'not ideal but legal' alternative to ripping out their kitchen or pulling up their expensive floor. We live in the real world rather than Utopia, where virtually no homes that I go into are wired up completely by the book.

Do you have the same cavalier attitude to compliance with gas regulations and laws?

 

[bengasman]

What's cavalier about a solution that is legal?

 

[JohnW2]

What's cavalier about a solution that is legal?

"Legal" is not the issue, since BS7671 is not law - but, as you've been told several times, quite apart from other issues, there is no BS7671-compliant way of connecting a 16A fuse to a ring final circuit. Whether on not you regard failing to comply with the regulations as 'cavalier', I obviously don't know.

Kind Regards, John

 

[ban-all-sheds]

What's cavalier about a solution that is legal?

OK - if you want to be picky, ignore the bit about the law, and just answer the question "Do you have the same cavalier attitude to compliance with gas regulations?"


And now, returning to the issue of the law, this is what it says:



Please give us a cogently argued explanation of exactly how choosing to deliberately contravene the Wiring Regulations qualifies as making reasonable provision for safety etc.

 

[ban-all-sheds]

as you've been told several times, quite apart from other issues, there is no BS7671-compliant way of connecting a 16A fuse to a ring final circuit.

It's becoming pretty clear that he doesn't want to hear that.

Whether on not you regard failing to comply with the regulations as 'cavalier', I obviously don't know.

Cowboys are always in denial.

 

[sgabello]

Interesting... how do I know what kind of circuit I have at the moment?
The MCB that connects the kitchen is 32A, and it has two red cables departing from the top (unlike the others with only one cable).

Could that mean that I have a radial circuit already?

No, it means that you are virtually guaranteed to have a ring.

It's also virtually guaranteed to be wired in 2.5mm² cable.

As a radial there's a very good chance you could have a 20A breaker, and a reasonable one that you could have a 25A one. You need an electrician to check how the cable has been installed, unless you know the details of the route? e.g. is it in thermal insulation anywhere, or in a bunch with other cables?

Thanks for the input! Unfortunately my knowledge on the matter stops here. I have the impression that the guy who came in to check my wiring, wanted to take home extra work for him.

Can you please tell me what I should ask exactly? So that if the next one tries to sell work not needed, I can reply asking: "Can you please check the wiring and tell me if this other option (yours) is feasible?".

 

[DaftPunk]

You have a ring circuit. You can not connect your proposed load to this circuit. Your electrician is not looking for extra work, he's looking to leave you with a safe, compliant and legal installation.

Despite what rouge traders and all these find a tradesman websites tell you, most electricians are just trying to do their job properly and not rip you off even if it means doing more work than you thought would be required.

 

[mfarrow]

What regulation specifies limiting the accessories on a 32A ring main wired with 2.5mm cable?

All it says is rings may be wired.... In much the same way as it says circuits may have a reduced csa without fusing if the load is demonstrated to be OK. If the council dropped a flyer through your door stating your house may be painted pink, would you go ahead and paint it?

We're only talking 2A extra on a cyclic load. A few good calculations should be able to demonstrate that will be acceptable.

 

[JohnW2]

What regulation specifies limiting the accessories on a 32A ring main wired with 2.5mm cable? All it says is rings may be wired.... In much the same way as it says circuits may have a reduced csa without fusing if the load is demonstrated to be OK. If the council dropped a flyer through your door stating your house may be painted pink, would you go ahead and paint it?

As so often, it's poorly (hence, I would say, unsatisfactorily) written. However, I think that most people take it as trying to say (not at all clearly or precisely) that the dispensation to allow a circuit wired in cable with 20A CC to be protected by a 30/32A OPD only applies if that circuit is a ring supplying (only) BS1363 accessories. That would also make sense, because it would have been a gesture on their part to reduce the likelihood of the very thing being discussed here - i.e. any single load >13A being run from the ring.

We're only talking 2A extra on a cyclic load. A few good calculations should be able to demonstrate that will be acceptable.

I agree that the after-diversity load is very marginal in the case being discussed in this thread, so (particularly given that the 'diversity calculation' is rather arbitrary) there is scope for common sense and pragmatism. However, if one takes that view, I think one probably should feed the cooker via a 13A-fused BS1363 plug or a 13A FCU, rather than feeding it directly from the ring (unfused) or trying to think up a compliant way (which I personally don't think exists) to include a 16A OPD.

More generally, I suspect that most of us don't feel that it is a very good idea to power a cooker this size from a ring final, whatever diversity and regs may say.

Kind Regards, John

 

[ban-all-sheds]

What regulation specifies limiting the accessories on a 32A ring main wired with 2.5mm cable?

433.1.103.

All it says is rings may be wired.... In much the same way as it says circuits may have a reduced csa without fusing if the load is demonstrated to be OK. If the council dropped a flyer through your door stating your house may be painted pink, would you go ahead and paint it?

You're misunderstanding what 433.1.103 is.

It's not saying that certain things may be wired in a ring, with the implication that other things could also be. It's an exemption from the rules on parallel conductors and the relationship between cable capacity and OPD rating etc that apply to everything.

Basically it's a case that the regulations say "These are the requirements for the relationship between cable capacity and OPD rating etc, and they apply to every situation unless specifically exempted. One exemption is that BS1363 accessories may be supplied by....".

The house colour analogy would be "Houses shall be painted in a colour chosen from {list} unless you have had a letter from the council telling you that you may paint it pink."

 

[mfarrow]

It's not saying that certain things may be wired in a ring, with the implication that other things could also be. It's an exemption from the rules on parallel conductors and the relationship between cable capacity and OPD rating etc that apply to everything. 

As far as I'm aware it's not an exemption to anything. It's a guidance note for electricians.

What regulations is it an exemption from? Do you means it's an exemption to the rules requiring proper calculations and allowing sockets to be thrown anywhere an electrician likes without doing any assessment of load?

 

[ban-all-sheds]

As far as I'm aware it's not an exemption to anything. It's a guidance note for electricians.

What regulations is it an exemption from?

The rest of 433.1, for a start.

Let's see you show how a socket circuit wired in 2.5mm² on a 32A breaker complies with 433.1.1.

 

[JohnW2]

As far as I'm aware it's not an exemption to anything. It's a guidance note for electricians.

I'm not sure what that means. It's one of the regulations in BS7671. Admittedly it's not mandatory but, for most people (including most electricians) complying with BS7671 is the only practical way of demonstrating compliance with Part P.

What regulations is it an exemption from? Do you means it's an exemption to the rules requiring proper calculations and allowing sockets to be thrown anywhere an electrician likes without doing any assessment of load?

I presume he means exemption from the regulation (I'm temporarily separated from BGB, so can't quote number!) which requires a cable with a CCC of 20A to be protected by an OPD with an In no greater than 20A - since that is what 433.1.103 is all about.

Kind Regards, John

 

[Adam_151]

Playing devils advocate here...

Assuming roughly mid point on the ring, if you spurred a 2.5 twin and earth off a point or a joint box and took it to an enclosure containing a 16A B type breaker and onto your 3.6kw load.

Now before you run off and all point at 433.1.5 it refers to accessories... could you call a MCB in an enclosure an accessory?

If I was to fit two single socket outlets on the ring supplying 1.8kw loads each which were run together. Would that be a problem?

What about a 15A switch-fuse off a busbar chamber in 2.5mm singles for a fire alarm?

We could prove that its sound engineering practice, but perhaps falls fowl of the exact wording in BS7671. Or do you disagree, what would your comment be upon finding such an arrangement on a EICR


Now... I've recently been looking at some luxury appartments where the electrical contractor has taken the ring into the supply terminals of a 20A double pole switch and taken a cable off the load side to supply a socket for a freezer / washer/ etc. What do you think the answer of the manufacturer was when I asked them if the supply terminals were rated to be part of a 32A ring final circuit? .