Two circuits off cooker switch?

[EFLImpudence]

Do you know some way of specifying a minimum required supply other than by specifying a minimum fuse/MCB rating?

Yes. The maximum load of this appliance is 10kW.

As I said before, there may also (but not necessarily) be a requirement for a maximum OPD for safety (in which case I see no alternative but to quote minimum and maximum OPD ratings

A maximum will be to protect a supplied flex.

It's all very well citing the instruction that installation should be undertaken by a competent person/qualified electrician - but, at least until some same next year, (s)he is, strictly speaking, constrained by whatever the manufacturer may 'instruct'.

Not if they are foolish enough to state a minimum opd size.
That should be ignored now.

 

[JohnW2]

I agree having a minimum is rather pointless, it's down to the person designing the circuit to make sure the appliance operates without tripping.

Well, even the designer needs to know what current is required, since the only way (s)he can design a circuit which won't trip is to have a fuse/MCB rated above that minimum.

The maximum, I would assume is to keep the appliance/cable operating within safe limits.

Indeed.

Not having the oven or microwave yet means I can't check what cable they supply. ... My problem is, running 2 dedicated 16amp supply's, as well as other supply's just for a tiny kitchen (70s house only 1 ring final) just seems bonkers.

I'm still a bit confused. The microwave appears to be only 2.4 kW total, so I would have expected it to come with a 13A plug - yet you say the instructions require a minimum fuse size of 15A (do I take it that no maximum is stated?). As I said before, if (whether they should or shouldn't!) the instructions for the oven also specified a minimum fuse size (and no maximum), and if no maximum is stated for the microwave, then there's no reason (subject to consideration of the flex) why you couldn't run both supplies directly off the 32A supply.

Kind Regards, John

 

[JohnW2]

Do you know some way of specifying a minimum required supply other than by specifying a minimum fuse/MCB rating?

Yes. The maximum load of this appliance is 10kW.

Fair enough, but that really boils down to the same thing. Since there is a design requirement that In≥Ib, specifying a maximum load is exactly the same thing as specifying a minimum In for the OPD, isn't it?

A maximum will be to protect a supplied flex.

Indeed, and maybe the innards of the appliance, if the manufacturer has not provided adequate internal protection.

Not if they are foolish enough to state a minimum opd size. That should be ignored now.

In common sense terms, I agree. In regulatory terms, many seem to feel that they are currently constrained to comply with MIs, even if daft! Were that not the case, there would, for example, probably be a lot fewer FCUs and 3-pole isolators involved in fan circuits! Hopefully a lot more common sense will come into the equation next year.

Kind Regards, John

 

[EFLImpudence]

Do you know some way of specifying a minimum required supply other than by specifying a minimum fuse/MCB rating?

Yes. The maximum load of this appliance is 10kW.

Fair enough, but that really boils down to the same thing.

Not really, it is up to us to design a circuit taking into account all the relevant conditions.

Since there is a design requirement that In≥Ib, specifying a maximum load is exactly the same thing as specifying a minimum In for the OPD, isn't it?

No.
There may be other loads on the circuit (as in this thread).
There may be diversity to apply.
They should say it requires a nnA supply. This does not mean it requires a nnA OPD.

The ONLY thing a manufacturer should specify is a maximum In of OPD should their appliance require protection for reasons which may not be apparent.
If they are going to advise on other things for information then they will have to explain cable installation methods, diversity (for cookers) and all the relevant regulations.

Specifying a minimum In for the OPD is irresponsible - well, it probably is just an irresponsible mistake.
"Oh, it requires a minimum 16A MCB, therefore as I only have a 50A that must be ok."

 

[JohnW2]

Since there is a design requirement that In≥Ib, specifying a maximum load is exactly the same thing as specifying a minimum In for the OPD, isn't it?

No. There may be other loads on the circuit (as in this thread). There may be diversity to apply. They should say it requires a nnA supply. This does not mean it requires a nnA OPD.

Agreed - but it does mean that it (itself, not counting any other loads on the circuit) requires a minimum OPD In of nnA (which is what we were discussing), doesn't it? (if diversity is applicable, it shouldn't really say that it requires a larger supply than the after-diversity demand, should it?)

Kind Regards, John

 

[ban-all-sheds]

Specifying a minimum In for the OPD is irresponsible - well, it probably is just an irresponsible mistake.

Why is it either?

"Oh, it requires a minimum 16A MCB, therefore as I only have a 50A that must be ok."

Would it not be?

 

[JohnW2]

"Oh, it requires a minimum 16A MCB, therefore as I only have a 50A that must be ok."

If the manufacturer did not feel the need to specify a maximum In, and if the cable of the 50A circuit were suitable for 50A, then what would be the problem?

Kind Regards, John

 

[EFLImpudence]

Agreed - but it does mean that it (itself, not counting any other loads on the circuit) requires a minimum OPD In of nnA (which is what we were discussing), doesn't it?

No, I am not going to agree.

A minimum OPD is NOT the relevant criterion to state.

(if diversity is applicable, it shouldn't really say that it requires a larger supply than the after-diversity demand, should it?)

Maybe not, but they will/do.

Conversely then, they would be stating a larger than necessary minimum OPD.

 

[ban-all-sheds]

No, I am not going to agree.

A minimum OPD is NOT the relevant criterion to state.

Why not?

 

[EFLImpudence]

"Oh, it requires a minimum 16A MCB, therefore as I only have a 50A that must be ok."

If the manufacturer did not feel the need to specify a maximum In, and if the cable of the 50A circuit were suitable for 50A, then what would be the problem?

IF?

Aren't we discussing the implications for DIYers?

What if the cable isn't suitable for fault current?

 

[EFLImpudence]

Why not?

You may disagree but haven't I explained what I think?

 

[ban-all-sheds]

Aren't we discussing the implications for DIYers?

No, we are discussing whether a manufacturer should state a minimum OPD rating.

What if the cable isn't suitable for fault current?

Well, durr.... you don't put it on a 50A device, do you.

 

[ban-all-sheds]

Why not?

You may disagree but haven't I explained what I think?

No

 

[sparkwright]

If say the cable is rated at over 50 amps, and the fuse is 50 amps, and the appliance is rated at say 15 amps, should we be concerned how small the appliance internal wiring is?

 

[JohnW2]

IF? Aren't we discussing the implications for DIYers?

I didn't think so - at least, not specifically or exclusively. As you've pointed out, anyone complying with the MIs who is connecting the appliance must either be a qualified electrician or consider themself to be a "competent person".

What if the cable isn't suitable for fault current?

Which cable - trhat in the fixed wiring of the circuit or the flex of the appliance (if it has one)?

Kind Regards, John