Heating an airing cupboard

[JohnW2]

Maybe that was their intent, but the "maximum 20A" will be taken by most readers to mean what it appears to say - and prior to July, even many electricians would probably have felt constrained to adhere to that.

Yes, lacking knowledge.

I'm not sure that's fair. Prior to July, many an electrician with 'infinite knowledge' would (if (s)he were constrained to full compliance with BS7671 - e.g by scheme membership) have felt obliged to take "maximum OPD 20A" in MIs to mean exactly what it said. (S)he is now theoretically able to use their knowledge to over-ride the MIs, but I wonder how many are actually comfortable to do that (CYA etc)?

Kind Regards, John

 

[JohnW2]

I agree that in many cases the supplied instructions clearly are trying to cover the very basics for somebody with little knowledge. We may well examine the instructions, the piece of equipment concerned, and come to our own conclusion about the acceptability (safety wise) of disregarding something in those instructions.

Indeed, but prior to July, 'disregarding something in those instructions' (on the basis of knowledge/judgement) would have been non-compliant with BS7671.

As I think both you and EFLI are saying, the main problem is that "manufacturer's instructions" are not really defined, and do not necessarily include every bit of paper, with every type of intended readership, that may come with a piece of equipment.

Kind Regards, John

 

[EFLImpudence]

Maybe that was their intent, but the "maximum 20A" will be taken by most readers to mean what it appears to say - and prior to July, even many electricians would probably have felt constrained to adhere to that.

Yes, lacking knowledge.

I'm not sure that's fair. Prior to July, many an electrician with 'infinite knowledge' would (if (s)he were constrained to full compliance with BS7671 - e.g by scheme membership) have felt obliged to take "maximum OPD 20A" in MIs to mean exactly what it said.

Not if they agree with me and think it only refers to the cable quoted.

(S)he is now theoretically able to use their knowledge to over-ride the MIs, but I wonder how many are actually comfortable to do that (CYA etc)?

Those who realise that >99% of cooker circuits are on a 30/32A 6mm², know about 433 and realise an oven is just a cooker without a hob.



In light of this thread, should you not stop advising posters to connect their oven which is supplied with 1.5mm² flex to the (30/32A-6mm²) cooker circuit?
If you think an oven can overload itself then it will also overload the flex.

 

[JohnW2]

In light of this thread, should you not stop advising posters to connect their oven which is supplied with 1.5mm² flex to the (30/32A-6mm²) cooker circuit? If you think an oven can overload itself then it will also overload the flex.

If the manufacturers have concerns, I would assume that they relate to (not negligible impedance) fault protection, not overload protection.

Kind Regards, John

 

[JohnW2]

Not if they agree with me and think it only refers to the cable quoted.

It's very poorly written. As has been pointed out 'minimum 2.5mm² cable' is not a reason for specifying a blanket '20A maximum' OPD. Any interpretation of the intended meaning (and reasoning behind it) is a guess.

In any event, who would install a 2.5mm² cooker circuit?

Kind Regards, John

 

[PBC_1966]

In any event, who would install a 2.5mm² cooker circuit?

Somebody who is fitting the oven in a different area of the kitchen from an existing stovetop and who sees that there's almost never likely to be a need for a heavier load at that location?

Somebody who is re-using a redundant 2.5 sq. mm circuit which is convenient to the new oven location?

 

[EFLImpudence]

In light of this thread, should you not stop advising posters to connect their oven which is supplied with 1.5mm² flex to the (30/32A-6mm²) cooker circuit? If you think an oven can overload itself then it will also overload the flex.

If the manufacturers have concerns, I would assume that they relate to (not negligible impedance) fault protection, not overload protection.

I do not follow.
1.5mm² flex has the same csa cpc as 4mm² t+e.

Not if they agree with me and think it only refers to the cable quoted.

It's very poorly written.

Precisely.

As has been pointed out 'minimum 2.5mm² cable' is not a reason for specifying a blanket '20A maximum' OPD. Any interpretation of the intended meaning (and reasoning behind it) is a guess.

If you mean they could have said 25A, then true, but they would hardly say 40A having stated 2.5mm² - albeit with 'minimum'.

In any event, who would install a 2.5mm² cooker circuit?

Someone not knowledgeable following these 'instructions'.

 

[JohnW2]

In any event, who would install a 2.5mm² cooker circuit?

Somebody who is fitting the oven in a different area of the kitchen from an existing stovetop and who sees that there's almost never likely to be a need for a heavier load at that location? Somebody who is re-using a redundant 2.5 sq. mm circuit which is convenient to the new oven location?

Barrel scraping! What percentage of UK cooker circuits do you think are wired with 2.5mm² cable (for the above {rare} reasons or others?!).

Kind Regards, John

 

[JohnW2]

If the manufacturers have concerns, I would assume that they relate to (not negligible impedance) fault protection, not overload protection.

I do not follow. 1.5mm² flex has the same csa cpc as 4mm² t+e.

I'm talking about protection of whatever conductors may be within the equipment in the face of a non-negligible-impedance fault.

As has been pointed out 'minimum 2.5mm² cable' is not a reason for specifying a blanket '20A maximum' OPD. Any interpretation of the intended meaning (and reasoning behind it) is a guess.

If you mean they could have said 25A, then true, but they would hardly say 40A having stated 2.5mm² - albeit with 'minimum'.

No, I didn't mean that, I was referring to the "albeit with 'minimum' ". If the cable specification is "2.5mm² or greater", then one could not sensibly state a maximum OPD rating if it were protection of the cable that one were talking about. That may well imply that they are 'talking about' protection of something (i.e. their equipment) other than the cable.

Kind Regards, John

 

[ban-all-sheds]

But at the same time, if the manufacturer really does have some technical reason for specifying a 20A max. fuse in the supply due to the internal construction of the equipment, surely that needs to be in the instructions?

What's needed, as I have consistently advised, is for him to be asked in writing to confirm that he has made a product which is so intrinsically unsafe that it has to rely on a protective device which it is not supposed to rely on.

 

[ban-all-sheds]

Prior to July, many an electrician with 'infinite knowledge' would (if (s)he were constrained to full compliance with BS7671 - e.g by scheme membership) have felt obliged to take "maximum OPD 20A" in MIs to mean exactly what it said.

Indeed, but prior to July, 'disregarding something in those instructions' (on the basis of knowledge/judgement) would have been non-compliant with BS7671.

I wonder what, prior to July, this electrician would have done if presented with MIs which, through being badly written/badly translated/written by an idiot without a clue, if followed would result in a dangerous situation, or one which contravened BS 7671?

 

[JohnW2]

I wonder what, prior to July, this electrician would have done if presented with MIs which, through being badly written/badly translated/written by an idiot without a clue, if followed would result in a dangerous situation, or one which contravened BS 7671?

You would have to ask him/her that - it's a question which we have often discussed in the past.

The wisdom of any Standard, regulation or law demanding, without qualification, compliance with something over which they have no control (and may not yet have even be written) and which, as you imply, might prove to be wrong or dangerous (or non-compliant with other requirements of the Standard, regulation or law) is, IMO, very questionable. The recent Amendment has taken one approach to overcoming that problem. Another might have been to require that installations should be "no less safe" than would result from following the MIs.

Kind Regards, John

 

[PBC_1966]

Barrel scraping!

Well, you did ask!

Although obviously the overwhelming majority will be on 30/32A circuits, I do think that perhaps over time with new homes and remodeled kitchens in which separate oven and cooktop, often some distance apart, are becoming more common in place of the traditional all-in-one British cooker, it's likely to be become more common to see such wiring for the oven though.

What's needed, as I have consistently advised, is for him to be asked in writing to confirm that he has made a product which is so intrinsically unsafe that it has to rely on a protective device which it is not supposed to rely on.

According to you. And again, if you are going to claim regulation such-and-such in BS7671 says so, have you missed the question which has been asked several times as to whether or not BS7671 also says that equipment should be installed in accordance with the manufacturer's instructions? (Although you've already acknowleged, indirectly, that it does.)

How many other pieces of equipment rely on something fitted externally to protect in the event of a fault? I have a gas water heater in the garage, for example, the manufacturer's instructions for which state that a temperature & pressure relief valve of whatever rating maximum must be fitted to protect against the possibility of the thermostat becoming faulty or some other problem resulting in an excessive build up of pressure inside. Is that wrong? Has the manufacturer built something which is "so intrinsically unsafe" that it has to rely on that external device for protection? If I were to remove the T&P relief valve and blank it off, "because the manufacturer shouldn't rely on it" and then a faulty thermostat resulted in the water heater exploding, do you think it would it be the manufacturer's fault for relying on that external device, or my fault for ignoring his safety instructions?

I wonder what, prior to July, this electrician would have done if presented with MIs which, through being badly written/badly translated/written by an idiot without a clue, if followed would result in a dangerous situation, or one which contravened BS 7671?

Ignore them and record it as a departure from the regulation in BS7671 which says that they should be followed, with an explanation as to why?

 

[ban-all-sheds]

Then perhaps this time you'll answer the question I asked you earlier: Does or does not BS7671 state that manufacturer's instructions should be taken into account when installing equipment?

Do you mean the one I answered here?

Besides, doesn't BS7671 itself say something about following manufacturer's instructions anyway? So how can it be an attempt to "superimpose" a requirement on BS7671 which BS7671 itself says should be followed?

BS 7671 does not say that attempts to subvert the design of the installation because the manufacturer has been unable to make a product which is intrinsically safe should be allowed.

if you are going to claim regulation such-and-such in BS7671 says so, have you missed the question which has been asked several times as to whether or not BS7671 also says that equipment should be installed in accordance with the manufacturer's instructions?

1. It has not been asked "several times". You seem to have a problem when it comes to paying attention.
   
   
2. I have not missed it. You seem to have a problem when it comes to paying attention.
   
   
3. BS 7671 does not say that equipment should be installed in accordance with the manufacturer's instructions. You seem to have a problem when it comes to paying attention.

I have a gas water heater in the garage, for example, the manufacturer's instructions for which state that a temperature & pressure relief valve of whatever rating maximum must be fitted to protect against the possibility of the thermostat becoming faulty or some other problem resulting in an excessive build up of pressure inside.

Fitted where, to what?

Is that wrong? Has the manufacturer built something which is "so intrinsically unsafe" that it has to rely on that external device for protection?

Is it relying on that device for protection of itself against its own faults?

If I were to remove the T&P relief valve and blank it off, "because the manufacturer shouldn't rely on it" and then a faulty thermostat resulted in the water heater exploding, do you think it would it be the manufacturer's fault for relying on that external device, or my fault for ignoring his safety instructions?

Why do you think that the maker should not integrate the necessary temperature & pressure relief valve into his equipment?

Why do you think that gas water heaters and pressure vessel protection are analogous to MCBs?

 

[JohnW2]

Well, you did ask! ... Although obviously the overwhelming majority will be on 30/32A circuits, I do think that perhaps over time with new homes and remodeled kitchens in which separate oven and cooktop, often some distance apart, are becoming more common in place of the traditional all-in-one British cooker, it's likely to be become more common to see such wiring for the oven though.

I suppose that might happen to some extent, although the fact that one might want 'cooking appliance outlets' in different places in the room does not necessarily mean that they have to be on separate circuits.

Whatever, it hasn't happened to any noticeable extent yet, and I very much doubt that it will any time soon!

Kind Regards, John