Oven Replacement - RCD?

[nicebutdim]

If one studies the definitions on page 18 of Guidance, Normative Element, Requirement, and Recommendation I cannot see how anyone would conclude:

I suspect if one's interests were heavily invested in the sale of associated goods, then it would be very easy to reach such a conclusion.

Is a trade association wilfully misrepresenting BS7671? I couldn't possibly speculate.

 

[DPG]

I would take that clarification with a ton of salt.

Page 18 of the new regs book has a little table. The 2nd column should be the first column, as the intent is to translate the verbal form in BS7671 to an implication.
It says "Shall" is a requirement and normative, and "Should" is a recommendation (and is not normative)

If one studies the definitions on page 18 of Guidance, Normative Element, Requirement, and Recommendation I cannot see how anyone would conclude:

There is a misleading view being communicated within the industry that use of such terms as ‘recommended’, ‘additional’ and ‘specified’ demotes the requirements within the associated regulations.

In particular, Recommendation is ONE possibility and does not exclude other possibilities (including doing nothing)

Excellent! I knew I'd seen that somewhere
It has to be the case, otherwise the requirements for where AFDDs are fitted wouldn't make sense in the way they are split.

 

[Pretty Mouth]

I would take that clarification with a ton of salt.

Page 18 of the new regs book has a little table. The 2nd column should be the first column, as the intent is to translate the verbal form in BS7671 to an implication.
It says "Shall" is a requirement and normative, and "Should" is a recommendation (and is not normative)

If one studies the definitions on page 18 of Guidance, Normative Element, Requirement, and Recommendation I cannot see how anyone would conclude:

There is a misleading view being communicated within the industry that use of such terms as ‘recommended’, ‘additional’ and ‘specified’ demotes the requirements within the associated regulations.

In particular, Recommendation is ONE possibility and does not exclude other possibilities (including doing nothing)

Nice one Tim! So it's the word 'should' that has been defined, rather than the word 'recommend'? Ok, now it's starting to make sense!

 

[timhoward]

Nice one Tim! So it's the word 'should' that has been defined, rather than the word 'recommend'? Ok, now it's starting to make sense!

The more you look into this, the more daft it gets.
Here's the table in BS7671:

Note the bit at the bottom.
Now, if we look at that joyous publication, it contains this table, the ancestor.

For a completely inexplicable reason some nitwit thought it made sense to invert the first two columns in BS7671. The only bit that adds clarity is that "Should" is always "Informative" in BS7671.

The BSI document also says:

So yes, the only way this makes any sense is if "should" is the thing being defined, which is how the drafting standard which BS7671 aspires to comply with has it.

 

[SparkyChick]

@timhoward ,

Thanks for that... makes much sense. I'm so glad I was in error.

 

[lozarus]

I'm employed directly by the organisation. Not a contractor, actual payroll. I've spent 3 nights thinking about this. Going by my salary thats over £345 worth of thinking hours. I proceeded to buy £360 of MR30 pods from Willrose in the end. I slept better for it. (Cue the argument about fitting used goods. They come tested, I retested them and all was fine and noted it on the cert. What more can you do other than replace an entire board). Ultimately as above, it's a bit of a **** situation on BSI's part. But I've gone above and beyond in making it safer than I found it if nothing else.

 

[timhoward]

I'm employed directly by the organisation. Not a contractor, actual payroll. I've spent 3 nights thinking about this. Going by my salary thats over £345 worth of thinking hours. I proceeded to buy £360 of MR30 pods from Willrose in the end. I slept better for it. (Cue the argument about fitting used goods. They come tested, I retested them and all was fine and noted it on the cert. What more can you do other than replace an entire board). Ultimately as above, it's a bit of a **** situation on BSI's part. But I've gone above and beyond in making it safer than I found it if nothing else.

You have followed the manufacturers recommendation, and no one could/shall/should (!) shoot you down for doing so!

 

[timhoward]

So thinking above oven elements….and I’m definitely over thinking here….
An rcd tripping is fairly common if an element is on its way out.
If the failure mode is leakage to earth, is it fair to assume that if there was no RCD this could degrade over time, and the fault resistance could get low enough to make the cooker a bit tingly to the touch but not super-low enough to trip an over current device.
Or does it tend to end up open circuit before that happens?
I’m just wondering how this played out before we had RCDs.

 

[mainline]

So thinking above oven elements….and I’m definitely over thinking here….
An rcd tripping is fairly common if an element is on its way out.
If the failure mode is leakage to earth, is it fair to assume that if there was no RCD this could degrade over time, and the fault resistance could get low enough to make the cooker a bit tingly to the touch but not super-low enough to trip an over current device.
Or does it tend to end up open circuit before that happens?
I’m just wondering how this played out before we had RCDs.

I can't think of one that I've seen that was tripping breaker/fuse.
I guess it depends on where the element fails and if that element touches the casing.

 

[AJB Temple]

I am a specifier, who employs electricians, and I am familiar with the regs. My actual background is lawyer. Perhaps professionals are looking at this (including AFDDs) the wrong way.

What I say to myself is "the manufacturer has recommended this, it is also strongly advised (at the least) in the regulations, therefore best practice and the most defensible position is to fit the device". If for any reason there is an accident or fire, the judge would want to know precisely why you ignored recommendations or regulatory guidance, and how you communicated and documented that, and how you mitigated the risks. If ever it got to court, you could be certain that the other side (insurance company barrister probably) would have an expert on hand to say that failure to follow recommendations is negligent. They would pay little heed to semantic discussions along the lines of "recommended means optional".

In our developments we fit AFDDs to socket circuits now as a matter of course, and in the example above where these are domestic ovens with an explicit manufactured recommendation of an RCD, I would specify that too. It is much better to do this than have to mount some defence later and try to convince a court that I know better than the manufacturer of the product.

Extra cost is peanuts in the context of a development or commercial installation. I accept that domestic remedial installers may have an uphill task getting people to accept the extra costs though.

 

[default]

I can't think of one that I've seen that was tripping breaker/fuse.
I guess it depends on where the element fails and if that element touches the casing.

So thinking above oven elements….and I’m definitely over thinking here….
An rcd tripping is fairly common if an element is on its way out.
If the failure mode is leakage to earth, is it fair to assume that if there was no RCD this could degrade over time, and the fault resistance could get low enough to make the cooker a bit tingly to the touch but not super-low enough to trip an over current device.
Or does it tend to end up open circuit before that happens?
I’m just wondering how this played out before we had RCDs.

When an element fails it is a dead short. Usually all three are down. Doesn't matter if its an emersion kettles, oven or any other element when they finally go it'd a dead short and the MCB,fuse,rcbo will trip. Most elements under 18 mega ohm will start tripping the protective device. I know some people will question that and yes your right it depends on the wattage of the element but in most domestic and commercial situations this is the fact.

 

[default]

When an element fails it is a dead short. Usually all three are down. Doesn't matter if its an emersion kettles, oven or any other element when they finally go it'd a dead short and the MCB,fuse,rcbo will trip. Most elements under 18 mega ohm will start tripping the protective device. I know some people will question that and yes your right it depends on the wattage of the element but in most domestic and commercial situations this is the fact.

And if the fault is between L&N then the RCD shouldn't be tripping first.

 

[default]

And if the fault is between L&N then the RCD shouldn't be tripping first.

Or more commonly

 

[mainline]

When an element fails it is a dead short. Usually all three are down. Doesn't matter if its an emersion kettles, oven or any other element

I have never seen a wire wound fire element go short, in fact, I don't think it's even possible as the heater element goes open in a failer and being as there is no earthed casing to contact it just sits there not working.

Most elements under 18 mega ohm will start tripping the protective device.

An 18 mega ohm element will trip ?????

That's around 0.0000127777778 amps, or 0.00293888889 watts.

and yes your right it depends on the wattage of the element but in most domestic and commercial situations this is the fact.

Nobody mentioned wattage.

When an element fails it will usually "open" the electrical circuit and no further heating will take place. When this happens, the element simply appears to have stopped working.In some rare instances the element will "short-out" against the sheath which is the outer visible part of the surface unit.

 

[default]

I have never seen a wire wound fire element go short, in fact, I don't think it's even possible as the heater element goes open in a failer and being as there is no earthed casing to contact it just sits there not working.

An 18 mega ohm element will trip ?????

That's around 0.0000127777778 amps, or 0.00293888889 watts.





Nobody mentioned wattage.

When an element fails it will usually "open" the electrical circuit and no further heating will take place. When this happens, the element simply appears to have stopped working.In some rare instances the element will "short-out" against the sheath which is the outer visible part of the surface unit.

I've been to numerous faults where the cooker circuit has tripped and will not reset. And the issue has always been the element. Same as 3kW emersion. Yes 18mw starts to nuisance trip. Don't know why this happens but it seems to.

 

[default]

I've been to numerous faults where the cooker circuit has tripped and will not reset. And the issue has always been the element. Same as 3kW emersion. Yes 18mw starts to nuisance trip. Don't know why this happens but it seems to.

If you can explain this then great.

 

[timhoward]

Let's keep this discussion civil gents!
I've certainly known elements that are measuring respectable values when cold but will trip an RCD when energised after a minute or two. It's been explained to me previously that this is due to trapped moisture in the element working its way to the ends.
I've also known elements fail open circuit. I believe I've seen short circuit but don't recall one

The reason I asked the question is that it's far more common for a customer to say "my RCD trips" if I turn the oven on than "my MCB trips". The early warning is commonly the RCD tripping.
That got me wondering if before the days of RCDs the leakage to earth could become noticeable to the touch.

 

[mainline]

If you can explain this then great.

I can explain why 3 ma of current wouldn't cause a trip, but not the other way around.

 

[mainline]

Let's keep this discussion civil gents!
I've certainly known elements that are measuring respectable values when cold but will trip an RCD when energised after a minute or two. It's been explained to me previously that this is due to trapped moisture in the element working its way to the ends.
I've also known elements fail open circuit. I believe I've seen short circuit but don't recall one

The reason I asked the question is that it's far more common for a customer to say "my RCD trips" if I turn the oven on than "my MCB trips". The early warning is commonly the RCD tripping.
That got me wondering if before the days of RCDs the leakage to earth could become noticeable to the touch.

It's also caused by the element expanding and contracting, which then causes the filler to break down.

 

[mainline]

Let's keep this discussion civil gents!
I've certainly known elements that are measuring respectable values when cold but will trip an RCD when energised after a minute or two. It's been explained to me previously that this is due to trapped moisture in the element working its way to the ends.
I've also known elements fail open circuit. I believe I've seen short circuit but don't recall one

The reason I asked the question is that it's far more common for a customer to say "my RCD trips" if I turn the oven on than "my MCB trips". The early warning is commonly the RCD tripping.
That got me wondering if before the days of RCDs the leakage to earth could become noticeable to the touch.

I guess so, especially on a TT earthing system that is going to have a high earth loop impedance, but personally have never come across such an occurrence.