Oven Replacement - RCD?

[lozarus]

Afternoon all. Apologies if this is a stupid question. I'm currently half part way through completing 2391 (second exam tonight) - so may be getting myself in a tiz overthinking things.

Either way, thought I'd put it out to the group.

Task is: Straight swap of existing x5 ovens with new - "like for like", if you will. Albeit cooker plate to appliance is also in T&E and I intend to replace this with a more suitable product - namely HO7.

Earthing arrangement is: TN-S.

Environment is: Educational establishment, cookery rooms.

Circuits for the room originate in a local 3P+E MEM2 board, no RCD's. Ovens are simply domestic 1P+E bog standard, cheap household jobs, wired from C32's at the DB to 45a Isolators (no socket) at each station, cooker outlet below. Room is only about 10m long.

EICR from 2020 is available, but quite a few tests missed out - IE: Zs for each oven measured well within limit. No IR or R1+R2 undertaken - I'll be doing this anyway. It's all PVC T&E - mainly in metal trunking. I think it's loose behind the cabinets for the last few metres however.

My big question here is RCD. I could take the "like for like" approach and just straight swap the ovens out as "maintenance". But the environment (education) makes me think I really should be pushing for RCD's.

Further to this, manufacturers instructions state "Additional protection by RCD is recommended".

With that in mind, I'm convincing myself these really should be going onto RCD shouldn't they?

Or convince me I'm wrong. Sorry if I've overcomplicated a simple job here.

Thanks.

 

[timhoward]

So your saying all new installations, DB changes you have to install AFDDs. EICRs, what code 2/3. Your wrong. Not mandatory.

No I'm not saying that.
Read 421.1.7
Note the word "shall".
Your original generalisation was not true.
What you guessed I was saying is also not true.

 

[DPG]

What a ridiculous situation. Obviously this is going to cause confusion.

I'd like to meet whoever approved that line about recommended=should and use him to test my AFDDs

 

[nicebutdim]

One point that's worth making is this 'clarification' of 'recommended' comes from a trade association and not the IET.

 

[default]

I don't have the BBB yet, but if this is what the regs actually say...

"Regulation 421.1.7 now states:

Arc fault detection devices (AFDD) conforming to
BS EN 62606 shall be provided for single-phase
AC final circuits supplying socket-outlets with a rated
current not exceeding 32 A in:

• Higher Risk Residential Buildings (HRRB)
• Houses in Multiple Occupation (HMO) i
• Purpose-built student accommodation ii
• Care homes iii

NOTE 1: Higher Risk Residential Buildings are assumed to
be residential buildings over 18 m in height or in excess of
six storeys, whichever is met first. It is anticipated that in
many areas higher risk residential buildings will be defined in
legislation which can be subject to change over time, as well
as in risk management procedures adopted by fire and rescue
services. Current legislation should be applied.

For all other premises, the use of AFDDs conforming
to BS EN 62606 is recommended for single-phase
AC final circuits supplying socket-outlets not
exceeding 32 A.

Where used, AFDDs shall be placed at the origin
of the circuit to be protected.
The use of AFDDs does not obviate the need to apply
one or more measures provided in other clauses in
BS 7671.

NOTE 2: For busbar systems conforming to BS EN 61439-6
and Powertrack systems to BS EN 61534, the AFDD may be
placed at a location other than the origin of the circuit."

Thats taken from this:-

https://www.beama.org.uk/static/60aec0d0-e6c8-4ca9-b486fb8a843d0c55/AFDD-fact-sheet-3-BS-7671-AMD2.pdf

Which also clarifies the "recommended = should".

I'd say there's no room for a choice in there.

Wow. Sorry dude. Need to look more into that. Need to see if we're just looking at new builds. And 18m is pretty high. I do mainly EICRS so need to see where this sits. Again, apologie

 

[timhoward]

Which also clarifies the "recommended = should".

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)

 

[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.