Introducing myself and some questions

[G Westmorland]

Hello,

I am not an electrician but a fairly experienced DIYer. I know a bit of theory, from my interest in Physics.

I am replacing an old ceramic hob with a new Induction hob. It is on its own 32a supply with an mcb.

Manufacturer's rather generic, to-cover-themsleves safety notice says among other things "shock protection must be included".

The house has no RCD protection (it was built in 2002). IMHO an RCD is desirable but not essential. Would folk agree?

The house has a 3-phase supply with 3 10oA Tenby Consumer Units. AFAIK RCD replacement 100A main breakers aren't available to fit, so if I wanted RCD protection for the whole house, I assume it would mean three new consumer units - expensive! Or would it?

I guess I could fit or have fitted, and MCCB just for the hob supply. Is that:
a. Really necessary?
b. A diy job?

One other question.

The breaker for the off-peak supply on one of my Dimplex Quantum storage heaters (which I find v good by the way), tripped the other night. There was no fault and having checked and reset it, the heater is now working OK .
But here's the question - in my testing I noticed that during the day with an unpowered off-peak circuit, there was a circuit between the neutral and earth - in the cabling, not in the heater - although I suppose it could be via another heater. That surprised me. It is all working OK, but is that normal and OK?

 

[Darkwood]

Hi welcome to the forum, if the manufacturers instructions recommend RCD protection then it in in the BS 7671 regulations that you should follow these recommendations.

In short, Yes! you need to incorporate RCD protection into the circuit, I would also add that swapping the hob might fall into the DIYer tag for the forum but we would often weigh that up on a case to case basis and the background of the member, upgrading the circuit is what we consider beyond DIY given the testing required to ensure the changes are safe and functioning in the case of an RCD within prescribed leakage and times given by the BS7671, which requires expensive test equipment you would not have or be able to interpret the readings either.

I believe you are confused with devices too, MCCB is not what I think you mean, I assume you mean an RCBO which is a combined overload/shortcircuit protection with earth leakage monitoring/protection.

Relating to the storage heater query, it could be a number of things, can you enlighten us on the tests you did and the results you got, to note a N/E could be normal depending on whether you isolated the incoming supply by isolating the circuit and/or board, you are getting confused because you have limited knowledge here which can be both confusing and dangerous in some situations so heed caution when carrying out any tests without a full understanding of the circuits and incoming supply system.

 

[G Westmorland]

Thanks very much for the reply.

I will certainly heed caution - I recognise the limits of my knowledge, and do take care. Keen to learn too.

I tested the resistance between the neutral and the earth, in the double-pole switch, with the switch in the off position. (I did this after I found the neutral to earth circuit on the heater board, to see whether the situation related to the heater or the wiring. It was the wiring and not the heater). When I found that the resistance was zero, I did the same test on the switch for a different heater, with the same results. I can't remember whether I tested it with the MCBs off or on though.

The Off peak supply to each heater is a star config with an mcb for each heater, as I guess is normal, with a huge relay that switches all the heater circuits on when a signal is received from the non-smart meter.

I would be more impressed with the Safety blurb from AEG if it didn't say, for a 7.4kw hob, that one mustn't pull out the plug by pulling on the cord. So this is clearly not device specific. Maybe I need to contact their tech folk and confirm that this is required. I get the impression that you are not saying that RC shock protection is always required for hobs - only if the manufacturer says so?

Any thoughts on the feasibility of possible cost of replacing the 100A MCCBs with RCBO type equivalents, on my old consumer units, would be appreciated.

On the subject of the RCBO, apologies for my terminology. I recently had one fitted by Chargemaster for a car charger. I purchased the RCBO, which was an option they offered, as it was cheaper than buying it from them. But my memory is that they called it an MCCB. Maybe my memory is playing tricks. Anyhow I managed to buy the right thing and it is definitely an Earth Leakage, or RCD device, with a test button.

 

[GeorgeCooke]

if the manufacturers instructions recommend RCD protection then it in in the BS 7671 regulations that you should follow these recommendations.

Manufacturers recommendations are guidance only, and don't have to be followed especially if they are wrong. Not saying they are in this case but there are plenty of examples where they are.

 

[Darkwood]

Manufacturers recommendations are guidance only, and don't have to be followed especially if they are wrong. Not saying they are in this case but there are plenty of examples where they are.

We have gone over this before, it is recommended in the BS7671 that manufacturers recommendations are followed, if you can however prove they are in error then clearly you have good ground not to (no one is discussing about them been in error here), that been said, if someone was to be injured or killed and it was found you hadn't followed the recommendations that could/would have prevented it then you legally are screwed, I will also remind you that the BS7671 are not statutory and are only guidance but in ignoring them you put yourself in a very weak legal stance.

May I ask, do you follow manufacturers guidance and the BS7671 (when it is not in clear error)?.. as if I recall you repeatedly raise this point so I am interested if you follow the BS7671.

 

[GeorgeCooke]

I use my common sense.

 

[Darkwood]

I use my common sense.

Without context that reply means nothing and is ambiguous at best and does not answer what I asked, so I will simplify it, would you ignore the manufacturers recommendations to fit an RCD if the premises had no RCD protection or would your common sense conclude you should fit one, if you would fit one then why did you even write post 4, no one is discussing or has even brought up about when guidelines are clearly incorrect so I fail to see where your input in the thread is going, you seem to have a hang up about anyone telling members that there should follow manufacturers guidance, this is written into the BS7671 so this is why I question your position here.
No one has to follow any regulations but they ignore them at there own risk and possibly risk to others and/or property, it is ignoring what essentially are only non statutory guidance be it in the BS7671 or in manufacturers recommendations that one could end up with no defence if ever an incident went to trial, showing you followed the best practices and guidance can in many cases clear you of ignorance/incompetence which will in no doubt support your legal position to defend your work and practices, without this position you will be screwed.

 

[GeorgeCooke]

The requirements are that you should take account of manufacturers instructions not follow them.

In post 4 I was merely correct your incorrect statement that you have to follow them.

 

[ipf]

I use my common sense.

Problem with that is that common sense and ignorance go together too well...…..in too many people's eyes.

 

[Darkwood]

@GeorgeCooke
It essentially means the same thing, one must weigh up what is been asked of the installer by the manufacturer and then one needs to see if say this is already covered for by other means.
I would be interested of an example to ignore manufacturers recommendations (other than them been in error) where you would not follow them when they were not covered in any other way in the existing installation.
I see why the regulations says take into account and not 'follow' because there are many cases where the instructions are generalised and do not account for alternatives approaches that satisfy what the manufacturer has initially added the recommendation for but for the most cases these instructions should be followed by the installer or have by design of the installation been already met.

 

[westward10]

If the instructions bizarrely say shock protection must be included this does not necessarily point to rcd protection unless they state this. For a TN earthing system shock protection, fault protection in new money can be provided by a fuse or mcb provided all measures are in place with regards to earthing, disconnection times etc..

 

[G Westmorland]

Thanks for the discussion re:BS7671

What is the realistic chance of receiving a shock from a hob that is fully covered by a glass surface, and whose controls are capacitive touch? (Unless it is severely damaged in which case it obviously should not be used).

Also, in the unlikely event of a court case, I wonder what weight would a court place on manufacturer's guidance, that for a permanently connected 7.4kw device includes the following:
"Do not use multi-plug adapters and extension cables."
"Do not pull the mains cable to disconnect the appliance. Always pull the mains plug."

and for an induction hob which does not use heating elements:
"Care should be taken to avoid touching heating elements".

It seems clear that these manufacturer's safety guidelines are very generic, and that it is necessary to use judgement to decide which of them apply. In which case, doesn't this requirement for judgement to be exercised also apply to the stated requirement for shock protection to be fitted for a device that physically isolates the user from all mains-conductive surfaces?

EDIT:
Also, as the manufacturer's safety instructions say:
" All electrical connections should be made by a qualified electrician":
- does this have to be followed according BS 7671?
In this case would doing it myself (safely and properly) also put me in a weak legal position if anything went wrong (that wasn't my fault)?​

 

[westward10]

Are you doing this in your own house?

 

[G Westmorland]

"If the instructions bizarrely say shock protection must be included this does not necessarily point to rcd protection unless they state this. For a TN earthing system shock protection, fault protection in new money can be provided by a fuse or mcb provided all measures are in place with regards to earthing, disconnection times etc.. "

Thanks! Not sure what a "TN earthing system" is -sorry. Is my situation likely to have this?

 

[G Westmorland]

Are you doing this in your own house?

Yes.
(By the way, I just checked the wording - it says "Make sure that a shock protection is installed.")

 

[G Westmorland]

Are you doing this in your own house?

Yes, in my own house.

 

[westward10]

Three earthing systems generally apply in this country, TN-S, TN-C-S and TT. The latter, TT employs an earth rod/electrode and in almost all cases will employ rcds for fault protection. The first two are variations of a TN system and generally do not require rcds for fault protection if correct measures are in place.

 

[GeorgeCooke]

This is a clear example where manufacturers instructions are wrong. A 16 amp oven currently available in B & Q. Should never be on a FCU and 16a fuse for FCU!

 

[richy3333]

The house has no RCD protection (it was built in 2002). IMHO an RCD is desirable but not essential. Would folk agree?

Well they potentially save lives in the event of a fault and as of January 2019 you'll hardly be able to fart in a domestic property without RCD protection! At the end of the day way up if RCD protection is required against the value of yourself or a loved ones life and then decide.

Ring the manufacturers and ask but I bet they are vague or refuse to comment just in case something ever happens. I guess they refer to installation by a qualified electrician as a get out clause for them in respect of DIYers doing the work?

 

[Darkwood]

View attachment 46408 This is a clear example where manufacturers instructions are wrong. A 16 amp oven currently available in B & Q. Should never be on a FCU and 16a fuse for FCU!

This goes to show you have not reading what I posted, I have on more than one occasion expressed we are excluding where the manufacturers instructions are clearly wrong so I am somewhat bemused as to why you have posted an example of one that clearly is.

 

[telectrix]

This goes to show you have not reading what I posted, I have on more than one occasion expressed we are excluding where the manufacturers instructions are clearly wrong so I am somewhat bemused as to why you have posted an example of one that clearly is.

he posted that to make your hair turn white. looking at your avatar i see it worked.

 

[ipf]

he posted that to make your hair turn white. looking at your avatar i see it worked.

Yep..…...and still waiting for King Kong and Mighty Joe Young showing their ugly mugs...

 

[Deleted member 26818]

I believe the Red book, or perhaps the Green, brought in a requirement to comply with Manufacturer’s instructions.
That requirement has (as far as I am aware) been dropped.
All we have to do now, is take account of the instructions.

As for the OP.
Installing up front RCDs or RCBOs to protect multiple circuits, is not a good idea.
Individual circuit protection is much better.

 

[G Westmorland]

I believe the Red book, or perhaps the Green, brought in a requirement to comply with Manufacturer’s instructions.
That requirement has (as far as I am aware) been dropped.
All we have to do now, is take account of the instructions.

As for the OP.
Installing up front RCDs or RCBOs to protect multiple circuits, is not a good idea.
Individual circuit protection is much better.

Thanks - that's helpful info.

Thanks to all for the replies.

My take on the situation is now:

1. The manufacturer's instructions do not say that an RCD is required, they say "Make sure that a shock protection is installed."
2. Westward10 advises that TN-S and TN-C-S installations generally do not require RCDs for fault protection if correct measures are in place, unless the earth is TT in which he says "in almost all cases will employ rcds for fault protection".
3. My system would appear to be TN-S or TN-C-S, as:
a. There is no RCD protection installed
b. The earth cables for the three phases are connected to a common earth in the meter cupboard goes down to join the supplier's cable where it enters the meter cupboard at its base. (I can't see what the common earth cable connects to though, that is out of sight).
4. After installation, there will be no physical access to any live parts, only to the glass topped hob, with capacitative touch controls. So in the unlikely event that shock protection is not provided by the current installation via the mcbs and earthing arrangements, shock protection is still provided by the glass surface which is not conductive of mains voltages. Or to put it another way, there is no actual risk of shock in using the appliance, unless the glass surface is smashed by a person falling onto it, which seems a very unlikely eventuality indeed.

So my plan is that I WILL have an RCBO fitted to this circuit, but only as and when I require a visit from an electrician for an additional purpose.

(P.S. Manufacturer specced cable is H05BB-F and hob rating is 7.4kw, so I plan to use 6mm cable, which is required for flex cable to carry 32 A. Am not relying on diversity because cooker has 4 heating areas each of which can in boost mode draw 3.2 kw for up to 10 minutes - which is power managed by the hob down to 7.4 Kw max. So an actual draw of the full 7.4 kw seems entirely possible).

 

[G Westmorland]

Thanks - that's helpful info.

Thanks to all for the replies.

My take on the situation is now:

1. The manufacturer's instructions do not say that an RCD is required, they say "Make sure that a shock protection is installed."
2. Westward10 advises that TN-S and TN-C-S installations generally do not require RCDs for fault protection if correct measures are in place, unless the earth is TT in which he says "in almost all cases will employ rcds for fault protection".
3. My system would appear to be TN-S or TN-C-S, as:
a. There is no RCD protection installed
b. The earth cables for the three phases are connected to a common earth in the meter cupboard goes down to join the supplier's cable where it enters the meter cupboard at its base. (I can't see what the common earth cable connects to though, that is out of sight).
4. After installation, there will be no physical access to any live parts, only to the glass topped hob, with capacitative touch controls. So in the unlikely event that shock protection is not provided by the current installation via the mcbs and earthing arrangements, shock protection is still provided by the glass surface which is not conductive of mains voltages. Or to put it another way, there is no actual risk of shock in using the appliance, unless the glass surface is smashed by a person falling onto it, which seems a very unlikely eventuality indeed.

So my plan is that I WILL have an RCBO fitted to this circuit, but only as and when I require a visit from an electrician for an additional purpose.

(P.S. Manufacturer specced cable is H05BB-F and hob rating is 7.4kw, so I plan to use 6mm cable, which is required for flex cable to carry 32 A. Am not relying on diversity because cooker has 4 heating areas each of which can in boost mode draw 3.2 kw for up to 10 minutes - which is power managed by the hob down to 7.4 Kw max. So an actual draw of the full 7.4 kw seems entirely possible).

EDIT - Going for 4.0mm² 3183TQ which seems to tick all the necessary boxes. (Have read that HO5bb-F is difficut or impossible to get above 2.5mm).

 

[Edtwozeronine]

We were told that manufacturers instructions need to be followed in college, they have to follow the same guidance in as the installers do and if they don't they could be in legal trouble for supplying potentially dangerous equipment. I very much doubt any manufacturers producing goods to UK standards want to be in that position.

 

[G Westmorland]

The Butyl 3183 TQ is heat ressistant to 90C rather than 60C, is flexible, and resistant to fats and oils. So it meets and exceeds the spec for H05bb-f.
Plus, , see Spinlondon's post above which says:
"I believe the Red book, or perhaps the Green, brought in a requirement to comply with Manufacturer’s instructions.
That requirement has (as far as I am aware) been dropped.
All we have to do now, is take account of the instructions."

 

[FatAlan]

After all this discussion about what the manufacturers instruct or not. You say at the start that it’s a replacement for a ceramic hob on a 32A MCB. Do you know the current size of the cable feeding the the cooker connection point, length of cable run to MCB and fixing method? Presumably the cable size you were discussing was just for the hob to the connection point?

 

[G Westmorland]

After all this discussion about what the manufacturers instruct or not. You say at the start that it’s a replacement for a ceramic hob on a 32A MCB. Do you know the current size of the cable feeding the the cooker connection point, length of cable run to MCB and fixing method? Presumably the cable size you were discussing was just for the hob to the connection point?

Am assuming that cable capacity must be at least 32a as it is on its own 32a mcb. If less than that, mcb will not provide proper protection and hob spur would be improperly installed. Think it's safe to assume that it was properly installed.

As cables are all hidden in property syructure, there is no other way to assess it.

Yes, cable size is for hob to connection point. Very short run as connection point is just below hob.

Had to go for H07 cable 6mm in the end as only suitable cable I can get in reasonable time.

 

[FatAlan]

If you ‘assume’ it does tend to make an ‘---’ out of ‘u’ and ‘me’
You are more than likely right with a pre existing cooker having been connected but you never know until it’s normally too late.

 

[G Westmorland]

Am assuming that cable capacity must be at least 32a as it is on its own 32a mcb. If less than that, mcb will not provide proper protection and hob spur would be improperly installed. Think it's safe to assume that it was properly installed.

As cables are all hidden in property structure, there is no other way to assess it.

Yes, cable size is for hob to connection point. Very short run as connection point is just below hob.

Had to go for H07 cable 6mm in the end as only suitable cable I can get in reasonable time.

OK. Got the H07RN-F. Can't find a spec online from the maker (Prysmian), but Eland publish a spec for theirs, which says:

"The H07RN-F trailing duty cable has a temperature rating of -30C to +60C for fixed installations (rising to +85C for fixed protected installations) and from -15C to +60C when flexed."

Please forgive my ignorance, but, as the manufacturer specified "H05bb-F or H03V2V2-F which withstands a temperature of 70C or higher"

- am I ok with the H07? (As i can't source the specified cable, esp in a sufficient size).

This is for a very short run of less than half a metre, inside a kitchen cabinet, to the switched outlet. Does that qualify as a "Fixed protected installation"?

Also, what does "when flexed" mean? Does it mean if there is significant movement going on, or does it mean of the cable has to be bent? There will need to be bends in the cable, obviously.

The hob does require ventilation gaps underneath it, and the install guide warns about possible damage due to overheating if insufficient ventilation is provided. So I deduce that:

a. There will be some heat coming from the hob, although I don't know how hot, in the region of the supply cable,
b. That heat will be in the form of blown air, which presumably has some degree of cooling effect, even though the air will be hot, due to air movement.

Or should I just order and wait for 3183TQ 6mm, to be on the safe side?