Safety issue with domestic appliance

ban-all-sheds · 17 Nov 2017

JohnW2 said:
ban-all-sheds said:

If a fault makes the item hazardous if there is inadequate earthing then the problem does not lie in, nor is the responsibility of the maker of, the item.

Click to expand...

Whilst I agree with most of what you say, I can't really agree that it is not the maker's responsibility if there is a design or manufacturing fault which results in the case of the appliance becoming connected to the 'live' supply.

I was talking more about the responsibility for hazards arising from inadequate earthing.

I agree that if there is a design flaw which makes faults within the appliance likely, then the maker should do something, but as you say, we have no idea what the situation with this appliance actually is.

stillp · 17 Nov 2017

ban-all-sheds said:
OK - I guess I wasn't aware that trade associations used their members' money to investigate complaints about things made by someone who was not a member, except in the context of self promotion and/or lobbying for some kid of statutory status.

Trade associations exist to promote and protect their members' interests, for example by taking actions to remove dangerous products from the marketplace

ban-all-sheds said:
If there are no problems in the electrical installation then the supply to the device will be interrupted before the voltage on the casing becomes dangerous - that's the whole point, that's why there are requirements for devices to act within a certain time, and requirements for maximum fault loop impedance.

Those requirements though are based on the voltage/time that will not cause significant harm to 95% of adults, and might not be sufficient to protect children or persons with pre-existing heart conditions.
You seem to be suggesting that it's OK for the casing of an appliance to become live since the protective devices in the installation will protect the user?

JohnW2 · 17 Nov 2017

stillp said:
Those requirements though are based on the voltage/time that will not cause significant harm to 95% of adults, and might not be sufficient to protect children or persons with pre-existing heart conditions.

In terms of 'protection' against the effects of an electric shock (when it happens), that's right. However, I suspect that BAS was probably thinking more about ADS clearing an L-E fault hopefully before (unless they were very unlucky) they had touched something which could give them a shock.

stillp said:
You seem to be suggesting that it's OK for the casing of an appliance to become live since the protective devices in the installation will protect the user?

He did, and I raised that with him earlier. He sort-of responded in his most recent post (immediately before yours).

Kind Regards, John

ban-all-sheds · 18 Nov 2017

stillp said:
Trade associations exist to promote and protect their members' interests, for example by taking actions to remove dangerous products from the marketplace

True. But call me a cynic if you will, but I don't think they do so selflessly - they do it to protect the financial interests of the people who fund them.

Those requirements though are based on the voltage/time that will not cause significant harm to 95% of adults, and might not be sufficient to protect children or persons with pre-existing heart conditions.

They have to be based on something. Can a cost-benefit analysis be made which justifies changing the requirements to increase that percentage?

You seem to be suggesting that it's OK for the casing of an appliance to become live since the protective devices in the installation will protect the user?

No, I seem not to be.

mattylad · 18 Nov 2017

As someone who works in the commercial catering equipment manufacturing industry I'd be very keen to understand the specifics of this claimed potential problem.
Maybe the Op needs to be writing direct to the MD or technical director of the firm concerned, with technical information, pictures etc. Put down when you expect a reply by or you may have to ask social media about it.

Do they have a twitter or facebook account? repeated requests on those generally gets a response as it causes bad press to them.

ericmark · 18 Nov 2017

jj4091 said:
I am genuinely concerned about other peoples safety rather than just trying to cause a fuss & feel that as the manufacturers do not seem interested then I MUST take it further.

If you are genuinely concerned then post on here at least what you found, giving make and model of the appliance, and if possible pictures, at least then those on here will be alerted of the danger.

With the Thirza Whittal case it was the house owner who was found responsible for the death for not getting the house tested before use, it was not the heater to blame although clearly it was the fact that the heater was faulty which caused the death, it was the lack of adequate earthing in the house. The whole reason for earthing a class I appliance is that the manufacturer can't be 100% sure a fault will not make the casing live.

I seem to remember some thing like "electrical bonding automatic disconnection of supply" we would write EBADS in the appropriate box on the schedule of test results. The point is if the oven has a fault to earth and also there is not earth on the supply, it would be the person who allowed the supply to be without an earth, not the manufacturer of faulty equipment who would be held responsible.

There is however with ovens a problem, it is common for an oven to be connected directly to a cooker connection unit, in doing this any fuse protection in the plug is removed, if ever fitted, although the oven in rarely rated above 16A it is common to supply from a 32A supply, in fact in some cases a 45A supply, the question arises with a supply three times larger than required, will the supply fuse rupture or MCB trip before any internal wires in the oven fail? If due to an oven fault there is a short to earth we would hope the fuse would rupture, however if the earth wire inside the oven failed first then we have a potentially lethal situation. There clearly must be a limit to the fuse size, however reading manufacturers installation instructions you see the minimum size but often no maximum size.

So if the manufacturer fails to indicate a maximum fuse size, if due to an internal fault the earth connection is lost, and as a result the case becomes live, who will the courts find responsible? As far as I know it has not happened, but it could, so if a oven designed to run on 13A is connected to a 45A supply and an internal fault causes a short which in turn causes the earth connection to be lost, then will the court find the installer or manufacturer at fault?

Since we don't know, information as to which ovens have potential faults is still good, I had a talk with my son on this, should he run two feeds from the consumer unit in parallel to where the cooker will be, so if stand alone is used both feed a cooker connection unit, or if split level is used they can be split, or would this cause confusion with the next EICR?

So lets have all the information on this oven you can provide please, at least then people on here will know what make to avoid.

JohnW2 · 18 Nov 2017

ericmark said:
If due to an oven fault there is a short to earth we would hope the fuse would rupture, however if the earth wire inside the oven failed first then we have a potentially lethal situation. There clearly must be a limit to the fuse size, however reading manufacturers installation instructions you see the minimum size but often no maximum size.

If the internal fuse of the oven (or anything else) is at the very start of it's internal wiring, then it would presumably be extremely unlikely that such a 'potentially lethal situation' would arise, no matter how high the rating of the circuit's OPD, since operation of that internal fuse would clear the fault (e.g. remove any dangerous voltage from the casing of the oven).

I can see that, for the reason you mention, there might be a case for prohibiting any internal fusing (of the 230V circuitry) anywhere other than 'at the very start of its internal wiring' in Class I equipment, since that could create a hazard, in some senses similar to (but arguably 'worse than') that which exists if one has a fused neutral.

Kind Regards, John

EFLImpudence · 18 Nov 2017

ericmark said:
There is however with ovens a problem,

Is there?

Is this going to be a new thing you frequently incorrectly post - like the three metre rule?

it is common for an oven to be connected directly to a cooker connection unit,

It is. You would think the manufacturer would know that.

in doing this any fuse protection in the plug is removed, if ever fitted, although the oven in rarely rated above 16A

Surely, that is the consumption of the oven.
Each internal part will be connected by the smallest sized wire possible for its consumption and they cannot cause an overload.
An oven is just part of a cooker; its internal wiring is no different.

it is common to supply from a 32A supply, in fact in some cases a 45A supply, the question arises with a supply three times larger than required, will the supply fuse rupture or MCB trip before any internal wires in the oven fail?

If not, then it should have internal protection and it would be the fault of the manufacturer,

If due to an oven fault there is a short to earth we would hope the fuse would rupture, however if the earth wire inside the oven failed first then we have a potentially lethal situation.

If the part inside the oven has an earth wire, presumably this is because it is not connected to the carcass.
Why not postulate that the line conductor will fail and remove the fault.
What is the csa of 45A fuse wire and MCBs are quicker?

There clearly must be a limit to the fuse size, however reading manufacturers installation instructions you see the minimum size but often no maximum size. So if the manufacturer fails to indicate a maximum fuse size

Then obviously it does not matter and it is up to the installer to ensure that fault protection is satisfactory for the cable used.

, if due to an internal fault the earth connection is lost,

The supply cable CPC(earth wire) is connected to the carcass and offers protection should it become live.

and as a result the case becomes live, who will the courts find responsible? As far as I know it has not happened, but it could, so if a oven designed to run on 13A is connected to a 45A supply and an internal fault causes a short which in turn causes the earth connection to be lost, then will the court find the installer or manufacturer at fault?

I hope they will better understand how it works.

Since we don't know, information as to which ovens have potential faults is still good, I had a talk with my son on this, should he run two feeds from the consumer unit in parallel to where the cooker will be, so if stand alone is used both feed a cooker connection unit, or if split level is used they can be split, or would this cause confusion with the next EICR?

After ovens have been in use for a few years perhaps we will know how they work and how to connect them.

JohnW2 · 18 Nov 2017

EFLImpudence said:
If not, then it should have internal protection and it would be the fault of the manufacturer,

I sort-of addressed that in my recent post. Eric is, of course, presenting a fairly unusual argument - that existance of an internal fuse could, in certain circumstances, theoretically create a hazard.

To extend what I wrote before, I have to say that I have seen appliances ikn which the internal fuses is quite physically distant from where the supply enters the appliance. In that situation, should a fault to earth occur in that wiring (upstream of the internal fuse), then the hazard which eric has mentioned could theoretically arise.

Whether or not any internal fuse would be likely to blow before the circuit's OPD operated is a different question - but I suppose it's not impossible if, as eric was suggesting, there were a ~13A internal fuse in the oven and a B45 protecting the circuit. It's those 'not quite negligible impedance faults' that could be the issue - a fault current of, say, around 100A would presumably blow a 13A fuse pretty smartish, maybe before it caused a B45 to operate (thermally).

Kind Regards, John

ericmark · 18 Nov 2017

It was not my intension so advocate an internal fuse could cause problems, EFLImpudence makes a good point, if the manufacturer has not stipulated the use of an external fuse, which since fixed he could do, then it must be considered that the manufacturer has instead provided some internal fusing, even if that is a short length of wire which will fail harmlessly first.

What I have seen in the past is where a spade connector has over heated and as a result lost its grip then fell off causing a short to earth, however I still remember the electric ring which was a porcelain former with a heating wire wrapped around it, when it failed it could touch bottom of the pan, today we take safety more serious and I am sure cookers are no longer designed where an element breaking or a terminal falling off could cause a danger.

And clearly with RCD protection it would trip the RCD. I don't have the latest version of BS7671 I assume from what you say that it is no longer permissible to wire with either one of the listed cables or surface to a fixed appliance, my old 2008 version still allows you to wire a fixed appliance without RCD protection, it was common because mineral insulated elements had a habit of absorbing water and tripping any RCD. Seems I am just an old guy who has not kept up with modern requirements.

However still think the oven should be named and shamed.

JohnW2 · 18 Nov 2017

ericmark said:
It was not my intension so advocate an internal fuse could cause problems ...

Fair enough. In reality, it would probably take two faults for it to create a hazard, but I suppose that's not impossible if the conductor of a 'melted' bit of cable was touching all sorts of things.

ericmark said:
And clearly with RCD protection it would trip the RCD.

Provided that the internal fuse did not blow first - but I imagine that is next-to-impossible.

ericmark said:
I don't have the latest version of BS7671 I assume from what you say that it is no longer permissible to wire with either one of the listed cables or surface to a fixed appliance, my old 2008 version still allows you to wire a fixed appliance without RCD protection

I'm not sure what you are talking about here. As far as I am aware, there is still no requirement for a fixed appliance to be RCD protected (unless it's in a bathroom) - although if it involves new buried cable, that could well require RCD protection.

ericmark said:
However still think the oven should be named and shamed.

If they deserve to be 'named and shamed', yes. However, I think we first need to be satisfied that there really is something to 'name and shame' them about, and we still don't really have the information that we would require for that.

Kind Regards, John

mwatsonxx · 18 Nov 2017

ban-all-sheds said:
If it is a Class I appliance, then all the exposed-conductive-parts (such as the casing) will be earthed.

Wrong, you're guessing again.

mwatsonxx · 18 Nov 2017

What is all this nonsense about, the op has not once mentioned what he perceives as being wrong with the appliance. You're all trying to fix something but you don't know if its broke.

EFLImpudence · 18 Nov 2017

Has he even mentioned it is an oven or did that come from somewhere else?

JohnW2 · 18 Nov 2017

mwatsonxx said:
What is all this nonsense about, the op has not once mentioned what he perceives as being wrong with the appliance. You're all trying to fix something but you don't know if its broke.

Exactly ....

JohnW2 said:
However, I wonder what is making you believe that the case is 'live'?

JohnW2 said:
...If you want to be taken seriously by whoever you report this issue to, you need to be able to give them a clear and credible explanation of what you have observed. That is why I asked you how you had ascertained that the case of the oven becomes 'live' when it heats up - and, indeed, what you mean by 'live' - can you gives us a little more insight into that?

JohnW2 said:
However, you still have not told us any details of the nature of what sounds like a design fault and, in particular, how you have ascertained that the case 'becomes live' (and how 'live' it becomes). As I've said, if you do not tell those things clearly to whoever you report the matter to, they are unlikely to take your report seriously, so I would have thought that you would also be able to tell us.

JohnW2 said:
In the case of this thread, despite my trying quite hard to get it, we have not received any information about the nature of the alleged fault, nor an explanation of how the OP determined that the case becomes 'live' when the oven is hot (or an indication of 'how live').

JohnW2 said:
If they deserve to be 'named and shamed', yes. However, I think we first need to be satisfied that there really is something to 'name and shame' them about, and we still don't really have the information that we would require for that.

Kind Regards, John

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Safety issue with domestic appliance

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