But for a permanently attached flex on an appliance - I'd accept that on the assumption that the manufacturer knows what they've put in the appliance.
At least in the case of the fridge-freezer, no-one is arguing about cable size in relation to the appliance - I'm sure that 0.75mm² is adequate for the appliance under normal circumstances. It's the rating of the fuse which is protecting it that's the issue - and I've addressed this one in my last post to you.
Well since sizes other than 3A and 13A are "deprecated" by some people, that means a choice of 3A or 13A. They might fit a 5A, but would need to consider that if it blows then the user would replace with either 3A or 13A.
3A may well be adequate for the running current - by a good margin - but there are significant starting currents and a 3A fuse may fail after some time from the repeated by minor overloads it gets asked to pass. I think it's safe to assume that "Mr Average with no lecky training" is not likely to replace with a 3A fuse a second time if he's had a freezer full of food thaw out after the fuse has blown.
I did in fact raise a question on here a while ago when I found a freezer with 13A fuse (placarded as such on the rating plate) - although it did appear to have a cable rated for that size fuse. Startup currents was (IIRC) one of the reasons suggested for what at first sight appears an oversized fuse.
I would think it extremely unlikely in that a connection between the element and casing would merely be a touching which would quickly be burnt out.
Consider the environment. Perhaps a minute crack allows water to get in and "fail" the (I assume) MI insulation. You've then got a current path in an enclosed space - so once it starts arcing there is nowhere for the melted/vaporised metal to go, so I could well see it collecting and causing a short
Also the statement that it is water cooled, if true, would only apply at the point of the casing damage; the rest of the element still being enclosed.
I was actually referring to the fact that the entire element is submerged. Whilst I'd agree that an overloaded element would quickly fail in an air cooled heater, the degree of water cooling is likely to significantly restrict the extra temperature rise.
My only personal experience is of seeing the aftermath of a failed cooker ring - and the hole it blew in a friends milk pan (which was warming milk at the time
)
It could be interesting to engineer faults and see what happens
Yes, it must look like that, but I suspect that many of the discussants are, at least to some extent, playing Devil's Advocate. Whilst many electricians may be obliged to admit that some 'seemingly inappropriate' fuse/MCB sizes may be compliant with the ('minimum') regulations, I strongly suspect that, in their hearts (and, more to the point, 'in their homes') they are not very happy with the idea, even if they can (and do) present arguments as to why the arrangements are probably technically compliant with the ('minimum') regulations.
Yes, there is an element of that, but it is an interesting discussion of an important point. I have myself expressed my opinion that the continental standard of having sockets "fused" at 16A and thin appliance cords and extensions does not provide any protection for the cord - and been smacked down that there is no doubt, the 16A breaker
does provide adequate
fault protection for even the thinnest of cords.
There is actually a situation close to home for me. When fitting out our server room there came a discussion about protection of power cords for equipment. In the end I went with the professional advice of the PDU (Power Distribution Unit) manufacturer (Olson). It struck me as "wrong" to have a 10 rated power cord protected by a 32A MCB. The Olson assured me that the regs allowed it as long we met two conditions :
1) That the connected equipment is internally fused
2) That the leads are no longer than 3m
In practice, knowing what's inside them, I can't see a typical PSU taking significantly more than 10A without self destructing - the bridge rectifier is likely to fail before the cable IMO. We have in fact had one situation where a server blew a power supply and tripped a breaker - taking out the whole PDU-worth of load.
The actual question I asked was :
When supplying IEC320 C13 sockets from a 30A supply, what overload protection do you provide to individual circuits since the supply breaker will not be able to protect individual circuits ?
And the answer was :
1. Asking what protects the 10A rated sockets is a very topical question and one I guess I should post the answer to on our web site.
We sell many PDU with IEC320 C13 sockets and 32A BS4343 (IEC309) plugs, some without fuse/circuit breaker protection and some with. Most customers don't what either fuses or circuit breakers fitted as they are worried that one faulty piece of equipment will take out a whole section of sockets. Others prefer the sockets to be protected.
...
They conform to the regulations because BS7671: 2008 allows distribution units to have circuits with unprotected connectors and cable as long as the length of cable connecting to the PDU is 3 metres or less in length AND the equipment that is being connected to the PDU has its own circuit protection such as a fuse or circuit breaker. If you want to use above 3m of cable or the equipment you are connecting do not have their own circuit protection then the PDU will need fuses or circuit breakers.
I know a bit more now than I did <cough> years ago when that exchange took place. I now wonder whether that applies in a situation where, at the time of designing the system, you cannot guarantee what will get plugged in in the future. I guess it comes down to "how valid is it to assume it's a controlled environment where people will have had instruction in what is and isn't allowed ?" In the big places BAS will be familiar with, they will have dedicated teams who are allowed to do the connecting up, but at my level it's less clear. I can give instruction, and put labels/placards up, but in practice certain members of staff don't (choosing my words carefully) always follow such instructions
