Which fuse rating to use in a plug

[Deleted member 142255]

It's 314.2(iii) which is usually the bit which has the widest range of interpretations, and readers are only asked to "take account of hazards that may arise from the failure of a single circuit such as a lighting circuit" - and you'd probably be hard-pressed to find two people who assessed "hazards that may arise" in the same way and/or "took them into account" in the same way!

I posted the full regulation. There is no 314.2 (iii)!

No mars bar this time, you lose.

 

[JohnW2]

I posted the full regulation. There is no 314.2 (iii)!

Apologies. Although I followed you in writing 314.2, I was actually talking about 314 in general (which is all about "Division of Installation") - and that led to my typo, since what I was referring to was actually 314.1(iii) - which, at least here, seems to be the most hotly debated (argued about) part of 314.

 

[Deleted member 142255]

Apologies. Although I followed you in writing 314.2, I was actually talking about 314 in general (which is all about "Division of Installation") - and that led to my typo, since what I was referring to was actually 314.1(iii) - which, at least here, seems to be the most hotly debated (argued about) part of 314.

It's quite clear to me.

 

[fixitflav]

there are no downsides of using the lowest possible rating of fuse

Except maybe for a freezer, as was discussed on here at some length a while back.

 

[Harry Bloomfield]

I have to agree with @JohnW2 I know it says loads over 2 kW to fixed equipment should be on a dedicated circuit, and over 18 kg and not on wheels makes it fixed, but to have a dedicated circuit for the tumble drier, dishwasher, washing machine, and immersion heater, is going OTT.

For such items, I would not be concerned, they are not in use 24 hours a day, or be described as essential that they work.

So we use some common sense, once the house is wired, adding circuits is expensive, the immersion is on a dedicated circuit, but the rest are plugged into one of the ring finals. Yes, I was careful to take the spur for washing machine from a different place as supply for tumble drier, but since drier is heat pump type, now no real need.

The splitting of a 3 kW supply (think 3 kW, not checked) to make separate circuits for the freezers and central heating seems daft. They will never add up to over 3 kW, and having one SWA around the outside of the house is bad enough, without a second one.

I agree that adding circuit is expensive, and disruptive, which was why for many years I tacked things on to existing circuits, despite the aesthetics of doing so 'bothered me'. Which was why, last year I set about to (mostly) tidy things up, in one swoop.

I simply cannot agree with John's point about fridges and freezers being better/safer on a general circuit, because on a general circuit the loss of power would be noticed. Mine are both are now on a dedicated single circuit, with no RCD protection. My decision!

1. Should that circuit fail, it would be quickly noticed - the fridge light, which we frequently go into, would obviously be off, and the freezer alarm would quick quickly be sounding.
2. On their own dedicated circuit, with no RCD, there is a greatly reduced chance of the circuit tripping due to a fault, more so whilst we are away on holiday. Sharing an RCD circuit, with multiple other items, multiplies the risk of one of the items suffering a fault, and tripping the circuit. I never like the idea of all of my eggs, being in one basket.

With multiple essential items on a reduced number of circuit (John's method), no doubt if a fault arose, and if I was here, I would be able to quickly identify it, and get the power to the essentials back on. I am not always here, so with supplies maintained separately to essential items, the whole thing becomes much less urgent, and pressing. Even if it is an essential supply which has failed, we have numerous extension cables, so power could easily be found from other outlets.

314.1 (iii) such as a lighting circuit.
Just an example, there are many others which could be listed..
(i)..minimise inconvenience.
It's very inconvenient, if your fridge, or freezer circuit develops a fault, when that circuit is a shared one which includes much of the house. For the normal householder, it becomes a very real problem, if the circuit will not reset, and they have to wait a week to get an electrician to attend, and just hope they have the skills to find the issue.

 

[JohnW2]

there are no downsides of using the lowest possible rating of fuse

Except maybe for a freezer, as was discussed on here at some length a while back.

I thought it would be obvious that my "Lowest possible" "the lowest appropriate rating that is possible"

 

[JohnW2]

I simply cannot agree with John's point about fridges and freezers being better/safer on a general circuit, because on a general circuit the loss of power would be noticed.

As I wrote, the fact that we have different ideas/approaches is healthy, not something to be worried about. Cats can be skinned in lots of different ways.

Mine are both are now on a dedicated single circuit, with no RCD protection. My decision!

Are they hardwired, or are you comfortable being a little non-compliant with BS7671?

1. Should that circuit fail, it would be quickly noticed - the fridge light, which we frequently go into, would obviously be off, and the freezer alarm would quick quickly be sounding.

As I've said, my view is that whilst my house is occupied (which is almost always, the most crucial things are the freezer alarms. We have a small freezer in our kitchen, plus a couple of fairly large chest freezers in the cellar, and we can go a week or more with needing to even look at the chest ones (or anything else in the cellar0. Had I not had the alams, we would very probably have lost the entire contents of a chest freezer on at least a couple of occasions - and since those events arose because of freezer (not power) failure, in the absence of the alarms we would very probably have lost the contents even if the freezer(s) were supplied from a dedicated circuit.

2. On their own dedicated circuit, with no RCD, there is a greatly reduced chance of the circuit tripping due to a fault,

I know you're not interested in probabilities/likelihoods (which is your prerogative) but my view would be that one has to consider what "greatly reduced chance" means when the chance it is reducing from is already very close to zero. In the ~40 years I've been in my current house, always with RCDs (initially just one covering all all circuits in each CU), I really can't recall any occasion on which we have lost a sockets circuit other than in the most obvious (and easily remedied) situations - such as 'switch on the kettle or toaster and the lights go out'!

.... more so whilst we are away on holiday.

That I don't understand. For a start, most people are not on holiday for more than about 10% of the time but. much more to the point, most (sensible) people will leave only the most essential loads (like freezers, and maybe heating systems) connected and switched on when the house is going to be unoccupied for an appreciable period of time - so the chances of a fault resulting in any supply failure ought to be much less when people are on holiday, shouldn't it?

so the 'near zero' probability of a cicuit failing

With multiple essential items on a reduced number of circuit (John's method)....

I don't think that is a fair description of John's method For example ....

It's very inconvenient, if your fridge, or freezer circuit develops a fault, when that circuit is a shared one which includes much of the house. ....

... that#'s not 'John's method'. I';m a great believer in multiple circuits - I think I have 40+, across several CUs, so not of them serve 'much of the house' I'm not talking about how many circuits (or of having only a small number of circuits) but, rather, my view of which loads I feel are most appropriately put on which circuit (with which other loads). In an ironic sense, it's a bit like an upside-down version of your view that :

....I never like the idea of all of my eggs, being in one basket.

.... in that I never like having only one egg in a basket if it's an egg whose distress I might not become aware of for a good while - I prefer there to be other eggs there that could alert me to the problem

 

[SUNRAY]

Try explaining this to children, and then have them return home from school, and tell you their teacher says I got it wrong. This was before everything had to come with a 13 amp plug, so school children were taught how to fit a plug. I have had this a few times with the kids at school, the classic was there are two types of transistor can anyone in the class tell me what they are, my son, who had passes his RAE answered bipolar and field effect sir. To be told no, it is NPN and PNP, to which he burst out laughing, he did not even attempt to tell the teacher his error, and was still laughing when he told me.

We were taught Geranium (yes) and silicon followed by geraniun are PNP and silicon are NPN. One of my class mates (A G8Dxx) asked if that was also true of diodes with PN Vs NP junctions and guess what; that proved to be the case. He then got his transistor data library book out and was told it was out of date.

 

[ericmark]

I am sure my books are out of date, there is no longer a RAE exam to take.

As to freezers, two on one RCD socket one on another, fed with SWA cable from the solar inverter together with the central heating, so with a power cut backed up with between 620 Watt/hour to 6.4 kWh battery depending on time of day when the power failed, plus the solar panels, how long they would run depends on the sun light.

It seems the back-up is 5 kW not 3 kW so suppose could use spare socket for the kettle.

 

[Harry Bloomfield]

Are they hardwired, or are you comfortable being a little non-compliant with BS7671?

It was a mid 1980's rewire, with no RCD's at all. I since covered all the circuits, with RCD's except for the freezers. So a major step up, even though not fully compliant. As I've said before - my home, my rules. I am happy it is much safer than it was before, as well as more sensible.

That I don't understand. For a start, most people are not on holiday for more than about 10% of the time but. much more to the point, most (sensible) people will leave only the most essential loads (like freezers, and maybe heating systems) connected and switched on when the house is going to be unoccupied for an appreciable period of time - so the chances of a fault resulting in any supply failure ought to be much less when people are on holiday, shouldn't it?

It may only be >10% of the time, but during that time, the big difference is - you would not be there to limit damage. A few years ago, we went away for the day, and returned home to find the electric shower had turned itself on. It was spraying mostly in the bath, but some over-spray on the bathroom floor. It had soaked the bathroom floor, the ceiling below, and flooded the downstairs toilet under that. Had someone been home at the time, it would have been quickly noticed and stopped.

When we go away, I program the boiler, with 'dates away', unplug TV's, isolate the electric shower, plug in smart plugs to operate lights, as if there is someone home, alarms, cameras, routers etc. remain powered.

So far as I am concerned - the fewer circuits a fault can affect, the better, but there are limits, so reasonable compromises have to be made.

 

[Harry Bloomfield]

We were taught Geranium (yes) and silicon followed by geraniun are PNP and silicon are NPN.

There are obviously both! PNP and NPN versions of germanium, and silicon transistors. All the early portable radios, used germanium.

When I did the RAE, I had time on my hands, working local, so I decided to take it at college to refresh my memory, rather than just going in for the exam. The German guy who was teaching it, tried to explain the action of a noise blanker circuit, but didn't understand the difference between a blanker and a noise limiter, he just didn't understand they were different things. He had the syllabus in his head, and couldn't veare away from it.

 

[fixitflav]

I thought it would be obvious that my "Lowest possible" "the lowest appropriate rating that is possible"

But what is "the lowest appropriate rating"? The question raised plenty of discussion Here

 

[JohnW2]

But what is "the lowest appropriate rating"? The question raised plenty of discussion Here

The lowest fuse rating which is appropriate for the load, both when 'running' and during 'start up'.

I admit that it may be difficult to be certain about the latter, so I would agree that in relation to anything which contains a significantly-sized motor (including a compressor), hence including fridges and freezers, one might have to be reasonably generous in deciding upon an appropriate fuse rating.

 

[fixitflav]

The lowest fuse rating which is appropriate for the load, both when 'running' and during 'start up'.

I admit that it may be difficult to be certain about the latter, so I would agree that in relation to anything which contains a significantly-sized motor (including a compressor), hence including fridges and freezers, one might have to be reasonably generous in deciding upon an appropriate fuse rating.

Agreed, that's what we discussed last time, the only reason I mentioned it.

 

[JohnW2]

Agreed, that's what we discussed last time, the only reason I mentioned it.

Fair enough - although start-up currents are so brief, and fuses so (relatively) slow to blow in the face of 'moderate overloads' that I would personally be pretty surprised if there were ever a problem with domestic refrigeration devices.