Uprating electric supply

dil1976

Just out of interest what is your job/knowledge of all this. Do you work on the installation side of things or more on design?

DVardysShadow

I have O levels in Physics and Maths. The rest you will have to speculate about.

robatwork

Fascinating discussions - my sparky mentioned diversity, and tempted as I was to counter that I was more of a JLS man, I did take his point. And now you bring up fuse discrimination...well I don't discriminate on fuse colour although I once knew a very un-PC acronym for the colours on a resistor.

But seriously - on further discussions it seems he is sure the supply cable can support 100A - it's just the fuse would need uprating. He is going to look into the maximum current draw in the house to see if we can use a 63A "other fuse" (sorry forgot the term) and stick with the 60/80A power company one.

Uselessly, the power company are quoting "£180-£1500" to uprate the supply....!

Oh and there's no power shower - just a normal gravity+shower pump.

And I won't be installing a sauna.

And finally, Congrats DVS on your 2 O levels

Ectophile

Meanwhile, back in the real world, the curves show that a typical 60A service fuse will actually let through 80A pretty much forever, and 100A for about 5-10 minutes before it blows. So a quick shower is unlikely ever to blow the fuse.

In practice, the service fuse will only blow if you overload it for a long time, or if there's a serious short-circuit.

http://www1.cooperbussmann.com/pdf/f5b2e5d9-2ddd-4332-bbb2-0f03ca7cf10e.pdf (graphs on pages 2 and 5)

In short, if the service fuse has never blown, then don't worry about it.

robatwork

Need to read that one again in the morning I think Ecto...

Damn you John Napier!

DVardysShadow

Ectophile wrote: »

Meanwhile, back in the real world, the curves show that a typical 60A service fuse will actually let through 80A pretty much forever, and 100A for about 5-10 minutes before it blows. So a quick shower is unlikely ever to blow the fuse.

On diversity, a quick shower would never cause a problem on its own.

But in the real world to which you draw our attention, while someone is having a shower, someone else could be boiling a kettle and cooking, 2 rings and an oven. As opposed to your theoretical world in which there is just one shower running.

And again, in the real world, discrimination has to be considered - a solid fault on a 45A circuit is a possibility. As opposed to your theoretical world where only diversity seems to matter.

I would draw your attention to BS7671

314 DIVISION OF INSTALLATION
314.1 Every installation shall be divided into circuits, as necessary, to:
.... minimize inconvenience in the event of a fault

.....

314.2 Separate circuits shall be provided for parts of the installation which need to be separately controlled, in such a way that those circuits are not affected by the failure of other circuits, and due account shall be taken of the consequences of the operation of any single protective device.

Plainly, it is pointless dividing the installation into separate circuits if a lack of fuse discrimination will take out the whole installation in the event of certain faults.

DVardysShadow

robatwork wrote: »

Fascinating discussions - my sparky mentioned diversity, and tempted as I was to counter that I was more of a JLS man, I did take his point. And now you bring up fuse discrimination...well I don't discriminate on fuse colour although I once knew a very un-PC acronym for the colours on a resistor.

But seriously - on further discussions it seems he is sure the supply cable can support 100A - it's just the fuse would need uprating. He is going to look into the maximum current draw in the house to see if we can use a 63A "other fuse" (sorry forgot the term) and stick with the 60/80A power company one.

Uselessly, the power company are quoting "£180-£1500" to uprate the supply....!

Oh and there's no power shower - just a normal gravity+shower pump.

And I won't be installing a sauna.

And finally, Congrats DVS on your 2 O levels

If your biggest circuit is 30A, I would not worry about discrimination - you can use fuse characteristics, but a good rule of thumb is a ratio of 2:1 will give discrimination on similar fuse types. Some will go to 1.6:1, but you need to do the research. So a 30A subcircuit fuse and a 60A main fuse are OK.

Where I agree with the others is on the diversity argument, it is probably not essential to uprate the fuse, unless there is a large number of final subcircuits and scope for several people undertaking activities which draw high currents. If you have a small 6 way consumer unit and lots of other use, you will only blow your own fuses.

The lower end quote will simply be to uprate the fuse, the higher end to replace the cable. They would need to make a site visit to assess whether the fuse could be uprated - I think I would consider to have this done if the electrician makes a good case about diversity

robatwork

Thanks both - food for thought - cooked on gas, fortunately.