Consumer board fuse allocation

[JohnD]

I would not think twice in using a 100W incandescent light bulb

why use new-fangled incandescent lamps, when you could illuminate your house with traditional rushlights burning tallow?

 

[JohnW2]

It is really that much. Blimy.

I think I got my sums right ...

300W for 4 hours per day = 1.2 kWh/day = 1.2 x 365 = 438 kWh/year

at, say, 16p per kWh, 438 kWh/year would cost 438 * £0.16 = £70.08

I did notice a reducion in kwh (over the year) at my parents are fitting a few LEDs.

Not surprising - see above!

Kind Regards, John

 

[ericmark]

The house electrical system is divided into circuits so that a fault with one will not affect another, and so that cable sizes can be reduced, the larger fuses were traditionally put next to the isolator and some boards you had no option, the first fuse had a slightly different base to rest. But for lights one does not want a fault with a power outlet in the same room to also affect lights, before the RCD or with RBCO's it was easy, but with just two RCD's it takes some careful consideration on which circuits come from the same RCD.

Personally I like the idea of ring finals on RCBO's make it far less likely that lights will be lost due to RCD trip. Years ago we had just 4 fuses, Cooker, Ring final, Immersion heater, and lights. However when we moved from the fuse to the MCB the built in fuse inside a light bulb was too slow to stop the ionisation inside the light bulb as it failed (the bright flash) from tripping the magnetic part of the MCB, also we went daft with lighting circuits exceeding 5 amp when the ceiling rose was only rated 5 amp so we started to split the lighting circuit into two.

The regulations advise any fixed item over 2000W should be on its own circuit so as well as the immersion heater we have washing machine, tumble drier, dishwasher, shower, although often we have a dedicated supply to the utilities room, often the kitchen is combined with utilities, so we have a dedicated ring final for that area.

We also have a limit of 106 meters of 2.5 mm² with a ring final to ensure volt drop is within limits.

So the designer has to decide how to best comply, in theory splitting the house side to side is likely best option, as running up to bedrooms uses less cable to down to living rooms, so two ring finals more even, and less likely either will be overloaded.

However for lights easier to split up/down which leaves the designer with a problem when using just two RCD's. So it's down to a risk assessment. This risk assessment may even take into account light from street lamps, and likely use of table or standard lamps.

As to order in the distribution box any fuse or MCB produces heat so putting a MCB which is light loaded next to a heavy loaded one will help even out the heat inside the unit, so simply moving down in size with a heavy bus bar taking the load MCB to MCB may not be best option, the two items taking heavy load for a long time, the washer/drier and the immersion heater should not be next to each other. Be it washer/drier or drier these take high power for long time, nothing else in the house takes power for an extended time, so although the regs suggest over 2000W has it's own circuit, the washer (without built in drier), dish washer, oven, and others may take over 2000W but really they are OK on any ring final, and having the two ring finals both serve the kitchen/utility room would help split the load between the two.

Now I am going to say opposite, we expect the ring is split up/down and to do otherwise could mean some one isolates wrong circuit, so not sure if one should design as to what is electrical best or what is expected?

 

[ericmark]

I think I got my sums right ...

300W for 4 hours per day = 1.2 kWh/day = 1.2 x 365 = 438 kWh/year

at, say, 16p per kWh, 438 kWh/year would cost 438 * £0.16 = £70.08
Not surprising - see above!

Kind Regards, John

How does this work out if you also consider how much energy is used to heat the house? The tungsten light bulb clearly help heat the house, and is only used when the room is in use. Clearly cost and economy only match if using electric to heat, so using oil or gas the difference in energy costs can change things.

 

[JohnW2]

How does this work out if you also consider how much energy is used to heat the house? The tungsten light bulb clearly help heat the house, and is only used when the room is in use.

I'm sure you know the answers as well as I do ...

... it obviously does not make any ('positive') difference at times of the year/day when one does not want heating (or, worse, at times of year/day when "the last thing one wants" is heating!). On the contrary, one might have to expend further energy (for fans or AC) to deal with the unwanted heat!

When heating is needed, then (as you go on to imply), the heating provided by incandescent lights would be far more costly than most people would usually spend upon the same amount of heating (using gas or oil etc.).

Kind Regards, John

 

[JohnW2]

The regulations advise any fixed item over 2000W should be on its own circuit so as well as the immersion heater we have washing machine, tumble drier, dishwasher, shower, although often we have a dedicated supply to the utilities room, often the kitchen is combined with utilities, so we have a dedicated ring final for that area.

The guidelines (which, as you know, are not regulations) to which you refer mention only immersions, space heating and cooking appliances, not washing machines, tumble driers, dishwashers etc.

We also have a limit of 106 meters of 2.5 mm² with a ring final to ensure volt drop is within limits.

You often refer to that, but how often have you seen a ring final anywhere near 106m long in any 'ordinary' house? Even in my (much larger than 'ordinary') house, none of the ring finals are anything like that long ... and, of course, the 'limits' are, again, only guidelines, not regulations (and only become remotely relevant if/when a circuit is 'fully loaded').

Kind Regards, John

 

[JohnD]

light bulbs are quite effective, but expensive, at heating small sections of the ceiling, even when you don't want to.

Since we are not spiders, this is not very helpful.

 

[ericmark]

The guidelines (which, as you know, are not regulations) to which you refer mention only immersions, space heating and cooking appliances, not washing machines, tumble driers, dishwashers etc.

Under 13A there are three items in the home today which can draw over 2kW for an extended time.
1) Immersion heater
2) Storage heaters
3) Tumble drier (either stand alone or combined with washer)
Even plug in electric fires will normally start to cycle before an hour has elapsed. And the dish washer holds very little water so does not heat for long, same with oven 20 minutes is around the max before it starts to cycle.
So 30 gallons raised from 10°C to 70°C at 13A will take around 3 hours, where a tumble drier only runs for around 90 minutes, however the immersion in the main switches off at 65°C and on at 55°C so in the main is same load as a tumble drier, so if a immersion needs a dedicated supply why should a tumble drier not need one when in the main the same draw on the system?

Not worried about dish washer, oven, or oil filled radiator as they do not draw high current for long enough, Immersion heaters and Tumble driers are the odd ones out.

 

[JohnW2]

Under 13A there are three items in the home today which can draw over 2kW for an extended time.
1) Immersion heater
2) Storage heaters ...

Agreed, and both of those would usually be on dedicated circuits. In fact, some storage heaters draw in excess of 13A, so have to be. ..

3) Tumble drier (either stand alone or combined with washer)

Maybe some. Mine draws about 2.2 kW max, and the heating cycles on/off, so unlikley to average at as much as 2 kW over any appreciable period of time.

So 30 gallons raised from 10°C to 70°C at 13A will take around 3 hours, where a tumble drier only runs for around 90 minutes, however the immersion in the main switches off at 65°C and on at 55°C so in the main is same load as a tumble drier, so if a immersion needs a dedicated supply why should a tumble drier not need one when in the main the same draw on the system?

See above. I can only speak for my tumble drier, but it runs for a maximum of 90 minutes and at an average current which I think is probably significantly under 2 kW (<~8.5A), whereas, if it starts 'cold', my immersion will draw ~13A continuously for 2.5-3 hours.

In any event, returning to realities, have you ever seen a domestic tumble drier on a dedicated circuit?

Kind Regards, John

 

[AndyPRK]

"Personally I like the idea of ring finals on RCBO's make it far less likely that lights will be lost due to RCD trip."

I thought differently.

I thought what is the most important circuit in the house? And my answer was the light circuits. Therefore I like to put lights on RCBO's
But yes it is also nice to put an important ground floor ring circuit (and boiler) on an RCBO too.

 

[JohnW2]

I thought differently. I thought what is the most important circuit in the house? And my answer was the light circuits. Therefore I like to put lights on RCBO's.

I suppose it depends upon what other circuits there are, and where the lights are getting their supply from (and what circuits one thinks are 'likely' to cause RCD trips).

I imagine that eric's thinking was that things plugged into sockets circuits are probably the most likely to trip RCDs, so if they are not protected by the same RCD as the lighting circuit(s) (one way of achieving which is to have sockets circuits on RCBOs), then the lighting would not be killed by a fault on one of those sockets circuits.

If lighting circuit(s) are fed (via MCBs) from an RCD then the degree of risk of losing lighting as a result of some other fault obviously depends upon what other circuits are protected by the same RCD, and how likely it is thought that a fault on one of those circuits will ever trip the RCD.

However, as I always say whenever people start talking about the inconveniences, and potential dangers, of losing a lighting circuit, at least for my personal position, such loss of lighting is far more likely to be due to a (brief or protracted) power cut than to an RCD trip, so those with such concerns really ought to be thinking about battery backed-up emergency lighting, rather than worrying about RCD trips!

Kind Regards, John