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The Knimbies who say No

Light circuit rating too high...?

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House has 2 lighting circuits, each covered by a 5A circuit breaker at the consumer unit. Seems that's pretty standard stuff, although with the advent of low energy lighting, it seems an absurd amount of headroom as In total on the upstairs circuit there is approx. 105W of LEDs plus one strip light plus one bathroom fan (which I guess runs from the light circuit although happy to be corrected. I know the strip light will involve a start up spike but sufficient to justify the fused rating? Seems like the contemporary equivalent of putting a nail in the fuse box. The strip light can(will) be removed at some point. Basically there is about 0.5A worth of lighting plus the fan and strip light. Similar story on the other circuit.

Can I down rate the circuit breaker to 1A, following removal of the strip light, and live happily ever after....?

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You could...but why on earth would you? The cable hasn't magically lost current carrying capacity.  Leave the circuit alone.

A little knowledge is a dangerous thing.

My Christmas callout callout charges double when evidence of DIY is evident...

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1A can still kill you.

Get a 30mA RCD fitted, they are designed to protect people, fuses are to protect cable.

5A sounds like a pretty old board but there are standalone modules that can be fitted to the main tails.  Not as good as a board change, but technically no different either.

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The OP does make an interesting point, though, about how the changing nature of technology isn't reflected in change in how we build things.  It would make sense, from a cost and safety point of view, to downrate lighting circuits to a lower voltage and total power.  

At the same time, the requirement for high potential-power mains-voltage sockets everywhere in new build is way in excess of the actual requirements -- sure, we need high power in the kitchen and similar areas, maybe one or two elsewhere for the rare high power item (eg, hairdryers, vacuum cleaners), but most requirements these days are for a load of way less than 500W per room.  For the majority of things these days the first action is an inline power supply to reduce the input voltage to something usable.  It could well be more efficient to mainly (ha!) have 20v sockets around the home for most purposes, with the occasional 13A 240V (or whatever) for the rare high power item.

Not saying that this would be trivial, etc.  Just that we have a high cost, high risk solution (necessitating expert intervention for otherwise simple problems) in our homes which isn't matched to the modern requirement.  

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How much is lost through the transformers? Keeping the higher voltage (and presumably lower current) circuit for appliances probably isn't that inefficient and saves having to have a separate circuit (as well as being more flexible).

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300mA RCD? Are you sure? It should be 30mA.

The lighting circuits will be 1 or 1.5mm cross sectional area and the breaker or fuse is to protect them and stop them melting in a short circuit situation. There's no real advantage to down rating the breaker and the real possibility of introducing nuisance trips. The RCD is what protects you by measuring the flow and return across live and neutral and tripping if the imbalance reaches 30mA.

Electrics are best left alone unless you really really know what you are doing.

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52 minutes ago, dgul said:

The OP does make an interesting point, though, about how the changing nature of technology isn't reflected in change in how we build things.  It would make sense, from a cost and safety point of view, to downrate lighting circuits to a lower voltage and total power.  

At the same time, the requirement for high potential-power mains-voltage sockets everywhere in new build is way in excess of the actual requirements -- sure, we need high power in the kitchen and similar areas, maybe one or two elsewhere for the rare high power item (eg, hairdryers, vacuum cleaners), but most requirements these days are for a load of way less than 500W per room.  For the majority of things these days the first action is an inline power supply to reduce the input voltage to something usable.  It could well be more efficient to mainly (ha!) have 20v sockets around the home for most purposes, with the occasional 13A 240V (or whatever) for the rare high power item.

Not saying that this would be trivial, etc.  Just that we have a high cost, high risk solution (necessitating expert intervention for otherwise simple problems) in our homes which isn't matched to the modern requirement.  

This is kinda what I'm driving at, overall. The lighting requirements for each room could mostly be easily driven from the 15W available from one of the  5V 3.1A USB outlets on the socket faceplates I'm installing. These aren't even switched! Of course, unless you want to rip everything out then you're stuck with what you've got, but it seems reasonable that cutting the demand on a circuit by a factor of 5 or more, as with a switch to new tech, should maybe drive a change to the fundamental design in time. Of course, it could be argued that the degree of redundancy with lightly using a circuit designed for a much greater load has increased, but it all seems a bit unnecessary, and as you say, introduces additional expense. Like running a complex IT setup when all you need is a tablet.

19 minutes ago, ntb said:

300mA RCD? Are you sure? It should be 30mA.

The lighting circuits will be 1 or 1.5mm cross sectional area and the breaker or fuse is to protect them and stop them melting in a short circuit situation. There's no real advantage to down rating the breaker and the real possibility of introducing nuisance trips. The RCD is what protects you by measuring the flow and return across live and neutral and tripping if the imbalance reaches 30mA.

Electrics are best left alone unless you really really know what you are doing.

Here it is..

image.jpeg

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5 minutes ago, The Knimbies who say No said:

This is kinda what I'm driving at, overall. The lighting requirements for each room could mostly be easily driven from the 15W available from one of the  5V 3.1A USB outlets on the socket faceplates I'm installing. These aren't even switched! Of course, unless you want to rip everything out then you're stuck with what you've got, but it seems reasonable that cutting the demand on a circuit by a factor of 5 or more, as with a switch to new tech, should maybe drive a change to the fundamental design in time. Of course, it could be argued that the degree of redundancy with lightly using a circuit designed for a much greater load has increased, but it all seems a bit unnecessary, and as you say, introduces additional expense. Like running a complex IT setup when all you need is a tablet.

Here it is..

image.jpeg

POE

power over Ethernet ;)

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Ok, that's for fire protection rather than shock protection. I recommend you get an electrician to inspect and replace with a 30mA unit.

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2 hours ago, chronyx said:

1A can still kill you.

Get a 30mA RCD fitted, they are designed to protect people, fuses are to protect cable.

Indeed a tenth of an amp is fatal, no fuse (or circuit breaker) of any useful rating will offer any meaningful shock protection, its simply not what they are designed to do. As above you need a Residual Current Detector.

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Where would this hypothetical new low voltage lighting supply originate? Volt drop will limit the distance of the LV cable runs.

The more fancy over-complicated stuff I get asked to fix/install/configure...the more I like conventional equipment.

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32 minutes ago, chronyx said:

Where would this hypothetical new low voltage lighting supply originate? Volt drop will limit the distance of the LV cable runs.

The more fancy over-complicated stuff I get asked to fix/install/configure...the more I like conventional equipment.

Also runs the risk of some numpty connecting mains to LV cable, if LV distributed all round the house.

A lot to be said for wireless light switching though  - fairly archaic idea that you have to route mains down walls to switchgear to go back up to light fittings. The less buried cable routes in walls the better in terms of safety/reliability/install hassles - just moving light switching around involves chasing out, laying cable and making good, much better to be able to move a remote switch to any location and program accordingly. Having said that the tech needs to be stable and reliable and not all is, but it will get there and there is the issue of later configuration when you know the instructions won't be around anywhere and you have the hassle of accessing/binding switch plates and remote relays.

 

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29 minutes ago, chronyx said:

Where would this hypothetical new low voltage lighting supply originate? Volt drop will limit the distance of the LV cable runs.

The more fancy over-complicated stuff I get asked to fix/install/configure...the more I like conventional equipment.

But that is someone in the industry talking.  It is like petrol, etc -- if you were to suggest now that we should start installing wires in every home with users only protected by thin layers of plastic it wouldn't get traction.  I'd say that safety would be vastly improved with low voltage supply everywhere, and only giving those lethal voltages where it was absolutely necessary.

In terms of installation -- it would be part of the CU.  Voltage drop is trivial to sort out -- power rating and distance would determine cable diameter -- but, given the very low currents you'd be talking about it wouldn't need a vast amount of copper, even with the lower voltage.

Frankly electrical installations is another of the ancient technologies which persist.  I mean, bits of copper laid by hand and connections made by squishing with a screw.  Technology could make things safer, but the industry is very resistant.  For example, we've only got start-of-circuit monitoring, not in-circuit monitoring.  

But it won't happen, as, like brick and block, there is such an expectation that every room will have at least 6KW of potential electrical supply that the status quo will continue.

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I agree with you, broadly - I got ripped to shreds for suggesting ring circuits are archaic and potentially dangerous on a trades forum.

That said, I think you mean 6kW per floor, not per room (Kitchen excepted) That's only 2 decent fan heaters.

My own annoyance is that as inspection and testing is becoming a requirement, test probe ports are not mandatory - disassembling crappy B&Q decorative light fittings (Normally DIY'd, badly) to get an earth loop reading gets old.

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8 hours ago, chronyx said:

1A can still kill you.

Get a 30mA RCD fitted, they are designed to protect people, fuses are to protect cable.

5A sounds like a pretty old board but there are standalone modules that can be fitted to the main tails.  Not as good as a board change, but technically no different either.

Yes 100%

Also if any of the lights on the circuit are outside you should really be using an RCBO rather than RCD these days.

I

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Interesting, so what could the lighting circuits of the future look like in a domestic home..? 

Might it cease to exists at all, eg light fitting with internal (wirelessly?)rechargeable battery, held on to the ceiling with eg magnetic plaster for easy positioning, also switched wirelessly?

 

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You could always wire in some lower rated protection further downstream for the low energy lights.

Certainly with solar panels, a leap to a separate DC circuit would also make a lot of sense. Given the amount of phone/laptop/tablet charging cumulatively the energy savings might be valuable.

I quite like the idea of using an electric car as a giant mobile UPS for the home. I'm surprised there hasn't been a case of someone using some employer green environmental initiative that provides free electric car charging points to, in a similar way to pens and bog rolls, rob electricity from work, on a daily basis, to power their house or even sell it back into the National Grid.

 

 

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24 minutes ago, Mikhail Liebenstein said:

Yes 100%

Also if any of the lights on the circuit are outside you should really be using an RCBO rather than RCD these days.

I

Just got one for my outside lights. Want them on while I go away over christmas but they're on the same side of the CU as the chest freezer so dont want that off when it trips out.

Theyre bl00dy expensive though. Got a 2nd hand one on ebay. A different brand to the CU box.  Im sure itll be alright though.

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43 minutes ago, chronyx said:

I agree with you, broadly - I got ripped to shreds for suggesting ring circuits are archaic and potentially dangerous on a trades forum.

That said, I think you mean 6kW per floor, not per room (Kitchen excepted) That's only 2 decent fan heaters.

My own annoyance is that as inspection and testing is becoming a requirement, test probe ports are not mandatory - disassembling crappy B&Q decorative light fittings (Normally DIY'd, badly) to get an earth loop reading gets old.

A 13a socket is rated at 3KW.  Lots of sockets per room.

I know the ring will only be rated at 7kw or so, but that is a nuance.  Every room in a modern house has power outlets capable of delivering at least 6KW.  Why?  Why is it demanded that such power is available?  It would make more sense for each room to have loads of safe, low power outlets, capable of safely powering laptop chargers radios, small tv, table-lamps, etc.  Leave the high power stuff to specific locations in the house where such power is necessary.  

Of course, so many people will say 'but what about xyz!' -- but they're just conditioned to vast power supply being distributed around the house.

And about the inspections -- it is of course madness that normal people buy cheap junk then stuff potentially lethal wires into it.  We'd all be safer if they could explore new light fittings etc with only exposure to low voltages.

15 minutes ago, The Knimbies who say No said:

Interesting, so what could the lighting circuits of the future look like in a domestic home..? 

Might it cease to exists at all, eg light fitting with internal (wirelessly?)rechargeable battery, held on to the ceiling with eg magnetic plaster for easy positioning, also switched wirelessly?

Well, I'd imagine you'd still use wire, but make it a safe voltage so that the user could easily re-wire / move the fitting without mucking about with lethal voltages.

For those that say 'numpties will do something stupid!' -- numpties currently do do something stupid.  All the time.  They've been conditioned to think that mucking about with lethal voltages is okay because that is what you have to do to do anything.  So you get loads of poor spurs, light-fittings, etc.  If there was a safe low voltage distribution they could mess about with that as much as they liked (well, without killing themselves or burning down the house / risking the future occupants) then they wouldn't have the exposure to the lethal stuff and would treat with with the appropriate respect.

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3 minutes ago, dgul said:

 

.  Why?  Why is it demanded that such power is available?

Because by the time you've piddled about running in these low power supplies you might as well install  normal mains cables.

Technically you are supposed to isolate the power and then perform dead tests, so it's not a factor realistically. If people want to tempt Darwin pratting about with 'lethal voltages' that's up to them. 

If Darwin isn't looking, the RCD will do its job and cut off the power before their heart goes into fibrillation.

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