random question....
If the entire lighing circuit is on LED bulbs only and there are no halogen or tungsten filaments or fluorescents, the load would be much lower so could one downrate the existing 6A MCB/RCBO down to 3A or do 3A RCBOs/MCBs not exist?
S.
6A seems to be the lowest rated RCBO for my consumer unit.
Plenty of 1A MCBs and even the occasional 0.5A, but smallest RCBO I can see is 2A
I have a 5 bedroom house and I have literally just counted the number of bulbs on all of my lighting circuits (I have 4 lighting circuits.)
The one with the most lamps is the ground floor with 55 lamps, all are LED lamps or LED Strips. All are at 4 to 6 watts.
So lets take the highest wattage bulb and multiply by 55. This gives 330 Watts. There is an extractor fan on the d/stairs toilet fed by this circuit.
The one with the highest wattage lamps is the outdoor floodlights circuit and there are 18 floodlamps with wattages ranging from 4 watts to 20 watts. Lets take the 20 watts figure as worst case and multiply by
18 which gives 350 WattsA 6A MCB or RCBO supports a continuous current of 1320 Watta at a supply voltage of 220 watts so 6A is cleary more than adequate.
Swapping to a 3A MCB or RCBO would support a continuous current of 660 Watts at a supply voltage of 220 watts which is almost double the the wattage assuming *all* lamps were all on at the same time. In practie very few of us actually have *all* the lamps on at the same time.
The main issue with swapping out NCBs/RCBOs/RCDs in a consumer unit is that it is mandataed somewhere that the consumer unit and the MCBs/RCBOs/RCDs *should* be from the same manufacturer.
S.
Coming back to the original OP's query,
It strikces me that there is a possible solution but with a Caveat (*)
Put in a dry lining box next to the light fitting.
Transfer the Power Loop in and Power loop Out cables from the existing light fitting to the new drylining box.
Then wire in some twin and earth cable from the new drylining box and then fit a FCU to this drylining box so that the bathroom light is now on its own 3A supply.
It is assumed that the wall switch also runs to the existing rose and that the 3 core & E is also taken from the existing rose to the isolator switch and thence onwards to the fan.
(*) you will need to pay attention to the special zones of bathrooms such that (a) the FCU is at a sifficient distance and hieght away from the bath or shower and (b) with it being a humid atmosphere, humidity may get inside teh FCU so it might be prudent to use a IP66 rated FCU enclosure OR extend the power loop in, power loop out and the bridging cable so that teh FCU can be mounted somewhere outside the bathroom.
As a side point, putting a 3A fuse into the Live in for the fan does not offer any protection to the switched live wire. Although you could put a
2nd fuse into teh Switched live, you then could have an unsafe situation where if a fuse opens, unless one is diligent about opening the fan isolator switch, one could be working on a fan thinking its completely dead when in fact either teh permanent Live or switched Live is still Live!
But if you suffered a power cut while they were all on, what sort of spike would all the PSUs in those LEDs generate?
The switched live might be a sensor input rather than supplying power. I note the wiring diagram:
Nevertheless I still feel that is an issue and would prefer the light and fan on it's own fuse.
As long as the wires are correctly sleeved, anyone gaining access to the terminals ought to be checking to see if a wire is live and remove power wherever possible.
That was my thought too. Some 3A MCBs do exist but relatively rare.
I would have thought the fan would have it's own internal fuse, even a non-replaceable one.
That all depends on the PSU design.... I have a chart somewhere that details something like 15 different PSU designs
Some PSU designs here:
Here are a number of options:
So far, that is true.
but that is where it argument collapses. If you add a socket without RCD protection, then you are not working to the current rules.
Actually you could if you really wanted to - there is no ban on having a circuit with a rewireable fuse.
However if it were a socket circuit then it would need RCD protection, as would any circuit with an unprotected cable run. So there are very limited cases were you could install a new circuit with a re-wireable fuse and no RCD.
(use of a rewireable also imposes a de-rating factor on the circuit cables since that type of fuse is slower in operation in some cases)
A RCBO includes over current protection as well as a RCD. So there would be no need for a fuse as well.
There is a little more nuance there though. There are some cases where you can't ignore what is there. Say you notice that the main equipotential bonding is missing. You can't sign off your work with it left in that state. So you would have to insist that the bonding fault is fixed, or decline the new work.
Likewise, if asked to add a new light to a circuit that is wired with twin cable and no earth. Then you would not be able to extend that, and work to the required standards.
That can work, but will be limited to fans with only one live connection.
If it has run on, then you would need a fuse protecting its permanent live and another one on the switched live. Now you have two fuses in parallel protecting the same device which is not good in a number of ways.
The Manrose install sheet only requires a fuse on the permanent live. Why the need for two fuses? The switched live can be treated a signal wire and I presume doesn't supply any current to the fan.
If that is the case there is perhaps no need for the triple isolation switch?
If the fuse is fan side of the 3-pole isolation switch then it can be changed, or altered, whilst being fully isolated without switching the lighting MCB.
Look again the diagram for the timer version shows the switched live tapped off the live connection after the 3A fuse
Fig 3 assumes you dont have power loop in and power loop out at the lighting rose....
The circuit digram would be more complex once the power loop in and power loop out is added....
You can't really extrapolate from one fan to all. If you need a 3A fused supply, then it is better IMHO to run all inputs to the fan from the same supply.
You need the triple isolator to make sure mains can't reach the fan while maintaining it. Some fans will run with neutral and a live feed to the switched live terminal. (they will only need the perm live connected to "run on")
Most faceplate installed fuses can be safely changed live anyway - the fuse carrier inserts and removes it, and the terminals are not (easily) touchable.
<snip>
And in my case *HAVE* to be, as it is a Crabtree Starbreaker, with their own design of busbar and devices that plug directly into it and have no incoming Live terminal.
Agreed. Having multiple, independently isolated, supplies to one device is a recipe for an unpleasant surprise for someone. My main point is that being able to directly control the fan has value, especially near a bedroom.
Take another look - in particular fig 3. The first two examples are only for single live feeds.
If you look at fig 3 - the first example with two live connections, you will note that *both* are derived from the fused supply.
If the switched live is feeding both the fan and the light, the they
*must* both be fed from the fused supply.
While true, that is no excuse for dangerous shoddy work.
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