ConFUSEd Power Rating

[Leckey]

I am currently looking into replacing the light fittings in a small church and have come across the following.
1. There are two fuses supplying the lighting circuits rated at 5Amp but one has a 10Amp wire in it
2. The 10Amp fuse has two output feeds.
3. Of 28 light fixtures 25 are supplied by BOTH fuses.
4. Calculating the circuit power rating (28 x 100 x 1.8 divided by 240) the recommended fuse rating would be 20Amps.
This leaves me with three burning questions .
1. Why would they be wired in this configuration.
2. Have I done my maths right and if so how come the fuses have not blown.
3. What would the recommended course of action be to remedy this situation.
Any advice appreciated

 

[ban-all-sheds]

...28 x 100 x 1.8 divided by 240...

What's the 1.8 factor for?

 

[breezer]

sorry to say this but i presume you have not got insurance, you are working in a public building if anything should go wrong YOU will be Liable.

I would strongly recomend that you bow out gracefully saying that it is a bit too big for you to handle.

also your maths is right, but calculations wrong.

sometimes with all the best will in the world, there are some things a D.I.Y person should not do and this is one of them.

 

[il78]

as breezer said above............

although.....the lights may have not blown because:

1) not all the lights are on at the same time.
2) not all the lamps are 100W
3) God has blessed them (sorry couldn't resist)

I would recommend that some-one rewires the lighting circuits to suit.

Regards

 

[ban-all-sheds]

1. Why would they be wired in this configuration.
2. Have I done my maths right and if so how come the fuses have not blown.
3. What would the recommended course of action be to remedy this situation.

1. They were wired up by an idiot.

2. According to my calculator, the reason they haven't blown is that they aren't drawing too much current.

If 25 of the lamps are fed by both fuses, that means that if we ignore the effect that the different resistances of 5A and 10A fusewire have on the currents (and the lengths of the cables, too), then the current for 12.5 of them goes through the 5A fuse. If they are 100W each, then that's 1250÷240 = 5.2A. Even if we assume that the remaining 3 lamps all on the 5A circuit as well that's still only 6.45A, which is nowhere near enough to blow a 5A fuse:

Time/current characteristics of semi-enclosed fuses to BS 3036

In reality the calculation above would be fairly inaccurate - the resistance of 5A fusewire is probably 4 x that of 10A, which would mean less than half the current in the 5A leg.

3. As Breezer said - get someone in - it's not a question of competence, it's a public building and unless you're properly qualified you won't have public liability insurance.

Are there no qualified sparks in the congregation?

 

[masona]

Ahhh men

 

[ban-all-sheds]

I'm sure a female electrician would be just as good....

 

[supersparks]

what ever rocks you boat masona

 

[masona]

Ahhh women then

 

[supersparks]

Ahhh women then

c'mon mate you have come out the closet! no point going back in!!
ill stop being evil now

 

[ban-all-sheds]

That would be the wiring closet, would it? Masona - you misheard - there are bus BARS in there, not bus BOYS.

And are you qualified to work on DC?