house light fuse 8amp blowing

I think you would be best off calling in experienced help but if you must, probably the first thing would be an examination of the ceiling wiring (all at your own risk !!) with the fuse pulled. If nothing can be seen then the idea would be to disconnect the first lighting junction from the switchboard, very likely a light fitting and that should remove the fault. Instead of plugging a fuse in use a 100watt lamp in a lampholder with a couple of wires which you can then bridge the fuse holder. If the short is still there the lamp will light instead of popping the fuse. If the short remains with the first junction open the obviously the fault will lay behind the switchboard or in the first cable. If it goes away then reconnect the junction and proceed to the next etc etc. All this is said without expecting you to do it but it would be one method that could be used and a professional would do it with 2 people to speed it up.

Rheilly P

What exactly is on that circuit? Would it be running any ceiling fans? Had some sudden hot weather?

Safer to totally kill the power when you're in the ceiling. The circuit you're poking around might be on a separate fuse.

Although not a popular stance with this NG at times, I'm inclined to say get a professional in for this one. Your life is more valuable than a couple of hundred bucks.

Seems more likely that than a fault in the wiring behind the giprock. In any case, if the wiring is anything like what I've seen in the past, the neutral conductor doesn't come down to the switches, and a short behind the giprock would simply result in lights being on when they shouldn't be.

I'd start be turning every light switch off, and see whether the fuse will then survive. If it doesn't that limits the location of any short to the wiring before the switches. If it does survive, then turning switches on one at a time would tell you where to look next.

Sylvia.

Some of what you state Sylvia is true BUT some sparkies DO run a blind neutral to a switch in addition to the return ( for additional additions). NEVER EVER trust the colour or the wire in a switch and assume it is a neutral. Some switches come in as a red and return as red. AND vice/versa. If the guy had any sense he'd buy a mcb to save rewiring the ceramic. But should only be carried out if you know what you are doing. I do think the adage' Ignorance is bliss' comes into play here. Good luck......

Metro

I'd never trust the colour of wiring at all. You never know who installed it.

Though if he'd had an MCB already, he'd be wondering whether it was itself faulty. At least with fuse wire, one cause is ruled out.

I suppose one comment should be made, which is that every time he replaces the fuse wire and tries again, there's a chance that the short starts a fire. If everything in the lighting circuit is turned off, then he could reduce the chance of a fire by using a much lower rating of fuse wire (since in the absence of the short, it wouldn't be carrying any current).

Sylvia.

thanks for replies;

Unfortunately there is no roof cavity and would have to lift many roof tiles and cut through that silver foil to see giprock and maybe some of the wiring - huge task.

there are only celing lights on the fuse circuit, some of them are CFL lamps some are incandecents (no fans) Either way all switches are off.

I thought it was strange how the fuse would survive a couple of days, then later in week only survive a couple of hours and now instant blowout. I thought it may be water but hasnt rained for a week now and everything would have dried up.

I thought about increasing the fuse wire to the heavier 15 amp powerpoint rating fuse wire but decided against it in case it starts a fire someplace in roof.

Having no access to cable that runs from fusebox, between wall cavity into the wood frame and up into ceiling with no access makes it hard.

If its not a rat carcass causing the short then Ill need to unscreww every celing lamp and check wiring to fitting. Perhaps there is a short to earth .

When checking I turn off all power at switchboard including the solarpanels!

Presumably you've established that the fuse blows *while* all switches are off, rather than the moment you turn one on. It may seem an obvious point, but I've certainly thought I've seen patterns in a failure which, with the benefit of hindsight (i.e., when I found out what was actually wrong) couldn't possibly have been present.

No. In fact I still think you should do any testing with a lower rating that the normal 8A. Even 1A will happily run several 60W lamps.

Unless someone's wired the light switches into the neutral circuit (and of course, that's entirely possible, though totally wrong), a short in a light fitting to earth (there may not be an earth in a lighting circuit of an older building) wouldn't blow the fuse while the switches are off.

Sylvia.

Although it's common practice to run the active to a light fitting to loop to the next room etc. So it would not be impossible there could be a short there which would produce the fault described.

Rheilly P

If you had had someone in each room when replacing fuse they may have heard or seen something, but I do not recommend you keep putting a wired fuse in to a short circuit. Get a plug in circuit breaker if you are going to continue this practice. You may find that a lampholder has carbonized somewhere which will mean removing one by one and checking

You will find that the cable for the lighting from the fusebox will run in turn to each light switch in the house. The nearest one to the fusebox will most likely be the first stop.

You simply disconnect the wires that are "downstream" from this switch, and then apply power.

Leave it and see if it blows. If it doesn't, you wire the first switch back up as it was before, then you go to the next switch disconnect downstream from it and repeat the process.

As you progress in this, you should go around and turn on each light in the house one by one, by observing which ones work and which don't, this way you can "map" which order the cable runs from switch to switch and get a fair idea of where they are likely to have run cables between switches.

This way, when you finally find the faulty section, you will know where to look (and where not to look) for the problem.

You may find that in some locations there might be 2 runs coming out of a switch, branching off in different directions. This might be running off to a side to a room etc, to save having to loop the entire cable through there just for one light switch. Just disconnect each one in turn.

if you get halfway through the house and have found the short, you can then leave that section IN, and go past it and disconnect switches starting at the other end until you work your way back to the problem area.

Even if it is difficult for you to fix at this point, and you decide to get in a qualified electrician, you can save time by having narrowed down the problem area and providing a "map" of where the cable runs.

Finally, make sure that no one has connected a power point to the lighting circuit - I have seen this done once many years ago What you do is pull the "light" fuse then go around every power point with a test lamp, and find any power points that now DONT work. IF any are found, then put the light fuse back and see if they DO work. If they do, then you need to have them connected properly to the power circuit. Power points on ceilings, high up on walls etc may have been intended for lighting and are supposed to have a round earth pin, (this is often done for lights over billiard tables, or standing lamps that people might want to have turned on and off with the room lights via the room light switch - though this is rare) but these days it seems to be normal to just use a standard power point instead, or someone might have just replaced a round pin socket with a normal one so that they can "use" it.

Kitchen and bathroom exhaust fans can run off the lighting circuit (though not always). This can be confirmed by pulling the light fuse and seeing if they stop working.

One dead giveaway for this is if the problem started since you bought a new appliance, or moved things around in your house, so that the suspect power point now has a bigger load on it. Something like a refrigerator or small air con for example, may pull enough startup current to blow the fuse, if there are a sufficient number of lights turned on at the same time, or might blow the fuse after a number of startups. This could account for it being intermittent and should be looked at, particularly if this seems to happen at night when the lights are on. Note that if it happens during the day when you have no lights on usually, you might not notice the fuse has failed until you go to use a light.

Also check the back of switches and light sockets for insects.

I recently had a double power point that didnt work on one side.

It turned out that it was chock full of ants !

Note that while this didn't blow the fuse, it might do on a light circuit where there is a lesser fuse value.

e

In Australia in most cases an active and neutral go from light to light and a twin drops to the switch (active and switch wire) So you may have to disconnect downstream wiring at the light socket.

That is rare in QLD, but have seen this once.

In this one case there was an active and a neutral at both light and switch, and a single dual sheathed cable (switched active) ran from switch to light.

I do not know if things have changed but in nsw they used to loop a twin+e (active neutral + earth to every lighting point or group of lights then drop a twin to each switch,except for two way or intermediate switching when a twin strap went between switches. very rarely did neutral end up behind a switch except in special circumstances. I have not looked recently so maybe they do things differently now

(active neutral + earth to every lighting point or

intermediate switching when a twin strap went between

Just had a look at 'Australian Electrical Wiring' Pethebridge & Williams and several possibilities for basic single-switching are shown :

1) looping-in at batten holder - twin (A+N) with earth between batten holders and twin drop to switch 2) looping-in at switch - twin to switch, twin to batten holder with separate earth to batten holder 3) looping-in at switch - twin and earth to switch, twin and earth to batten holder (but a protected straight-through earth OR an approved earth joint at the switch is required) 4) looping-in at junction box with twin and earth to batten holder and twin to switch 5)surface conduit system - actives are looped at switch, neutrals and earths at the batten holder.

The important thing is that all batten holders must have an earth available - old installations did not do this.

Other possibilities are allowed as long as they comply with the SAA wiring rules. For example, when adding a new light and switch to an existing installation it may easier to use two junction boxes etc.

(active neutral + earth to every lighting point or

intermediate switching when a twin strap went between

circumstances.

I was not discussing what is legal,I was discussing common practice. Economically they did not take wires where they were not needed. The discussion was about fault finding and the place to isolate further down the line is at the lighting fixture as most of the connections are done there. Single switches usually have only two wires. Most fuse blowing faults are at the fixtures.

In the days of split conduit,cabling was a bit different as single wires were used and cables went direct to where they were going ie less connections.

(active neutral + earth to every lighting point or

intermediate switching when a twin strap went between

circumstances.

The quoted source was (is?) widely used as a textbook for the Electrical Trades. I provided it to indicate the common practise as electricians are taught to do. I assume the installation was done legally, are you suggesting the faulty installation was not compliant ?

They still should have complied with the rules.

the line is at the lighting fixture as most of the

fuse blowing faults are at the fixtures.

As in 1), 4) and 5) above,

used and cables went direct to where they were going

That is case 5), the system is called surface conduit because that's how it is most often mounted (not inside walls etc.). Single wires are usually used. It is all explained in the quoted source, Pethebridge & Williams.

The rules change.

Sylvia.