house light fuse 8amp blowing

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My lighting  ceramic fuse  has started blowing  this week, I replaced
it with 8amp lighting fuse wire from bunnings and it was ok for 2 days
then blew again.  I dont have any obvious shorts on lighting
circuit.   After replacing it 3 times this week it now blows
immediately EVEN though nothing is switched on, ie no loads.

Now I fear the worst rats chewed and shorting the active/neutral in
the ceiling?? unlikely..

Q; how do I trace a damaged power line in the walls/ceiling without
breaking giprock everywere??    What do electricians do in these
cases??  rewiring the entire lighting circuit is too huge a job.

Any trick appreciated..

Re: house light fuse 8amp blowing
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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

Re: house light fuse 8amp blowing

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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.

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Re: house light fuse 8amp blowing
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What exactly is on that circuit?
Would it be running any ceiling fans?
Had some sudden hot weather?

Re: house light fuse 8amp blowing
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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.


Re: house light fuse 8amp blowing

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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......


Re: house light fuse 8amp blowing
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I'd never trust the colour of wiring at all. You never know who
installed it.

 > Some switches come in as a red and  return as red. AND vice/versa.
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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).


Re: house light fuse 8amp blowing
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

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

Re: house light fuse 8amp blowing
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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.

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<shudder> 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.

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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.


Re: house light fuse 8amp blowing
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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

Re: house light fuse 8amp blowing
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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

Re: house light fuse 8amp blowing
thanks for the valuable tips n info,  I will be splitting the cable
run as described to isolate  section shorting.  But first  I thought I
would quickly check the closest light switches to the powerboard which
is the bathroom.  I have had termite problems in this area before and
when I pulled out the switch I found ant saw dust caked around the
wires. I cleaned it off and rewired the fuse hoping this was a lucky
find but fuse blew 2 seconds later instead of instantaneously.  There
may be more ant gunk on other switches which I will investigate.

BTW;  the first switch has ridiculous amount of stiff wiring hanging
off the light switch.  ie they are using the spare holes on switch as
a terminal connector for 5 neutral wires and 4 actives.   This doesnt
look like good practice.  I was thinking of buying some large screw
connectors and joining all the neutrals and another for the actives
and dropping them behind the switch to relieve all the strain and
close proximity of the actives/neutrals, and may as well buy a new
switch also.

here is a pic

this pic is after cleaning all ant sand of exposed wires.

Re: house light fuse 8amp blowing
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If it ain't broke....


Re: house light fuse 8amp blowing
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I described section isolation in another thread.

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It looks like your electrician has elected to do his loops at the switches and
not at the ceiling lighting points.
This may actually work out better for you, if you can't readily access the
ceiling wiring.

Your problem appears to be a short between a neutral and an active. Possibly
even an earth and an active.

There may well be similar wiring behind most switches, stretched and many
conductors crunched into a single terminal.
When the cable is new, and you are young, nimble, and confident, it is very easy
to grind 4 or 5 conductors into a
twisted pattern with a pair of bull nose pliers, so they will squeeze into a
switch terminal and be locked up with the
screw. I could virtually do it with my eyes shut, and I'm sure most good
sparkies can.

So it may be quite a job to actually rewire and add new terminals to each point.
You have opened up a switch with
multiple actives near the switchboard.

Next step would be to get an 8A circuit breaker if you don't already have one,
and use it. Drop the 4 actives out of the
switch and separate them. Test it. If the breaker doesn't trip, you are getting
started with section isolation.

One of the actives will be the incoming active from the switchboard, or a
previous switch. Easiest way of finding it is
to use a meter to check for 240VAC between your neutrals and actives. When you
find it, screw just this one active back
into the switch, and see if you can get your first light to work.

You then add actives until the breaker trips. Get the picture, and know where to
go next?

Again if you aren't confident about this, get an Electrician. I would hope that
you can safely use a meter in this
fashion, if you are reading this news group.

Cheers Don...


Don McKenzie

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Re: house light fuse 8amp blowing
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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

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

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.

Re: house light fuse 8amp blowing
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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.

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Re: house light fuse 8amp blowing
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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.

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Re: house light fuse 8amp blowing

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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.

Re: house light fuse 8amp blowing
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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
I have not looked recently so maybe they do things differently now

Re: house light fuse 8amp blowing

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(active neutral + earth to every lighting point or
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intermediate switching when a twin strap went between
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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.

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