I carry a neon tester in my shirt pocket. On a 120V circuit it draws
somewhat less than 1mA. That is around the edge of what you can feel as
a shock. It will light up at much lower currents. One of the reasons I
carry it is you can hold one of the test leads and touch the other lead
to a wire. If the wire is hot, the neon lamp lights up dimly. That is
with the capacitance between me and the 'world' as part of the circuit.
Neon testers can have the same problem as digital meters - they can
indicate when there is no real voltage. If my tester indicates there is
voltage, if it is not bright I know the indication may not be real.
What is the leakage current for a fuse that is blown - with vaporized metal.
I don't buy that the fuse was "failed - not blown"
Further investigation is going to be necessary, because last night I
did notice that lights were dimming, almost imperceptibly. And not
necessarily just the ones on the aforementioned affected outlets.
<Further investigation is going to be necessary, because last night I
did notice that lights were dimming, almost imperceptibly. And not
necessarily just the ones on the aforementioned affected outlets.>
I thought about this for a while and it's possibly that the flickering is
not just in your house, but on the whole local circuit. At night, the power
companies continuously adjust the system and you might be seeing the effects
of those adjustments. I say that based on the fact that all lights are
flickering, not just the one on the bad fuse circuit.
You probably have an intemittent connection. Because messing with the
fuse fixed it once I'd suspect that area first. Your electrician
should be able to tighten all the connections where the wire enter and
leave the box. If that doesn't solve it then the problem may be in
That's certainly my take on it, but there's always the possibility of
"inherent vice." If it were my problem, I'd be examining that fuse with a
both an ohm meter and a Dremel tool. I'd probably hook it up to an audible
continuity meter with sturdy spring-type battery clamps connected to each
end so I could shake it, pound it, put it in the freezer for a while and
heat with a heat gun to see what, if anything, allowed current to pass
before I sliced it open to see how cooked it was.
That's a very good point. With the high possibility that the fuse holder
has metal parts with dissimilar coefficients of expansion, an intermittent
based on changing temperatures from a loose connection is a very likely
We had a disposal problem that only showed up in the spring and fall. It
would kick off, and then restart, usually when you jiggled the switch.
Turned out to be a bad backstab connection that flaked out every time it got
suddenly cold outside (the switch and outlet is was linked to were on an
outside north-facing wall). Since circuit panels are often located near
outside walls and are typically not well insulated, I believe as you do that
a loose connection to the fuse could be the real problem here. Especially
now that the OP has reported that the lights are still flickering. That's
no bad fuse, I'm afraid.
Hopefully the OP will keep us updated . . .
I don't know how you can say that without examining the fuse close up.
Sounds like it may have crumbled from excessive heating from carrying too
much of a load. Only a hands-on inspection will determine that, and it
would probably mean cutting open the fuse to determine the failure mode.
Jumpin I would say *exactly* the reverse is true when dealing a lethal
entity like 240VAC where a main fuse has failed and with so many other
unknowns. Not being concerned enough might lead to a similar set of
circumstances where a badly manufactured Chinese replacement fuse FAILS to
blow and there's a meltdown as a result. A blown fuse is a warning that
something's wrong. Assuming it's just a failed fuse and moving on seems to
be bordering on terribly careless. Each to his own, I guess.
FWIW, hearing about a fusebox in a home in this day and age raises an alarm
in my head that there's a potential overload situation. While fuse panels
of 200A certainly exist, every *residential* fuse panel I've ever seen in
the NE USA was a four banger with 15A screw-ins and a 60A total rating. I
realize that experience is terribly limited, but regardless, a blown main
fuse is not something to take lightly.
I don't know what the rules are up in the "Great White Way" or in other
parts of the US, but I assume one of the safety reasons for switching to
breakers is that they are much harder to override with pennies or aluminum
foil. Not sure what the NEC has to say about installing new 200A service
with screw-in fuses in the USA and I certainly know that my limited
experience does not even speak for the USA NE - just the houses whose panels
I have seen. All I know is when a fuse protecting an entire incoming phase
fails, an investigation is warranted to determine the cause. Assuming it's
simply a bad fuse is bad troubleshooting.
In this case, caution is especially called for because we just don't have
the information necessary from the OP to make a good call. We have no
information at all about the daily peak load he's putting on the panel,
either. We don't have a picture of the panel with the cover off, which can
often tell you what kind of workmanship is involved or if the wiring is
shoddy or deteriorating.
I recall seeing one poster here show us a picture of his circuit box with
all of the single wires laid out as neatly as the strings of a harp! I had
never seen and will probably never again see such incredibly precise work -
I wish I could remember the dude's name - when you see workmanship like
that, you can usually discount poor wiring - but I digress.
With all the unknowns, it seems far more prudent to raise a caution flag
than to give him the green light and say "bad fuse, replace and
fuggedaboutit." The part of this that really gives me pause is that he
reported that it's an intermittent fault. Yes, fuses, light bulbs and most
anything electrical can fail that way, but when a safety device fails, it's
far more serious than a light bulb failure. When the fuse protecting an
entire leg fails, I consider that especially serious because it can easily
indicate too much current is flowing through that leg, something that
individual circuit fuses will not catch.
The truth is that we don't know a whit about either of those big IFS in this
case. We don't know how well the loads are balanced in the house - many
times one leg is bearing much more of the load than the other. That can be
simply plugging in space heaters into the "wrong" outlets. In a house with
a bigger circuit panel than the feeders dictate, that can happen easily.
I've seen more than one "heavy up" that didn't include an appropriate
upgrade from the feeder.
All we know here is that one leg of the incoming power lines had an
intermittent, not quite completely failed fuse. We know very little else.
(Since writing this, the OP has added a post indicating that he's got 200A
circuit panel but we don't know if it's really 200A service or a 200A box
sitting on 60A feeder lines.) With no ability to go onsite, we've got a
barrel full of IFs that raise the caution flag.
Yes, I agree with you that fuses do fail from inherent vice but IMHO *every*
fuse failure or circuit breaker pop warrants an investigation to find out
what popped it. In this case, I would be looking at the total KWh's used
monthly in relation to the size of the panel and also whether the panel was
properly balanced with each leg carrying as close to half the load as
possible. I'd turn everything in the house on and get out my tong meter to
see what branch circuits were carrying in terms of load. I'd visually
inspect the outside feeders to make sure they were sized for 200A and not 60
IIRC, the panel should be sized so that even if every device in the house is
running, the main fuse won't blow. I am not sure that's the case here. We
also know fuses fail in multiple ways: in addition to failing
intermittently or "popping" correctly in an overload, they can also fail to
blow and thus not protect the wiring. That's an extremely hazardous
If the two fuses for each leg are of the same vintage, I would replace both
of them if I wasn't going to heavy up the panel and the load appeared to be
well-balanced. My best guess, from the limited facts we've been presented,
is that the load is too great for the panel and that one leg was carrying a
heavier share of the load than the other, causing the fuse on that leg to
deteriorate and partially fail.
But in reality, we don't even really know whether the fuse was bad.
Replacing a fuse in a loose fuse holder could jiggle bad electrical
connections just enough so that the intermittent disappears for a while. We
can't know that unless somebody actually checks the dead fuse with an
ohmmeter and carefully inspects the connections coming from the pole.
Running a cartridge fuse hot for a long enough time could easily cause
serious deterioration. If that leg's overloaded, simply replacing the fuse
could lead to tragedy, especially if the bad fuse is replaced with one that
doesn't operate at its rated load, but higher than rated. And before you
say that's unlikely, consider that you're the one saying we're dealing with
a bad fuse to begin with. (-: Who's to say, without an examination, whether
that intermittent fuse *should* have opened completely but didn't?
I've seen people ask very "shocking" questions, that indicate a lack of
knowledge about electrical work. My favorite is whether it's OK to use a
ground as a neutral. These kinds of comments lead me to almost always err
on the side of caution when giving advice on the net, especially with things
that have the lethality potential of possibly overloaded circuit panel.
There's almost *never* enough information given by the OP to make a clear
call. That's just the nature of Usenet.
In my limited experience, it's far too common for people to add circuits
without thinking about the total load. I'm partially guilty of that crime.
I've added the skinny "two in one" breakers to my house that have the
potential to overload the main fuse if I run every circuit to capacity. I
definitely should have heavied up the incoming feeders to meet code but I
added the new circuits not to draw more juice, but to replace the old cloth
covered circuits one-by-one with 12/2 romex w/ground and GFCI protection.
I left the all the old circuits in place because they serve porch and
overhead lights that would have required major demolition to replace. Now,
almost all the large loads like space heaters and window ACs run off 20A
grounded circuits. I've got sensors on the incoming feeders that connect to
my HomeVision controller to let me know the overall current draw on each
phase. I used that information to switch circuits around until they were
balanced, at least for the static large loads. I monitor it periodically to
ensure the loads have stayed balanced.
I have a lot more breakers than I should, but the overall load has not
changed - it's just been redistributed and rebalanced so each leg shares the
load as well as I could balance it. The only difference in the overall load
occurs at peak cooking times. One of the reasons for the rewire was to add
an XTB coupler/repeater/amp for my X-10 stuff, and more importantly, to be
able to use the microwave, the toaster oven and the refrigerator in this 70
year old house without blowing a breaker. That's not going to put a strain
on the main fuses for each incoming leg because the kitchen outlets are
served by different phases, a trick I learned right here in AHR.
Unfortunately, that's not the case in many other installations where there
are too many circuits drawing from one phase and overloading it. I don't
think replacing a fuse is going to get the OP off the hook. It could still
be something like a bad connection to the main feeder in the circuit panel
that's heating up and heating the fuse, too. Again, only an on-site
inspection will reveal things like that.
I hope the OP continues to post his progress in running the problem to
ground. (Electrical pun!) My money's on something other than the fuse being
defective. There's something rotten in Denmark (do we even know where the
OP lives, BTW?).
On Sat, 20 Nov 2010 20:04:45 -0500, "Robert Green"
You need a picture of mine? 22 circuits, one of which is a 30 amp 220
pullout, and the other is a 50 amp 220 pullout.
Installed in 1978 when the house was built.
It also has a fused disconnect for the central AC beside the panel
Other than the garage circuits, which I have blown numerous times with
table saw, compressor, and various other "tools of high demand"I've
only replaced 2 fuses in 29 years. One of which was DEFINITELY a
simple fuse failure, and the second almost definitely (a lighting only
circuit with less than 800 watts maximum load on a 15 amp fuse - which
has not blown for the second time in more than 8 years.) It was
cracked in the "blow zone", the crack not visible to the naked eye
The first fuse, which was intermittent, had failed where the fuse
element contacts the threaded shell. The solder didn't fail, so it was
not a loose or oveheated fuse - the fuse element just cracked, right
next to the soldered joint. If the lights or TV were on for a while
they'd start to flicker a bit, then go out. Turn them off for an hour
and turn them back on, and they'de work. Being wired with aluminum
wire, I checked every connection on the circuit before thinking to
replace the fuse. All outlets are now CO-ALR devices. Maximum load at
any time during the problem time was less than 300 watts. Max circuit
load in previous 15 years or so? Who knows, but in the 8 years I'd
owned the house not likely more than 1500 watts or so - back before we
got the central vac it had likely run the vacuum a few times. That
(replacement) fuse has been there now something like 10 or 12 years.
My panel looks about the same, as did virtually every panel my
electrician father ever installed.
It is just as irresponsible to scare the guy into spending big bux to
replace what may be a perfectly safe and serviceable fuse panel
Except in the case of cheap chinese automotive mini-fuses I've never
seen or had first-hand knowlege of a fuse failing to blow.
There was a whole batch of ATO fuses recalled by Princess Auto that
were made in China with the element made of too heavy a guage material
that would blow on a short circuit, but required over 300% of the
rated current, IIRC..
A properly operating fuse does not "blow" as soon as it's rated
current is reached. Generally a 25% overload should blow in less than
10 minutes. A 100% overload MAY take up to 4 or 5 minutes to blow the
fuse, and still be operating "correctly".
However, a BLOWN fuse, in my experience, is ALWAYS an open fuse, with
enough metal melted out of the element to be both obvious and
A FAILED fuse, on the other hand, can be failed in such a way as to be
visibly impossible to detect, and intermittent.
In a cartrige main fuse, of course, it is impossible to visibly
inspect the fuse without dismantling it, although at least in years
past, there were some that quite visibly changed colour when blown -
and some had neon bulbs in them that glowed when the fuse was blown.
There was a line of pole fuses that also had the neon in them - the
hydro crew could tell immediately if the feeder fuse on the pole was
Quite possible - even iff that leg was never over 50 or 60% capacity.
A good idea to check the load and load distribution? Most definitely.
But don't condemn the panel or the installation without checking it
It now appears he still has flickering lights, so there is most likely
a bad connection involved.
A whole lot more difficult to do and more unlikely with a fuse panel.
Not quite sure why the fuses with different sized cones, that did not
allow a heavier fuse to be installed than the socket was designed for,
never caught on. Likely because the American manufacturers took a
"not invented here" attitude. (I believe it was a Canadian inovation)
Required by code in Canada - split countertop receptacles.
But bro, you're a *Canadian* (-: They've always done things a little
differently. I don't doubt you have a fuse panel, but that doesn't change
my experience, which is that fuse panels in the US are typically associated
with 60A service and most houses that I have seen that have changed hands
even once have had those panels upgraded to get approval for a loan or to be
This site says:
<<Many jurisdictions, particularly in Canada, no longer permit
fuse panels in new installations. The NEC does permit new
fuse panels in some rare circumstances (requiring the special
inserts to "key" the fuseholder to specific size fuses)>>
So while you and others may have them, fuse panels are definitely on their
That site also goes on to say:
<<Fuses are prone to explode under extremely high overload. When
a fuse explodes, the metallic vapor cloud becomes a conducting
path. Result? From complete meltdown of the electrical panel,
melted service wiring, through fires in the electrical
distribution transformer and having your house burn down.
[This author has seen it happen.] Breakers won't do this.>>
Gack! You've got TWO items that are no longer considered codeworthy.
Aluminum wire and perhaps the last fuse panel installed in Canada. (-:
I don't doubt that, but most panels I've looked into don't.
No, I don't think so. If fuse panels were as safe and reliable as you've
been portraying them, then why aren't they allowed in new service? It's
because they have serious safety issues compared to breaker panels. "Safe
and serviceable" is hard to evaluate without seeing the box but we already
have good reason to believe there's something very wrong with it since a new
fuse didn't cure the flickering.
I also base my comments on the fact that I've never seen a screw in fuse
panel in all the new homes I've every looked at and I bought my first house
in 1984 and my parents bought several houses before that. The NEC decided
against fuses, and I'll bet those reasons are safety related. I assume the
primary reason is that fuses are too easy to bypass with higher-than-proper
rated fuses, pennies or foil. I assume a secondary reason is that when they
are unscrewed you can get shocked a lot more easily than when a breaker
trips. A tripped breaker has no potential exposure to electrical current.
More reasons? Fuses may not be screwed in completely and thus make
We know none of those things. Another site says this about fuse panels and
why they've disappeared from new home wiring:
<Old style distribution panels, those with screw-in fuses are generally
considered fire hazards. The contact between the base of the fuse and the
buss bar oxidizes or charcoals from poor contact. In order for the current
to continue to flow heat is generated. In many areas, insurance companies
will not renew homeowner insurance if the home is equipped with an
electrical distribution panel that has screw-in fuses. . . .Electrical
panels typically last 20-25 years. Sure signs of a failure in your
electrical panel are flickering lights and excess heat at the circuit
Well, our OP certainly has experienced the flickering lights part.
Well, explain why they're no longer going into new work if what those sites
are saying is true. The NEC wouldn't abandon a successful technology for
absolutely no reason, would they? (-:
As I am researching this, I keep seeing comments like this:
"I need to update the old screw-in fuse box on my cabin to modern breakers
per my insurance company. What should I expect to pay for a 100 amp service
upgrade? Wiring is modern 3-wire system, but for some reason, they never
upgraded the fuse box."
If the guy had flickering lights throughout the house, there's good evidence
the panel isn't working properly.
Those are Type S fuse receptacles that used different threads on each value
of fuse, making it impossible to substitute the wrong size. I had them in
this house when it had a 60A fuse panel. Different color fuses, too.
Since we're now >>>>>> six quotes in, we're just kicking the football around
now. It will be interesting to see what the final resolution of the problem
will be, but I am betting it's going to end in a panel upgrade.
says: "I've upgraded a number of panels from fuse to circuit breakers
because some Insurance Companies will no longer insure with fuses."
"In California, if a home is equipped with an electrical distribution panel
that uses screw-in fuses, many insurance companies will not renew homeowner
It really seems that I am not the only one who believes that fuse panels
should be replaced with breakers. Apparently the people that have to pay
out for electrical fires do, too.
Breakers can explode under extremely high overload. They can cause the
same arc flash and burn down.
If you have a solid short at a panel, the current is the "available
fault current". (For a house service it is likely 5,000 - 10,000A).
Electrical apparatus, particularly fuses and breakers, has a rating for
the "available fault current" of the source. If you use a fuse or
breaker (or motor starter...) at a point where the available fault
current is higher than the rating for the fuse or breaker it can explode.
Fuses are readily and cheaply available for circuits with available
fault currents of 200,000A. Breakers are not readily or cheaply
available with that rating.
If apparatus is applied within its rating - current, voltage, available
fault current - it doesn't explode. The NEC requires apparatus be used
withing its rating - including available fault current. I expect the
"site" knows nothing about this.
<Problem solved. Contractor's estimator checked everything, double-checked
and discovered a main fuse that was bad. Replaced it and solved the
For now. The failure of just one leg, at least in my limited experience,
could indicate that you're drawing too many amps through one leg of the box
in total, or that you've got some other intermittent problem in the box
itself. Simply replacing the fuse may mean it will happen again in the very
near future. What was the rating on the fuse? What are the ratings of the
four screw-in fuses?
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.