Fuse Box Stumper

[jeff43222]

I had a troubleshooting call this morning like none I've had previously. Homeowner tells me that when he replaces a blown fuse with a new one, the new one blows immediately and a separate fuse also blows. I tried it myself, and sure enough, both fuses blew right away.

The house was built in 1960, and the fuse box is original (manufactured by Walker Electrical). Here's what I found in the box:

Brown wire connected to one of the blown fuses. Black wire connected to the other blown fuse. Red wire connected to another fuse as part of a multiwire circuit with the black wire. Black and red wires feed split-wired receptacles in the kitchen. Brown wire feeds the bathroom light/receptacle fixture, two bedrooms' lights and receptacles, and a hallway light.

If black and brown are both fused, both will blow. If black is fused and brown is open, nothing blows, and black's devices work fine. If black is open and brown is fused, brown's devices don't work at all (no voltage on hot). If black is open, red's devices also lose voltage, despite red being connected to a different fuse altogether. Red's fuse never blows. Black and red exit the fuse box through one run of Greenfield, and brown exits through another run. I found no evidence of black/red and brown meeting each other in any outlet boxes or j-boxes. None of the wires in the panel looked like they were connected wrong.

I opened up the outlets (red/black's and brown's) to look for shorts, but everything looked good. The only conclusion that makes any sense to me at this point is that the fuse box itself is the culprit. I can't think of a scenario where wiring downstream would cause this kind of behavior.

Anyone ever have one like this?

 

[hbiss]

Re: Fuse Box Stumper

Why is there a brown wire??

Since both hots are on different phases and this a multiwire branch circuit everything you said points to the two hots connected together someplace. Keep looking!

-Hal

 

[paul32]

Re: Fuse Box Stumper

That was my first thought also, but he said:

If black is open and brown is fused, brown's devices don't work at all (no voltage on hot).

Which suggests black and brown aren't shorted.

Jeff, when brown is open and black is fused, black works, but what about brown? If brown doesn't have power then, does it ever have power?

 

[mdshunk]

Re: Fuse Box Stumper

Sounds like the classic split wired receptacle that got replaced somewhere without the tab being broken out. Kitchen perhaps?

 

[growler]

Re: Fuse Box Stumper

It's easy to eliminate the fuse box, Just pull all of the suspect wires loose and see if it's still shorted. I've never seen one that was but why take chances when it will only take a minute and you need the wires off anyway. Then take your meter and see if any of the wires are shorted to each other, If not, check to see if they are shorted to ground. Just because a system is not grounded doesn't mean that the wires are not. Plenty of metal water pipes out there. If you are blowing fuses, you have a current path that should not exist. When you find the shorted wires you just have to trace them down. I once spent three hours in an attic trying to figure out why all the wires were melted. Three circuits all tied together in a junction box, all on the same phase, three different fuses. What are the odds. I thought they were shorted because of the fire.

 

[jeff43222]

Re: Fuse Box Stumper

Thanks for all the replies.

Not sure why the wire was brown, but the color made it easy to distinguish it from the other two wires.

Black and red are part of a multiwire circuit; brown has its own neutral. Black/red and its neutral leave the fuse box via one Greefield run, and brown and its neutral has its own Greenfield run. Much of brown's Greenfield run is visible in the basement, and based on what I saw, I think it's fairly unlikely black/red and brown came together in a j-box somewhere. Not impossible, though.

I'm not completely certain which phases each of these circuits is on. Black and red are on opposite sides of the panel, and I couldn't determine how the two hot buses were laid out (panel was full, couldn't figure out how to remove the fuse cartridge blocks without my hammer). So it's anyone's guess as to which circuits are on which phase.

As for the brown wire, it didn't work any time I was in the house. If I fused it with black open, there was no voltage at the outlets. If I fused it with black fused, both black and brown blew. Homeowner told me that brown did work up until a few days ago when someone plugged in an air conditioner to it. I also noticed brown was #14 copper, but the homeowner fused it with a 20.

Now that you mention it, I did find one split-wired receptacle in the kitchen that looked much newer than the others. I forgot to check to make sure the tab was broken out. Even if the tab is still in place, how would that cause brown and black to both blow? Brown isn't connected to the red/black kitchen receptacles as far as I can tell.

 

[rcwilson]

Re: Fuse Box Stumper

Originally posted by jeff43222:
. So it's anyone's guess as to which circuits are on which phase...."


Jeff - Can you determine phasing by measuring voltage between circuits? All ciruits on phase L1 should read 0V to each other and 240V to the L2 circuits. Or am I missing something?

 

[jeff43222]

Re: Fuse Box Stumper

Yeah, but the only way to do that would be to stick the probe into the fuse's hole, and I was imagining the old "Operation" game with a lot more explosions if I happened to touch the side of the fuse hole with the probe.

 

[rcwilson]

Re: Fuse Box Stumper

Good point. Better be safe.

My dad's old VOM has arc marks on the probes from that.

I've been sketching and thinking something has to be connecting brown and black except brown should be hot when black is. Can't see it on paper. Good luck chasing it.

 

[Jay Zimm]

Re: Fuse Box Stumper

Jeff,

I am sure that you unplugged the A/C but if not try that. Another thing is that and I don't know the conditions but it might be easier to run new wires. You mentioned a basement just fih new ones around and cap off the old stuff. But if I had to bet that air condtioner has to have something to do with it. Heck talk the customer in to a new service and a rewire job.

 

[jeff43222]

Re: Fuse Box Stumper

The A/C was already unplugged when I got there this morning.

I agree that brown and black have to be connected somewhere, as they both blow when both fuses are in at the same time. But even if they are touching somewhere outside the panel, if they are on the same phase, all that would do is provide power from more than one fuse, not blow both of them. If they are on different phases, the effect would be 240V rather than 120V, but that shouldn't blow the fuses either (and there were no reports of anything blowing up from over voltage).

Black works just fine as long as brown is open.
Brown doesn't work at all.
Black fuse + brown fuse = BOOM!
Red only works if black is plugged in.

The only thing in the house that looked like it needed rewiring was a light fixture box with fried wires. The light fixture was a flush-mount sealed globe with no provision for the heat to dissipate, so no surprise the wires fried. I isolated that, too, but it didn't solve the short.

A service upgrade isn't a bad idea, as the unit (half of a duplex) only has 60A service, and they are using an electric range and multiple A/C units.

 

[hurk27]

Re: Fuse Box Stumper

Kill the circuits and see if there any 240 volt loads that don't work. Maybe that when you put both fuses in a contactor or relay pulls in also and trays to energize a appliance with a short in it?

Most fuse centers are wired with one leg on the left and one on the right. all fuss on left are on the "A" leg and all the fuses on the right are on the "B" leg, for 240 volt/multiwire loads the circuit would hook up with one wire going to the left side and one going to the right side. There also should be a set of feed through lugs that stick out from each side, I have seen many that are just taped for an extra circuit and the only fuses that protect these lug are the ones in the main pull out.

Without this then it come down to turning off these circuits and then checking each junction (that you can get to) and separating each conductor to see if you can map out the system with a long wire and a continuity tester or some other kind of tracer.

Inferred can trace the circuit but it takes getting the house temp down and loading each circuit down until it starts to show up on the camera. This can cause other problems like blowing a connection apart in the process but some times its the only way. Most circuit will show up with it just below the max the circuit can carry and bad connections will show hotter but again in a metal raceway you would have to wait until the raceway heated enough to show up on the camera.

 

[jeff43222]

Re: Fuse Box Stumper

The only 240V load in the house is the range, and judging from the freshly rotting breakfast on the stovetop, I'm guessing it works OK.

The fuse box in question has both legs completely covered up with cartridge blocks. The design is such that one cartridge fits on each side. Each cartridge takes two fuses. The 120V fuses are side by side. The most I was able to determine was which screw on the cartridge block corresponded to which fuse, but I couldn't see which fuse corresponded to which leg. Maybe they are both on the same leg. Also, under each cartridge block I could see a black wire coming out and connected to a screw, presumably on the bus (but which one?). It looked like the cartridges were somehow wired into the bus rather than plugged into it.

I agree about flying splices being a problem in old houses, but I have a feeling that's not the case here. I mostly work in houses built in the 20s and 30s (or earlier), so this 1960 house is "new" as far as I'm concerned. I didn't see any evidence of any DIY-style work; everything looked professionally done. With the exception of the 6-3 NM feeding the range, all the wires coming out of the panel were in BX or EMT. Every outlet box I opened up was also fed with BX.

[ July 20, 2005, 08:55 AM: Message edited by: jeff43222 ]

 

[charlie b]

Re: Fuse Box Stumper

As this appears to be a new symptom, and that the brown has worked in the past (or else you would have gotten this trouble call years ago), then my initial focus would be, "what changed recently?" You got the call today. OK, what did the homeowner do yesterday?

 

[charlie b]

Re: Fuse Box Stumper

Here's my theory: The neutral shared by black and red is open. Also, there is at least one load on red and one load on black that are turned on at all times.

With black and red both fused, on one half cycle current goes from the black fuse to the black load, through the red load, and into the red fuse. On the other half cycle, current also goes from the red fuse through the red load, through the black load, and into the black fuse. All loads are getting 120 volts (or nearly so), because of the voltage drop through the black load and the voltage drop through the red load. That is why the red loads do no work if you remove the black fuse. It also explains why this has not been noticed before. The neutral could have been open for years, and the voltage across any single load could have varied up and down as things are turned on and off. Most household loads would operate on a wide range voltages.

To test this theory, plug in the black fuse, and remove the red fuse. If the black loads do not work, my theory is proven.

Why is this finally coming to light (sorry about the pun)? Because something happened yesterday to cause a short circuit between brown and black. A new item of equipment was installed. Or a split receptacle was installed between black and brown, and the tab was not removed. Whatever caused the short is still there. My guess is that the black/red multi-wire circuit goes beyond the kitchen. You have what would be a violation under today's code: bathroom receptacles and hallway lights on the same circuit. Who's to say that there aren't any others? Perhaps the black/red and the brown make their way to the garage, and perhaps the owner plugged in a new toy in the garage. This part of the mystery has to be resolved by the owner fessing up to something he did recently.

 

[ceb]

Re: Fuse Box Stumper

I agree with charlie b if it has been working in the past. what has happened to change this? I am guilty of getting tunnel vision on some of these problems myself instead of starting at point A you need to find point C or D and work backwards get the HO to admit what he has done to change this situation

 

[jeff43222]

Re: Fuse Box Stumper

Charlie's theory is interesting, and perhaps on the mark, but I have a feeling it might be something else.

When I was at the panel, I held my voltage detector next to the red wire as I pulled out black's fuse. The voltage detector immediately went out. If the shared red/black neutral was open, and if black's fuse was pulled out, I should still have detected voltage on red, right? At that point, there would be no return path on red, so there wouldn't be any voltage drop, as no devices would be consuming power.

I would like to test the open-neutral theory, though. It would probably shed some light on the situation. The kitchen did have one split-wired duplex receptacle that had the fridge on one and the stove and hood on the other. Presumably, the stove was consuming a little power for the clock, so red and black would each have a continuous load on them.

As for the "What happened?" issue, the homeowner told me the problem began when someone plugged in an air conditioner in a bedroom. The bedroom receptacles are theoretically all on the brown circuit, which incidentally was 14 AWG "protected" by a 20A fuse. I wasn't able to check the bedroom next to the kitchen because there was apparently a girl sleeping in the room, and the last thing I needed was for her to wake up and start screaming (in Spanish) about the scary man sneaking around in her room. I have enough problems as it is.

Still, I'd be pretty surprised at this point if black and brown came together somewhere. Black/red disappear into the wall right away after leaving the panel, but brown's conduit is mostly visible (and traceable) in the basement.

So the precipitating event was the air conditioner being plugged in. I imagine the load could have overwhelmed the 14 AWG brown wire somewhere along the line and blown something loose.

 

[bigjohn67]

Re: Fuse Box Stumper

Lost neutral......

turn off everything and unplug everthing.

Then test the backfeed..

 

[celtic]

Re: Fuse Box Stumper

Originally posted by ceb:
...instead of starting at point A you need to find point C or D and work backwards get the HO to admit what he has done to change this situation

Well said...
I had that a couple of weeks ago (Troubleshooting ~ elusive neutral ??? )...traced back to a HO "improvement" involving a through-the wall AC installed 10 years prior. I suspect my case was the result of a sawzall mishap. I am also surprised the "flying splice buried in the wall" survived 10 years.


Not that there is an science to finding buried splices (luck and common sense seem to prevail)...we started at the suspected end of the run and worked our way "home" - opening everything in our path and "discovering" some interesting things along the way (clock outlet run on 30' of zip cord IN the wall; 12/3 MC split to 2 12/2 circuits ~ green taped white; etc)

I suggest you keep a camera handy - wish I had one with me/remembered it during our search...some of what we found was completely dangerous.

 

[charlie b]

Re: Fuse Box Stumper

Originally posted by jeff43222: I held my voltage detector next to the red wire as I pulled out black's fuse. The voltage detector immediately went out. If the shared red/black neutral was open, and if black's fuse was pulled out, I should still have detected voltage on red, right?

I don't know what kind of "voltage detector" you have, and I don't know how it works. If you had used a voltmeter, with one of the two probes touching a wire downstream of the red fuse and the other probe on the neutral bar, and if you said voltage went to zero when you pulled the black fuse, I would be at a loss. But magnetic fields are caused by current flow, not by the presence of voltage. So if your device, which you described as being held "next to" the red wire, works by detecting the presence of a magnetic field, then perhaps it is misnamed as a "voltage detector," and should be called a "current detector." You would have to tell me more about the voltage detector, for me to help with this part of the mystery.

As for the "What happened?" issue, the homeowner told me the problem began when someone plugged in an air conditioner in a bedroom.

That's a good start, but it begs a number of additional questions. Was this a brand new air conditioner being plugged in for the first time? If not, did it ever work before (i.e., in this same location and plugged into this same outlet)? Was anything else ever plugged into this same outlet, and did it work properly?

Does that outlet work now (i.e., plug in a lamp, and see if the lamp works)? I am guessing not. Your first post said that if you pull the black fuse and put in the brown fuse, you get no voltage on brown. But that brings me back to my question on your voltage detector. When you did this test (i.e., pull the black fuse and put in the brown fuse), did you use that same voltage detector to conclude that you had no voltage on the brown hot? This may be a big, big clue! Here is what I think:
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• <font size="2" face="Verdana, Helvetica, sans-serif">Your "voltage detector" cannot detect the presence of voltage unless that voltage is causing current to flow. It is giving you a misleading indication that there is no voltage on brown or on red, in the two situations you described.</font>

<font size="2" face="Verdana, Helvetica, sans-serif"></font>

• <font size="2" face="Verdana, Helvetica, sans-serif">The neutral is open on the red/black circuit. See my earlier discussion.</font>

<font size="2" face="Verdana, Helvetica, sans-serif"></font>

• <font size="2" face="Verdana, Helvetica, sans-serif">The a/c unit overloaded the #14 wire. It not only blew the fuse, it also "fused" the brown wire (i.e., melted some of the insulation and some of the copper, so brown is now an open circuit).</font>

<font size="2" face="Verdana, Helvetica, sans-serif"></font>

• <font size="2" face="Verdana, Helvetica, sans-serif">The fault on the brown wire caused it to also damage insulation on black, resulting in a black-to-brown short circuit. I think you are right in suggesting that this happened within the panel, or perhaps it happened at the point the wires leave the panel.</font>

<font size="2" face="Verdana, Helvetica, sans-serif"></font>

• <font size="2" face="Verdana, Helvetica, sans-serif">Black and brown are on opposite poles. That is why if you put in both black and brown fuses, both fuses will blow.</font>

<font size="2" face="Verdana, Helvetica, sans-serif">To test this theory, you need to use a voltmeter, and you need to have access to wiring downstream of the fuses. Try this: Put in red and black fuses. Go to the split outlet in the kitchen. Using a voltmeter, check for voltage from hot to neutral on both sides of the duplex. Now remove the black fuse. See if you have lost voltage on one half of the duplex, but still have voltage on the other.