Circuit Dead, Fuse Fine

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  #1  
Old 08-02-07, 04:42 AM
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Circuit Dead, Fuse Fine

This is a weird one. Last night one of the house's circuits powers off. Now I think, "Ah, with the heat, the AC's caused the fuse to blow." Thing is, when I went down to the fuse box, all the fuses were fine. I swapped out the fuse to the circuit that's gone down, and literally nothing happened - the appliences on the circuit stayed dead and the new fuse showed no sign of blowing.

This incident happened out of the blue, with no recent changes to any outlets, and no new appliances added. What could possibly be the cause, and how do I handle it?
 
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  #2  
Old 08-02-07, 04:57 AM
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Assuming there is no GFCI involved and that the fuse is fine, the likely cause is an open circuit.

High current through a circuit causes heat. Heat causes weak connections to open. When a connection fails you have an open circuit. This is most likely the problem.

The connection could be anywhere on the circuit, even at a receptacle that still works. The problem could even be at the panel. Failed back stab connections are usually the culprit. Back stabs are the push in type connectors at the back of some (less expensive) receptacles and switches. The wire is pushed in to a hole in the rear of the device, and is held in place by a spring pressing a plate against the wire. Over time and due to expansion caused by heat, the spring fails and the connection opens. However, other improperly done connections at wire nuts or at screw terminals can also fail.

To find an open circuit you must check each and every location on the circuit. Start with locations that have no power, but also check locations where power is still present, as the problem could be an outgoing connection. With the power off open the box and check all the connections. Redo any wire nut connections, and move any back stabbed connections to the screw terminals. Verify that all screw terminal connections are properly done. Then replace the device and turn power back on. If you fixed the problem, great. If not, move on to the next device on the circuit. The problem will either be at the first non-working location on the circuit or the last working location on the circuit, so if you know how the circuit is laid out you may be able to find it quicker.
 
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Old 08-02-07, 05:17 AM
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Thanks. Hmm, I've replaced most of the old receptacles over the past year or two, some of the new receptacles used backstabs, others didn't. Worst, it's an old 18th centure home, with wiring added sometime in the 30's or so, making the wiring layout uncertain at best.

:sigh:

I forsee much time lying on my side today.
 
  #4  
Old 08-02-07, 06:55 AM
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It will help if you give us a list of everything that is now without power. In other words, what exactly is on the dead circuit?
 
  #5  
Old 08-02-07, 07:29 AM
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Originally Posted by John Nelson View Post
It will help if you give us a list of everything that is now without power. In other words, what exactly is on the dead circuit?
We're actually in the process of of figuring that out at the time, but with the circuit dead we can now say 3 air conditioners, my mother's wheelchair battery charger, a 7 year old computer, and a handful of small items. (And yes, we are currently in the process of redistributing the Air Conditioners to connect to different circuits.

Oh, this incident is also working as an impetus to try and figure out the load that all the circuits are bearing, any advice on the best procedure, or any online aids?
 
  #6  
Old 08-02-07, 07:42 AM
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Three air conditioners on a circuit should have caused a tripped breaker a long time ago. Please tell me that you don't run them all at the same time, and that all your fuses (except for special circuits like an electric dryer or electric water water heater or electric range) are 15 or 20 amps, as they should be. If any of these are larger than they should be you have a real fire hazard.

I'll give you my standard talk, but you have already figure this out. The time to determine what is on each circuit is BEFORE you have a problem. You need to do this shortly after moving in. You do this so that when you have a problem (like now) you know where to look. However, you also do this so that in an emergency you can quickly shut off power to some location in the house without shutting off power to the entire house. This could save your life.

To determine what is on each circuit is easy, but time consuming. Have someone help you. One at a time remove each fuse (or shut off each breaker) and figure out what in the house no longer works. You need to check each and every receptacle, light and appliance. Don't make assumptions that an entire room is all on the same circuit and don't forget outside receptacles. Plug in radios work well for this.
 
  #7  
Old 08-02-07, 08:24 AM
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Whenever you frequently heavily load a circuit, such as with three air conditioners, open circuits are quite common. For some reason, the neutral is much more likely to open than the hot. So we're back to Bob's original reply as being the most likely cause and the most profitable course of action.

A $6 outlet tester, the kind that plugs in and has three lights, is often useful for narrowing down the problem and reducing the search time.
 
  #8  
Old 08-02-07, 09:26 AM
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First off, no the AC's were run at different times. Though in point of fact, I hadn't determined which outlets went to what circuit until after setting up the AC's (A fuse had blown due to 2 Air Conditioners and two computers being on the same circuit (and all the circuits but the specials use 20 amp fuses) so I plugged it into a different circuit, not properly identifying that there were two other AC's also running on it) Though this is now a motivator to go through the house and nail down the circuits, not just in terms of which room, but isolating each outlet and fixture and identifying it's circuit.

But anyway, as far as the initial problem goes, I was able to identify one outlet that was still functional. A little evaluation in the cellar confirmed that the cable leading to it was the first in the line. Judging from advice offered that this or the next outlet(Which I also identified from the cellar) was at fault, I selected the working outlet as the one to test first. Unplugging things from the outlet immediately confirmed that this outlet was the problem - One of the plugs showed definate scorching, If you want to see I've put a picture here: http://img175.imageshack.us/img175/9623/p8020002as6.jpg
I of course am very thankful for my luck that this problem only shut down the circuit.

Note, the plug going into the damaged half was from my mothers electronic recliner (She has MS). The chair is draws power to run it's functions, but it also maintains a small battery with enough power to complete a raise or lower operation itself in case the outlet dies.

Now, I've gotten rid of the old outlet and replaced it with an industrial grade one my brother got from an electrician friend of his (Well, the plug itself has the label Hospital Grade). Still, this raises the question of what happened, and how to make extra sure it doesn't happen again, possibly doing much worst.
 
  #9  
Old 08-02-07, 09:36 AM
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I am concerned because you state that the house is 18th century, and that the fuses are 20 amp. My experience is that a house that old with fuses will have many circuits that are 15 amp. It is possible that someone used 20 amp fuses, either because that was all they had or because they wanted more power available on the circuit.

I strongly suggest that you evaluate all the 20 amp circuits, looking for 14 gage wire. If you find 14 gage wire, immediately replace the fuses with 15 amp ones. You can determine the wire size by looking at the cable itself for markings, or by comparing the size of the copper wire with known samples of 14 and 12 gage wire (the insulation size is not an accurate indicator of the actual wire size). You can purchase (or sometimes get for free) small lengths of wire at the home stores.

Obviously this receptacle needs to be replaced. It would help to know if the wires were back stabbed or attached to the screw terminals (you didn't tell us), and if the the wires were pigtailed or if they were both attached to the receptacle.

My suspicion is that too much heat was generated by the current passing through the receptacle, because of a weak connection and because the circuit approached (or exceeded) full capacity.

I suggest that you investigate the other receptacles on the circuit and possibly replace those as well. Certainly correct any back stabs and look for signs of damage.
 
  #10  
Old 08-02-07, 10:15 AM
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Just to add a bit each of the ACs (best practice) should to be on their own dedicated circuit. You really need to seriously consider adding at least three circuits just for the ACs.

Now for the even worse news.... maybe. How many amps is your fuse panel? If it is 60 amp or perhaps even a 100a you may need a major upgrade. I'd guess 60 amp from what you have written. If so that is way too small for three ACs a battery charger and heaven knows what else.
 
  #11  
Old 08-02-07, 11:18 AM
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Originally Posted by racraft View Post
I am concerned because you state that the house is 18th century, and that the fuses are 20 amp. My experience is that a house that old with fuses will have many circuits that are 15 amp. It is possible that someone used 20 amp fuses, either because that was all they had or because they wanted more power available on the circuit.

I strongly suggest that you evaluate all the 20 amp circuits, looking for 14 gage wire. If you find 14 gage wire, immediately replace the fuses with 15 amp ones. You can determine the wire size by looking at the cable itself for markings, or by comparing the size of the copper wire with known samples of 14 and 12 gage wire (the insulation size is not an accurate indicator of the actual wire size). You can purchase (or sometimes get for free) small lengths of wire at the home stores.

Obviously this receptacle needs to be replaced. It would help to know if the wires were back stabbed or attached to the screw terminals (you didn't tell us), and if the the wires were pigtailed or if they were both attached to the receptacle.

My suspicion is that too much heat was generated by the current passing through the receptacle, because of a weak connection and because the circuit approached (or exceeded) full capacity.

I suggest that you investigate the other receptacles on the circuit and possibly replace those as well. Certainly correct any back stabs and look for signs of damage.
Thanks for the advice. Although, when my brother's friend (The professional electrician) took a look at our wiring a few years ago (My brother was wondering if it would make sense to swap the fuse box for circuit breakers), he looked over the wiring and didn't see any problems - and also didn't make any suggestions to swap our fuses for 15 amp.

Still, relying on one peripheral opinion is never wise so we will be setting up a schedule to go over every outlet in the house to evaluate it's gage.

As for your question, by your description a Back Stab is a setup dependant on a spring to hold the wires in place right? The outlet I replaced had holes in the back, but they were connected to be tightened by the screw terminals, is that the same thing, or something different. In any case the new outlet is hooking the wire directly to the screw terminals.

Oh, and the wires for the recepticle, and indeed for every recepticle I've swapped in this house (Except the ones at the end of a circuit) have not been pigtailed, but have rather gone through the recepticle.

On a preventitive note, we've already gone over the fuses and reconnected every air conditioner on the house to tie into a different circuit.
 
  #12  
Old 08-02-07, 11:27 AM
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Originally Posted by ray2047 View Post
Just to add a bit each of the ACs (best practice) should to be on their own dedicated circuit. You really need to seriously consider adding at least three circuits just for the ACs.

Now for the even worse news.... maybe. How many amps is your fuse panel? If it is 60 amp or perhaps even a 100a you may need a major upgrade. I'd guess 60 amp from what you have written. If so that is way too small for three ACs a battery charger and heaven knows what else.
I'm not sure the fuse panel's capacity off hand. I know that it's got 12 20 amp circuits plus higher gage Stove Drier and Range circuits coming off it.
 
  #13  
Old 08-02-07, 07:09 PM
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You need to look on the panel for a sticker that gives that info. As suggested you need to map out what is on each circuit. The pros here can help you do a load calculation to determine if your panel has enough capacity.
 
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