Why Did My Power Cord Act Like a Fuse?

I don’t know enough about electricity to troubleshoot problems, so I’m looking for some answers.

All my electronics are fed AC through a pair of Porter Port outlets housed side-by-side in a single box. Each receptacle is on a dedicated line to a separate circuit breaker in the panel. This is all I could do to improve the wall wiring, because I live in a rented apartment. The apartment house was built in the early 70s, and the electrical panel is almost certainly original. My mono-block amps are plugged directly into the two receptacles of one of the Porter Port outlets. Plugged into the other outlet is my pre-amp and a good quality power strip to which my CD player and transport are connected. All power cords are good quality after market cords. The electronics are all solid state and left on all the time.

The other night when I came in from work, I put on a CD to play. The display panels of the CD player and pre-amp, which are clearly visible, were on and the digital readout on the CD player showed the disc was being read, but no sound. I then noticed that the small “power on” lights on the amps were off. Hmm. Flicking the on-off switches on the amps did nothing.

Another electrical circuit in the apartment sometimes cuts out for no apparent reason, which I can “fix” by flipping the circuit breaker off and on. So that’s what I decided to do for the circuit on which the amps were connected. When I flipped the circuit breaker back on, I heard a loud “pop” and quickly looking around the corner to the equipment rack saw a wisp of smoke. Ugh oh.

When I removed the amp power cords from the outlet, I saw that one cord had a neat little 1/4" hole on one side about three inches from the wall plug. I plugged the amps into the power strip, using a replacement for the damaged cord, and the system played. That was a relief. Later, when I went into my bedroom, the time display on my clock radio was flashing, indicating that the power to the entire apartment had gone off and come back on.

I contacted the electrician that wired the separate circuits for his thoughts on what happened. He thought the problem was a defective power cord, not the outlet or wiring. He suggested that I test the outlet where the problem occurred using a night light or cheap lamp, I did, and the lamp worked fine.

I have three questions.
First, when a circuit breaker is tripped, should equipment be turned off before the circuit is turned back on? If so, why? If there is a “surge” when the power is restored, why didn’t the power coming back on knock out any of my other audio equipment? I have flipped circuit breakers controlling lights on and off when the light switches are in the “on” position (to determine what fixtures were on which circuits), and the light bulb filaments (certainly more fragile than power cords) were not vaporized.

Second, it appears that the breaker on the amp circuit tripped while the other breakers did not. Is that because that breaker is defective or because the amps place greater current demands upon the electrical system than the other electronics? Incidently, my amps are each rated at 150 watt output, but the manufacturer does not provide specifications for power or current draw. They do have substantial toroidal transformers and run cool.

Third, even thought the lamp worked in the affected receptacle, could the problem possibly be with the wiring connections at the panel or the outlet but only become apparent when the amps are connected?

Fourth, is there any safe way I can test my damaged power cord to see if it still works? I plan to have it fixed, but I'm curious if only the insulation and jacket were affected or whether the conductor was fried.

Thanks for any answers to these questions and any ideas as to what went wrong.
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Lucky there was no fire, in the event of a loss your insurance company would not pay up if the after market cords were not rated by Underwriters Laboratories (UL Listed)
What it sounds like is an arc fault in the power cord. This type of fault occurs at broken wiring, loose connections and damaged insulation with bare wiring touching (grounded) metal. It is likely that your power cord has a strand or two that broke apart. When you turned the breaker on, the power arced or jumped the air gap between the broken wires. This is similar to what spark plugs and electronic lighters do. The resulting energy then burned a hole in the outer jacket.

As for your questions:

1. It's a good idea to turn off expensive equipment before cycling circuit breakers.

2. Breakers become more sensitive with time. There is a chance that the breakers "nuisance trip" but it is more likely that the breakers are simply protecting the circuit. Breakers can also trip when connection to the outlets are loose.

Two monoblock amps on one circuit is pushing it. Each amp I guess has a 750 watt power draw or 1500 watts total. If the breaker is 15 amps, it's too short; if it's 20-amps it should take it provided that the wiring is sound.

3. Anything is possible - but if your electrician gave the panel and wiring a looking over, then it's not the problem. If the lamps worked at the affected receptacle and you have a gaping hole in the power cord, it's not your receptacle or wiring, obviously.

4. To test your power cord, drop it in the garbage.

As an aside, this type of fault is what burns down houses. You drive a nail in the wall, nick the power wire behind it, and the resulting spark sets fire to the loose fill in the wall cavity. This is why the new electrical codes require arc-fault breakers for bedrooms - prevent this arc from forming in the first place.
Why Did My Power Cord Act Like a Fuse?
It didn't act like a fuse.
The two current carrying conductors of the PC shorted together or the hot conductor shorted to the equipment grounding conductor and caused the dedicated branch circuit breaker to trip open due to the high current overload.

Aftermarket PC? A Listed Power cord?
*Made by a reputable manufacture?
*Do you by chance have the specs for the PC?
Wire size?
Type of insulation used for the current carrying conductors?
Make up of outer jacket?

*By chance can you provide a web link picture of the PC?

When you inspected the cable, any evidence the PC had been chewed on by a pet?

Any evidence the outer jacket of the PC, around the bad area, had been physically damaged in any way?

Jmho a power Surge did not cause the PC to fail.
Just curious - which powercords are UL rated? I rarely see any UL signs on high end powercords....
"I have three questions.
First, when a circuit breaker is tripped, should equipment be turned off before the circuit is turned back on? If so, why?
You have to remeber that breakers like many switches are mechanical and when they are thrown or switched they bounce making and breaking contact several times before coming to rest. Sensitive electronic utilize circuits to make power application a controlled event. USE THE POWER SWITCH ON THE DEVICE ITSELF, on a side note make sure your smoke detectors are working!
Here is a great example why an isolated dedicated equipment ground rod should never be used. (A separate equipment ground rod that is not connected to the main grounding system of the electrical service)

If the short in the PC was from the hot conductor to the equipment grounding conductor the fault current would have had to travel out to the separate ground rod, then travel though the earth and find its way back to the source, (the utility transformer). It may simply travel through the earth and re-enter through the earth ground the electrical service is connected to. Or if your neighbors earth ground is closer it will travel up the ground wire to his electrical panel then on out to the source.

At any rate because of the resistance of the earth I doubt very much if the fault current flowing will be high enough to cause the branch circuit breaker to trip open and stop the current flow.

So now we have a case where current is flowing because of a short condition of the hot conductor and equipment grounding conductor, bared conductors touching one another. The connection is poor at best. Still could have several amps flowing, maybe 5, 10, 15 amps?? While all this is going on the two conductors are arcing. Heat is being generated. More arcing, sparks begin to fly. Carpet, nylon?, begins to burn.......
Another electrical circuit in the apartment sometimes cuts out for no apparent reason, which I can “fix” by flipping the circuit breaker off and on. So that’s what I decided to do for the circuit on which the amps were connected. When I flipped the circuit breaker back on, I heard a loud “pop” and quickly looking around the corner to the equipment rack saw a wisp of smoke. Ugh oh.
Sorry, after rereading your thread I realized the dedicated branch circuit breaker was not found tripped off as I thought.

Gs5556 hit the nail on the head with his post.
I agree with Gs5556.
As Warrenh asked, and I would like to know also, what’s the name of the power cord that was involved? If it’s a major brand name, I’ll bet it was some how damaged accidentally without you realizing it.
Many thanks to all who responded. As I hoped, I learned a lot.

First, I can count, notwithstanding that I said I would ask three questions and posed four. That’s what happens when you think of one last question just before you click the “submit” button, without bothering to re-read what you have already written.
Here is an update and some additional information about the power cord in question.

Update. The lights in my kitchen and dining area are on the circuit that I previously mentioned has been acting up for the last year. When I went to bed last night, those lights were functioning, but this morning they would not turn on at their switches. I have been “fixing” this problem by flicking the breaker on their circuit, but this morning that did not work. Before I started this thread, I did some research about circuit breakers in the archives and learned that repeated flipping of a breaker will wear it out. I guess that is what has happened to the breaker controlling the lights in question. I don’t blame myself for the current (no pun intended) situation, because the only alternative to flipping the breaker is to permanently stumble around in the dark. I’m going to have the landlady send around her electrician to replace the breaker, but while the electrician is here I’m going to ask him (no offense intended, Elizabeth, but the electrician is probably going to be male) to look at the breaker on the circuit to which the amps were connected. The age of the panel (over 30 years) and the failure of one breaker suggests that the breaker on the amp circuit might be suspect. I’m still puzzled why only that breaker tripped when the power went out and came back on.

Outlet for amps. Gs5556 made an interesting point about not putting to much electrical “stress” on a 15 amp circuit. In the future, I will connect each monoblock to a separate outlet (circuit). My choice of outlets for the amps shows how, in the absence of specific knowledge, you can be trapped by your own thought process. When I had the outlets rewired to create dedicated circuits, I planned to have one 20 amp outlet (for the amps) and one 15 amp circuit (for everything else). Porter Ports are rated for 20 amp, but that requires a 12 AWG wire, which could not be installed without tearing out the wall (not an option in a rented apartment). The electrician had to work the new wire through the wall cavity using the same sleeve as the existing wire and a 12 AWG cord would not fit so another 14AWG wire was used. Notwithstanding this change in the amperage rating of the outlet, and not knowing better, I stuck to my original plug arrangement.

Power cord. Despite the request of several posters, I am not going to disclose the maker of the power cord because I now believe that my deployment of the cord may have had something to do with its failure. I will say that this maker sells directly, makes cables to order and has an excellent reputation both as to the quality of his product and the way he does business. I have not discussed this matter with him, but will do so shortly. The amp cords had been in continuous use for 2.5 years before this incident with no problems.

My amp power cords are only about 3 feet long, because my equipment rack is up against the wall and, even though the rack is unusually deep, the distance between the amps and the outlet is short. On a stiffness scale of 1-10, I would say the cords are a 7.5. They flex easily but they retain the shape into which they are put and will stay elevated in mid-air rather than drape over the rack. It turned out that even 3 feet of chord was too long for the distance between outlet and amp, so the cords had to be shaped in an S curve. The manufacturer did say that I had to be careful about bending the cord to avoid damage. I took my time and made the curves as rounded as possible, but that is a lot of curvature over a short distance. The shape of the cords remained as originally set up, so they were not subject to repeated flexing. The damaged cord is now coiled, so I can no longer tell whether the place where it failed was where it was flexed. The cord jacket is mesh and the conductor is silver. I don’t know if the conductor is stranded or solid, and I have no idea what the insulation is.

One option I am considering is to send the cords back for shortening so they can run pretty much straight from outlet to amp. To obtain maximum straightness for each cord, the length of the cords might be a few inches different, which I don’t think will make a difference in their performance. I am sure there are some who will advise not to use either cord and start all over. I'll discuss this with the manufacturer as well.

In response to some other specific questions and comments

1. No pets have been in the apartment. Also, no small children.

2. Jea48. The dedicated breaker DID trip off on this occasion. The other breaker, which controls the kitchen and dining area lights, had been going off for some time.

Again, thanks to all who responded.
"Another electrical circuit in the apartment sometimes cuts out for no apparent reason, which I can “fix” by flipping the circuit breaker off and on"

There is a real reason that circuit breaker is tripping. It is either an overload on the circuit that MUST be repaired, or a weakened breaker that must be renewed, or a poor connection in the breaker panel that heats, then cools and allows you to reset the breaker. The poor connection can be either the wiring or the lug where the breaker makes its connection. Check everything, and find and fix this problem.

Your power cord had a real reason for failing, and the circuit breaker prevented a fire. I'd suggest returning the cord to the maker for their analysis of the cause of the problem. They may also help you out with the cost of replacement.