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My wife was trying to “multi task” and now I’m freaking out that we maybe damaged some wires in walls ( I’m paranoid )

She had connected hair dryer and clothe steamer to bedroom outlet

Outlet 15 AMP @ 120V ( 2nd floor bedroom so decent run of copper )

14/2 Wire (Romex)

Hair Dryer 1875W

Steamer 1300W TV 200W?

So circuit was loaded 30AMP ( and rated for Max 15AMP)

All this was connected for maybe 2 minutes and I noticed …

Breaker didn’t trip for some reason it’s newish Siemens CAFCI so don’t think that it’s faulty?

I used KillAWatt and the devices do use the wattage that they are listed for.

I did remove outlet to inspect visually the wire and it does not appear to be burnt ( maybe just half way in box a bit darker but could be in my head no discoloration at first inch from outlet screw )

So question is did I maybe melt wire in wall and why breaker didn’t trip.

Sorry for long question

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  • Was everything turned on and operating at max load?
    – Hearth
    Sep 20 at 0:33
  • @Hearth Yes, it was turned on for 2 minutes maybe less
    – NotSoHandy
    Sep 20 at 0:38
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    A comment was made on an answer, but I think it's worth repeating here. Heating devices (heater, toaster, steamer, etc.) do not run at full capacity all the time. They heat a bit above the set temp, then the element turns off and the device is allowed to cool a bit below the set temp, then turns on again. Just like your home heating. It's very possible that there was never much more than 15A being drawn at any one time because of the cycling of the heating elements in the 2 devices.
    – FreeMan
    Sep 20 at 13:37
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    Just a quick update, I think I checked all connections and all looks ok ? There was a black spot on neutral wire ( I think comming from downstairs feed ? ) but it just scraped off, maybe it was just dirt/scratch marks. But all connections appeared not melted, sadly two outlets were back stabbed down the circuit, but those outlets were recently replaced by electrican as they were yellowed from sun ( so backstab was hopefully good ) - no signs of overheating at those outlets, i took quick glance at lights without removing much and nothing obvious
    – NotSoHandy
    Sep 20 at 17:01
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    @NotSoHandy, the connections are where hotspots usually form. If you didn't see any melted or charred spots, you should be good to go.
    – Mark
    Sep 21 at 22:24

3 Answers 3

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Here's the thing: circuit breakers are not designed to trip instantly as soon as current exceeds the rated limit. Instant trips happen only when the current flow is many times the rated amperage (i.e. a short circuit). This is called a magnetic trip.

Otherwise, for excess current up to low tens of the rated current, the trip is delayed, somewhat in proportion to the multiplier. This is called a thermal trip and is specified by a trip curve chart. This is matched to the expected heating of the protected wires and prevents nuisance trips.

With a typical residential CB, for 2X the rated current flow, the trip time is measured in minutes! It is perfectly acceptable for a 15 amp CB to carry 30 amps for more than two minutes, because it will take more time for the wires to get hot enough to pose a hazard.

My expectation is that if you had waited 5 or 10 minutes, the CB would have tripped.

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  • Thank you, I was ready to have electrican rip all wires and re wire, this put my mind at ease, I guess I can sleep at night and carry on with circuit use as normal just light loads
    – NotSoHandy
    Sep 20 at 1:12
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    Agree with all of DoxyLover's explanation BUT, your load--using your numbers-- gives 28.125A, which exceeds the ampacity of 14awg copper. It is unlikely the wire was damaged, but you need to upgrade to 12awg copper or ensure you never load it more than 15-20A in the future. I hate 14awg in almost every possible residential circuit for this reason.
    – peinal
    Sep 20 at 12:06
  • @peinal Would that also not factor in to this answer in the same way? Ampacity is a max value for continuous current flow, and also has to do with the wire heating. Wouldn't the trip curve on the CB be such that it trips before the wire overheats too much? Like my understanding is that the reason the breaker doesnt trip right away is because a 15A circuit can handle that 30A without issue for a short time.
    – JMac
    Sep 20 at 17:51
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    Exactly. Breakers are expected to trip before the rated wire insulation temperature is exceeded. So if you heat up a breaker "slowly" the wires would also have heated up slowly. And the breaker would still trip before the wire becomes an issue. If everything was installed and working correctly then there is no issue.
    – ontrack
    Sep 21 at 12:24
  • JMac--not necessarily. If the CB were too large, the wire could melt before tripping. They are related, but both must be correctly sized for the load.
    – peinal
    Sep 21 at 19:37
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I found one Siemens trip curve at this link for PDF. It shows roughly 17 seconds to 75 seconds (yes, that big a range) for a 2X trip. 2 minutes is longer than 75 seconds (1.25 minutes), but not that much longer and your usage may have varied within that time. I would expect that within another 30 seconds or so you would have had a trip.

A couple of other notes for future readers of this question:

  • CAFCI, AFCI, GFCI, etc. have nothing to do with this. If you have faulty wiring then under load an arcing problem will get worse, triggering AFCI trip, and a loose connection might overload causing a break of sorts which could trigger a GFCI. But basically if the wiring is in good shape then the only thing that will stop an overload situation is the basic breaker functionality, which is independent of the other stuff.
  • With modern good quality breakers (Siemens, Eaton, GE, etc.), even if several years old, there is every expectation that an overcurrent trip will happen in a reasonable amount of time. However, there are certain older types - e.g., Federal Pacific, Challenger - where they may not trip, or may fail closed rather than open. Those can and do catch fire. So if anyone reading this has one of those breakers (or any other breaker not already listed, as there are other good breakers and other bad breakers) search to find out what may be going on.
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  • Thank you!, Based on this information, all should be ok and I can sleep well ?, should I cut open drywall and check wires
    – NotSoHandy
    Sep 20 at 2:45
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    connections (wire directly into back of receptacle instead of into a screw/clamp or wrapped around a screw - back stabs are worth redoing as screw connections), etc. and then put the cover back on. Only do any real work if you find indications of problems. Otherwise you run the risk that you might take off a good connection and put it back together as a not as good connection. Really. Sep 20 at 3:26
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    Thank you, will do, I’m sure some were backstabbed as this was cookie cutter builder that build 200 of same homes. ( but hopefully the backstabs didn’t get chance to go bad )
    – NotSoHandy
    Sep 20 at 3:27
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    Understood, thank you
    – NotSoHandy
    Sep 20 at 3:51
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    Hairdryers don't necessarily run full power all the time anyway. Depending on how many positions the switch has they can run e.g. hot (max rated power), less hot (reduced power), or cold (very little power). And a steamer will have a thermostat so once the water is boiling the element will turn on and off - if that was plugged in a few minutes before the hairdryer it won't have been drawing full current all the time. That could easily explain it not tripping in 2 minutes when the spec is 75s.
    – Chris H
    Sep 20 at 10:47
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I may get snipped for this, but frankly, most electrical has some level of safety margin built into it. Normally a couple of minutes of over-use won't hurt anything. The wires in the wall won't melt except under EXTREME overloads, connections are much more likely to fail first.

Since the breaker didn't trip, it probably wasn't too much of an over use. The wires / connections might have gotten warm, but since connections are required to be in boxes, you're pretty safe. Still, you did due diligence in checking the outlets.

If the real load was as high as you think it is, I am worried that the breaker didn't trip with that amount of load...something to look into.

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  • Hi George, not sure if important I think this outlet is almost at the end of circuit. The breaker is literally 3 weeks old installed by electrican, old breaker was AFCI and new CAFCI, should I check downstream outlets or if the overloaded outlet connections don’t appear to be melted there is no need ), I’m positive it was 30AMP for sure :(, I think 30AMP was Extreme overload no ?, googling stuff on breakers apparently there is “trip time”
    – NotSoHandy
    Sep 20 at 1:02
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    If the wires in the wall, whether copper or aluminium, 'melt', you'd know, because your house would be burning down. Sep 20 at 9:24
  • @MichaelHarvey It would be the insulation melting or burning off, and even in that case it is quite rare for anything else to ignite. Possible, sure.
    – jpa
    Sep 21 at 8:06
  • @jpa - The OP says 'did I melt wire'. Copper can melt in an overcurrent situation, as any electrical engineer will tell you. Of course, it is unlikely that an ordinary load would draw enough current, even if the company fuse or other protection allowed it. But the conductors could get hot enough to ignite wood, some plastics, and the vapours and gases from the overheated insulation would be toxic. Sep 21 at 8:22
  • @MichaelHarvey I guess we have just different interpretations :) I consider the insulation as part of the wire, and a melted wire to look like this. House not burning down is by no means a good indication of not having damaged cables.
    – jpa
    Sep 21 at 10:58

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