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Any forensic skills here? Trying to figure out if this fire hazard is due to crappy adapter plugs or difference in voltage/hertz in Japan.

Got this plug in China (cheaply...) where they use 230V/50hz, and have been using it in Japan where they run 100V/60hz to connect a (sturdy Chinese) extention cord, but yesterday when using an electrical kettle (Japanese so made for 100V/60hz, but pretty high W), then this happened.

I didn't see it so I tried with an identical plug and saw electrical arcs from inside the plug, seemingly between the two connection points of the prong and connecting plate. Does anyone know what happened?

Update: The kettle is 1250W, and the adapter plug lists 10A

enter image description here

...so with the help of the forum the problem was seemingly P/V=I , 1250/100=12.5A, which was just too much for my crappy adapter plug. Thanks!

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    \$\begingroup\$ "high W" on 100V implies very high current. Inspect what's left for a current rating (like 10A) and inspect the kettle for its current rating (like 16A). \$\endgroup\$
    – user16324
    Commented Sep 15, 2016 at 23:48
  • \$\begingroup\$ Hi Brian, thx for your reply, appreciate it. The kettle is 1250W, and the adapter plug lists 10A \$\endgroup\$
    – Antman
    Commented Sep 15, 2016 at 23:54
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    \$\begingroup\$ At a guess, the cheapo Chinese unit is marginal in its original country (230 VAC). The same power at 100 VAC will require 2.3 times the current, and the conductors and contacts are simply inadequate. The get hot and then all sorts of interesting things happen. \$\endgroup\$ Commented Sep 15, 2016 at 23:55
  • \$\begingroup\$ OK that seems like a likely explanation, thank you very much! \$\endgroup\$
    – Antman
    Commented Sep 16, 2016 at 0:05
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    \$\begingroup\$ The lower voltage and different frequency will not be a problem. What you need to look out for is the higher current, which is an indirect consequence of lower voltage. \$\endgroup\$ Commented Mar 29, 2018 at 4:12

3 Answers 3

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There are a few factors here.

  1. Kettles are high power loads, often close to or right at the limit of what the domestic socket standard in the country in question can safely supply
  2. Items bought cheaply in china are likely to be of low quality. Your adapter looks like the "pin" part of the adapter is only connected to the socket part by pressure from the case.
  3. The socket holes on that adapter look to be some kind of multi-standard compromise, accepting a bunch of plug types, but none of them well.

Put it all together and you have a recipe for failure.

Such adapters are sometimes a necessary evil when travelling but I would strongly advise avoiding their use for long term or high current applications.

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It seems you exceeded the rated current with 12.5A on 10A rating which was not shown on your original question. With additional contact force on the receptacle, more current can be transferred with less heat loss at the expense of increased plating wear.

Some Chinese outlet plugs and sockets do not provide the necessary friction fit with tension and possible are too smooth. The result is low contact area and high contact resistance. Instead of <0.05 Ohms it might be > 0.1Ohms and thus heat loss at 12.5A is 15W, which can heat up a small contact area pretty high with no air flow... enough to melt plastic eventually like a soldering iron tip.

Some plugs have a circular hole in each blade in North America to scrape off carbon or oxide each insertion.

Ensure plug and receptacle is rated for appliance in future, because it is the receptacle contact force and contact area that enables higher current.

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Possible that one or more wires was not properly secured inside the housing, leading to a reduced cross section for current flow. I have seen this before on mains power plugs running hot. I opened one up and the wires were loose.

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