Just before the New Year, Fox News reported that an iPhone 6 Plus allegedly caught fire while it was charging. Now this isn't the first such report that I’ve heard of, but when I looked at the images something struck me - how ratty looking the charging cable was.
Here's a screen grab of the image in question:
Now before you all jump to tell me how bad Apple's cables are, save yourself the typing. I know I use and sell their products.
Once frayed they're potentially dangerous. An iPhone charger puts out 5 volts at 5 watts/1 amp (an iPad charger puts out 12 watts/2.1 amps), and while that doesn't sound like much, it's more than enough power to cause overheating and the beginnings of a fire. On top of that, a frayed cable can also cook the battery by causing a short circuit, which again can result in a fire.
Apple recommends that you charge its devices using genuine Apple chargers and cables. If you're going to replace old charger or cables, do so with either a genuine Apple part or a decent third-party product (preferably one featuring the "Made for iPhone" logo).
I can't comment on whether the cable had anything to do with the fire in the report, but I certainly would not use a cable in that state. I seen cables that have been repaired but that’s usually a temporary solution. The safest thing to do is to replace any damaged cables.