What is not Safe in MagSafe?

We have already mention in the past numerous cases of defective MagSafe PSU, mostly due to auto twisting of the wire, leading to a short-circuit, and in some extreme cases burning and fire ignition. Couple of months ago, Apple published a TechNote explaining how to roll the cable around the unit to prevent any auto-twisting.
However, I personally own 2 MagSafe units, and for one of them the cable is already looking like it is being twisting inside the plastic shield. Last week-end I went to a friend whose MacBook PSU is just looking like it is going to fail apart, with the cable near the lead completely malformed.
Hereafter is an interesting story from Crispy, a hardmac forum member, reporting his experience with MagSafe units, and describing how defective manufacturing could be responsible of failure in some cases.

My second MacBook Pro power supply failed! the first one was replaced under guarantee the second lasted 16 months with lots of care! I asked the Apple tech support guy if it would be better to mistreat the cable and get it replaced under guarantee every 12 months .... he declined to comment!
Well I thought I would take this one apart to see if it could be fixed. I thought it would be complicated as there are 5 pins on the plug. First you have to cut through the moulded plug:

then you have the silicone like gel to remove and finally you find a little PCB.

It turns out to be rather simpler to fix that I thought. True the soldering is tricky but its just 1 power core with the earth shielding split and soldered on both sides of the PCB. I think the cable is broken about 1 cm from the end so I will have to trim it back and refix the connector.
Now All I need is some solder ... the cupboard was empty DOH!
So now its put back together and strapped up with gaffa tape, cheaper than the £59 or $120 it costs for the replacement in the UK.
Good job I didn't try to fix it immediately as the new power supply died after 12 hours! kept blowing fuses!
.......................
My new power supply has arrived and works, and since they didn't ask for the old one back I took it apart to see if I could use the new MagSafe lead.
It’s not easy!
Firstly the whole assembly is glued together so you inflict serious damage on the plastic housing getting in! This alone kind of rules out repairs.

Secondly the innards are all glued up with a white cement so it looks a right mess. It’s so tightly packed in there that there is no access to the end of the MagSafe lead! That’s where I give up! It’s not a serviceable unit!!

I think I will use a junction box to connect the new lead to the old power supply externally.
The cable started to melt next to the MagSafe connection, so I called it a day and dissected the lead!
It revealed that just the shielding had failed not the inner core!
I guess this means that you could fix the lead by taking the plastic sheath off and repair the shielding. If you can get heat shrink tubing over the MagSafe connector you could have a tidy fix.
I didn't take many pictures of the dissection but this pic shows the inner core is ok and the heat causing the cable to melt came from arcing across the failed shielding.


The final fix looks like this.. not the prettiest sight but it works and the bonus is that I have a new MagSafe connector on a double length lead!

So an improper shielding near the MagSafe lead might explain why in some cases the area start twisting, leading to heat release and short circuit. Last but not least, one could ask what is the impact of the magnet on the lifetime of the solder/wire connection of the MagSafe plug. For sure, over my long history with Apple notebook, I have never seen so many cases of defective PSU units. So, is the MagSafe really safe for the user?