Thanks to sar2012 for this one. (from this thread //www.diynot.com/forums/viewtopic.php?p=532142#532142)
How not to connect your cooker:
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Thanks to Taylortwocities for this one. (from this thread //www.diynot.com/forums/viewtopic.php?t=80067)
I found it during a kitchen refurb. The old cabinet had been removed and I found that the mounting screw had gone straight thru the lighting cable behind.
It wasnt the fitter’s fault - the cable went straight down the wall and then turned left for 6” to go into a light switch that some muppet had moved.
Unbelievably the light had worked for 10 years since the cabinet was fitted and nobody got a belt! 
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Thanks to Pensdown for this one. (from this thread //www.diynot.com/forums/viewtopic.php?t=80440)
How not to use a TP isolator for single phase connection
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Thanks to steve1811uk for this one. (from this thread //www.diynot.com/forums/viewtopic.php?p=541965#541965)
Damaged cooker cable, with very poor repair.
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Thanks to turkish for this one. (from this thread //www.diynot.com/forums/viewtopic.php?t=81095)
This I found in the kitchen. They had somehow managed to drill through the metal capping just clipping the cables to secure some worktop. When I got the cable out copper could be seen.
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Thanks to IJWS15 for this one (from this thread //www.diynot.com/forums/viewtopic.php?t=79046)
[This was] installed by a professional (you cannot install these alarms yourself - well known security company!)
Faults:
The obvious white low voltage alarm cable sleeving on the earth wire for the alarm panel!
The live wire to the alarm is connected to the feed supply of the two pole switch, the neutral is connected to the load side. Result - when you turn off the switch all the neutrals on the central heating control circuits are live and this is why I was getting a live at the boiler connection with the switch off. 
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Thanks to Securespark for this one (from this thread //www.diynot.com/forums/viewtopic.php?t=83788)
It’s 1.5 4 core SWA with EC14’s on either end (YUK) and two cores each in L & N, with a 40A breaker. The circuit length is about 10m, with no RCD protection, feeding a detached garage & utility building with several appliances (freezer, washing machines, TD etc). Good, eh? 
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Another one from Securespark (from this thread //www.diynot.com/forums/viewtopic.php?t=86244)
Found this running a washer & dishwasher… 
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One from mdbalson (from this thread //www.diynot.com/forums/viewtopic.php?t=101630&start=15)
I found this joint, buryed in the plaster, the cable with the joint in, goes to the bathroom light
How NOT to Join a Cable 
Close up of the Bad Joint
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Thanks to jimbojones for this one (from this thread //www.diynot.com/forums//viewtopic.php?t=149267)
On the off chance anyone thinks upgrading your wiring isn’t important when you get that all new singing, dancing shower…......... 
Thanks to vera121 for this one (from this thread //www.diynot.com/forums//viewtopic.php?t=185132)
Melted Consumer Unit!!
And another one!