Two or more conductors fastened under a terminal is called "double-tapping".   This method is not allowed, except when the manufacturer has designated it so, and is considered an unsafe wiring method.

Another example of "double-tapping" conductors at the over current device terminal.  The black (positive) and the white (neutral) conductors attached to the copper buss bar extension has no over current protection.

Many years ago the code allowed, or rather, did not specifically disallow, additional appliances to be added with a conductor attached at the top feeder terminals, or "top lugs".   This method is not considered safe by today's standards and should be corrected when encountered.   Another example of "thrill-seeker wiring".

The plastic hole cap is puckered outward and cracked on the fuse holder.   This is an indication of previous overheating of the fuse holder metal parts.   Replacement is required for safety.   The fuse holder's spring metal has lost its temper (ability to hold its shape under normal heating conditions) and will become loose again when heated with sustained, continuous current feeding through the circuit.

If you look closely, you can see that the grounding conductor attached to the grounding rod is a "stranded" aluminum conductor.   Stranded conductors were in use at one time but should be replaced when found for user safety.

The scorched inside cover of the main disconnect enclosure is historical evidence of previous overheating or a lighting strike.   Replacement is recommended.

Close up of the damage from overheating inside fused main disconnect.

Looking closely at the black insulation around the two aluminum, stranded feeder conductors in this breaker panel you can tell that the top lugs and conductors have become overheated.   The insulation is melting off the conductor beginning at the closest point to the lug terminals.   The panel is overloaded for the size of the feeder conductors.   Another electrical contractor oversight.

The "electrician" installing this circuit believed in the immense powers of "electrical" tape to protect the new conductor and prevent any overheating inside the panel enclosure from migrating inside the wood framed structure.   Fortunately, we discovered the incorrect installation and recommended that our client consult with a "licensed" electrical contractor for corrections.

This panel was installed 25 -30 years ago in a laundry room during construction of the home.   Subsequently, one of the owners built cabinets over the panel enclosure making access extremely difficult.

The crimped plastic cover in the center of the photo is a "spliced" ground to the panel.    Grounding conductors should never be spliced.

Holes in the metal panel enclosure should be avoided.   Panels are constructed of "gauged" metal that is resistance to heat.   Opening holes for conductors to pass through defeats the safety aspect of the panel's design.

A close up of a different panel with a similar opening....different house, same problem.   All openings should be filled with a "grommet", made of metal or a clamp designed to secure the conductor and fill the opening.

You can easily see in this photo how the insulation is likely to be damaged on the sharp edge of the knock-out opening.    A wire grommet is badly needed here.

The installer of this new circuit decided it would be better to go in from the lower left side.   Consultation with an electrical contractor recommended here as well.

The owner of this property decided that a new wood deck was more important than proper access to the exterior mounted panel.

You can see in this photo that standing in front of this main disconnect/distribution panel is impossible, especially if the panel door is raised open for viewing.   The NC Electrical Code was not consulted while building the deck.

Photos about panel enclosures just wouldn't be complete without this one.   The house was built around 80 years ago and a new fused switch disconnect was added (you can see 6 enclosures if you look close) each time a new appliance was installed.   The gray enclosure to the far left (the latest, most modern addition) does have a breaker disconnect.  

I included a photo of this "pointed" screw I removed from a panel enclosure dead front cover.   "Pointed" screws are not allowed to be used to secure a dead front cover because the sharp point can tear insulation from a conductor if there is contact when re-installing the cover.   Having had the experience of "shorting" a circuit (you don't want to do that often) while re-installing a pointed screw it has become our practice not to reinstall improper screws if there are enough blunt screws available to hold the cover in place.