[300.13(A)]. Generally, you can't leave a splice in a raceway. But
there are a few exceptions, such as 300.15. Even where permitted, it's best not
to do it simply from an engineering and maintenance standpoint.
[300.13(B)]. The pigtail. You can't let the terminals of a device
become a means of disconnecting the neutral. In all other types of circuits,
pigtailing isn't required but it's a good practice. If you always pigtail the
neutral, then you never disconnect it by simply removing a device from the
[300.16]. This is a common point of misunderstanding. The rule exists to allow
an electrician to be able to work with the wiring. There are actually 2 minimum
lengths. Normally, you must leave at least 6 inches of wire from the point where
the wire enters the box. If the box is less than 8 inches in any dimension, each
conductor must be long enough to stick out of the box with 3 inches left over.
How much is too long? The NEC does not say. You can always cut a wire twice to
make it shorter, but you can't cut it twice to make it longer. If in doubt,
leave it (hanging) out.
[300.18)B)]. Generally, no. And if your boss finds out you've been wasting time
this way, you'll probably be fired. However, there are special circumstances in
which welding is permitted by the NEC and is actually appropriate in all other
concerns. These are covered in application-specific Articles.
[Table 300.19]. Yes. Use this table to sort out what's what.