Terminology and abbreviations

PE and the earthing symbol
Terminology and abbreviations 1:

PE is the abbreviation for "protective earth" and has the same meaning as the earthing symbol
Terminology and abbreviations 2:

Earth, ground

This document uses the term “earth” which is the same as the U.S. term “ground”.

t.b.d.

Still to be defined, value or description will follow in due course.

DC 48 V

A figure displayed with the AC or DC before the value represents a nominal voltage with standard tolerances included.

Example:
DC 12 V refers to a 12 V battery, regardless of whether it is fully charged (13.7 Vdc) or discharged (10 Vdc).

48 Vdc

A value followed by the unit Vac or Vdc is an instantaneous value that does not contain any additional tolerances.

may

A keyword indicating a choice without implied preference.

shall

A keyword indicating a mandatory requirement.

should

A keyword indicating a choice with a clearly preferred method of implementation.