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Wire crossover symbols for circuit diagrams. The CAD symbol for insulated crossing wires is the same as the older, non-CAD symbol for non-insulated crossing wires. To avoid confusion, the wire "jump" (semi-circle) symbol for insulated wires in non-CAD schematics is recommended (as opposed to using the CAD-style symbol for no connection), so as to avoid confusion with the original, older style ...
Safety regulations of the utility must prevent any attempt to open the disconnector while it supplies a circuit. Standards in some countries for safety may require either local motor isolators or lockable handles (which can be padlocked). IEC standard 62271-102 defines the functionality and features of a disconnector.
These pieces of glass were positioned on a tapered wooden pin, vertically extending upwards from the pole's crossarm (commonly only two insulators to a pole and maybe one on top of the pole itself). Natural contraction and expansion of the wires tied to these "threadless insulators" resulted in insulators unseating from their pins, requiring ...
Reference should be made to codes and standards. For example, IEC 60027, and Letter Symbols in Electrical Technology. Here are tables of widely accepted symbols. They are meant to be a guideline: Using the same symbols for the same things in different articles will increase their consistency, making them easier to understand and to improve.
Form A [4] Single pole, single throw, normally open A simple on-off switch. The two terminals are normally disconnected (open) and are closed when the switch is activated. An example is a pushbutton switch. SPST-NC Form B [4] Single pole, single throw, normally closed A simple on-off switch.
In the US, where split-phase supplies are common, in a branch circuit with more than one live conductor, each live conductor must be protected by a breaker pole. To ensure that all live conductors are interrupted when any pole trips, a common-trip set of breakers must be used. These may either contain two or three tripping mechanisms within one ...
A three or four-pole isolator or circuit breaker is used for three-phase loads, for devices with both permanent and switched supplies (such as bathroom extractor fans) and also at the distribution board to isolate all the phases. A three-phase installation with a TT earthing system is an example where four-pole devices would be required.
A pin insulator is a device that isolates a wire from a physical support such as a pin (a wooden or metal dowel of about 3 cm diameter with screw threads) on a telegraph or utility pole. It is a formed, single layer shape that is made out of a non-conducting material, usually porcelain or glass. It is thought to be the earliest developed ...