Neutral conductor or not 1

[the369apprentice]

I am new to the electrical industry and would like to ask a question that I have posed to many Journeymen electricians without receiving a single coherent answer: what standard, rule, equation, or other method is used to determine if a circuit requires a neutral conductor or not? The most popular answer I receive is that " well, the neutral carries the unbalanced load, and as far as when a circuit needs a neutral or not, if the specs call for it, then it gets one".

 

[DRWeig]

Dude,

The circuit needs a neutral whenever the load has a voltage rating that requires a neutral. Couple examples: In a 208V three-phase system, any 120V loads better have a neutral. 208V loads don't need it, whether they're three-phase or not. Watch out for packaged equipment, though -- might have 208V motors but expects to receive a neutral to power 120V controls.

Make sense? Say so if not, there are lots of folks in the forum better at explaining than me...

Good on ya,

Goober Dave

 

[waross]

"Neutral" is a definition of one conductor in a circuit.
You run the conductors that you need for a load or a circuit. One of those conductors may be defined as a "Neutral".
The basic definition of a neutral has to do with carrying unbalanced currents.
This is an international forum and the definition varies from place to place in the world.
In North America, a single phase, 240 Volt circuit usually does not need a neutral and may not have a neutral. An exception may be a 240 Volt circuit fed from a 240/416 Volt transformer bank.
In the UK a 240 Volt single phase circuit probably will have one of the conductors defined as a neutral. It depends on what or which unbalanced current is referred to in the definition.
The UK definition is based on three phase utilization circuits. The NA definition may be based on either single phase or three phase utilization.
Don't fight the definition.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rbulsara]

Firstly, look up the explanation of a neutral in electrical code book such as NEC.

If the voltage rating of the equipment the circuit is feeding matches the voltage between neutral and line of the source, the circuit needs a neutral.

Supposing the source is a 208Y/120V panel board. Then 120V, 2 wire loads will require a neutral. 208/120V single phase, 3-wire load such as a cooking range will need a neutral. But a 208V, single phase AC unit will not nor would a 3 phase 208V motor.

It is also true that the installation instruction of a particular appliance/equipment will spell out what type of connection is required, usually tailored to conutries they are intended to be used in.

As waross said, depending on the voltage system you have in different places, whether one of the used conductors is a "neural" varies.

 

[MagneticFlux]

"what standard, rule, equation, or other method is used to determine if a circuit requires a neutral conductor or not?"

The need for a Neutral conductor is determined by the load. It is not something determined on the job site.

I am not sure if you are asking specifically about feeders or branch circuits so i will briefly explain both.

First, definitions:

Feeder Circuit: Are conductors between two OCPD
Branch Circuit: Are conductors between a OCPD and the load

A neutral conductor is installed in a feeder circuit because it is not possible to perfectly balance the loads of a distribution system.

A neutral conductors is installed in a branch circuit because it is required, by design, by the load.

There are equations to determine the amount of Neutral current in single and three phase systems. They are in your reading material (specifically in your Delmars Handbook).

Feel free to contact me if I can be of any more help...

In Solidarity,

L-481