DIfference between single line & schematic drawing?

ckchew666

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Aug 2003
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Hi,

I've come across this 2 terms frequently, but what's the difference between single line & schematic drawing?

Referring to attachment, are they consider single line or schematic?

Drawing1


Drawing2


Drawing3



Thanks...
 
To me they are all schematics. A One Line drawing is ussually used in power distribution drawings, where it is understood that the single line represents a 3 phase power system.
 
Maverick said:
To me they are all schematics. A One Line drawing is ussually used in power distribution drawings, where it is understood that the single line represents a 3 phase power system.

They are of sorts, but a true schematic drawing is detailed to the point of showing all the required connection points to complete a circuit. As you said, the one line drawing is used mostly in power distribution and is not intended to show connections as much as the general layout of a power circuit.
These two definitions are for schematic:
Of, relating to, or in the form of a scheme or diagram.
A structural or procedural diagram, especially of an electrical or mechanical system.
 
We use 'Single Line' to describe drawings that show cables and connection or junction boxes. They have cable ID, wire ID and junction box ID. They do not show terminations. They are divided into power, instrumentation and control. They act as a road map to follow how the plant is wired.
We use 'Schematic' to describe drawings that show how a specific unit is wired including power, control and instrumentation on one drawing. Often these drawings are vendor supplied.

Hope this helps,
Brian.

Oh to answer your question, I agree that you would call your drawings schematics from the thumbnail pics.
 
Schematic

I think of a schematic as a drawing that lets you see how the circuit works. A wiring diagram will show you exactly how the circuit is wired. For example the wiring on the load side of contacts CR4-2 and CR5-2 can accomplished many ways, but the schematic doesn't show the details. A one-line is for power distribution.
 
Thx for all the replies, another relevant question, I'm working on the PLC programming side, thus I'll create the IO list (which PLC IO points are wired to which devices in an excel table format), another department is doing the wiring & panels.

Who's the correct party to come out with the schematic & single line drawings?
 
In general, as stated above, all are schematics, as are Process and Instrumentation diagrams and flow charts. Schematics show iterconnections and relationships of elements without trying to show the physical for of objects or the precise physical placement of them.

To me a one-line diagram is generally used for three phase power distribution. However, I have seen a trend lately of using a "one-line" diagram to show instruments and panels with connections, but not necessarily showing all of the wiring between them. In some cases the single line between a motor, for example, and a panel, may include the callout of the number and type of connductors. For example, a motor starter to control panel line may include the callout "4-#12 AWG THHN" to indicate the control wiring to the starter for line, neutral, run command, and run status.

The typical schematic, often referred to as an elementary diagram or ladder diagram, shows all of the electrical connections inside and outside the panels and can be used by the panel builder and installing electrician to understand not only the number of wires, but also their function and to illustrate the way the circuit functions.
 
All of your examples are schematics.

There is no hard and fast rule that determines the how/what/why of a one-line drawing. The basic concept behind a "one-line drawing" is "minimalism". That is, using one-line to represent many lines.

A true "one-line drawing" is used to provide a general indication of the relationship between the various aspects or components of a process or system.

If you have a physical module sitting "here", and another physical module sitting "there", and let's say there are 100 wires between the two modules... you can present the information in a few different ways...

TYPE-1:
You can draw each wire between the two modules, indicating the identity of the wire and the appropriate connection point on each of the modules. That would be a full blown, wire/connection, schematic... at least in terms of the connections between the two modules. It might, or might not, provide the internal circuitry in the modules.

TYPE-2:
You can make a drawing that identifies each wire and connection point at the connector of one module, then compress ALL of those individual lines into one single line. It would look as if all of the individual conductors were all part of a single cable... which might, or might not, be true. You then carry that one-line to the destination. At the destination, you break-out all of the individual conductors, show their identities and connection points.

Along the way, other "one-lines" might join, or leave, the original one-line. In automotive wiring, this would be representative of a wiring harness. The content of those "one-lines" joining or leaving is not known at that point. You would have to follow the "joiner" back to its' source to determine the content. You would have to follow the "leaver" to its' destination to determine its' content.

That technique helps to keep the "clutter-factor" down. There is a great advantage in having the appropriate amount of "white-space" in a schematic, a drawing, text, whatever. It simply makes it easier to read. Type-2 is not a classical "one-line drawing".

TYPE-3:
Then there is the true "one-line drawing". While it is conceptually helpful, in general, it is technically useless. These are generally used to provide a general description of the concept. It could be used in terms of hardware, software, or...

In the case of a true "one-line drawing", there would be a single line between the modules indicating only that there is a connection of some sort between the two modules. This is the kind of drawing that someone would bang out on a napkin while having a beer at the bar... very few details, if any, only the general indication of a connection.

As in Type-2, along the way, other "one-lines" might join, or leave, the original one-line. However, in this case, the content of the "joiners" and "leavers" is simply not known. All you know is that there is a connection of some sort that involves other modules.

Power Distribution Drawings generally fall under Type-2.
Detailed cable connections fall under Type-1 or Type-2.
General cable connections fall under Type-3.
Modern automobile electrical schematics show up in all three types.
 
"Who's the correct party to come out with the schematic & single line drawings?"

I do ALL of the drawings... I/O listing, schematics, component layout (inside and outside the panel), wire-routing (inside and outside the panel), field-device locations, the operator's manual, the technical manuals for troubleshooting, detailed descriptions of how each part of the process is controlled and... ?

I use one-line drawings only for the highest level of conceptual description. They are generally not helpful when it comes time to turn a wrench or screwdriver.
 

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