Single Line Drawing Guidelines

Overall plant single line diagrams show the electrical power distribution system, in simplified form, from the utility and/or generated supply to the load side of substation protection devices. Exceptions include substations 600 volts and over.

The size of the power system determines the number of drawings required.Generally, the overall plant single line diagrams do not include breakdowns of distribution panels, motor control centers, motors or similar electrical equipment located on the load side of the substation.

Single line diagrams, be it for a project or overall power system, show the electrical power distribution and utilization for a particular project, local plant area.

These diagrams are the continuation of overall plant single line diagrams and indicate the power distribution from the load side of the substation protective device to the final point of utilization on a branch circuit.

Project single line diagrams include:

1) Devices which consume, convert, or control power.
2) Power handling and utilization devices (the control circuits for these devices are referenced and shown on elementary drawings)
3) Electrical power distribution beginning at the power source of electrical construction and ending with the last power utilization device

Plant Single Line Diagram

This drawing shall show the overall power system from the utility to the distribution equipment.Single Line drawings include Overall Power Single Line(s), Medium Voltage Switchgear Single Lines, Unit Substation Single Lines, MCC Single Lines and PDP Single Lines.

Overall Power Single Lines show the electrical power distribution system, in simplified form, from the utility and generated supply to the utilization equipment. The size of the power system determines the number of drawings required.

Single Lines for individual items, such as Medium Voltage Switchgear, Unit Substation, MCCs and PDPs, should contain
more detail.Provide “to” and “from” references to allow easy access to upstream or downstream drawings.Single Line drawings should be closely coordinated with the Raceway Plans that are created for construction and installation

In general, Single Lines should be the controlling document and should show all pertinent equipment/component size, type, enclosure type and material type information.

The plant single line drawings should show electrical power flow beginning with details of the utility supply and/or generating facility and terminating with the last major distribution point (if substation) as follows:

1) Power Source (Utility, or generating facility)

i. Voltage, phase frequency

ii. Conductor type, size and quantity

iii. Raceway type & size

iv. Available short circuit current at source

v. Generator and/or utility transformer

vi. Generator reactance and/or utility transformer impedance including X/R data

vii. Grounding including neutral resistor rating

viii. Protective relaying

2) Power Distribution Equipment

i. Main bus rating (amperes, phase and MVA capacity)

ii. Bus bracing

iii. Available short circuit current at main bus

iv. Feeder and sub-feeder protective device continuous rating. Include trip setting for low voltage breakers.

v. Fuse and/or breaker type (i.e. RK-5 fuse)

vi. Protective relaying

vii. For potential transformers, indicate the primary and secondary voltages

viii. For current transformer, indicate CT ratio

ix. Include the shop order number for the equipment.

3) Transformers

i. Type (e.g., cast coil, silicone filled)

ii. KVA ratings, including those based upon insulation temperatures and fan-cooled ratings

iii. Impedance and X/R ratio

iv. Primary voltage, secondary voltage and winding configuration

4) Feeder Circuit Wiring

i. Conductor type, size, quantity, number per phase, length, magnetic or non-magnetic

ii. Raceway type and size

iii. Ground wire size

5) Short Circuit Information

Short circuit information should be displayed on distribution equipment, all substation secondary buses and the utility supply.


Lemau is Owner of .Involved in Electrical & Automation Engineering since 2001. Passionate to shared all experience & knowledge about Electrical.

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