Key:circuits
 circuits
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Number of electrical circuits in a power section, line or cable.  
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| Group: power |
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| Useful combination |
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| Status: in use |
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Use circuits=* to note the number of electrical circuits (601-02-28) of any power section, line or cable. The tag was primarily intended for underground cable connections where the number of physical cables is unknown or has no simple relationship with the number of circuits and is now used on any section or segment.
Background
In power transmission, a circuit (as defined in Electropedia 601-02-28) consists of required conductors to allow current to flow from a power source to the load and back to the source. Think of a battery and a load such as a light bulb connected by two wires. Current will physically flow from the battery to the load via the negative wire and return to the battery via the positive wire. For three-phase AC power transmission things are slightly more complex as three different AC currents flow in the three conductors forming a circuit. The currents flowing in the three phase conductors will tend to cancel out one another and unless there is an additional neutral conductor the net current will be zero.
One-phase AC transmission systems are also known. One example is traction power systems for railways using two-conductor one-phase transmissions. Sometimes one-phase systems require just one metallic conductor by using earth as the return conductor. Examples are Single Wire Earth Return systems used in some rural areas and monopole HVDC connections using earth or seawater as the return path.
How to map
Add this property to a power segment power=line, power=minor_line, power=cable or power=line_section.
You may try to deduce the appropriate number of circuits from cables=* but this may lead to mistakes.
See the open discussion on Talk.
Beside describing the amount of circuits on power segments, you may also model each individual circuit with power=circuit relation. You will find more information about power routing on this tag's page.
These relations don't replace circuits=* and both are valid.
When to use
Note that this tag should not replace the cables=* tag.
The circuits=* tag should be used in the following situations.
- Underground or underwater cable sections (
power=cable). Even ifcables=*is still relevant to describe physical layer, it may be useless for calculating the number of circuits here since the number of physical cables per circuit varies (typically 1, 3 or 6 independent cables per circuit). The amount of cables can be seen at section extremities when it comes overground and be unknown to mappers once underground/underwater. - Overhead power lines (
power=lineorpower=minor_line) in the following situations:- The physical line supports several circuits (whatever how many cables compose a single circuit)
- Several apparent circuits (2 * 3 cables for instance on a continental three-phases network) are operated as one effective circuit. This means that the several apparent circuits are wired in parallel and connected to a single bay in the substation.
Historically, the wiki said that, when circuits=* is not mapped, it could be calculated from cables=*. This is no longer recommended. Mappers are encouraged to add circuits=* wherever known, and data users should not make assumptions when it is not mapped.
How do you know the number of circuits?
The amount of cables can be seen at section extremities when it comes overground and be unknown to mappers once underground/underwater.
When a link between two substations is entirely underground the data may sometimes be available in public information from the grid operator. However, always verify that such information is available under a license that is compatible with the ODbL license before using it!
Example
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1014083928  1014083928
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power=linevoltage=150000circuits=2cables=6
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Power line transition to underground cable section. The overhead line clearly appears to support 2 circuits.
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