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Public-images-osm logo.svg voltage:tertiary
Voltage of a transformer interface which delivers power to small loads or auxiliary services Edit this description in the wiki page. Edit this description in the data item.
Group: power
Used on these elements
may be used on nodesshould not be used on waysshould not be used on areasshould not be used on relations (except multipolygon relations)


Useful combination
Status: approvedPage for proposal

A transformer is a power device and it has got different interfaces that can be documented separately.
See dedicated documentation about those interfaces.
Some configurations may be complex, see windings=* also for more information.

The tertiary voltage is the voltage bound to the tertiary interface of a power transformer, that outputs the power to small (local) loads.
It may correspond to (auxiliary winding) when feeding auxiliary services of local power grid facilities.
It's a constant design convention we intend to describe here. As of today, power can actually flow in every direction connected to a power transformer depending on power grid operational status OSM isn't aware of and then won't change tertiary side established during mapping.

How to find the value

For every transformer=*
Tertiary voltage is lower than minimum of voltage:primary=* and voltage:secondary=*.
It usually has a limited rating than primary and secondary interfaces.

It doesn't matter of the purpose of the transformer, in a power plant or not.