I HIGH
Maximum-current monitoring relay
A maximum-current relay changes its output when the measured current meets a configured high-current condition.
SLD / Schematic
Symbols · K
Reverse-current measuring relay
Measuring relay that operates when current flows in the opposite direction to normal, such as back-feed into a DC source.
In plain English
What does Reverse-current measuring relay mean?
A reverse-current relay compares the direction of current with a reference and operates when current flows the wrong way. Classic uses are DC generators and battery chargers in parallel, where a failed source would otherwise draw current from the bus, and rectifier feeders where back-feed indicates a fault.
A simple example
On the schematic the relay box carries a current quantity with a direction additional drawing mark, and its contacts are drawn elsewhere in the trip or alarm circuit. The box does not show the pick-up level or time delay, and in AC systems the equivalent requirement is usually met with a directional power function rather than a simple current-direction element.
What the drawings help you do
Identify which direction is treated as normal for the source. Find the contacts that trip or disconnect the source. A reverse-current relay responds to current direction; a maximum-current relay responds to magnitude regardless of direction.
This particular reference
Measuring relay that operates when current flows in the opposite direction to normal, such as back-feed into a DC source. A reverse-current relay responds to current direction; a maximum-current relay responds to magnitude regardless of direction.
- DC
- Direct current: electricity flowing in one direction.
- AC
- Alternating current: electricity whose direction changes periodically.
- Normally open / normally closed
- The contact state in the normal condition defined for the drawing.
Read the source: AutoCAD Electrical: Current monitoring relays · IEC graphical symbols for diagrams
Schematic / SLD · K
What it represents
A reverse-current relay compares the direction of current with a reference and operates when current flows the wrong way. Classic uses are DC generators and battery chargers in parallel, where a failed source would otherwise draw current from the bus, and rectifier feeders where back-feed indicates a fault.
On the schematic the relay box carries a current quantity with a direction qualifier, and its contacts are drawn elsewhere in the trip or alarm circuit. The box does not show the pick-up level or time delay, and in AC systems the equivalent requirement is usually met with a directional power function rather than a simple current-direction element.
How to read it
- Identify which direction is treated as normal for the source.
- Find the contacts that trip or disconnect the source.
Information to show or reference
- State normal current direction
- Give pick-up and delay
- Reference the trip contact
A distinction that matters
A reverse-current relay responds to current direction; a maximum-current relay responds to magnitude regardless of direction.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
AutoCAD Electrical: Current monitoring relays
Public AutoCAD Electrical relay listing that names the Come Back Current Protection block; the illustration is independently drawn.
IEC graphical symbols for diagrams
IEC context for graphical symbols used in diagrams; no IEC graphic is reproduced.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
Explore related references
Put the reference into a drawing workflow.
Elora Grid helps electrical teams work with drawings, specifications and equipment information. Explore the drafting workflow or join the early-access waitlist.