DC
Lightning protection down-conductor
The conductor carrying lightning current from air terminations on a structure down to the earth termination system.
GA / Schematic
Symbols · TJ
Lightning protection test joint
A disconnectable joint near the base of a down-conductor that allows the earth termination to be tested separately.
In plain English
What does Lightning protection test joint mean?
Each down-conductor usually has a test joint at a convenient height above ground. Opening it separates the above-ground lightning conductor from the earth electrode, so electrode resistance and conductor continuity can be measured. Elevations show it as a small box or clamp mark on the down-conductor.
A simple example
The test joint is not an isolating device for electrical work; it is only opened for inspection with no storm risk. The symbol does not specify clamp type or whether it is housed in a box. Missing or painted-over test joints are a common inspection finding.
What the drawings help you do
Locate the test joint on each down-conductor. Confirm it is reachable for inspection. A lightning test joint separates the down-conductor from its electrode; an earth test link separates the installation MET from its electrode.
This particular reference
A disconnectable joint near the base of a down-conductor that allows the earth termination to be tested separately. A lightning test joint separates the down-conductor from its electrode; an earth test link separates the installation MET from its electrode.
- Normally open / normally closed
- The contact state in the normal condition defined for the drawing.
- Schematic
- A drawing showing function and connections rather than physical appearance.
Read the source: Building protection system · Earthing connections
GA / Schematic · TJ
What it represents
Each down-conductor usually has a test joint at a convenient height above ground. Opening it separates the above-ground lightning conductor from the earth electrode, so electrode resistance and conductor continuity can be measured. Elevations show it as a small box or clamp mark on the down-conductor.
The test joint is not an isolating device for electrical work; it is only opened for inspection with no storm risk. The symbol does not specify clamp type or whether it is housed in a box. Missing or painted-over test joints are a common inspection finding.
How to read it
- Locate the test joint on each down-conductor.
- Confirm it is reachable for inspection.
Information to show or reference
- Show a test joint on every down-conductor.
- State mounting height.
- Number joints to match inspection records.
A distinction that matters
A lightning test joint separates the down-conductor from its electrode; an earth test link separates the installation MET from its electrode.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Building protection system
Public installation-guide description of lightning protection earth leads and down-conductors.
Earthing connections
Public installation-guide earthing elements.
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.
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