# Lightning protection test joint

Canonical URL: https://eloragrid.ai/symbols/lightning-test-joint
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: TJ
Drawing use: GA, Schematic
Reference families: IEC, IEEE / ANSI

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.

### Terms

- 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.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [Building protection system](https://www.electrical-installation.org/enwiki/Building_protection_system)
- [Earthing connections](https://www.electrical-installation.org/enwiki/Earthing_connections)


## 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.

## Important distinction

A lightning test joint separates the down-conductor from its electrode; an earth test link separates the installation MET from its electrode.

## Facts

- Graphic cue: Small box or clamp mark near the base of a down-conductor
- Use: Electrode and continuity testing
- Preview: Original educational illustration; consult the publisher and applicable standard for the exact graphic

## Public references

- [Building protection system](https://www.electrical-installation.org/enwiki/Building_protection_system) — Schneider Electric, Electrical Installation Guide. Public installation-guide description of lightning protection earth leads and down-conductors.
- [Earthing connections](https://www.electrical-installation.org/enwiki/Earthing_connections) — Schneider Electric, Electrical Installation Guide. Public installation-guide earthing elements.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.