1. What Is Equipotential Bonding? (Principle)
Equipotential bonding = connectingall metal pipes, structural rebar, and equipment enclosureswithin a building to the same potential reference point (the equipotential bonding terminal box) with conductors, eliminating potential differences. With no potential difference, there is no electric shock — even with leakage current, no current loop forms through the human body.
2. MEB (Main Equipotential Bonding Terminal Box) (Building Entry)
The MEB is installed at thepower supply incoming point(such as the electrical room or floor distribution room), and connects:
| What it bonds | Conductor Size |
|---|---|
| Power supply incoming PE bar | Copper bar ≥ 25×4mm |
| Water/gas/heating pipes | Copper wire ≥ 6mm² |
| Building structural rebar | Copper wire ≥ 6mm² |
| Grounding electrode | Copper wire ≥ 25mm² or copper bar |
3. LEB (Local Equipotential Bonding Terminal Box) (Bathroom/Equipment Room)
The LEB is installed inbathrooms, shower rooms, swimming pools, hospital operating roomsIn damp or special locations, bond the metal pipes, rebar and equipment enclosures in that area to the LEB terminal box, then connect it to the MEB. The LEB terminal block is typicallycopper busbar, with 4–8 terminals.
4. LEB wiring examples (bathroom)
Bathroom LEB terminal box (flush-mounted, 250×180×80mm) wiring:
① Run the PE conductor from the floor PE bar to the LEB;
② Bond the water pipes (hot/cold) to the LEB with BVR-6mm² yellow-green conductor;
③ Bond the metal floor drain / metal fittings in the shower area to the LEB;
④ Bond the local structural rebar in the bathroom to the LEB;
⑤ Connect the LEB to the MEB with BVR-16mm² .
5. Common equipotential bonding errors (3 red lines)
- LEB not connected to the PE conductor→ the equipotential bonding terminal box is not continuous with the PE bar → no protective function.
- Water pipe joints overlooked→ when a water pipe becomes live, a potential difference exists between the pipe and the equipment → shock hazard remains.
- Conductor cross-section too small→ using 1.5mm² instead of 6mm² → fault current may burn through the conductor.
FAQ FAQ
What is the difference between MEB and LEB?
MEB ismain equipotential bonding(at the building entrance, bonding all main pipes and rebar); LEB islocal equipotential bonding(for local areas such as bathrooms or equipment rooms, bonding local pipes and equipment). The LEB is connected to the MEB.
Must the equipotential bonding terminal box be connected to the PE conductor?
Yes, it is required. The LEB terminal box must be continuous with the PE bar, otherwise the equipotential bonding provides no protection.
Where is the bathroom LEB box installed?
Flush-mounted in the bathroom wall,0.3–0.5 m above floor, for easy access without getting in the way. It must not be installed where the shower sprays directly onto it.
What is the conductor cross-section for equipotential bonding?
LEB to pipe/equipment ≥ 6mm²; LEB to MEB ≥ 16mm²; MEB to grounding electrode ≥ 25mm².
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