What Is an Earth Terminal Block? Types and Selection Criteria
An earth (ground) terminal block is a yellow-green DIN rail terminal block that connects the protective conductor (PE) to the mounting rail through its metal foot.
An earth terminal block is a DIN rail terminal block with a yellow-green housing that electrically connects the protective conductor (PE) to the mounting rail through its metal foot; it is also called a ground or PE terminal block. In control and distribution panels it terminates the protective conductors of field cables in the same terminal row, next to the phase and neutral terminal blocks.
Types of protective conductor connections in a panel
| Product | Design | Use |
|---|---|---|
| Earth terminal block | Single-conductor block that sits on the rail, with a foot in contact with the rail | Terminating each cable's PE conductor next to its own phase and neutral blocks |
| Panel earth terminal block | Multi-hole busbar | Collecting the PE conductors in the panel at one point |
| Screw connection DIN rail terminal block | Feed-through block with an insulating foot | Phase and neutral conductors; no electrical contact with the rail |
Selection criteria
- Protective conductor cross-section: Choose the block by the cross-section of the PE conductor to be connected. The Onka MTK series is available in 2.5, 4, 6, 10, 16, 25 and 35 mm². How the PE cross-section is determined is in the FAQ.
- Match with the terminal row: The housing height and width should match the phase and neutral blocks on the same rail; prefer the same manufacturer's series so that markers, jumpers and covers can be shared. At 35 mm², the standard and tall housings are separate products.
- Rail and contact: The metal foot of the block makes the PE connection through the rail. Check the suitable rail type in the datasheet; mounting rail dimensions are defined in IEC 60715.
- Connection technique: The MTK series has screw connections. Tighten the screw to the torque in the datasheet; check in the datasheet whether a ferrule is needed for stranded conductor.
- Voltage: The series is rated 750 V; it is sold per piece.
Common mistakes
- Not connecting the rail to the protective conductor: The earth terminal block only connects the conductor to the rail. If the rail is not separately connected to the panel's PE busbar or panel earth terminal block, there is no protection.
- Mounting on a dirty or oxidised rail: The metal contact between foot and rail is weakened.
- Taking a green feed-through block for a PE block: Housing color alone does not show the function; the foot of a feed-through block is insulating and does not contact the rail.
- Choosing a block with too small a cross-section: In a fault, the PE conductor and its block carry the fault current; the block should not be smaller than the conductor's cross-section.
Related standards
- IEC 60947-7-2: Protective conductor terminal blocks for copper conductors; the standard for this product group.
- IEC 60364-5-54: Earthing arrangements and protective conductors; sizing the PE conductor.
- IEC 60445: Identification of conductors; yellow-green is for the protective conductor only.
Earth terminal blocks in the catalog
Welibaba has 8 active earth terminal blocks; all are Onka MTK series, yellow-green and 750 V:
| Cross-section | SKU |
|---|---|
| 2.5 mm² | `1010219` |
| 4 mm² | `1010220` |
| 6 mm² | `1010541` |
| 10 mm² | `1010221` |
| 16 mm² | `1010532` |
| 25 mm² (ferrule-less) | `1010223` |
| 35 mm² | `1010533` |
| 35 mm² tall type | `1010225` |
Frequently asked questions
What is the difference between an earth terminal block and a panel earth terminal block?
An earth terminal block is lined up on the rail and earths a single PE conductor through the rail. A panel earth terminal block is a multi-hole busbar that collects all the protective conductors in the panel at one point.
What cross-section should an earth terminal block have?
The block is chosen by the cross-section of the PE conductor. Under IEC 60364-5-54, a PE conductor of the same material as the phase is equal to the phase cross-section up to 16 mm², 16 mm² for phases between 16 and 35 mm², and half the phase cross-section above 35 mm².
Does an earth terminal block earth the rail?
No, it connects the conductor to the rail. The rail itself must be separately connected to the panel's protective conductor system.
Can an ordinary green terminal block be used for earthing?
It should not. A feed-through block does not contact the rail and has not been tested as a protective conductor block; for PE, use a yellow-green earth terminal block covered by IEC 60947-7-2.