How Terminal Blocks Work: Current Paths and Contact Pressure
Antong product selection reference · Updated 2 November 2026
A terminal block works by combining a conductive path with a controlled mechanical contact. The metal connects the intended conductors; the clamp maintains their contact; the housing supports the assembly and separates it from other circuits. Each part solves a different problem.
Trace a complete electrical path
| Sequence in a basic through terminal | Function |
|---|---|
| Wire A → contact interface A | Current enters the terminal through the clamped wire surface. |
| Conductive insert or bar | Current travels across the terminal. |
| Contact interface B → wire B | Current leaves through the other clamped conductor. |
The mounting support is not normally part of this through-current path. A protective-earth terminal specifically designed to bond to a rail is a different arrangement and needs the corresponding product and installation instructions.
Why touching metal is not enough
Two metal surfaces touch at many small points rather than over a perfectly continuous plane. Contact pressure helps establish and retain an effective conducting interface. Loose insertion may look connected while providing an unstable electrical joint.
The heat generated in a resistance is P = I²R. In an illustrative calculation, 10 A through a 0.01 Ω resistance produces 1 W. At 20 A, the same resistance produces 4 W. These are arithmetic examples, not acceptable resistance limits for a terminal. They show why a poor contact becomes more consequential as load increases.
How different clamps apply force
| Mechanism | How the conductor is held | Installation variable |
|---|---|---|
| Screw clamp | A threaded fastener loads the conductor directly or through a clamping element. | The specified torque, wire preparation and permitted conductor arrangement. |
| Spring cage | A spring closes on the conductor after the operator opens it for insertion. | Correct opening, full insertion and release of the operating tool. |
| Direct push-in | A permitted conductor operates the entry and is retained by the connection mechanism. | The exact accepted conductor type and insertion procedure. |
Mechanism names do not prove a universal vibration performance or eliminate all inspection. Product-specific designs can differ substantially. Antong SP002 illustrates another distinction: its wire-protection spring is part of a screw-operated assembly, not a statement that the product uses direct push-in termination.
The housing keeps connections separate
The insulating body positions the conductive parts and helps maintain separation between neighboring circuits. The distance through air is called clearance; the path along an insulating surface is called creepage. The relevant requirements depend on the product and application conditions.
Damage, contamination or an unintended loose wire strand can defeat the intended arrangement. A mounting method that distorts the body can also change how the connection behaves. Correct ratings therefore depend on installing the complete product as specified.
Read symptoms as clues, not a single diagnosis
| Observation | Questions to investigate |
|---|---|
| Localized discoloration or heating | Is the load correct? Was the conductor fully inserted and prepared correctly? Is the contact damaged? |
| Wire pulls out unexpectedly | Was the wire size and construction permitted? Was the clamp operated correctly? |
| Intermittent continuity | Is the conductor secured? Is a mating interface fully engaged? Is the wire itself damaged? |
| Cracked housing | Was the support aligned? Was the fastener or conductor forced beyond the intended arrangement? |
Inspect only using the equipment’s safe isolation procedure. Repeatedly tightening a damaged joint is not a substitute for identifying the cause and replacing an unsuitable component.
From mechanism to product selection
Antong SP014/SP015 lists separate conductor configurations, ratings and dimensions for its models. Select those values together with the installation instructions; understanding the general mechanism does not supply a missing torque or strip length.
For exact product comparisons, continue to screw terminal blocks or screw versus spring versus push-in. For the circuit layout distinction, see feed-through and distribution connections.
Product references
Model values above come from the linked Antong product pages. Confirm the ordered version and installation instructions before final selection.