Contactors & Relays for EV Charging Explained
Contactors & Relays for EV Charging Explained
In a custom-built or component-level EV charge point, the contactor is what physically makes and breaks the power connection to the vehicle once the EPC has verified it's safe to charge. It's a mechanically simple part, but getting the pole count and rating wrong is a common mistake for anyone building their own EVSE — this page covers what you need to know.
2-pole vs 4-pole: which do you need?
| Type | Switches | Used for |
|---|---|---|
| 2-pole (2P) | Live and neutral | Single-phase EV charge points (most UK domestic installs, up to 7.4kW) |
| 4-pole (4P) | All three phases plus neutral | 3-phase EV charge points (11kW–22kW), or single-phase builds where full isolation of all conductors is preferred |
A 4-pole contactor can usually be wired for a single-phase application too (using 2 of the 4 poles), which is why some installers standardise on 4-pole across single and 3-phase builds — check the specific contactor's datasheet to confirm.
Normally open (NO) vs normally closed (NC)
| Type | Default state (coil de-energised) | Used for |
|---|---|---|
| Normally open (NO) | Circuit is open — no power flows until the coil is energised and pulls the contacts closed | The standard configuration for EV charger main power contactors. The vehicle only gets power when the EPC actively closes the contactor, which is the safe default state. |
| Normally closed (NC) | Circuit is closed — power flows by default, and energising the coil opens the contacts | Interlock and safety-cutout circuits, where a fault or loss of control power should immediately break a different circuit. Rarely used for the main charging contacts themselves. |
Almost every contactor used for the main switching circuit in an EV charge point is normally open (NO) — this is a deliberate fail-safe design. If control power is lost, or the EPC isn't actively signalling "safe to charge," the contactor drops out and power is cut. Some contactors are supplied with a mix of NO and NC auxiliary contacts for status signalling and interlocks alongside the main NO power contacts.
AC vs DC contactors
| Type | Switches | Used for |
|---|---|---|
| AC contactor | Alternating current — the coil is typically AC (e.g. 230V AC) and the main contacts are rated for AC switching | Standard AC EV charge points (all Type 2 home and commercial chargers). This covers the WCED, Chint and Doepke contactors on this page. |
| DC contactor | Direct current — used where DC power itself is being switched, not just a DC control coil | DC fast chargers, solar PV systems, and battery storage circuits, where switching DC current requires contacts designed to handle DC arcing characteristics |
This distinction trips people up because a contactor can have a DC-rated coil while still switching an AC load — the coil voltage and the switched current type are separate things. For standard AC home and commercial EV charge points (which is what this page covers), you need an AC-rated contactor with contacts sized for AC-1 or AC-3 duty. DC contactors are a different, higher-spec component used for DC fast-charging infrastructure or solar/battery DC switching — they're not interchangeable with AC contactors, because switching DC current causes a sustained arc that AC contacts aren't designed to break safely.
Matching contactor rating to charger power
Contactor current ratings (25A, 40A, 63A, 100A) should be sized with headroom above your circuit's design current — not matched exactly to it — in line with the protective device (MCB/RCBO) and cable sizing for the circuit under BS 7671. As a general reference, here's how common EV charging currents relate to power output:
| Supply | Current | Approx. power | Typical contactor rating used |
|---|---|---|---|
| Single-phase (230V) | 16A | 3.6kW | 25A–40A |
| Single-phase (230V) | 32A | 7.4kW | 40A–63A |
| 3-phase (400V) | 16A | 11kW | 40A–63A (4-pole) |
| 3-phase (400V) | 32A | 22kW | 63A–100A (4-pole) |
These are general reference figures, not a substitute for a proper circuit design. Always size the contactor, protective device, and cable together according to BS 7671 and the specific equipment manufacturer's instructions.
Understanding current ratings: continuous, inrush & utilisation category
A contactor's headline current rating (e.g. 63A) isn't the whole picture. A few other figures matter when specifying one correctly:
For EV charging, AC-1 (non-inductive or resistive loads) and AC-3 (inductive loads such as motors) are the utilisation categories most commonly referenced. EV charging is largely a resistive/near-resistive load from the contactor's perspective, so AC-1 rated contactors are generally suitable — but always check the specific EPC or charge point manufacturer's requirements, since some specify a higher-duty contactor for extra longevity under frequent daily switching cycles.
Contactor brands & ranges we stock
| Brand | Range | Notes |
|---|---|---|
| WCED | 2-pole & 4-pole, 63A & 100A | DIN rail mounted, 230V AC coil, IP20 (enclosure required for outdoor use) |
| Chint | 2-pole & 4-pole, 40A | Modular DIN rail contactor, compact footprint |
| Doepke | 4-pole, 25A & 40A | Can be wired for single-phase or 3-phase applications |
WCED, Chint and Doepke contactors — 2-pole and 4-pole, 25A to 100A. In stock, trade pricing available.
View contactors & relays →Frequently Asked Questions
What does a contactor do in an EV charger?
The contactor is the switching component that physically connects and disconnects the vehicle from the mains supply. It's controlled electronically by the EVSE protocol controller (EPC), which only closes the contactor once it has confirmed the vehicle is properly connected and it's safe to begin charging.
Do I need a 2-pole or 4-pole contactor?
A 2-pole contactor switches live and neutral, and is suitable for single-phase EV charging installations. A 4-pole contactor switches all three phases plus neutral, and is required for 3-phase installations. Some installers use 4-pole contactors even on single-phase builds for full conductor isolation — check the product datasheet to confirm it supports this.
What size contactor do I need for a 7kW EV charger?
A 7.4kW single-phase charger typically draws around 32A. Contactors are usually specified with headroom above the circuit's design current, so a 40A or 63A rated 2-pole contactor is commonly used — but the exact rating should be confirmed against the specific circuit design, protective device, and cable sizing under BS 7671.
What's the difference between a contactor and a relay?
Contactors and relays work on the same basic principle — an electromagnetic coil closing a switch — but contactors are built to handle much higher currents and are used for the main power-switching circuit. Relays are typically used for lower-current control and signalling circuits, such as interlocks or status signals within the charge point.
Can a 4-pole contactor be used for single-phase?
Yes, in most cases — a 4-pole contactor can be wired using just 2 of its 4 poles for a single-phase circuit, leaving the other poles unused. This is a common approach for installers who want to standardise on one contactor type across both single-phase and 3-phase builds. Confirm compatibility against the manufacturer's wiring diagram before installing.
Should an EV charger contactor be normally open or normally closed?
Normally open (NO). This is a deliberate fail-safe: the contactor only closes and allows power to flow when the EPC actively signals it's safe to charge. If control power is lost or the EPC stops signalling, the contactor drops back to its open, de-energised state and power is cut automatically.
What's the difference between an AC and a DC contactor?
An AC contactor switches alternating current loads and is what's used in standard AC EV charge points, including all the contactors on this page. A DC contactor is a different, higher-spec component designed to switch direct current — used in DC fast chargers, solar PV, and battery storage systems. DC contacts need to handle a sustained arc that AC contacts aren't designed to break, so the two types aren't interchangeable. Note this is separate from the contactor's coil voltage, which can be AC or DC regardless of what type of current the main contacts switch.
What does AC-1 and AC-3 mean on a contactor?
These are utilisation categories that define the type of switching duty a contactor is rated for. AC-1 covers non-inductive or resistive loads, while AC-3 covers inductive loads like motors, which draw a higher starting current. EV charging is largely a resistive load from the contactor's perspective, so AC-1 rated contactors are generally suitable, though it's worth checking the specific charger or EPC manufacturer's recommendation.