Buyer’s guide
How to Select a Contactor & Overload
Sizing contactors and overload relays for motor and load switching — utilisation category, AC-3, and coordination.
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Overview
How to Select a Contactor & Overload
A contactor is an electrically operated switch for power circuits; an overload relay protects the load (usually a motor) against sustained overcurrent. Together they form the heart of a motor starter. Selecting them correctly is about matching the device to the load, the duty and the fault level — not just the current.
This guide walks through the parameters that matter and the common mistakes that lead to nuisance tripping or premature failure. Emirates Panel supplies contactors and overloads from ABB and Lovato as an authorized distributor.
Utilisation category
Why AC-1 and AC-3 are not the same
The utilisation category describes the duty the contactor is rated for. AC-1 covers resistive or lightly inductive loads; AC-3 covers squirrel-cage motor starting, where the in-rush is several times the running current. A contactor’s AC-3 rating is therefore lower than its AC-1 rating for the same frame.
Always select on the category that matches your load. Sizing a motor contactor on its AC-1 figure is a classic error that leads to contact welding and early failure under the real starting duty.
- AC-1: resistive / low-inductive loads
- AC-3: squirrel-cage motor starting (in-rush)
- AC-4: plugging and inching duty
- Match the rating to the actual duty, not the headline current
Sizing the overload
Set it to the motor, not the contactor
The overload relay must be set to the motor’s full-load current (FLC), within its adjustment range. Choose an overload whose range brackets the motor FLC comfortably, and set the dial to the nameplate value — not to the top of the range.
A correctly set overload protects the motor windings from sustained overcurrent while allowing the normal starting in-rush to pass. Too high and the motor is unprotected; too low and it nuisance-trips on every start.
Coordination
Type 1 vs Type 2
Short-circuit protection upstream (a breaker or fuse) and the contactor/overload must coordinate. Type 1 coordination allows damage to the starter under a fault provided it is safe; Type 2 allows no damage beyond light contact welding, so the starter can return to service.
For critical processes, specify Type 2 coordination and use the manufacturer’s coordination tables to pick a matched breaker, contactor and overload set. Our team can help you read those tables.
Key points
At a glance
Contactor
Switches the power circuit; rated by utilisation category.
Overload relay
Protects the motor against sustained overcurrent.
In-rush
Motor starting current is several × running current.
FLC setting
Set the overload to the motor nameplate full-load current.
Coordination
Match breaker + contactor + overload (Type 1 / Type 2).
Standards
Specify to IEC 60947-4-1.
Avoid these
Common mistakes to avoid
The classic mistake is sizing a motor contactor on its AC-1 rating instead of AC-3, which ignores starting in-rush and leads to contact welding. The second is setting the overload to the top of its range rather than the motor’s actual full-load current.
Teams also overlook coordination — pairing a contactor and overload with an unmatched upstream device — and ignore the duty cycle, under-sizing for frequent starting. Reading the manufacturer’s coordination tables avoids these.
How we help
From this guide to delivered product
Reading the theory is one thing; applying it to your project is another. The Emirates Panel technical team turns this guidance into a specific recommendation — the right device, rating and accessories for your duty — and supplies it as genuine, authorized product with the documentation your consultant needs to approve it.
Send your requirement, a one-line or a parts list, and we respond with pricing, availability and lead time, backed by EP Group sourcing across the UAE and GCC.
FAQ
Frequently asked questions
How do I size a motor contactor?
Match the contactor’s AC-3 rating to the motor power and current, not its AC-1 rating — the AC-3 figure accounts for starting in-rush.
Where do I set the overload?
To the motor’s nameplate full-load current, within an overload whose range brackets that value comfortably.
What is Type 2 coordination?
A coordination level where the starter suffers no damage (beyond light contact welding) under a short circuit, so it can return to service.
Which contactor brands do you supply?
ABB and Lovato contactors and overloads, genuine and warranted, as an authorized distributor.
Need help specifying?
Our technical team helps you select the right product and supplies it genuine, with documentation.
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