Safety Contactor vs Normal Contactor: Key Differences
The usage of safety contactors is increasing day by day in automation systems. A safety contactor is a unique device and has some differences from a normal contactor.
Let’s check these differences one by one.
Differences Between Safety and Normal Contactor
Differences between safety contactor and normal contactor are:
Safety contactor provides mechanically linked positively guided contacts, required in feedback circuits of modern safety applications. The mechanically linked N.C. auxiliary contacts do not change state when a power pole welds. A normal contactor changes its state due to coil energization and de-energization.
2. Mechanically linked contacts
The safety contactor has mechanically linked contacts. Some other names may also be given to this same requirement of the standard in technical documents, such as forced contacts, positively activated contacts, linked contacts, and positively guided contacts. This is the main difference between a safety contactor and a normal contactor.
Applicable to the auxiliary contacts used in auxiliary control circuits, those contacts can be built into the contactor or blocks of external auxiliary contacts mounted on the contactors. According to IEC/EN 60947-5-1 – Annex L, open contacts and closed contacts cannot be simultaneously closed. In case welding occurs on the NO contacts, the NC contacts must remain open, and in case welding occurs on the NC contacts, the NO auxiliary contacts must remain open.
3. Auxiliary contact types
Safety contactor has auxiliary contacts permanently connected to the contactors. You cannot snap them off. This feature avoids the possibility of the auxiliary contacts becoming separated from the contactor due to environmental causes such as shock and vibration.
The normal contactor has both snap-on and snap-off auxiliary contacts.
4. Unintentional touch
Safety contactor is protected against foreign bodies and unintentional touch. You cannot change the position of the main contacts from the front of the safety contactor. This design feature avoids the possibility of personnel creating an unsafe state due to unexpected start-up.
On the other hand, you can change the main contact position of the normal contactor by hand.
The specific yellow or red color of a safety contactor enables easy identification on panels of machinery and equipment. During routine maintenance work, these unique colors save valuable time. On the other hand, the color of the normal contactor varies. White and gray are the most popular colors.
6. Prices and market sizes
If you compare the same kW ratings, the price of a safety contactor is more expensive than a normal contactor. Besides the market size of a safety contactor is really small compared to normal types.
There are lots of brands available in the market that produces normal contactors. But safety contactor portfolio is available in companies ABB, Eaton, Rockwell, Siemens, and Schneider.
You can use a safety contactor in e-stops, light curtains, safety gates, safety interlocks. It has a limited usage area. But normal contactors can be used in any type of application in the industry. Besides the product standards of these contactors are different.
The dimension of a normal contactor is more compact than a normal contactor.
10. Direct control
Safety contactor is reliable in any network. Direct control by safety PLCs or safety relays ensures the required safety performance. But a normal contactor cannot be controlled directly by PLC systems.
11. Response times
The response time of a safety contactor is faster than a normal contactor. In safety applications speed is essential. Safety contactor features fast opening times, down to 20 ms. ensuring that when a dangerous failure is detected the operator is kept out of harm’s way.