Relay Basics and Manufacturers

This page covers the fundamentals of relays and lists some relay manufacturers. A relay is essentially a switch that’s operated by an electromagnet.

It’s particularly useful when you want a small current in one circuit to control another circuit, perhaps one that powers a device like a lamp or an electric motor.

The figure below shows the standard symbol for a relay.

When a controlling current flows through the coil, the soft iron core becomes magnetized. This magnetization attracts the L-shaped soft iron armature. The armature then pivots, which either opens, closes, or changes over electrical contacts in the circuit being controlled.

The minimum current required to activate the relay is known as the “pull-in current.” Conversely, the “drop-out current” is the current level at which the relay deactivates.

For example, consider a relay with a coil resistance of 190 Ohms and an operating voltage of approximately 10 volts. The pull-in current of the relay can be calculated using Ohm’s Law:

$I = \frac{V}{R} = \frac{10}{190} = 0.052 \text{ Ampere}$

Relay Manufacturers

Here are some well-known relay manufacturers:

• American Relays Inc. (High voltage power relays)
• Altech Corp (Safety relays)
• Aleph International Corp.
• American Electronic Components Inc. (Large current relays)
• Comus International
• Clare (Reed relays)
• Celduc Group
• Finder relays Inc. (Power relay - Monitoring relays)
• Greenwich Electronics Inc.
• Hamlin
• Hasco Components International Corp.
• Leach International Corp.
• MEDER electronic
• NTE Electronics Inc.
• Panasonic Electric Works
• Phoenix Contact
• Pickering Electronics
• Schneider Electric
• Teledyne Relays
• Tyco Electronics