Reed Relay
A reed relay electrically controls a sealed contact arrangement. Coil requirements, contact form, insulation and switched-load limits are separate specifications. The relay's name alone does not tell you which pins to connect or what load it can switch.
The energized coil produces the magnetic field that operates the reed contacts. Coil current, temperature and nearby magnetic fields can affect operation. Contacts may switch only within their specified voltage, current and power limits; carrying current through already-closed contacts is a different rating from interrupting it.
In plain terms
Imagine a small magnetic hand moving a switch through a sealed wall. The coil provides the command, while the contacts handle a different circuit. How long the switch lasts depends heavily on what it has to make and break.
Why designers use it
- Select signal paths with a physical contact arrangement.
- Use a specified coil-to-contact insulation barrier.
- Build switching systems where the chosen contact ratings and life suit the load.
Best for
- Compatible signal switching
- Test-system switching
- Low-load relay applications
Key specifications
- Contact limits: Switching voltage, current, power and carry current (Check all applicable limits together.)
- Coil: Nominal voltage, operate/release limits and polarity (Temperature and magnetic interaction matter.)
- Life and connections: Load-specific life and exact pin diagram (Contact form and optional diode change the selection.)
When not to use it
- When load inrush, switching voltage, current or power exceeds the contact ratings.
- When neighboring fields or the operating temperature prevent reliable coil operation.
Common mistakes
- Assuming a billion operations is guaranteed under every load.
- Treating maximum carry current as maximum switching current.
- Ignoring capacitive inrush or inductive turn-off energy at the contacts.
- Assuming package appearance establishes pinout, or ignoring polarity when an internal diode is fitted.
Where you will find it
- Pickering's Series 80 and 85 have related electrical options but different pin configurations. Their data sheet explicitly shows why the exact type number and diagram matter.
- Pickering's help guide explains why low-load or cold switching can last longer, while abusive capacitive inrush can shorten contact life.
A short history
This guide uses Pickering's reed-relay documentation to explain coil operation and load-dependent contact behavior. Advertised construction advantages are manufacturer claims, not proof that every competing relay is inferior. No particular telephone exchange or commercial instrument is assumed to use a specific relay.
Good to know
- A relay can be within its carry-current rating but outside its switching rating.
- Long cables can add capacitance, so the load seen at the moment of contact closure may differ from its steady-state current.