# Relays: understanding "Rated carry current" and "Maximum contact current"

I'm trying to understand the limitations of connecting multiple relays, and how it relates to current.

Consider a relay with the following specs (rounded for easier math):

• Rated current: 100mA
• Rated voltage: 12V DC
• Rated carry current: 3A
• Maximum contact current: 3A

Let's also consider a power supply of 12V DC and 10A.

Is the following correct?

1. I could wire 100 (10A / 100mA) of these relays in parallel and be at the theoretical limit of my current.
2. I could wire 30 (3A / 100mA) of these relays in series and be at the theoretical limit of the relay themselves. At that point, the contacts would get too hot or the device would fail in some other way.
3. The power supply wouldn't really care how the relays are connected, as long as the total current draw is under its maximum. That is, "Rated current" * "Num Relays" <= "Power Supply Current"
4. I could mix and match parallel and series connections as long as stay under the limits in #1 and #2.

I'm new to hardware and I'm trying to not kill relays or burn down my house.

• Consider what happens during the time that relays are opening and closing, especially if they don't all switch simultaneously. Mar 30, 2017 at 22:59
• @supercat, makes sense that since these are physical devices, there will be some delay when opening closing. Mar 30, 2017 at 23:20