Relay jumpers can reduce wire count in your industrial control panel by 2*(N-1) wires, where N is the number of relays in the group. For example, a trio of relays is shown in Figure 1. Instead of running 6 discrete wires (three for coil returns and three for the shared contact-common), only two wires are required: one shared coil return and one shared contact supply.
This optimization is important because the task is greater than just the wire. It’s the wire plus the ferrules, the wire labels, the routing in the wire duct, the documentation, and all of the time embodied in the process. This approach extends beyond the initial installation to clarity for troubleshooting and ease of future modifications.
Things are less likely to get lost in the wire duct when there are fewer things to lose.
Key Takeaways
- Jumpers can save time and effort for the installer.
- Jumpers reduce the total number of wires but introduce single points of failure.
- Reduced wire count reduces the total number of initial installation, latent defects, and errors that emerge after years later.
This article is part of the DigiKey Field Guide for Industrial Automation
Location: Understand It → Relay Logic
Difficulty: 
Student — difficulty levels explained
Author: Aaron Dahlen | MSEE | Senior Applications Engineer, DigiKey
Last update: 01 Jun 2026
Figure 1: Foreground: trio of SPDT relays with a single wire shared for the contact-common terminal. Background: independent relays with a wire for each.
The jumper bars, also known as combs, are available for many relay control families. The images and concepts in this article are demonstrated using Phoenix Contact products:
- Phoenix Contact type 2903370 SPDT Relay. This is a relay-and-socket assembly sold by DigiKey as a single SKU.
- Red Jumper for contact-common connections
- Blue Jumper for coil-common connections
Tech Tip: Panel designers may select a PLC with solid-state outputs to drive interposing relays. This adds complexity but externalizes the natural relay wear that occurs over the decades-long life of the machine. Instead of replacing the PLC, they replace the external relay. The relay jumper simplify this type of construction. Jumper are available to join from 2 to 10 relays.
What Jumpers Actually Connect
Jumpers allow a group of relays to establish a common A2 node for all coils. They also allow a common connection for the contact side by joining the common (terminal 11) for each SPDT contact set. An example is the A2 (supply return) terminals as shown in Figure 2. Two jumpers are shown in this image: a spare jumper on the workbench while another is installed thereby joining the A2 terminals for all three relays.
Figure 3 presents the wiring diagram for the trio of relays. A dashed line represents the boundaries of each relay. The jumpers are shown in the center of the image:
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Blue: all A2 terminals are joined together
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Red: all terminal 11 (common) contacts are joined
Finally, two common wires remain. A single wire is used for all A2 terminals and a single wire for all terminal 11 connections within the relay group.
Figure 2: The blue (coil) jumper joins the A2 terminals for each of the three relays.
Figure 3: Wire diagram for three SPDT relays with blue coil and red contact-common jumpers.
Failure Modes
Without the jumpers, each relay is independent. A single wiring error would cripple a single relay circuit but leave the remainder untouched.
With jumpers, the relays operate as a group. Loss of a common coil return wire or a common supply wire will disable all relays within the group.
From a failure perspective, carefully consider how each type of failure will impact your specific application. On the one hand, independence is desirable as the damage from a single wire failure is constrained. On the other hand, the jumpers reduce total wire count and complexity which reduces the potential number of errors that could occur.
Parting Thoughts
Jumpers reduce the total number of wires but introduce single points of failure.
Sincerely,
APDahlen
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About This Author
Aaron Dahlen, LCDR USCG (Ret.), is a Senior Applications Engineer at DigiKey in Thief River Falls. His background in electronics and industrial automation was shaped by a 27-year military career as both technician and engineer, followed by over a decade of teaching.
Dahlen holds an MSEE from Minnesota State University, Mankato. He has taught in an ABET-accredited electrical engineering program, served as coordinator of an electronic engineering technology program, and instructed military technicians in component-level repair.
Today, he has returned to his home in northern Minnesota, completing a decades-long journey that began with a search for capacitors. Read his story here.