Protective relays are a complex and critical part of electrical engineering, especially in the solar and energy storage industries. While they may seem intimidating at first, they don’t have to be! This three-part series is designed for non-engineers who want to understand the basics of protective relaying.
**Intro to Relays #1 – What Are Relays, CTs, and PTs?**
**Intro to Relays #2 – ANSI/IEEE Relay Device Numbers**
**Intro to Relays #3 – What Does SEL Stand For? (Below on This Page)**
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**What Does SEL Stand For?**
If you're involved in any conversation about protective relaying, you'll likely hear the term “SEL†quite often — maybe every third sentence or so.
**The Company Name**
SEL stands for **Schweitzer Engineering Laboratories**, a leading manufacturer of utility-grade protective relays and other monitoring, protection, and control devices. They are widely used across the electrical industry, and if you're working on a solar or energy storage project with a relay, it's very likely made by SEL.
Here’s a look at the SEL logo:
While companies like GE, Basler, and Beckwith also produce protective relays, SEL is by far the most commonly used in our projects. Their reliability, performance, and wide range of products make them the go-to choice for engineers around the world.
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**Model Numbers**
In addition to being the company name, "SEL" is also part of the model numbers for their products. This makes it easy to identify both the manufacturer and the specific device.
All SEL relays start with **SEL-**, followed by three digits and sometimes a letter. Here are some common models:
- **SEL-751** – Feeder Protection Relay (often used by Pure Power)
- **SEL-351** – Protection System Relay
- **SEL-551** – Overcurrent Relay
- **SEL-587** – Overcurrent Differential Relay
- **SEL-651R** – Recloser Control
Here are images of some of these devices:
Beyond relays, SEL offers a variety of other products, such as:
- **SEL-735** – Power Quality and Revenue Meter
- **SEL-3530** – Real-Time Automation Controller (used by Pure Power for dynamic solar system control)
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**Conclusion**
At a high level, understanding relay device numbers is straightforward, but the topic can quickly become more complex. However, developers and project managers don't need to be experts in relays — especially when working with experienced teams like Pure Power.
Our team of 80 engineers has designed over 2,000 commercial and utility-scale solar projects, and we ensure that all relays are properly designed, programmed, and commissioned — efficiently and cost-effectively.
If you need help with your project’s relays, contact us today to learn more or schedule a consultation. We’re here to make sure your system is safe, reliable, and up to standard.
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