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In the complex world of solar interconnections, cable limiters have long been a point of confusion, debate, and evolving regulation. They are key in ensuring safe and compliant system design and operation. This brief update allows developers, EPCs, and project stakeholders to stay ahead of the curve and avoid costly project delays and compliance issues due to inadequate use of cable limiters.
What Are Cable Limiters?
A cable limiter is a protection device used in electrical systems. Its main use is fault isolation. Cable limiters are designed to isolate a faulted conductor by opening under fault conditions, thus opening the fault current path. Unlike fuses, cable limiters do not offer overload protection; however, they limit the detrimental effects of short circuits. Cable limiters also do not have the typical current rating that a fuse has; they are rated for a specific conductor size and material. The range of available cable limiter ratings narrower than that of fuses, reducing the size and material of the protected conductor that can be used.
In solar applications, cable limiters are typically required in line-side interconnections where overcurrent protection isn't immediately available, depending on circuit length and location. The NEC has refined its requirements over time, with the latest important updates in the upcoming 2026 version.
How NEC Rules Have Changed
The NEC rules reflect an effort to balance safety with practical installation constraints. One of the challenges for PV project developers is the varied applicability of NEC in any given location. Every state, county, and municipality may apply a different NEC version. You can’t assume that 2023 or 2026 NEC applies. It’s not uncommon to find 2020, 2017, or even 2014 and earlier NEC applicable in jurisdictions across the US.
A Chronology of Cable Limiter Regulations in NEC
- 2014 NEC: Introduces requirements for cable limiters in line-side solar interconnections where overcurrent protection is more than 10 feet from the connection point.
- 2017 NEC: Maintained the same requirements.
- 2020 NEC: The distance allowance is extended to 71 feet, provided cable limiters are installed within 16.5 feet of the interconnection.
- 2023 NEC: Direct cable limiter requirements are removed, and installers are referred to service entrance requirements in Article 230 instead.
- 2026 NEC: Restores and refines cable limiter use, now allowing for:
- Overcurrent protection within 66 feet without requiring cable limiters.
- If beyond 66 feet, a cable limiter must be installed within 16.5 feet of the interconnection.
- Engineering supervision required for the use of cable limiters and the service voltage is limited to 1,000V or less.
Different Options for Cable Limiter Installation
There are two primary installation methods for cable limiters:
- At the termination point (utility side) – Installed at the end of the conductor where it connects to the bus, similar to a fuse.
- Inline installation – Placed anywhere along the conductor’s length within the required NEC distance, often used when space constraints prevent termination point installation.
NEC does not require cable limiters on both ends of the conductor. However, manufacturer guidelines may suggest dual-end installation when using three or more parallel conductors. In parallel conductor installations, cable limiters on one end of conductors in parallel with the faulted conductor are unlikely to open and the fault will not be isolated. Again, installers are well advised to check local requirements, i.e., which NEC version is applicable to the project’s location.
It should also be noted that when a conductor in a parallel conductor circuit is isolated then the other parallel conductors may become overloaded. Since cable limiters do not protect against overload this condition can result in overheating damage to terminals, insulation damage of conductors, and future conductor failure.
Indoor vs. Outdoor Installations
While previous NEC versions did not specify indoor or outdoor use, NEC 2020 includes more specific guidelines. It states that if interconnections occur inside a building, cable limiters are required to reduce the risk of electrical faults causing fires. Outdoor interconnections, where conductor failure is less likely to cause fires, generally do not require cable limiters.
Why it Matters: Avoiding Costly Project Delays
Failure to properly account for cable limiter requirements can result in significant project setbacks. Consider this real-world example:
An EPC firm scheduled a critical shutdown for a solar interconnection, only to realize the day before that cable limiters were required under the applicable NEC version. Because cable limiters are not always readily available, the project had to be postponed, causing major delays and financial strain on all parties involved.
Another scenario involves utilities or AHJs (Authorities Having Jurisdiction) inspecting an installation and denying permission to operate due to missing cable limiters. In such cases, the project team must schedule a second utility shutdown, rework the installation, and bring in a nationally recognized testing lab (NRTL) to recertify the system—an expensive and time-consuming process.
How Pure Power Engineering Helps
With 2026 NEC nearing adoption, developers and EPCs need to be well-versed in cable limiter specifications. Thoroughly understanding the regulations ahead of time will make projects flow smoothly, prevent compliance issues, and keep installations on schedule.
Pure Power Engineering proactively addresses potential pitfalls through code-compliant full-scope system design and implementation. Our engineers:
- Stay abreast of NEC updates to assist clients with compliance.
- Explicitly specify cable limiter specifications on plan sets, so contractors are aware of them beforehand.
- Provide expert advice to avoid last-minute surprises and costly delays.
For further insight and expert guidance on NEC compliance and solar project design, get in touch with Pure Power Engineering—your partner in effective, code-compliant engineering solutions.
