Don’t Get Buried in Problems: Understanding Load Ratings for Underground Enclosures
When you’re working on a project that involves underground enclosures, it can be easy to overlook the importance of load ratings. However, choosing the right enclosure with the appropriate load rating is critical for ensuring the long-term safety and reliability of your installation. We will break down what you need to know about the ANSI/SCTE 77 specification and why it matters.
What are Load Ratings and Why are They Important?
Load ratings, as defined by the ANSI/SCTE 77 specification, are a tiered system that classifies the performance of underground enclosures, in non-deliberate traffic situations. Think of it as a way to match the strength of the enclosure to the amount and type of traffic it will encounter. For example, an enclosure in a pedestrian-only area will have a much different load rating than one in a parking lot where it might be occasionally driven over by a car.
ANSI/SCTE 77 tiers and examples:
- Light Duty – intended for areas with only pedestrian traffic.
Example: grassy areas in residential properties that are located away from any vehicular traffic. - Tier 5 – for sidewalk applications and includes a safety factor for occasional, non-deliberate vehicular traffic.
Example: a residential sidewalk that is not crossed by a driveway. - Tier 8 – also for sidewalk applications, this tier has a higher safety factor for non-deliberate vehicular traffic than Tier 5.
Example: most public sidewalks or areas within the parking curbs of a parking lot where it is highly unlikely to be run over. - Tier 15 – designed for driveways, parking lots, and off-roadway applications that may be subject to occasional, non-deliberate heavy vehicular traffic.
Example: sidewalks in residential or public areas where a passenger vehicle might occasionally drive over it. - Tier 22 – the highest tier and is for driveways, parking lots, and off-roadway applications that could be subject to occasional, non-deliberate heavy vehicular traffic, including trucks.
Example: a non-paved median between a divided highway or a non-paved shoulder area of a road.
The right load rating ensures the enclosure can withstand the expected forces without failing. A failure could mean a number of things, from the cover bowing inward and creating a tripping hazard to a complete collapse of the enclosure. By choosing the correct tier, you’re not just buying a product; you’re investing in the safety and longevity of your project.
The ANSI/SCTE 77 Testing Process
To earn a specific tier rating, enclosures must go through a rigorous three-part testing process. This isn’t just about placing a weight on top and seeing if it breaks. The testing simulates a real-world scenario of a vehicle approaching and driving over the enclosure. This involves applying both lateral (sideways) and vertical forces to the sidewalls and a vertical load to the cover.
But it’s not just about strength. The enclosure must also stay within specific deflection limits. This means that even if the enclosure can hold the weight, it can’t bend or deform too much. A cover that bows inward, for instance, could be just as dangerous as one that breaks completely.
It’s also important to note that while a single successful test allows a company to list a tier on their product, continuous testing is a better indicator of a product’s reliability and a company’s commitment to safety.
More Than Just Weight: Other Environmental Factors
The ANSI/SCTE 77 specification goes beyond just load-bearing capabilities. It also includes tests for a variety of other environmental factors to ensure the enclosure can withstand the elements and remain safe over time. These tests include:
- Chemical resistance
- Sunlight/UV exposure
- Water absorption
- Flammability
- Impact resistance
- Friction
By considering all of these factors, you can be sure you’re choosing a product that is not only strong but also durable and safe for everyone.