– Joel Young, Engineer at Emcor Enclosures (www.emcorenclosures.com), says:
Determined to select the ideal seismic-rated electronics enclosure, a decision-maker examines myriad options and narrows them to two finalists. Both cabinets are heralded by their manufacturers as delivering “seismic” protection, but they wear different price tags. How does the customer decide which proposal offers the right seismic solution for the application?
Given the matching “seismic” labels, the cost-conscious choice might seem prudent. However, before acquiring earthquake protection for critical data center equipment, the customer should understand that all seismic-rated enclosures are not created equal. In fact, there can be significant disparities in the testing achievements behind manufacturers’ seismic labels — and a corresponding variance in the caliber of earthquake protection provided to electronic equipment.
There are two standards by which enclosures are deemed seismic — Telcordia Technologies GR-63-CORE Network Equipment Building Systems (NEBS) requirements and the International Building Code (IBC). While both standards have their strong points, many would argue that they are too different to be used as a means to achieve the same label for a product. To better understand their differences, it is important to understand their origins.
History
In the years following AT&T’s monopoly lawsuit, a flood of competitive local exchange carriers arose, bringing a slew of new and varied network equipment to the once homogenous collection of AT&T equipment housed in central offices throughout the country. It quickly became apparent that there was a need for a standard to which network equipment had to adhere in order to ensure network compatibility and uptime. What came to be were the NEBS requirements, of which, section GR-63 applied specifically to protecting equipment in the event of seismic activity. Because of the essential nature of telephone communication service, GR-63 requires that in the event of an earthquake, “The equipment shall sustain operation without replacement of components, manual rebooting, and human intervention.” In other words, an enclosure must provide a level of protection such that the network remain active during an earthquake.
While GR-63’s history is based on preventing network downtime, IBC was formed as a broad collection of structural building requirements to prevent human injury and reduce equipment damage during an earthquake. Following the 1994 earthquakes in Los Angeles — during which more than 40 percent of the $80 billion in damages were non-structural — it became apparent there was a need to create guidelines for securing objects within buildings to the floors, walls or ceilings. In 2000, the IBC was created as a guideline to which businesses must adhere in order to receive funding from the Federal Emergency Management Agency (FEMA) in the aftermath of an earthquake. In short, the IBC is a set of guidelines on how to mount objects, so that they do not tip over during an earthquake.
With two very different origins, there are bound to be inconsistencies in what these standards measure, how they are measured and how they are applied. While GR-63 requirements and testing procedures are consistent across the board, IBC requirements differ from city to city, state to state and building to building. Thus, not only are GR-63 and IBC inconsistent with each other, but there can be major inconsistencies from one IBC-compliant enclosure to the next. Many of these inconsistencies are related to the varying methods of calculation, testing and certification.
Calculation, testing and certification
To achieve GR-63 compliance, enclosure manufacturers turn to independent, third-party testing facilities. An enclosure is loaded to its capacity and mounted to a shaker table. The shaker table then simulates an earthquake, shaking in every potential direction at varying levels of intensity up to the equivalent of 8.3 on the Richter scale. Accelerometers are attached to the enclosure to measure its vibration and sway during the test. In order to pass the test and achieve the seismic rating, the enclosure must not sway more than three inches in any direction and all components must remain operable during and after the test. This test is the same for every manufacturer of enclosure, regardless of where that enclosure is going to be used or its intended purpose.
IBC compliance on the other hand, can be achieved through three different methods, leading to further inconsistencies in the label. The most stringent of these methods requires a shaker table test similar to the one used in GR-63 certification. The other two however, are quite subjective — one being a mathematical equation that compares potential seismic effects to objects mounted in a building and the other being the use of experience data. The latter would require the manufacturer to reference an enclosure’s performance during a specific earthquake, and design the enclosure to the same specifications as the enclosure from the referenced event. The issue with this method is that there are a number of variables that cannot be accounted for with historical record, for instance, how the enclosure was mounted and loaded, and with what type of electronics.
The equation used to calculate IBC compliance is also quite subjective, consisting of several variables that are impossible to predict by the enclosure designer unless the enclosure is being built specifically for an individual building. These variables revolve around where the enclosure is being used. A value called the “seismic design category” is assigned based on the building’s location. This is calculated based on the distance of the building to the anticipated location of an earthquake as well as the type of soil beneath the building and on which floor the enclosure will be mounted. The building is also given a value called an “importance factor,” which is either 1.0 or 1.5. An “essential” building — such as a hospital, where uptime is critical — is given the 1.5 value, whereas a “non-essential” building is given the 1.0 value. The essential value would require that the electronics continue to function in the event of an earthquake whereas the non-essential value would simply require the enclosure to remain standing. Regardless of which variables are used — the most stringent or least stringent — the enclosure manufacturer can label their product as seismic-rated, which leads to significant disparities in quality and strength of products being marketed as something able to withstand an earthquake.
Structural integrity
Because GR-63-compliance requires that all components of the electronics and the enclosure continue to function during and after an earthquake, a number of special considerations in the design process must be made. At the very minimum, a fully welded frame is recommended. Further, heavy-duty doors with extra latches and locking hardware should be used to absorb vibration. In its most stringent enforcement, an IBC-compliant enclosure would be designed with the same considerations in mind. However, becoming IBC-compliant in its least stringent form would require little more than some extra mounting hardware — which in essence, would be the same design consideration made for a file cabinet.
Regardless of which standard is used to certify a product and how stringently that standard is applied, an enclosure can only offer sufficient protection from seismic activity if properly mounted and loaded.
Installation
When it comes to installation recommendations, IBC is once again rather subjective when compared to the consistent guidelines of GR-63. IBC-compliant mounting is generally achieved through the certification of a building engineer. The engineer will make recommendations on minimum requirements for bolt diameter and depth as well as minimum compressive strength of the concrete floor based on a number of factors similar to those used in the equation for calculating IBC compliance. On the other hand, GR-63 requires that the bolts are 3.5 inches long and 0.5 inches in diameter. These are the size of bolts used in testing procedures and thus, are meant to correspond to the real-world scenario.
When it comes to loading, IBC and GR-63 are actually quite similar. All the standard rules of physics still apply. It is important to remember that the lower the center of gravity, the more stable an enclosure will be. So, when loading to capacity, the heaviest items should be loaded toward the bottom and the lightest toward the top. Both standards account for weight, but it is the responsibility of the installer to ensure the weight is distributed as low as possible, as both standards assume.
Conclusion
While both standards serve important purposes, there are too many variables in the way IBC is calculated to be used as a means to apply the same label to an enclosure as GR-63. When selecting an IBC-rated enclosure, it is important to look at how the manufacturer arrived at that label. If certification was achieved through testing on a shaker table and remained intact and functioning throughout the test, it is likely going to live up to the quality of a GR-63-compliant enclosure, and will likely reflect that in the price tag. However, buyers should be wary of IBC-compliant seismic enclosures with a significantly lower price than others. When it comes to seismic-rated enclosures, the old adage still applies — you get what you pay for.
