Ken's Korner

 

Testing and Exercising Branch Circuit Breakers

Any significant down time at my previous data centers could potentially cost the company millions of dollars in lost revenue, so I looked for every possible problem area and implemented preventative maintenance measures to ensure that downtimes were either minimized or eliminated. One preventative maintenance measure was to pre-test all branch circuit breakers prior to installation.

 

The last line of defense protecting your critical servers on the raised floor are the branch circuit breakers located within your PDU/RPP's. Considering how many breakers are produced each day, regardless of the brand name, some may have defects. This can lead to several problems. If the branch circuit breaker does not trip on a direct short, the next breaker in line will be the main breaker in your 42 circuit panel and can lead to widespread failures of your critical servers on the raised floor. In the event of an overloaded circuit, if the individual branch breaker does not trip, over time, it can cause a fire.

 

I found from my years of experience of testing branch circuit breakers installed in our data centers, between overloaded branch circuits and direct shorts, about a 4% failure rate. Even though 4% may not seem like a large percentage, in most data centers, 4% of the thousands of circuit breakers used can still place a significant number of servers at risk.

 

The solution I implemented and recommend is to purchase a circuit breaker tester, train staff and set up a test station onsite so branch circuit breakers can be tested in-house prior to installing them in your critical environment. If that is not an option, consider having a local vendor test the breakers for you. Each circuit breaker that passes the test should be labeled, dated, signed, and inventoried for future installation.

 

Another very important maintenance practice is to exercise the breakers at least every two to three years. This should not be overlooked when implementing scheduled maintenance shutdowns.

 

My recommendation is that each branch circuit breaker is exercised by turning them off and on at least three to four times. This will ensure the breaker does not become seized in the closed position which could prohibit them from tripping in the event of a direct short or overloaded circuit.

 

If it is continuous uptime you are seeking to achieve, along with a good maintenance program, testing and exercising branch circuit breakers is a proactive maintenance measure well worth implementing.

Ken Koty

kkoty@pducables.com

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