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Guest View: Fuses or Breakers: Beyond the last line of defence

Mike Jansma | Oct. 10, 2013
Mike Jansma, Co-Founder and CMO at Enlogic, looks at how a simple short circuit could bring a data centre to its knees, and what can be done to spot and fix issues before they happen.

But it's not just the PDUs that are at risk. When electrical circuits are exposed to overcurrent or excessive temperatures, the conductor insulation melts and there is a real danger of smoke, fire and electrical shortage faults - all of which create a dangerous data centre environment.

Don't blow a fuse 

Just like at home, a fuse embedded within the PDU can step in and cut power supplies in the event of a fault (or surge in current). However, fuses have other negative attributes when used in a data centre environment. Once a fuse has blown, it must be replaced. Not only is this replacement a dangerous task, but the whole PDU rack must be powered down.

The good news is that there is a far more reliable and safe alternative. Circuit breakers (embedded within a PDU) detect overcurrent or fault situations and break the electrical circuit providing power in the case of any emergency.

One of the most important differences between the two is that, unlike a fuse, when a circuit breaker trips because of a circuit overload, then no replacements are required. It can be reset manually or automatically by data centre operators.

Data centre managers would be well advised to opt for the hydraulic-magnetic, or hy-mag, circuit breaker. The hy-mag breaker is independent of temperature as a tripping mechanism, and is not affected by ambient rack temperature. Rather, the current load is connected through a solenoid coil. At currents above the circuit breaker rating, the coil generates the magnetic flux needed to force a spring mechanism to open the electrical circuit and prevent current flow through the breaker. What this means is that the tripping current is related to the amount of current only; the hy-mag breaker will keep consistent tripping characteristics across the entire range of data centre ambient temperatures.

Technicians can also independently eliminate the fault condition and reset the circuit breaker without powering down the remainder of the rack PDU. In fact organisations don't even need trained personnel to reset the device after failure, and the whole rack can be reset in as little as three minutes.

The worrying truth is that there are PDUs in data centres around the world that have no fuses or circuit breakers, leaving servers exposed and vulnerable to fluctuating power supplies. With ever-growing rack power density, and increasingly variable power loads in the IT rack, protection against circuit overload and the ability to instantly spot and fix faults has become paramount. Without these abilities, the data centre will always be at risk. 

Mike Jansma is Co-Founder of Enlogic.

[1] Circuit Breakers in Data Centers: The Hidden Danger,



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