3-Phase Power Principles and Challenges

The principles of 3-Phase power are not always well understood by the installer, whose only task is to power up the equipment being installed in the computer rack. Load balancing (matching current draw on each phase) is critical in these applications for multiple reasons: • If the three phases are not balanced, heat is generated resulting in higher cooling costs. • Unbalanced loads lead to inefficiency and higher power bills. • High loads on a single phase means greater chance of tripping either a PDU or upstream breaker, and losing power at the rack Good practice in the data center is to install rack mounted equipment so that the current draw is similar on each branch. This is relatively easy if the rack is filled with only one type of device. Unfortunately, this is often not the case. Mixed devices such as switches, storage devices, blade servers and different brands and types of 1U/2U/3U servers can create a crazy mesh of power cables in the back of the rack. This can potentially inhibit airflow and add to the heat problems mentioned above. The issues above are compounded by the move to higher density racks that demand more kilowatts of power. Higher power distribution at 60A and 100A force even more complex PDUs with six, nine, and twelve branches. The power draw still must be evenly distributed across these branches.