May 2010

Data Center Power Connections

The Layman’s Guide to Data Center Power Connections

By: Jim Higgins,

Data Center power connections have changed significantly over the last two decades. Once as simple as using the common home NEMA 5-15 plug, today’s data center continually migrates towards higher amperages and voltages. This migration poses many power connection complications. A basic understanding of the changes that have occurred in data centers and the electrical factors at work is necessary to understand the potential complications and evaluate the solutions.

Increasing Wattage and Its Effects on Receptacles and Plug Types

More robust servers and higher density installations are the driving force behind the power connection changes taking place in data centers worldwide. As wattage requirements continue to increase the conventional power distribution systems are dramatically altered.

The result is more exotic receptacles in the data center and an even greater variety of plug types shipping with equipment. This may seem to defy logic, but the genesis of this response harkens back to high school physics: Wattage equals Amperage multiplied by Voltage (Watts = Amps x Volts).

NEMA Straight Blade Migrates to Twist Lock

NEMA (North American Electrical Manufacturers Association) has long been the stalwart standard for power interfaces. Virtually every home has NEMA 5-15 (1,875 watt) receptacles and most businesses use NEMA 5-20 (2,500 watt) receptacles to provide power.

However, this presents a problem. Straight blade NEMA interfaces lack a crucial element for those with critical data environments because the straight blade plug can be inadvertently disconnected from the receptacle. Hence, the first leap in the power receptacle migration was to Twist Lock©.

Twist Lock© receptacles eliminate the potential for accidental disconnection because the blades are oriented in a circular manner with a twist feature to seat the plug that locks it into place. Because of this, NEMA L5-20 (2,500 watt) and L5-30 (3,750 watt) receptacles were very popular for some time and are still found in many data environments. Part numbers are created based on the actual specifications: L = Twist Lock, 5 = 125 Volts, and – 30 =30 Amps.

As wattage continued increasing the next change affected the voltage side of the equation instead of the amperage. The solution was to switch to NEMA L6-20 (5,000 watt) and L6-30 (7,500 watt) because it has 250 volts and it doubles the wattage. This provided an easy and affordable solution for data center environments that had reached the maximum wattage under their existing distribution system. The investment to double the wattage capacity was as simple as buying new power strips and usually new power cords in addition to minor electrical rework. Today, there are still many organizations using this method to double their wattage, but it is not feasible for all data center environments.

For example, very dense data center environments encountered problems with proper air flow as a result of the number of L6-30 power distribution cables running under the floor not to mention the expense. As a result, many data centers embraced NEMA 3 phase because the number of under floor cables could essentially be reduced by a third. The number of in-cabinet power strips could also be greatly reduced. There are two types of 3 phase power: Delta and WYE. Delta uses 4 wires and WYE uses 5 wires.

Popular 3 phase installations include Delta L15-30 (12,990 watt) and L16-30 (24,941 watt) as well as WYE L21-20 (7,205watt) and L21-30 (10,808 watt). The formula for calculating three phase power is kW= (VxIxPFx1.732)/1,000.

NEMA Amperage Limitations = Implementation of California Standard

Unfortunately, NEMA standard twist lock options max out at 30 amps. Interestingly, NEMA did publish 50 amp and 60 amp Twist Lock© versions, but they are not manufactured. As a result, Non-NEMA approved power connections entered the data center arena and they are often UL (Underwriters Labs). The most popular version found in the data center world is California Standard 50 amp Twist Lock©. This marine standard became popular in data centers due to the locking capability and the high amperage. There are six receptacles in this series: CS6370 (6,250 watt), CS8269 (12,500 watt), CS8469 (24,000 watt), CS6369 (12,500 watt), CS8369 (12,500 watt), and CS8169 (37,411 watt). Many data centers have implemented this standard.

Going Global- IEC60309

Despite these solutions, the worldwide race for watts does not abate. An interesting dynamic of data centers is their 24×7 operation. As a result, global organizations and US companies reaching international markets often deploy equipment around the world. The transition to a global market has exposed more US companies to the international standard IEC 60309.

This has become the de facto electrical standard for higher wattage installations for an increasing number of US organizations’ outposts abroad. The standard is very logical and appealing because it reaches 125 amps and 600 volts. Due to the IEC 60309 advantages, many US companies are implementing this design at home.

Deconstructing Part Numbers

Part numbers are not just a list of numbers and letters. Instead, they are constructed based on the specifications of the particular part. For example, part 4100R9W can be deconstructed and “read” like this: 4= # of wires used, 100= amperage, R=Receptacle, 9=ground pin location, which identifies the voltage and W=Watertight. The W means the receptacle is IP67 compliant. Part numbers without a W mean the receptacle is splash proof and IP44 compliant. The low range is 316R4 (2,080 watt) and 5125R6 (129,900 watt) is the high range.

Typically, in the United States there are four amperage ratings used: 20 amps, 30 amps, 60 amps, and 100 amps. These correspond to international ratings: 16 amps, 32 amps, 63 amps, and 125 amps. As a rule of thumb, U.S. and international units are interoperable. However, you should always consult your owner’s manual to verify.

Can You Plug it In?

Understanding the evolution of receptacle options and the solutions available is important. This is especially so when a new piece of equipment arrives that can’t be plugged in. Instead of reporting to your boss that the mission critical piece of equipment can’t be plugged in, you can experience a career defining moment by ordering the correct power adapter that will keep business moving and make you the hero.

Power Adapters can be used in a multitude of scenarios to solve power connection problem. In fact, Stay Online offers an online configuration tool where you can create a custom cord, add to cart, and order in real time for same day shipping.