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Power and cooling are some of the most over looked or misunderstood components of deploying IT infrastructure. Power in particular poses a problem for the average IT department because it is often considered the domain of the building maintenance or an electrical subcontractor.

Electricians are necessary to install your power receptacles but most fail to understand the needs of your IT equipment. Even electricians with IT infrastructure experience will often only give you a receptacle on the wall. It is up to you, or your IT support team, to know what you need and how to balance the equipment load.

Step one is to know what you have at your Load Center. Load Centers (sometimes calls Breaker Boxes) will be your starting point for designing your power infrastructure that will support the IT equipment. You need to know if you have residential class Single-phase 240V, or industrial 3-phase power. You will also need to know the Amp rating of the panel and what is being served from that Load Center already.

All this info should be attainable from the inside of the Load Center’s door.

Most properly maintained Load Centers have a label that lists the voltage and phase of your power. This can be a paper sticker on the door or a stamped plaque bolted to the faceplate. A notation of 120/240 Volt should indicate you have single-phase 240 services, found in most North American homes. 240 Volt service consists of two in-phase 120 Volt cables and one common neutral wire. If you see 120/208Y listed, than you have 3-phase power. There are a few varieties of 3-phase power, based on the transformer used, but in general offices have four-wire 3-phase power. The 4^th wire is a common neutral, similar to residential Load Centers.

The Amp rating should be listed near the voltage, but it is best to look for a Main breaker. This can be a large breaker at the top or bottom of the Load Center. Sometime you will be using a sub-panel of the main Load Center. In that case you should find the breakers that feed the sub-panel in the main Load Center.

Look at the listing printed on the lever or body of the breaker. Typically you will have 100 Amp, 200 Amp, or 300 Amp service. The Amp rating is per hot wire. Some times a breaker will be wide, with one lever, and other times they will look like two-three leavers held together with a bar. In the single lever instance the amperage will be printed on top of the lever or the body. In the case of the bar joined levers, you may see up to three numbers. Do not add them up to find your available amperage. Just reference the Amp rating found on one.

An electrician or other competent technician should calculate your current usage of the Load Center. It often requires the use of a clam meter to monitor the current flow through each main conductor. The faceplate of the Load Center will need to come off but power needs to be left on in the Load Center to get a reading. This is dangerous and takes some advance knowledge to avoid injury.

Aside from the clamp meter work, you can determine if the available power in a Load Center is sufficient by taking some basic calculations. Add up the Amp rating of every breaker in the Load center and compare it to the available amperage of the Main. If all the breakers are singlewide you can add up all the breakers and subtract the total from twice the Main breaker, if it is 240Volt, or three times the Main breaker if it is 3-phase power. If you have anything left over you should safely be able to add a new circuit for the IT equipment you plan to install.

Often your basic Amp/breaker count will be larger than the available Amps provided by the Main breaker. This is because circuit breakers are selected based on the wires used to connect the load / device to the Load Center, and not the actual Amp draw of the equipment. In these cases a clamp meter will be you only option to estimate your current Load Center usage.

The reason for going through this exercise is that most poor installs of IT equipment start with bad Infrastructure planning. The equipment is purchased and delivered as the first step in the install. Then, as an after thought, people look around for a half-empty closet with an available outlet. The Installing engineer knows nothing about what other devices share that circuit or what the active Amp draw of the Load Center is. Instead they grab a UPS unit and trust that the UPS will make up for the lack of infrastructure planning. This type of deployment is not only destined to to fail but will also increase the length and severity of equipment downtime.

Stay tuned! Next time we will go over the exciting world of UPS selection and redundant power design.