Electrical infrastructure in a server room: dedicated line, panel and grounding

Why a separate line and a separate panel?

In many small businesses, the server, the recorder and switchall run from a UPS plugged into any outlet in the office. The same line also has the tea kitchen, the photocopier or an electric heater. When the heater switches on, the fuse trips and the UPS goes onto battery. By the time someone who does not know this looks for the panel in the corridor to reset the fuse, the UPS may already be drained.

Running a separate line for the server room removes this problem. The line leaves the main panel with its own fuse and arrives at a small panel in the server room. In this panel, the UPS input, the air conditioner, the lighting and the service outlets are fed through separate fuses. A fault in one circuit does not affect the others.

Having the panel inside the server room or right next to it speeds up response when a fault occurs. What each fuse feeds should be written on the panel.

The cross-section of the line is chosen by thinking of the devices that will be added over the next few years, as well as today's load. Server rooms grow over time: a second recorder, a new server, a bigger UPS. If the line was sized exactly for today's need, new cable has to be run with every expansion. The cross-section and fuse values must be calculated by an electrical engineer; a cable chosen by eye heats up under load.

UPS and distribution

The UPS is fed from the server room panel. The UPS output is delivered to the devices in the cabinets through outlet distribution units called PDUs. A PDU is a multi-outlet strip mounted inside the cabinet, into which the devices' power cables are plugged. Household extension cords and power strips should not be used inside the cabinet; their capacity is unclear and they come loose easily.

For servers and switches with dual power supplies, two separate PDUs are installed in the cabinet. If possible, these PDUs are fed from two separate UPS units, or at least from separate circuits. If one PDU or UPS fails, the device keeps running from the other source.

The air conditioner is not connected to the UPS output. The air conditioner's starting current strains the UPS and drains the batteries quickly. If you want cooling to continue during long outages, the air conditioner is powered by a generator.

Expert note: Check whether the UPS has a maintenance bypass switch. This switch lets you take the UPS out of the circuit without shutting down the load when the UPS fails or the batteries are replaced. If there is none, every UPS intervention means the whole system shuts down.

Why is earthing so important?

Earthing lets dangerous voltage that may appear on device housings flow to the ground and protects people from electric shock. In a server room it has a second job: creating the same reference potential between devices. In a room with weak or no earthing, network ports burn out, interference lines appear in the camera image, and devices restart for no reason.

Surge protectors also work through the earthing. Installing a surge arrester in a building without earthing gives the impression of protection but may not actually work. In some old buildings in Şanlıurfa and in structures that were renovated later, you may come across cases where the earthing line is missing or broken.

How are cabinets and devices earthed?

There is an equipotential bar in the server room, and this bar is connected to the building's earthing system. Each cabinet is connected to this bar with its own earthing conductor. The cabinet doors, side panels and shelves are bonded to each other, because contact between painted surfaces does not provide an electrical connection.

The points watched in practice are these:

• Each cabinet is connected to the bar with its own conductor; cabinets are not daisy-chained
• Doors and side panels are bonded to the cabinet with a braided conductor
• Cable trays and metal ducts are also included in the equipotential system
• The earthing points of patch panels and switches are connected to the cabinet rail
• Paint is scraped at the connection points and the contact surface is kept clean
• Earthing conductors are labeled and marked on the diagram

Earthing measurement

The existence of earthing and its adequacy are different things. A conductor being connected to the bar does not show that the earth resistance is at a suitable value. This value is measured with a measuring device and reported by a qualified electrician or engineer.

Earthing measurements and the periodic inspection of the electrical installation are an obligation under the regulations; for workplaces, how often and by whom these inspections are done is set in the relevant regulations. Check your organization's situation with your occupational safety specialist and your electrical engineer.

Earth resistance can rise in the dry season. A measurement taken in Şanlıurfa's long, dry summer can give a different result from one taken in the rainy season. That is why the report should state the measurement date.

Surge protection

Surge protectors are used in the main panel and in the server room panel against sudden voltage spikes coming from the power line. This protection is staged: coarse protection in the main panel, finer protection in the server room panel. Protectors have a lifespan; after a large surge they may no longer do their job, and their indicator windows should be checked.

Data cables coming from outside also need protection. Copper lines to cameras outside the building, antenna cables and copper links between buildings are passed through a protector before entering the server room. Preferring fiber for links between buildings reduces this risk from the start.

Check before installation or renovation

When assessing an existing server room, these questions are asked: Is the room fed from a separate line? Are the fuses labeled in the panel? Does the UPS have a maintenance bypass? Are the cabinets earthed, and when was the last earthing measurement done? Which circuit is the air conditioner fed from?

If there are no answers to these questions, the electrical infrastructure is fixed first, and the equipment investment comes after. Putting an expensive server in a room without earthing means putting it at risk in the first storm. Electrical installation work must be done by qualified electrical teams.

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