LV Switchgear and MCC Basics for Data Centers
After the transformer, power reaches the loads through low-voltage switchgear. Here is what it contains, how it is rated and what to check.
Typical arrangement
- Main LV board (MLVS/PCC): receives transformer or generator supply, with incoming and bus-tie breakers.
- Distribution boards: feed UPS inputs, mechanical boards, lighting and small power.
- MCC: motor feeders for the cooling plant.
Key ratings
| Rating | Check |
|---|---|
| Rated current of busbars and breakers | Design load plus allowance, at the operating temperature inside the enclosure |
| Short-circuit withstand and breaking capacity | Above the prospective fault level at that board |
| Form of separation | Matches the maintenance and availability requirements |
| Breaker type | Air circuit breaker or moulded-case breaker, by current and function |
Design checks
- Size each breaker from the load and the cable it protects. See the breaker sizing calculator.
- Verify the fault level and that downstream devices discriminate. See protection coordination.
- Check bus-tie and changeover logic for the redundancy scheme.
- Plan metering and monitoring points.
- Allow clearance for access and arc-flash considerations. See arc flash basics.
Written by the Vision Matrix Institute editorial team. Worked examples use stated, illustrative assumptions; check them against your project data, the applicable standards and manufacturer datasheets before use.
Frequently Asked Questions
What is LV switchgear?
Assemblies of circuit breakers, busbars and protection that distribute and protect circuits at low voltage, typically up to 1,000 V AC. Main LV boards receive the transformer output and feed distribution boards and motor control centres.
What is an MCC?
A motor control centre groups starters, drives and protection for motors, such as chiller, pump and fan motors, in one assembly.
Which standard covers LV assemblies?
The IEC 61439 series covers low-voltage switchgear and controlgear assemblies. Check the edition and local requirements.
What is a form of separation?
A classification of how busbars, functional units and terminals are separated inside the assembly to limit the spread of a fault and allow safe work on one section.
Want to learn this properly?
This topic is covered in depth in our Electrical Design – Data Center Specialist program.
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