Power Distribution Equipment Explained: Spider Boxes, PDUs, and Load Centers

The Link Between Your Generator and Your Work

A 500 kW generator sitting at the edge of your site doesn't do much good if you can't get that power to the workers who need it. Power distribution equipment is the infrastructure that bridges the gap — safely, efficiently, and in compliance with OSHA and NEC requirements.

Understanding the basics helps you spec the right equipment, avoid costly delays, and keep your crew safe.

Spider Boxes (Portable Power Distribution Panels)

Spider boxes — also called power distribution boxes or job boxes — are the workhorses of temporary jobsite power. They take a single high-amperage input (typically 100A–400A at 120/240V or 120/208V) and distribute it to multiple 20A or 30A GFCI-protected outlets.

Key specs to know:

• Input voltage: Match to your generator output (120/240V single-phase or 120/208V three-phase)
• Amperage: 100A, 200A, and 400A are the most common rental sizes
• GFCI protection: Required by OSHA for all temporary power on construction sites
• Outlet configuration: Look for a mix of 20A duplex, 30A twist-lock, and 50A outlets to cover all your tools

Power Distribution Units (PDUs)

PDUs are the heavy-duty version of spider boxes, designed for larger loads and more complex distribution needs. They typically handle 400A–2,000A inputs and include metering, circuit breakers, and sometimes automatic transfer switches.

PDUs are the right choice when:

• You're powering multiple buildings or work zones from a single generator
• You need metered circuits for billing or load monitoring
• Your project requires 480V three-phase distribution
• You're running sensitive equipment that needs clean, regulated power

Load Centers and Temporary Panels

For projects that need a more permanent-feeling temporary power setup — multi-month construction projects, large events, or disaster recovery operations — temporary load centers provide a full panel board experience with individual breakers for each circuit.

These are particularly useful when your electrician needs to wire multiple sub-panels throughout a structure, or when you need to maintain separate circuits for different trades working simultaneously.

Feeder Cables and Cam-Lock Connectors

Distribution equipment is only as good as the cables connecting it. Cam-lock connectors are the industry standard for temporary power connections — they're color-coded by phase, rated for the full amperage of the circuit, and designed for quick connect/disconnect without tools.

Always match your cable ampacity to your breaker rating. Undersized cables are a fire hazard and a code violation. Our rental packages include properly rated feeder cables sized for your specific distribution setup.

OSHA and NEC Compliance

Temporary power on construction sites is governed by OSHA 29 CFR 1926.404 and NEC Article 590. The key requirements:

• All 125V, 15A–20A receptacles must be GFCI-protected
• Assured Equipment Grounding Conductor Program (AEGCP) as an alternative to GFCI
• Temporary wiring must be removed immediately upon completion of construction
• Flexible cords must be protected from damage and not run through walls, ceilings, or floors

Our equipment ships pre-configured for compliance. If you have questions about your specific setup, our team can walk you through the requirements before delivery.

Getting the Right Distribution Package

The most common mistake we see is customers renting a generator without thinking through distribution. You end up with a 500 kW generator and a single 50A outlet — not useful. When you call us for a generator quote, tell us about your distribution needs too. We'll spec a complete package that gets power where it needs to go, safely and efficiently.

Call 888-702-0440 or request a quote online. Same-day dispatch available for emergency power needs.