by Simcona on Sep 12, 2023 9:39:04 AM

It’s not just the product – it’s also how you use it.

There are many right and wrong ways to wire an industrial control panel according to NEC (National Electric Code) standards. Sure, the specs of the wire itself matter (and we’ll cover them below), but layout and safety planning are arguably even more important.

Stick these eight guidelines as virtual Post-It notes in your mind whenever you begin a high-stakes control panel wiring project:

Control Panel Wiring Design Tips for Meeting NFPA Standards

Cable and wire are an underappreciated step in executing a great industrial control panel design. To help your final product run safely and smoothly, follow best practices for:

1. Size
2. Wire type
3. Space
4. Routing
5. Safety circuits
6. Termination
7. Grounding
8. Labeling
   
   

1. Size

Wire Gauge

NFPA 79, a standard produced by National Fire Protection Association, outlines wiring regulations for industrial control panels that operate at 600 V or less. Part of its purpose is to help you select the right wire size.

AWG (American wire gauge) is a measurement of diameter that clues buyers in to the expected performance of a given wire. Using cable components with the proper insulation thickness for your application results in a just-right amount of voltage and a more efficient panel.

Excessive current flow can damage components, while a lack of voltage can limit device effectiveness. In general, the more electrical juice you need, the thicker cable insulation you’ll want to keep heat radiation from causing a short-circuit or fire.

Remember that electrical panels must manage multiple voltage levels, and you’ll need different wire gauges for each.

Wire Length & Slack

There’s good and bad to a connection having more wire than it needs at the moment (hint, hint).

The bad first: Excessive wire length can cause:

• Tangling
• Wasted space
• Increased resistance

Keep wire lengths reasonable, but not so short that they cause problems for the operator later.

The good side of slack: It can save you a huge hassle when expanding or rearranging the control cabinet after installation. This is why we’re also pro-service loops – having an extra few inches is infinitely more convenient than having to find and label a new wire.

(Pro tip: Store wire slack under the main wireway and away from devices.)

Cable Tray & Duct Size

Don’t forget that the supporting trays and ducts need to fit the job too!

Using the right cable trays and ducts helps keep the cabinet organized, reducing the chance of damage from neighboring components.

Fortunately, NFPA 79 helps out again by providing specs for wire trays and conduits. When planning to run wires, consider both “how much” and “how big.” Then size your ducts, conduits, and other raceways to match.

2. Wire Type

Stranded vs. Solid Wire

The physical build of an industrial wire falls under one of two categories: stranded or solid.

A solid wire has a single, solid core. A stranded wire is actually a twisted-up bundle of several thinner wires. 

Stranded Wire

Solid Wire

Affordability

✅

Current Capacity

✅

Current Distance

✅

Flexibility

✅

Durability

✅

Maintenance

✅

Overall, when in doubt, lean toward stranded wire (but ask an expert first). 

This wire type generates less heat, and its conductors can withstand up to millions of flex cycles. If a thread of stranded wire breaks, you can get away with repairing only the broken strand. If part of a solid wire breaks, the whole thing goes in the scrap heap.

A disclaimer on current capacity: Although stranded wire has less resistance overall, each strand is more resistant than an identical-size solid wire. Using stranded wire may lead to disappointing results in high-current applications.

Wire Material

Cable jacketing and wire insulation material determine the wire’s self-preservation abilities. Many industrial-grade wire materials need to be extremely durable to withstand their environments.

Depending on application, the top design factors in choosing a wire material may be:

• Mechanical performance – crush and cut-through resistance

• Temperature & flame resistance

• Flexibility

• Corrosion resistance

• Processability

3. Spacing

NEC’s Article 409 (Section 104, to be exact) is all about wire spacing. And for good reason – it’s probably the aspect of panel design that engineers botch the most.

Many spacing catastrophes start with the control panel’s surface area being too small to begin with. Right away, the assembly can’t meet wiring space and bending space requirements.

It’s incredibly easy to avoid these violations with a little foresight:

• Before your design gets too far, create a detailed control panel wiring diagram. Give equal consideration to electrical and physical implications of the design. Recognizing and fixing pitfalls in this stage will keep them from popping up during assembly or maintenance.

  
  
  

• Give some personal space to sensitive wires (i.e. CAN bus and Profibus).  They should never be neighbors with main power supply cables, which can hamper transmission; or heat-generating components, which can cause deterioration. Proper wire management (see section 4) should give you enough space to accommodate sensitive wires.

  
  
  

• If there’s a more than 0% chance the panel will change or add functions someday, don’t build it “fit for purpose.” Leave room for remodeling so that a simple addition of a relay or terminal doesn’t trigger a violation. 

Follow these tips, and you’ll be known as the hero who extended your panel assembly’s life span.

4. Routing

With all the expensive and intricate devices you need to accommodate in a control panel layout, it’s easy to prioritize the wiring last. But those fancy parts will perform better if you give equal attention to the supporting cast.

One way to start? Grabbing a CAD tool that optimizes routes for you. While you’ll need to check the software’s work and tweak as needed, using CAD ultimately saves material cost and install time.

Your goal is to make a clean, logical, and protected layout:

1. When you path a wire, go top to bottom, then through. Stick to the beaten path – taking a diagonal path or crossing over devices is usually a bad idea.

   
   
   

2. Arrange the wires logically to minimize risk from other panel components. Consider what’s nearby that could cause a short circuit, disconnections, or signal interference.

   
   
   

3. Secure the wire layout with cable ducts and raceways. Holders will keep the wires from tangling or loosening, while covers will keep out dust, moisture, and other harmful substances.

Other practices to keep in mind:

• When using flexible cables, install them in a way that allows moisture to drain away from fittings & terminations.

• Don’t use cable ties – trays & raceways are more professional solutions.

• When you verify the system’s functionality, cover the wireways last.

  
  
  

5. Wiring Safety Circuits

Failing to wire certain components in a certain way will spell certain doom.

Safety circuits protect a panels’ control and power devices. These protective elements include fusible switches, circuit breakers, and relays. 

For example, safety relays detect wire breaks (among other faults) by sending an electrical pulse through the wiring. The relay measures the flow of current, detecting any interruptions. Also, most electronic safety circuits keep the machine from operating if the circuit is open. 

An interesting and nuanced concept in safety circuits is wiring them in series. This strategy can keep wire layout simple, effective, and low-cost.

Wiring safety components in series means that if any section isn’t properly closed, the entire circuit will open, stopping the machine. Safety circuit controls can require series wiring so that the panel remains safe if a connection suddenly loosens or breaks.

There’s one drawback to weigh: Series-wired circuits with 5+ safety switches, or those with heavy-use switches or gates, don’t perform quite as well. They also carry a higher risk of fault masking, which means fixing one switch or fault may deceive the technician into missing a second issue. If this sounds like too much trouble for your particular application, consult with a panel expert about a more sophisticated solution.

6. Termination

Secure and well-insulated connections are key to reliable control panel performance. Loose terminations can cause safety hazards and voltage drops. 

A good termination process begins with using a connection method appropriate for the application. It should end with covering the connection with a terminal block or heat-shrink tubing so there’s no accidental contact.

Some additional best practices for panel wire termination:

• Tighten terminal screws securely. At the fitting location, use the provided screws or clamps to fasten the wire to its mating socket.

  
  
  

• Don’t force in extra conductors.

  Most connecting blocks only accept one or two conductors.

• Don’t solder terminals unsuitable for it. Instead, retain conductor strands with crimping or bootlace ferrules.

• Prevent fraying in shielded or screened wires. If the screen needs connected, use a sleeve and soldered pigtail; if not, trim it back and add the sleeve.

  
  
  

7. Grounding

Poor electrical grounding is one of the top causes of control panel failure. It’s a human safety risk and produces electrical noise that hampers device performance.

Route your grounding wires separately from power cables. This prevents the current from cross-mingling among wires and becoming a shock risk.

There are other ways your control device layout design can promote safe, effective grounding:

• Include a dedicated grounding busbar. Mount this in an easy-to-access spot for connecting all grounding conductors.

• Avoid ground loops. Route grounding conductors in a direct, single-point fashion with the minimum length needed. This keeps connections from causing unwanted noise or voltage differences.

• Be extra-careful with safety circuits. Properly grounding these components will protect users from shock. 

Grounding best practices can vary based on your industry’s electrical panel and wiring standards, codes, or other requirements. If you’re outsourcing the panels’ manufacturing, your contracted panel engineering company may be able to help with compliance.

8. Labeling

Sometimes, the single action of trying to locate a wire inside a panel can translate to long production outages. Think about how much 1 hour of downtime could cost you or the end buyer.

And you don’t need us to tell you the safety risk of labeling wires poorly or not at all.

Whether you prefer wraps, flags, or direct labels, the basic rules are the same. All control panels should have clear and visible labels, identifying each component’s function and its wiring points. They should be durable enough to remain readable through years of use in the panel’s environment.

Other points to consider when labeling industrial wires:

• Think like a service tech consulting the schematic. If there's an issue post-deployment, how can you make it as easy as possible for them to ID which wire to trace?

• Use industry-standard color codes for power, signal, and control wires. This helps electricians quickly ID wires, their functions, and the underlying problem.

• Include an SCCR mark. Short-circuit current ratings, required by NEC, help switching isolate a shock or fire hazard of a component not rated for that current.

  
  
  

More Guides on Control Panel Design

Proper panel wire management is crucial for control device operation and maintenance that’s safe, yet efficient. 

Commit best practices to memory, whether your control panel production happens in-house or elsewhere. Even today, some panel manufacturing happens in small, local shops that specialize in instrumentation, but lack understanding of NEC requirements.

To learn more about the right and wrong of control panels, from insulation thickness to design-for-serviceability, visit our resource center: