I always find it a bit humorous when I notice someone overreacting to a “Danger: High Voltage” sign. I want to tell them that there is no need to fear voltage it is the current that can kill you. But, I was once an electrical novice myself, so I understand those signs do look ominous. And in fact, as Ohm’s Law clearly indicates there is a direct proportionality between high voltage and high current. So, to be on the safe side, it is probably best to avoid high voltages.

Just as with most things, high voltage can also be very beneficial. For example, high voltages are used in industrial equipment to supply automated production processes, help move heavy items, and animate robotics. Although there is no need for fear, there are special requirements for developing high voltage electronics and PCBs. First, let’s look at how and why these boards are used in production systems and then what high voltage PCB design considerations can be applied to ensure safe and reliable industrial boards.

High Voltage Boards for Production Systems

In the US, commercial and industrial facilities are supplied with varying voltage levels from the grid. Voltage levels are set by the grid’s distribution system configuration (wye or delta) and the cable connection to the facility. However, the level supplied is determined by the needs of the industrial location. Industrial production facilities may be supplied by one of the following:

INDUSTRIAL VOLTAGE SUPPLY LEVELS IN US
1𝚹/3𝚹 Wye	Delta	Typical Uses
120/208VAC @ 60Hz	208VAC @ 60Hz	Computers, small HVAC systems
230/400VAC @ 60Hz	400VAC @ 60Hz	HV industrial equipment
240/415VAC @ 60Hz	415VAC @ 60Hz	HV industrial equipment
277/480VAC @ 60Hz	480VAC @ 60Hz	High voltage lighting and larger HVAC systems
347/600VAC @ 60Hz	600VAC @ 60Hz	HV industrial equipment

The AC voltages in the table above are the root mean square (RMS) levels, which are essentially the DC equivalent for the same power. The peak value, which is the absolute value of the amplitude assuming no DC offset, is approximately the √3 times the RMS value. For example, the actual voltage peak from a 600VAC supply is ≅ 1kVAC (1039V). Although uncommon, higher AC voltages and DC voltages may be supplied to some industrial facilities.

According to the National Electrical Code® (NEC®), which is used in most areas of the country to set safety standards for electrical wiring in residential, commercial and industrial facilities, electrical circuitry is categorized as class 1, class 2 or class 3 based upon usage and power limits, as listed below.

• Class 1
  • Power limited circuit
    • Maximum output voltage - 30V
    • Maximum output power - 1000VA
  • Remote control and signal circuits
    • Maximum voltage - 600V
• Class 2
  • Voltage range 0 - 30V
    • Maximum power - 100VA
  • Voltage range 30 - 150V
    • Maximum power - 0.5VA
• Class 3
  • Maximum voltage - 100V

The classifications above apply to circuitry internal to a plant or factory and exclude mains supply power and lighting circuitry. Although power supply circuit boards are classified according to their output voltage and power. There is no universally accepted definition for high voltage; however, the generally accepted level for industrial circuitry is ≥ 100V (AC or DC). Thus, your HV boards will typically fall under class 1 or class 2.

NEC® and other industrial circuitry regulations and guidelines are utilized in industry to provide a safe working environment for personnel, as well as to protect equipment from damage. The primary hazards are electrical shocks and fires, which can occur on cables and high voltage PCBs, as shown below.

Result of PCB hazard event

For circuit boards, the primary causes are overvoltage, where the voltage level spikes above the nominal level and lasts for more than one second (shorter spikes are usually not a problem), shrinking clearance, the shortest distance between conductive elements (traces, pads or components) on the board through the air, and inadequate creepage , the shortest distance between conductive elements along the board surface. Although, preventing these high voltage PCB hazards depend to a high degree on interconnected circuitry and the industrial environment, there are design considerations that can aid in preventing them.

Essential High Voltage PCB Design Considerations for Industrial Electronics

Voltage spikes that may appear on your board can create a large potential difference between nearby conductive elements causing arcs through the air or shorts where the creepage or clearance distance has been effectively reduced or eliminated by dust or other debris. The resulting current can damage components, the board and pose a hazard to personnel. To reduce the possibility of these events, high voltage PCB design considerations, as listed below, should be implemented.

High Voltage PCB Design Considerations for Industrial Boards

Choose appropriate creepage and clearance distances

Probably, the most design decision to minimize the probability of an HV hazard event is to route traces and place components and drill holes with adequate clearance and creepage distances. The IEC 60950-1 and/or UL-60950-1 standards provide guidance for these determinations.

 Avoid using sharp edged terminal pads

Using elliptical or circular pads is preferable to rectangular or square pads as they contribute to increased clearances.

 Select high voltage materials

It is also important to select board substrates and laminates that are rated for high voltage and/or power.

 Utilize board surface finishing

Protecting your board during manufacturing is important. And you should employ the best surface finish for your design during fabrication to protect your board from debris that may become trapped during board assembly and present a conductive target during operation.

 Apply conformal coating

Although sometimes omitted, having the right conformal coating type applied to your board during the PCBA manufacturing stage should always be done for high voltage industrial boards to mitigate hazards and protect the board from environmental debris.

Incorporating the above list into your design along with following good guidelines and tips for high current PCB design will help reduce the possibility of high voltage hazards for your industrial PCB.