High Voltage Clearance Calculator

1. High Voltage Clearance Calculator Chart
2. High Voltage Clearance Calculator Formula
3. Osha High Voltage Clearance Chart

Minimum Electrical Clearance As Per BS:162. INDOOR Voltage in KV Phase to earth in mm Phase to phase in mm 0.415 15.8 19.05 0.600 19.05 19.05 3.3 50.8 50.8 6.6 63.5 88.9 11 76.2 127.0 15 101.6 165.1 22 139.7 241.3 33 222.25 355.6 Minimum Electrical Clearance As Per BS:162. High Voltage Arc Gap Calculator This arc voltage calculator can help you understand how a Dielectric Withstand Test helps your quality process. This calculator also shows how using a Helium atmosphere can help your test be more stringent. If you have any questions about high voltage testing or this calculator please call us - 1-800-441-9910. The minimum clearance distance (up to installation heights of 2000 m above sea level) is determined from the rated surge voltage and the pollution severity. A detailed overview of the calculation of the clearance and creepage distance is available as a download.

The Insulation, Pollution Degree, Nominal AC Mains, and enter the Working Voltage (peak or dc), then click on the button to get the corresponding Clearance in mm and mils.

Several years ago, Sierra Circuits published a guide toward the design and manufacture of high voltage circuit boards, with potentials up to 40,000 V.

Considering Creepage and Clearance

Much of the advice in that brief regards a narrow project category, and I have an idea that a review of the basic layout precautions for any board that would carry what is considered hazardous voltage—greater than 30 VRMS, or 60 V dc—would have a much wider audience. There's no harm reiterating such rules now and again, which could save a lot of headaches and perhaps liability down the road.

If the system or product for which your board is destined must meet IEC or UL standards, the minimum distance permitted between conductors that are subject to hazardous voltage will include a wide margin for safety, which depends on the peak working voltage, the laminate material, the operating environment (moisture, particulates, altitude), the circuit location relative to human access or proximity, and whether the traces involved are on an internal or outer layer. The spacing required on outer layers also depends on whether traces are coated or bare.

If the clearance is too small, a transient over-voltage event can result in arcing between the conductors. This is a virtually instantaneous fault that does not recur until another such over-voltage event. Faults resulting from insufficient spacing for creepage can take much longer to occur.

Determining what spacing to use is simple if your system or product requires compliance with international safety standards. Find the standard relevant to the product category and adhere to the tabulated values with respect to the details of your application as noted. For example, IEC-60950-1 (second edition) is the document to consult for most IT products to be sold internationally that are powered from ac mains, or batteries, and applies both to the primary side and the dc secondary circuits within those products.

Starting with section 2.10.3, midway through the document, the standard defines what clearances are required so that over-voltages, including transients and peak voltages that may be generated within the equipment, cannot cause faults. A series of tables, 2J through 2M, explains how to calculate clearances with respect to the details of your application. Next, section 2.10.4 explains how to determine the spacing required for creepage.

Clearance vs. Creepage

What's the difference between clearance and creepage? Clearance is the shortest distance between two conductors measured through air. Creepage is the shortest distance between two conductors, measured along the surface of the insulation separating them. Consider the ways an electrical fault between conductors can occur if the clearance or the creepage spacing is too small. If the clearance is too small, a transient over-voltage event can result in arcing between the conductors, especially if there is dust in the air or humidity. This is a virtually instantaneous fault that does not recur until another such over-voltage event. Faults resulting from insufficient spacing for creepage can take much longer to occur.

Over time, usually stemming from dust buildup and moisture, a path (in other words, a track) for current to leak from one conductor to another can develop and cause a gradual breakdown of the surface of the insulating material between them. The mechanism for this is not a voltage spike—though that could contribute—but the continual presence of high voltage combined with an insulating material whose Comparative Tracking Index (CTI) is too low.

CTI is a measure of a material as an electrical insulator and is expressed as the voltage at which the surface of a material breaks down under a standardized test. The manufacturers of PCB laminates publish CTI figures for their products. For convenience, the breakdown voltages are lumped into six categories: The highest rating is 0 for withstand values of 600 V and greater and the lowest is 5, for less than 100 V. For example, conventional FR4 has a Comparative Tracking Index of from 175 to 249 volts, which places it in rating category 3.

Conventional FR4 has a Comparative Tracking Index of from 175 to 249 volts.

The paramount objective of all electrical safety standards is of course to prevent any danger of shock. If no one will ever be near a circuit while it is powered, the clearance and creepage allowances among its conductors that are subject to hazardous voltage can be the minimum that ensures the circuit will function and not deteriorate. IEC-60950-1 specifies five increasing levels of mandatory insulation related to the physical location of a circuit relative to human contact, the voltage, and the operating environment. Naturally, the best tactic to avoid the danger of shock or circuit degradation is to space traces as far apart as possible but very often that distance will not meet creepage requirements. What can be done in those cases?

If turning to a material with a better CTI is not feasible, routing a slot in the space between two traces can increase the creepage distance. Leakage from one trace to the other along the laminate surface would have to travel around the air gap. Alternatively, a vertical barrier of insulating material could be placed in the space, which would increase both the creepage and clearance distances.

Keep in mind the spacing on assembled boards when you consider creepage and clearance requirements for layout. The distance between an uninsulated edge of a charged component and the edge of an adjacent component could be too small to meet a clearance requirement, even though the creepage distance between their traces is sufficient. Moreover, there may be some operations needed during assembly to meet clearance requirements: for example, applying potting compound to isolate the leads on the package of a power semiconductor from some nearby component.

If your project does not require compliance with a particular safety standard, you can rely on the latest version of IPC-2221, the generic standard for PCB design, for clearance and creepage guidance. In any case, consultation with your PCB fabricator and assembler regarding suitable materials (you can read our article about choosing the right material) and design alternatives will help you achieve a safe product that meets your performance objectives at the lowest possible cost.

Our quick trip through the basics of laying out boards that involve hazardous voltage amounts to just a first step, simply an opportunity to point to out some helpful and hopefully familiar guideposts as you start your journey.

For more information on design rules, check with our DESIGN SERVICE team.

I got my first exposure to PCB creepage and clearance standards way back in college at my first internship. I was tasked with developing a spark ignition circuit that needed to take 120 V and transform it up to 20 kV to create an electric spark between two electrodes. I was young and didn't even know the words 'creepage' or 'clearance' yet, so when I plugged in my protoboard circuit the incoming power arced across the board and it exploded. If you want to learn from the mistakes of my youth, you'll need to design your boards with creepage and clearance in mind. These two attributes specify the distances between conductors on high voltage boards. Requirements for clearance and creepage are governed by several standards, including IEC 60601 and IPC 2221. There are several design methods you can use to help you meet these standards so you can keep your circuitry and customers safe.

What Are Creepage and Clearance?

High Voltage Clearance Calculator Chart

If you primarily design low voltage circuits, chances are you haven't had to deal with creepage or clearance very often. So what exactly are creepage and clearance, and when do you have to start thinking about them?

Clearance- Clearance is the shortest distance in the air between two conductors. You can think of this as the line of sight distance between two mountain tops. If you had a jetpack, as I often wish I did, you could fly directly to the other peak in a straight line.

Creepage- Creepage is the shortest distance to another conductor along the surface of the insulating material of your PCB. This time you have to walk all the way down the side of the mountain, through the valley, and up the other mountain to get to the top, without jet packs.

These two definitions become important when you're designing a 'high voltage' board. Meaning if your board uses more than 30 VAC or 60 VDC then you need to start paying attention to spacing. If you don't your PCB might end up like mine from earlier, burned and smoking. This is because at higher voltages conductors can arc to one another or to other components if they're too close together. More and more designers have to learn about creepage and clearance as boards increasingly mix analog and digital circuits with high voltage circuits.

What Are the PCB Creepage and Clearance Standards?

For those of us who don't want to learn about the importance of creepage and clearance from direct experience, there are a few standards to help us. Primarily you should look into IEC 60601 and IPC 2221. These two standards detail spacing between conductors for different voltages and scenarios.

Sometimes there will be gray areas where the standards won't tell you exactly how to solve a problem or layout your conductors. Although, your CM's DFM rules will ensure manufacturability you should have your boards tested to ensure the safety requirements for creepage and clearance are met. The most well-known testing service is Underwriter's Laboratory (UL), which will validate your boards, give your customers confidence, and provide you with protection against a related contingency. At the end of the day, it's important for you to know the principles of design for creepage and clearance so you can ensure your board is compliant.

High Voltage Clearance Calculator Formula

Design for Creepage and Clearance

The most obvious solution to creepage and clearance problems is to move components or conductors further apart. This strategy doesn't really work anymore with shrinking form factors and the increasing necessity of high-density PCBs. Let's look at some specific strategies for both creepage and clearance, and examine some other factors that you'll need to take into account.

Clearance- When looking at clearance you must remember that it is the shortest distance in the air between conductors or nodes. One good solution is often to add an insulating barrier between the two points in question. If you have a double-sided board one easy way to do this is to locate high voltage components on the top and low voltage components on the bottom. Sometimes high voltage conductors that are at the same voltage do not need excessive clearance from each other; however, they do need to be separated from low voltage conductors. If that is the case for your board then the insulation of the PCB substrate makes an excellent barrier.

Creepage- When it comes to creepage you can't always just stick things on opposite sides of the board. Remember that creepage is the distance between nodes along the surface of the insulator. Thinking back to the mountaintop metaphor, one way to increase creepage is to make a valley between the peaks. You can cut grooves or troughs into the PCB substrate to increase creepage. You can also sometimes cut slots all the way through the insulator to increase the distance. This is the same strategy used on high voltage insulators on power lines, those insulators have ridges down their length to increase the creepage distance.

Material- When dealing with creepage the insulating material you choose also matters. This is because when a voltage creates a conductive path along the surface of the insulator it can break down the surface of the insulator, resulting in a more conductive path between components. The characteristic that measures this is called the CTI (Comparative Tracking Index). The higher the CTI of a material, the more insulating it is. If you're worried about creepage creating a conductive path on your board opt for a higher CTI material.

Bounding Surface - Creepage and clearance apply to your PCB's enclosure as well as its conductors. This means that when you're working with your mechanical engineer to design the enclosure you'll need to take creepage and clearance into account. You can often use the same strategies discussed earlier to handle this requirement.

My boss once told me that frying a circuit or two isn't a problem, but when I start making three or more of the same mistake, it becomes a problem. Following creepage and clearance standards for high voltage boards will ensure your PCB's safety compliance and keep it from blowing up. Remember that you can look at IEC 60601 and IPC 2221 to see what standards you need to meet. If you're at a loss for how to fix a certain problem try asking your CM for help. Lastly, you should get acquainted with some design techniques for clearance and creepage so you can be sure your PCB is safe when it ships.

Osha High Voltage Clearance Chart

Here at Tempo Automation, we have a wealth of knowledge and experience to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you're an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.

If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on PCB creepage and clearance standards, contact us.