IPC-2221 is generally accepted in electronic industry as a generic PCB design standard. However, when it comes to distances between the PC traces, in my view, the IPC-2221 table 6-1 stepwise limits are mostly baseless: the curve for spacing vs. voltage should be linear. Of course, it is not the only standard that defines the electrical clearance. For power conversion circuits IPC-9592 initial draft provided the following linear circuit board spacing recommendations: SPACING (mm) = 0.6 + Vpeak x .005. In general, a linear relationship makes more sense. However, these requirements were also too conservative and at low voltages were not even practically doable. The latest IPC-9592B document left the above equation only for V≥100V. At other voltages the limits are as following: 0.13mm for V<15V, 0.25mm for 15V≤V<30V and 0.1+Vpeak×0.01 for 30V≤V<100V. Note that all IPC standards are voluntarily rather than mandatory. Conversely, for the products covered by safety standards the creepage and clearance requirements of a respective UL/IEC standard are mandatory. For example, for most ITE applications you need to use UL 60950-1 Tables 2K to 2N.

One would think that UL norms should be most stringent than IPC. However, it is interesting to note that when it comes to functional insulation in secondary circuits, UL requirements are not necessarily more stringent than IPC. See our calculator and guide to PCB creepage vs. voltage for a comparative analysis of different IPC and UL requirements.

Internal layers External conductors,
External conductors
Vpk, V mm inch mm inch mm inch
15 0.05 0.002 0.1 0.004 0.05 0.002
30 0.05 0.002 0.1 0.004 0.05 0.002
50 0.1 0.004 0.6 0.024 0.13 0.006
100 0.1 0.004 0.6 0.024 0.13 0.006
150 0.2 0.008 0.6 0.024 0.4 0.016
170 0.2 0.008 1.25 0.05 0.4 0.016
250 0.2 0.008 1.25 0.05 0.4 0.016
300 0.2 0.008 1.25 0.05 0.4 0.016
500 0.25 0.01 2.5 0.1 0.8 0.032
1000 1.5 0.06 5 0.2 2.33 0.092
2000 4 0.158 10 0.4 5.38 0.22
3000 6.5 0.256 15 0.6 8.43 0.34
4000 9 0.355 20 0.79 11.48 0.46
5000 11.5 0.453 25 0.99 14.53 0.58
Note that if your ITE is manufactured or sold in China, their standard GB 4943.1-2011 assumes your unit must be suitable for use at altitudes up to 5000 m. This will require clearance limit 1.48 times of IEC/UL 60950-1 unless your device marked as suitable for use only up to 2000 m. Also note that the discussed requirements here are related only to breakdown safety. From the standpoint of PC trace temperature rise, you may want to increase the distances between power tracks (see this analysis and calculator).

The chart to the left is adapted from columns B1, B2, B4 of IPC 2221B Table 6-1. It lists recommended minimum spacing between internal and external conductors as a function of peak working voltage level for intended use at altitude below 3050 meter (10.007 feet). The official IPC table also provides the numbers for external conductors at elevations >3050m as well as requirements for assemblies, which I omitted here. Note that IPC gives the spacings only up to 500V and provides formulas for calculating their values above 500V. For example, for uncoated tracks it is 2.5+(V-500)×0.005 (mm). For your convenience, in this table I've added calculated distances for higher voltages based on these formulas. All my calculated numbers of course are rounded.

Note: This guide is provided for informational purposes only and does not constitude a professional or a legal advice- see the Disclaimer linked at the bottom of this page. Consult with respective standards for final design decisions.

IPC-2221B is Copyright ©2012 IPC, Illinois ( All rights reserved.

Privacy | Contact us | Disclaimer | Disclosure

©2008, 2012-2014 Lazar Rozenblat