Eric, I had a similar problem with a DeviceNet interface. Both sides are low voltage and the spec says it should have a 500V isolation. I do not consider this a safety spacing as such but my PCB designers needed some guidance. I used the full 500V spacings but not from the Overvoltage Category IV, III or II. Since I considered this to be functional/operational spacing Overvoltage Category I is appropriate. The tables I used came from EN50178 which is a derivative of the IEC 664-1 and is similar to EN61010-1. The results are as follows:
500 V isolation; OV Cat I; Pollution Degree 2 ------------------------------------------------ Functional Clearance = 1.3 mm PCB creepage = 2.5 mm Impulse withstand = 2.2 kV Hipot test = 2000 V, 60 seconds ------------------------------------------------ With proper isolating components bridging the gap this provides a functional working voltage of 500V which might be over-kill, but without more knowledge of the intent I took this option. Naturally if the "isolation" voltage is considered a hipot test voltage then the spacings could be greatly reduced. Using the same logic, a 250V isolation boundary can be designed as follows: 250 V isolation; OV Cat I; Pollution Degree 2 ------------------------------------------------ Functional Clearance = 0.4 mm PCB creepage = 1.0 mm Impulse withstand = 1.3 kV Hipot test = 1500 V, 60 seconds ------------------------------------------------ Opinions are my own..... Doug Powell Advanced Energy Industries, Inc. Ft. Collins, Colorado USA [email protected] ---------- From: Eric Henning To: 'EMC POST' Subject: spacings List-Post: [email protected] Date: Wednesday, February 11, 1998 11:22AM for several I/O circuits rated at less than 30V but with an isolation rating of 250 V, what is the spacing requirements between isolated i/o's? That is say you have two i/o circuits, extra low voltage, but in the specs say they are isolated, 250V. If you're using IEC 1010 do you use the 50 V spacings from the tables or use the 300 V spacings from the tables for spacing between the two circuits? thanks for any input eric [email protected] ps - my opinion is use the 300 V spacings.
