nygrenm92
Member
- Location
- Massachussetts
Is there a standard for minimum clearances for DC (interested in 1250V) from phase to ground (edge of cabinet), and phase to phase (pos to neg)?
Minimum Clearance for DC
- Thread starter nygrenm92
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FWIW..
We did a lot of DC to DC converters at around 1,000 Vdc at quite large powers. We spaced the bus bars 50mm (2 inches) apart. I don't recall there being any regulations requiring us to do this.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
For manufactured gear, there are guidelines, but no absolutes. Basically speaking, if a design passes testing, it's good. The guidelines are pretty much what is KNOWN to fail at different levels.
Read this White Paper, it sums it up very well.
https://www.powellind.com/sites/dow...Bus Spacings in Metal-Enclosed Switchgear.pdf
Read this White Paper, it sums it up very well.
https://www.powellind.com/sites/dow...Bus Spacings in Metal-Enclosed Switchgear.pdf
If the insulating media is air, the dieletric strength of air is about 30 kV/cm. Your disruptive voltage would be the DC voltage as this voltage does not change with time! Assume a smooth conductor and the STP temp and pressure air density factor as 1.0. The formula I remember back in school was:
Vc (disruptive voltage in kV) = (cond. surface factor) X (STP temp and density factor) X (dielectric strength of media) X loge(d/r), where d= spacing of conductor, and r is the radius of the conductor!
Depending on the conductor size, my quick calc tells me is about d= 1.0425 X r (in cm). IDK about busbars that are rectangular!
junkhound
Senior Member
- Location
- Renton, WA
- Occupation
- EE, power electronics specialty
1250 Vdc
Fully sealed raintight cabinet, or other type cabinet?
If any possibility of any critters (spiders, inchworms, silverfish, etc) getting in you need to insulate all conductors.
Have tested spiderwebs and at 550 Vdc and above a spiderweb can initiate an arc - and unless current limited, a dc arc does not extinguish easily.
Repeated wet and dry on almost any surface gap between 1000Vdc (or even ac) uninsulated lugs will eventually track across even 2 inches.
Fully sealed raintight cabinet, or other type cabinet?
If any possibility of any critters (spiders, inchworms, silverfish, etc) getting in you need to insulate all conductors.
Have tested spiderwebs and at 550 Vdc and above a spiderweb can initiate an arc - and unless current limited, a dc arc does not extinguish easily.
Repeated wet and dry on almost any surface gap between 1000Vdc (or even ac) uninsulated lugs will eventually track across even 2 inches.
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