Creepage distances for aircraft power supplies

Double or single insulation? If I recall, its 4mm single 8mm double. And a whole other story above 150v.

Cheers

That sounds too high. Mil allows down to 1.5mm for low power stuff in some situations (under 150V). Lower power usually meaning that it does not exceed 50W. Medical is 4/8mm.

Do you remember what the standard was called?

| > Double or single insulation? If I recall, its 4mm single 8mm double. And | > a whole other story above 150v. | >

| | That sounds too high. Mil allows down to 1.5mm for low power stuff in | some situations (under 150V). Lower power usually meaning that it does | not exceed 50W. Medical is 4/8mm. | | Do you remember what the standard was called? |

Well, yes, that's my home turf: Medical. But it is different for nearly all other markets.

Well, whichever one it is, I'd say if you follow what the medical one says, it should be stringent enough to cover airplanes. (unless there's a military one). The only other concerned parties should be the people in the airplane and the insurance company. ;-)

Good Luck! Rich

Well, the medical one costs too much space. And I've only got the military regs, was hoping someone would know the civilian ones.

It is probably less than the medical numbers, so if you go with the medical numbers, you will likely be inside the mil/aviation numbers.

Atmospheric air at 70,000 feet has a higher breakdown voltage than at sea level.

Hello Joerg,

Your creepage and clearance distance depends (as you know) on Peak Working voltage, Transient voltages, Insulation surface and alltitude. Maybe IEC 60664-1 can help you (table A.2).

One example, up to 33000ft, for clearance, you need to multiply with

Best regards,

Wim

Hello Joerg,

After 12 hours my posting did not appear over here. I already sent you a reply directly.

Creepage and Clearance distances depend on working voltage, maximum transient voltage, surface characteristics of creepage paths and air pressure.

IEC 60664-1 deals with these issues, many product standard derive there creepage/clearance requirements from this std. Table A.2 gives the multipliers for higher altitudes. For example for 33000 ft (10 km), the multiplier for clearance through air is 3.02.

Best regards,

Wim PA3DJS

You could do worse than to consult IEC60664, or even the ancient VDE0804. These all have pressure/altitude information.

Aircraft standards tend to be controlled by conformance documents relevent to the model, issued by their manufacturer. This is a pretty specialized field of power conversion , possibly approached most sensibly for the first time from the ground support or test/diagnostics end.

In military standards, more emphasis is actually placed on creepage and clearance at the connector set, where it is assumed that the most fragile and concentrated safety interface will occur, not in the built-in isolators or enclosed printed wiring.

MIL HDBK 5400 and NAVSO P-3641 make good reading on power assemblies for hi-rel applications.

RL

Thanks, Wim, it did appear over here. Also got your PM. Sometimes posts propagate onto your ISP's server later than onto other. I've never quite understood why.

Thanks, I'll check that out this afternoon. Hopefully it will be on the web somewhere, I only have the medical IEC/EN standards here on the table. In English and French ;-)

I am afraid we may have to go that route. In the end everything neeeds to be STC'd anyhow but we don't want to risk a black eye at that point.

Thanks, RL. I've got the military ones here and was surprised they allow down to 1.5mm for low power gear.

That's the problem, we do not have that much real estate here. Otherwise I usually go with medical because it is stricter than pretty much anything else.

Have you tried EUROCAE

They usually do not conflict with RTCA....

The military regulations are probably easier. They expect losses anyway.

regards, Gerhard

Thanks, Gerhard. Things is, RTCA DO-160 does not spec it. We must comply with US regs.

That wasn't nice ;-)

Usually the mil stuff is really good.

Yes, but the breakdown curve goes DOWN from sea level to about 30k ft, and then starts going back up. WHich has ABSOLUTELY NOTHING to do with the breakdown in insulation.

Jim

-- "It is the mark of an educated mind to be able to entertain a thought without accepting it." --Aristotle