# How does the insulation breakdown strength of insulating materials change with altitude in aircraft?

#### muhammetkose

Joined Aug 1, 2023
3
Have a good day,

Let's consider a scenario where we have a single box, and the outer surface of this box is insulated with an insulation material. Imagine this box being inside an aircraft. As the altitude of the aircraft increases, how does the new breakdown voltage of this insulation material change? Is it possible to calculate this change?

Thank you.

#### ronsimpson

Joined Oct 7, 2019
2,795
The insulation property of air changes with altitude. Any break in the insulation and electricity can get out. I have never had a problem with insulation. Even a thin layer of paint stops the sparks. (experience not knowledge) I live at altitude and know of the problems with CRT-TVs.

#### dl324

Joined Mar 30, 2015
16,129
As the altitude of the aircraft increases, how does the new breakdown voltage of this insulation material change? Is it possible to calculate this change?
This is what Bing's AI bot says:

"Electrical derating for altitude is necessary because altitude affects the heat dissipation capability of the heat sink and units in locations at 3300 ft (1000 m) above sea level must be derated. A common rule of thumb is a 2% derating for every 1000 ft above the 3300 ft altitude level. Dielectric strength is derated at a rate of approximately one percent per 100 m /1000m ASL. For elevations above 6562 ft (2000 m), the operational voltage (UN) should be derated according to Paschen’s Law1.

I hope that helps!

1. electriciantalk.com
2. cigreconference.ca
3. eng-tips.com
4. eaton.com
5. nepsi.com
+3 more"

I saw references to ANSI C37.30 and IEC/DIN DVE 0111 and the following table on eng-tips.com while searching:
Code:
Altitude Derating Factor
Altitude:               Dielectric(pu)     Current (pu)
>3,000 ft (1000 m)         1.00              1.00
4,000 ft (1200 m)          0.98             0.992
5,000 ft (1500 m)          0.95             0.980
10,000 ft (3000 m)          0.80             0.96
12,000 ft (3600 m)          0.75             0.95
14,000 ft (4200 m)          0.70             0.935

#### DickCappels

Joined Aug 21, 2008
10,104
It is the air, nothing more.

the thinner the air the lower breakdown

#### BobTPH

Joined Jun 5, 2013
8,098
I don’t think he is talking about air.
Let's consider a scenario where we have a single box, and the outer surface of this box is insulated with an insulation material.

#### muhammetkose

Joined Aug 1, 2023
3
I don’t think he is talking about air.
Maybe I misunderstood, sorry. I'm asking for the systems inside the aircraft. For example, I'm asking for an epoxy or silicone coating on the surface of an avionic unit. I could not understand the connection between this change in the air condition and the insulating material (such as epoxy resin) used.

#### BobTPH

Joined Jun 5, 2013
8,098
I could not understand the connection between this change in the air condition and the insulating material (such as epoxy resin) used.
What makes you think it does? I would agree with you that it does not make sense, but what do I know, perhaps air pressure has an effect on insulating materials.