Surrounding atmospheres in hermetically sealed switching devices significantly affect their arc extinctionand electrical endurance. To better understand the effects of atmosphere on arcing duration and erosion of the con-tact

experiment was conducted with the CuW70 contact material under the DC supply voltage of 200

5

00V

the re-sistive load current of 40

1

50A

and the respective surrounding atmospheres of air

N

2

CO

2

and O

2

. It was found thatthe sequences of breaking arc duratiom for these atmospher

es changed with the supply voltage. O2 always had the lon-gest breaking arc duratiom

and N

2

showed shorter breaking arc duratiom than CO

2

in the case of 200

3

00V

but CO

2

showed shorter breaking arc duratiom than N

2

in the case of 400

5

00V. Experiment also indicated the anodes sufferedmass loss in all atmospheres

however

the cathodes suffered mass loss in air and N

2

but gaied mass in CO

2

and O

2

.