When the circuit breaker cuts the electric current, an electric arc is created
between its electrodes. The success or failure of breaking the electric current
by the circuit breaker depends strongly on the physico-chemical properties of
the electric arc created, such as the composition of which depends on the
material of the electrical contacts. In this work, we determine the equilibrium
composition of the electric arc in the low voltage air circuit breaker with sil-
ver tin dioxide alloy contacts, in a temperature range from 500 K to 15,000 K
and at atmospheric pressure. We use the Gibbs free energy minimization
method and develop a computer code to determine the equilibrium composi-
tion of the created plasma. The analysis of the results obtained shows that O 2
particles with a dissociation energy of 5.114 eV, NO with a dissociation ener-
gy of 6.503 eV, and N 2 dissociation 9.756 eV dissociate around 3500 K, 5000
K, and 7500 K, respectively. We note that the electro-neutrality is established
between the electrons and the cations: Ag + and NO+
, for temperatures lower
than 6500 K. For temperatures higher than 6500 K, the electro-neutrality is
established between the electrons and the cations: N + , O+ , and Ag + . The nu-
merical density of the electrons increases when the proportion of the vapor of
the electrical contacts increases in the mixture, in particular for temperatures
lower than 11,000 K.

Plasma, Electric Arc, Gibbs Free Energy, Circuit Breaker, Electrical Contacts, AgSnO2