The laws of Maxwellian electrodynamics are used in an analysis of the structure of the 4-potential of radiation fields. The paper examines multi-particle and single-particle effects of a radiating source. Causality of electromagnetic processes is an important element of the analysis. Covariance properties of the relevant variables are examined and the apparent non-covariance of the radiation 4-potential where A_{0}≡0 in all frames is explained. It turns out that the origin of this feature stems from the multi-charge properties of radiation. It is also shown how in every Lorentz frame one can use covariant properties of radiation fields and reconstruct an appropriate 4-potential.