  We reconsider the effect of electromagnetic radiation from superconducting
strings on cosmic microwave background (CMB) mu- and y-distortions and derive
present (COBE-FIRAS) and future (PIXIE) constraints on the string tension,
mu_s, and electric current, I. We show that absence of distortions of the CMB
in PIXIE will impose strong constraints on mu_s and I, leaving the possibility
of light strings (G mu_s < 10^{-18}) or relatively weak currents (I < 10 TeV).
