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 } \lesssim 10 ^ { -18 } ) or relatively weak currents ( I \lesssim 10 ~ { } { TeV } ) .