A flame-retardant flat electrical cable has a magnesium oxide dielectric layer. A plurality of spaced apart substantially parallel electrical conductors generally lie in the same plane and extend along the length of the cable. A dielectric layer is disposed on the top and/or bottom sides of the cable and covers the conductors. The dielectric layer comprises at least 90% magnesium oxide by weight. The dielectric layer exhibits good dielectric properties and is flame retardant without the use of halogens.