The usual British practise calls for a maximum copper temperature of about 50 deg. cent, for transmission cables. Correspondence with English consulting engineers and cable manufacturers shows that their high-voltage cables have about the same dielectric losses as those furnished by the leading manufacturers in this country, that is, if measured at 85 deg. cent, the dielectric losses on their 20-kv. Cables would be of the order of one watt per foot. By referring to Fig. 14, it will be noted that for a dielectric loss of one watt per foot and a copper temperature of 50 deg. there is a rather wide margin between the operating current and the critical current which might result in cable failures due to dielectric losses. Apparently therefore our British friends are of the opinion that as long as they continue to operate their cables under conditions which eliminate burn-outs caused by dielectric loss heating, then they can secure satisfactory operation with an insulation thickness less than two thirds of what is considered necessary in this country.