Martindale lok7 black slimline mcb isolation lock martindale lok7 p the slimline martindale lok7 is less than half the width of a standard mcb lock and around 30 shorter the reduced size makes it ideal for use where clearance around the breaker is limited p p the slimline design is particularly well suited to breakers where the position of the test button may prevent the use of conventional lock outs p martindale lok7 mcb small black isolation lock