Dishwasher keeps tripping out?

I have a Whirlpool dishwasher that for some reason keeps tripping the mains when it is switched on. For some time now though whenever we use the washing machine and it drains out, it backfills into the dishwasher, sometimes flowing out onto the floor, instead of it all going down the drain. Both machines are plumbed into the sink waste pipe. I have taken the waste pipes off and they are both clean, there is no blockage in the u-bend either. If anyone has any idea as to what is making my dishwasher trip out, then please share it with me. Many thanks