my zanussi built-in double oven trips out when both ovens on together?

what is causing the problem of tripping the electric in the house when both ovens are turned it usually takes aminute or two for it to happen, they both work normally seperatley but
not together and as christmas is around the corner remembered it was a nightmare last year trying to get the food cooked at same time [zda45w] and is it easily repairable