Thousands of customers of the Salt River Project's prepayment electricity program are at risk of losing their power. Customers of the project, called M-Power, use an electronic card to purchase power at any of the utility firm's 100 payment machines installed across the Valley.

Starting Saturday morning, the company began receiving calls from confused customers who said that they could not buy power. "We're still working on it. We still haven't found a root cause", said  Jeff Lane, an SRP spokesperson.

Customers can, in the meanwhile, call 602-236-8888 can get a code from a customer representative which they can then use on their digital box terminals at home. As confirmed by the spokesperson, the code will put customers in "friendly credit mode", so that they can gain access to power for up-to 7 days. They would be charged for the amount of electricity used.

The project is 15 years old and the largest system in North America by SRP, and Lane has confirmed that the company has not "had a problem with (M-Power) that (lasted for) more than an hour in five years".

M-Power is currently used by an estimated 93,000 customers.