this is the situation:

We have supplied a paralleling switchgear that synchronize a 2500kw Generator with the local utility. The first time they run the equipment using their actual loads, it did synchronized and run for several days already. Then due to bad weather the there was a power disturbance causes the utility mains circuit breaker to trip off ,same with the generator breaker. In other words there was total shudown inside the plant.
Productions and operation was stopped. Now the customer is charging us for the production loss , and machine's electronic parts were damaged due to power outage as what they were claiming.

Are we liable to pay for it? W e dont have a contract or agreement for such liability or damages. They only gave as Purchase Order for the supply of Paralleling switchgear.

What is your stand about it. In your opinion what will be my strong defense againts this kind of situation.

In addition , we have still 50% balance uncollected to this customer and the they are charging us a 48% percent of the total amount.