I got a call on a job saying that every time the power goes out, all seven garage door fuses blow. These openers are a new design from Overhead Doors. When the controls see an overvoltage, they cause the fuse to blow. During the first 6 months after commissioning, this small town had at least 4 outages including a direct lightning strike that toasted a pole mounted transformer in the field next door and took out one phase of the surge suppressor with no other damage to the building. Three of the outages were due to the local utility and one was due to Duke who provides their power for distribution locally. Several were single phase conditions.
The facility has a generator. It is the fastest starting generator I have ever seen.
The power system is 240V open delta. Voltage on A to neutral and C to neutral is 122V. B is 212V to system neutral. The garage doors were initially wired 240V. No neutral. The first attempt at a solution was to rewire them 120V and made sure they were all on A or C, some on each. Voltage was verified as being 120V on each source. The power went out. All the fuses went out. The power goes out a lot.
These control fuses blow whether all phases go out or whether the A-C phase goes out. (I don't know if the B transformer is BC or BA so I will just call it B). Doesn't matter whether it is Duke or something local. Doesn't matter if it is very short or very long. Every time those 7 fuses go out and nothing else goes out in the whole building. So, I thought maybe there is a utility capacitor switching surge when the power comes back on. Sure enough - a capacitor six blocks away.
I told them I bet $50 that if they pulled the power on the local pole, that the fuses would be okay. Thank God nobody took my bet. They pulled the A-C disconnect on the pole, the generator came on and all 7 fuses went out. We replaced one fuse - these fuses are 30' up - and opened the generator breaker and tried again. Thought maybe the generator was coming on so fast that it was causing issues. Fuse went out. Maybe the circuit board didn't like any outage. Opened the breaker. Closed the breaker. The fuse was fine. Opened the main, closed the main - fuse still fine. Maybe a switching surge? Opened just the B disconnect. Fuses were fine.
The theory of the moment is that the boards are super sensitive to transients of any kind on A-C and that putting a time delay on them so that they come on after the power has been restored is going to solve the problem.
Has anybody seen anything like this? And what do you think of the problem and solution?
Additional facts: power outages have occurred at night when nothing was on. Today was a beautiful day and the HVAC should not have been on. There is one three phase load, a compressor, and it has not been on. At night, the only thing on are three security lights - the fuses still go. These are control fuses. The garage doors are not operating when they blow in general.