Loud BOOM! in Upper Ajijic this morning around 7:00am...

...followed by a strange lack of electrical power.  I guess a transformer blew!  What was strange was the electrical voltage  measured in different parts of the house after the event.  28-30 VAC in the kitchen.  97-98 VAC in the bedroom.  128-133 VAC in the bodega.  Weird!  A couple of hours later everything was back to normal.

Was this a rare, one-off occurrence in Ajijic?

Nope, transformers blowing and/or having a phase or two down occurs a few times each year. Even more depending on where you are located.

Happens in Chapala several times a year too.

As Bob says, the loss of a phase or two explains the different voltages you measured in different parts of the house. Do you know if you have a 3 phase service entrance to your main fuse panel? In our area we have lost a couple of 3 phase motors (on water pumps) due to this condition as the motors overheat when trying to run on this kind of a power condition. There is a new type of overload protector that can detect a phase imbalance like this and disconnect the supply going to the motor. The overload protector circuitry then checks periodically to see if the imbalance is gone and if so, will reconnect the supply. It can also detect ground fault conditions. More info at Siemens for a device called the ESP-200.

Ezzie,

I have a 3 phase service and also a solar system on the roof.  I know virtually nothing about the solar panels and how they integrate into the main electrical service.  I have only lived at this house for the last couple of months.  I did wonder if the solar was providing some feedback during the outage though.

Good question you raise about whether the solar system is "feeding back" power during a drop out of one or more of the CFE supplied phases. If you don't have a clear understanding of how the system is integrated, I would suggest you start asking some questions of the original installer or someone who is familiar with your type of system. It could be a dangerous condition unless there is some sort of protection circuitry to prevent sending power down a dead CFE feed.

Most solar systems cannot support themselves unless they have battery packs (most systems don't). They only generate power to put back into the electrical grid to gain credits which are applied towards your usage.

At 8 this morning the fuse for one phase blew up at Angel Flores and Tempisque. That was the boom you heard. Fixed by 10:30am. Same fuse blew up yesterday in afternoon in a smoking sizzle rather than a boom. My Casita phase was fine but all over the place as OP posted the wierd voltages.

As far as putting electricity back into the grid on a dead line I doubt if anything would happen other than the electrical equivalent of stalling a car with a clutch. I can't imagine what kind of system could take a dead load like that. If the electronics don't sense proper AC on the grid I doubt if they would even try to sync up.

Z

I hope so - there must be some sort of fail safe that prevents a solar system from feeding back into a dead CFE line. There have been instances NOB where linemen have been accidentally killed by people running backup generators without the proper disconnect switches in place.

Must have been a big generator or small load for a generator to stay energized connected to the dead grid. You would have to generate all of the load on the grid or the generator would stall or disconnect depending on design. Solar systems inverter and electronics sync to the grid sine wave so no sine wave AC voltage present no connection to the grid. They can't and shouldn't work on a dead grid.

Well, if fuse is down, there may not be a big load facing a standby generator and if a lineman forgets to follow SOP or a ground is bad (unthinkable here in Mexico...LOL) you could have a dangerous situation. Just sayin ... the OP needs to know what he has there. The following is from the California Energy Commission's website regarding the use of portable generators.

"Don't connect your generator directly to your home's wiring.

Connecting a portable electric generator directly to your household wiring can be deadly. A generator that is directly connected to your home's wiring can 'backfeed' into the power lines connected to your home.

Utility transformers can then increase this lower electrical voltage to thousands of volts. That's more than enough to kill a utility lineman making outage repairs many miles away. You could also cause expensive damage to utility equipment, your home appliances, and your generator.

If you wish to hard-wire a generator to your home, it should be installed by a licensed electrician with an approved cut-off switch that will automatically disconnect the home from the power grid when the generator is being used. Please check with your local utility company and building office before installing a hard-wired generator."

Many people don't understand how the electrical grid works. No lineman NOB would work on the line without first putting on his high voltage gloves, then attaching ground clamps on the line which he would use a hot stick to attach them, also he would be in a bucket truck or an insulated ladder and wearing insulated boots so he is well protected. After 40 yrs in the Kitchener Waterloo Cambridge area I can not remember a lineman being electrocuted, falling off a ladder ......yes...

A high school friend of mine went on to become a lineman for Ontario Hydro and was electrocuted while working on a power line near Woodstock, ON about 40 yrs. ago.  With all the training they get, sometimes accidents can still happen.

Well we lost the same fuse this morning again and were down to one phase. They just rewired the 45kva transformer and hopefully our daily fuse going pop or smoking will be a thing of the past.  They also found another problem in the hood and fixed that. Always fun to watch them put the fuses back in 40 ft in the air with a fiberglass pole.  Steady hands and skill to do that.  Hopefully this thread can die in peace now. I am tired of moving extension cables to run the house fridge off the other phase in the casita.

I never wanted to suggest that anybody run a generator without being disconnected from the grid. I still think it unlikely anything will happen but a stall but I didn't think about the transformer issue.