Help Identifying Cause of Total Power Outage in Commercial Unit – Suspected Builder-Related

F

fireshaper

New User
Location
Australia
Occupation
business owner
Hi everyone,

I’m seeking insight into a mass electrical outage that occurred at my commercial premises, a hot yoga studio located in Australia—on May 28, 2025. The incident resulted in a complete loss of power to my unit and significant damage to equipment. I’d greatly appreciate expert perspectives on what might have caused the issue and whether liability could fall on a builder working on the roof at the time.

Background:

  • My building is a single-level commercial complex with 7 units, all connected to a main switchboard at the opposite end of the property from my unit.
  • I have one main panel and one subpanel inside my unit.
  • The subpanel feeds 24 Far-Infrared heating panels, wired as 2 panels per circuit (12 circuits total).
  • All equipment was functioning normally in the early morning (heating panels, AC, lights, computer).
Incident:

  • Around mid-morning, my entire unit suddenly lost power—every circuit tripped, including the main switch at the external building switchboard.
  • At the same time, roofing contractors were replacing the metal roof across the building. They claimed to be working only at the opposite end of the building, focusing on air conditioners.
  • My staff immediately consulted the builder, who began flicking breakers at both my internal panels. When nothing restored power, he brought in two workers and later accessed the main external switchboard.
  • Shortly after they left, power returned to lights only. Heating panels and several devices remained non-functional. The builder had energized all the switches in my main panel and sub-panel. He then went down to the other end of the building and energized the main power switch which was in the off position (no one knows why it was off).
Findings (from Licensed Electrician Contractor):

  • All 15 sub-circuits were tested: 12 failed insulation resistance tests, with faults between active/earth and neutral/earth.
  • 11 of those 12 faulty circuits were connected to the heating panels.
  • A total of 23 heating panels were damaged, along with a computer and 2 LED panels.
  • They suspect a massive inrush current occurred when the builder reset the main breaker without isolating any downstream circuits.
  • The inrush current estimate was 188A (24 x 1800W panels), which likely exceeded the breaker’s rating and triggered the damage.
  • They concluded the most probable cause was improper energizing after an initial trip—everything was left ON during reset.
No storms, grid faults, or external electrical events were reported in the area that day.

​
What I’m Seeking Advice On:

  1. What would cause every circuit in a unit to trip simultaneously—including the external main switch—if not external grid issues?
  2. Could roofing work (e.g., screws through beams or AC service) feasibly damage internal wiring or cause a fault?
  3. Is it reasonable to suspect the builder caused the fault through improper handling of electrical infrastructure (e.g., flipping breakers without isolation)?
  4. What further tests or investigations would you recommend to conclusively determine the root cause?
  5. Any insights on how to support a potential liability claim (e.g., evidence, legal steps, typical builder responsibilities)?
  6. Is there a test that can be performed on the main power feed line from the main switch board at the other end of the building to my unit that could detect if the cable was “screwed” into or damaged and consequently had the screw removed leaving a damaged cable which is not currently shorting?
Thanks in advance to anyone who can offer guidance. I’m trying to get clarity before pursuing the matter further.
 
fireshaper said:
They concluded the most probable cause was improper energizing after an initial trip—everything was left ON during reset.
Click to expand...
If this was the case, what would have happened during a thunderstorm when the power goes out and then comes back on all by itself. Or are you supposed to go turn off all breakers each time the power blips?

Insulation takes much more than just 188A of inrush to cause it to fail.
 
fireshaper said:
Findings (from Licensed Electrician Contractor):

  • All 15 sub-circuits were tested: 12 failed insulation resistance tests, with faults between active/earth and neutral/earth.
Is there a test that can be performed on the main power feed line from the main switch board at the other end of the building to my unit that could detect if the cable was “screwed” into or damaged and consequently had the screw removed leaving a damaged cable which is not currently shorting?
Thanks in advance to anyone who can offer guidance. I’m trying to get clarity before pursuing the matter further.
Click to expand...
The contractor did insulation resistance testing and didn't test your main power feed line?
 
Sounds like a high voltage surge, that would explain the insulation damage. Most likely a lightning strike close by, can’t think of anything happening on the utility side unless a utility line of a much higher voltage fell across a lower voltage line. Both would be very evident. Running a screw into a branch circuit or feeder would not cause insulation failures on 12 other circuits. It could trip the main due to poor coordination though.
 
Is it possible the roofing contractors managed to cause a fault from the utility medium voltage to the skin of the building? After they changed their shorts, they decided not to admit their involvement.

I am not familiar with Australian services.
 
Any time other work is going on in the building I would be suspicious. "The roofers did it". Possible the builder is covering up something. On the other hand if they did how did they repair it to get power back on?
 
The only way I could see the roofers causing that damage, is if they contacted an overhead powerline, and if so, there should be some fatalities, or extremely damaged equipment at minimum.
 
In my opinion, a MV to building fault could have occurred mimicking a lightning strike and could have caused a surge and damaged the circuits. Where that damage is will be on the electrician to sort out. With damage to a computer, I can almost guarantee it is a surge. Most static shocks can damage sensitive electronics. But I don't know how Australia electrical code works and wouldn't want to rule out something that might be specific to Australia. A lot of sensitive equipment will fail on the smaller surges but to have faulted circuits that won't reclose is either a failure at the equipment end and they would work if you replaced the equipment or a failure in the wires. If the equipment failed than you will see some like burn marks between the neutral and ground on the PCB or some kind of remnants of an arc.

I am also not familiar with the terms, "with faults between active/earth and neutral/earth." My guess is neutral to equipment bonding might be damaged on the equipment's end rather than the wiring itself? Is the heating equipment on the roof at all? Or did the roofers need to reconnect anything that should have been reconnected by a licensed electrician? Did they mistakenly bond equipment grounds to the neutral ground?

It is also possible that the metal roofing could have reflected light on non-metallic wiring and damaged the conduit or wire. Depends on how long it would have been reflecting / what the metal roofing looks like. Possible, but not likely.

It is also possible that the wiring around the heating elements was exposed to direct sunlight melting something or rain / moisture while the roof was being replaced, damaging the circuits out of the panel because water or something penetrated in. Small shards of metal could have also caused conductors to arc between. Like screws. But some of this can be ruled out by where they were working and where all the panels / equipment are located.
 
One would think that an infrared heating panel is relatively simple and would not be damaged easily.
 
We were installing some boilers in a boiler room remote from the main building. The EC had disconnected the power to the panel and had refed the panel temporally. He used SER run between the bar joists and the ceiling deck. It was 480 3 phase. The roofers were on the roof and were cutting the roof deck to drop a large steam condensate tank through the roof as it wouldn't fit through the boiler room doors.

You guessed it they cut the 480 with the sawzall. I never heard a BOOM like that it was like a bomb going off. No one got hurt
 
Inrush current would make a breaker trip, but loads (like the IR heating units) themselves do not care about the current happening elsewhere.

Massive equipment damage is generally the result of a high VOLTAGE situation, as in a higher voltage wire crossed up with a low voltage wire somewhere. THAT would have possibly caused a current spike that then caused all of the breakers to trip at once, AND damaged the equipment downstream. That could have happened almost anywhere upstream and had no connection to the roofing work. But I have also seen a situation where someone was using a crane to lift equipment to a roof and hit a utility line, which shorted down to the metal roof. Who knows this late in the game...
 
You must log in or register to reply here.
Top