This was the cause. Power strip, one to three adaptors, zip cord extension cords...

What were the loads plugged into this?

I only saw a fish tank (aquarium), but there had to be other items. Damage: scorched wall; fish tank; 4' hole in ceiling by FD; water/smoke. No visable damage to the receptacle this was plugged into.

This is a nice one

That's a classic!!

Let me guess.

Continental US.

Public area. Probably flea market.

Powering up "temporary" food vendors.

How close am I?

Kinda look like what I grew up in... I wonder the place I grew up predisposition me be a sparky?

Power strips typically contain MOVs (metal oxide varistors) for surge suppression. When an MOV ages, its trigger voltage can drop below the peak to peak line voltage, causing it to draw current and heat up. If the power strip has a plastic housing, the burning MOV can set the plastic on fire.

Another bad practice is the "3 way" surge configuration that places MOVs line-to-neutral, line-to-ground and neutral-to-ground. This is strictly for marketing to the dumb masses who think that more is always better. Dumping surge current into the protective ground pulls it off of ground potential. Since this is the zero volt reference for sensitive electronic equipment, bad things can happen (like fried serial ports).

Typically, the neutral-to-ground MOV has an extremely low trigger voltage, so that a loss of neutral will cause it to try to pass the full circuit load current to ground. Obviously, it then burns up.

I worked in an office with modular furniture. Some amateur electricians did not get the wiring harness connectors securely locked together. Over time, they would separate, and when the neutral connection was broken, power strips would melt all over the place. Disassembly revealed it was always caused by a burned neutral-to-ground MOV. One time, a power strip actually broke out in flames. Someone hit it with a fire extinguisher before we got to find out if the sprinkler system worked.

In conclusion, I will bet dollars to donuts that the fire was caused by an MOV, not an overload. Most power strips have a resettable circuit breaker to protect against overload.

BTW, if you want serious surge suppression, put a UL-approved surge suppressor on the service entrance and look at zerosurge.com for point of use protection. They are one of the few companies that make surge suppressors that actually work. No, I am not affiliated in any way with this company.

Bavmar:

Welcome to ECN, and thanks fo te input.

Last I heard from the FD was 'inproper use of extension cords, adapters, & power strip' was the cause.

A lot of aquarium equipment will state in the instructions not to use a power strip. I've witnessed the reason why at a service call... Condensate will tend to gather on the power cords sometimes and roll down the wire and into the power strip or extension cord. I think the mfr's thinking was that plugging directly into the wall outlet will keep a drip loop in the wire...

Here's a pic of my modest aquarium, and it's attendant:



Now, that aquarium has a light, a pump, a heater, and a UV sterilizing light. That's four plugs. Most aquariums also have an air pump (I don't need one because of that 'quite waterfall' you see).

It's kind of hard to put five plugs into a duplex receptacle. Most folks are not about to rip the walls apart to install additional receptacles- especially if they're renting. With 'starter' aquariums around $20, you can be sure plenty of renters have them.

My desk has 10 receptacles, and there have been times where every one was in use. Here's the count of current things plugged in:
Computer: 3 + printer = 4
Modem & router: 2 (located elsewhere)
Desk lamps: 2
Paper shredder: 1
Under desk heaters: 2 (becomes 1 fan in summer.
Cell phone charger: 1

Lucky for me I still use the old-fashioned manual pencil sharpener and stapler.

Face it: Power strips are here to stay.

Plus .... let's look at that desk again. 4 or 5 plugs under the desk, 4-5 above the desk. That's a situation just begging for two power strips ... meaning, regardless of what the "White book" says, you'll see the things daisy chained.

There are various experts' and parts of the listing standards that want to obstruct the use of power strips. They're not only tilting at windmills, they're also preventing QUALITY strips from being made. They've set their doctrine against the customers' wishes.

There are countless examples of what the result is when that happens: Doctrine fails, and bad things happen because of attempts to impose the doctrine. "Prohibition" is probably the grandest of such failed experiments.
Doctrine has to change.

Reno:
Just to back up a little. My OP was not meant to trash power strips. My intent was/is to 'define' the fire cause.

Inproper use of electrical equipment, like zip cord extension cords, or power strips, usually result in the 'cause' being marked off as 'Electrical'. That's my intent!

You are correct. Lots of bad things happen when stuff is mis-used.

Frankly, no one is helped when a fire is called 'electrical' when 'abuse' or 'stupidity' are the real causes.

I'd like to see better, more substantial power strips. I'd like to see 'better' cord use. Yet, too often we find our 'rules' prevent us from doing these things 'better.'

There's also a mindset that considers all 'extension cords' the same - that treats a 4-wire #8 SO cord the same as a #18 zip cord, that treats a 3-ft cord for the desk the same as a 90-ft. cord that snakes through the house.

There's a 'snob factor' that sneers ar Wiremold ... which results in cords being used everywhere, forever.

It's particularly annoying when folks take pride in their abilities to pervert logic.

I have a Plugmold power strip I use at my nightstand for an alarm clock and a couple chargers. Under my desk is an APC UPS with a power strip from the back up side and one from the just surge suppressed side. 4 external drives, modem, router, stereo, 40" LED screen and a 22" LED screen, server unit, magicjack, cordless phone charger, X-Box 360... In all, there's around 900 watts if I run it all at once. I just needed more physical outlets.

There's always someone that knows enough to get into trouble...

I know, right?

I've briefly seen (on YouTube) those transparently insincere PSAs against plugging heaters into (your) power strips. They might appear convincing enough to the layperson, but I ain't having them; I do still have a few older Australian power-boards (as we call them) with proper contacts, and they can sustain the full 10A through any one socket while keeping their cool.

Of course, the units available at modern "discount" stores are total junk (although to be fair, most electrical products sold there are); so given my past incident, I wouldn't even trust those with an office PC (much less any substantial load). Even they can survive full load initially, though; 10A is no big deal until the contacts are well and truly knackered, and that's exactly what happens in these cheaper power-boards (reportedly much like your "residential grade" wall outlets, which thankfully aren't a thing in Australia).

Indeed, it's my experience that products in general are way more reliable in the absence of such theoretically baseless cop-outs as have been mentioned, and this applies to high-tech products (e.g. hard disk drives) just as it does to low-tech items...

They were self generating power, the cord was plugged into itself, induction caused racing power loop, like a hadron accelerator.