On the other hand, it seems to me that, in typical usage, the receptacles on a power strip don’t usually see very many mating-demating cycles. Most people will put on in below their computer desk, and never unplug anything until they replace the computer.
Maybe that’s the assumed use-case that they’re tested for, and the failures you read about are from atypical users who are unplugging things frequently?
[QUOTE=Ironfoot]
I tried to pick up the plug and it was stuck to the carpet, pulled a 2x3" piece of melted carpet up melted to the plug which was on top of the carpet.
The male plug on strip was partially melted.
The plugs on the ext cord were repkaced and were thise cheap feel, molded plastic type installed by my neighbor, a licensed electrician.
I never leave heater on if I go out, but over time, this combination of heater, ext cord, plug strip, creating heat, molded plastic plugs, amazing it did not catch fire… /QUOTE]
And this is why arc-fault protection is required now. When AFCI breakers first hit the market, they were largely limited to bedrooms due to cost, but as of 2014, they’re required pretty much everywhere except outside and in the garage.
There’s a pretty decent chance that at some point during all that melting, some arcing was taking place. An AFCI breaker would have sensed it and killed the power.
Don’t AFCIs trigger from motors, though? Where are you supposed to plug in a vacuum cleaner?
“The contact components of a receptacle shall have a voltage and current rating equal to that of the attachment plug on the power-supply cord.”
Well that explains why everything is rated at 15A, you can’t get UL approval for one without a 15A fuse and plug it into a 15A circuit.
It seems that a desire to qualify for the UL sticker, yet provide a product at a competitive price point. As this thread demonstrates it is a pity that those standards are probably pretty well fixed now.
They generally look for a sustained arc. Low-duration arcs from plugging in a device, arcs between a brush and commutator in a DC motor, etc. shouldn’t trigger it. A sustained arc from melted insulation should trigger it.
That said, I don’t have a good feel for how well the discrimination works in practice.
The plastic these things are made from should be fireproof.
Sometimes someone is either (a) too cheap, or (b) too ignorant, and the material is not fireproof.
In category (a), we had a recall here (aus) of electrical supply wire imported from China that turned out to not meet the standards it claimed. Some of that got into houses.
In category (b), there were some fatalities here many years ago from heaters made from non-fireproof plastics. For several years after the police tried to get a manslaughter case up, which wonderfully raised the level of awareness in the industry. And computers used to be non-fireproof, being the cause of many office fires.
But I would be bitterly pissed off if an exposed power strip caused a carpet fire when it failed. The carpet is supposed to be fire resistant, and the power strip is supposed to be fireproof.
It’s interesting that power board failure seems so common in the USA. It seems rarer here. Perhaps it is now rare to have full-power (10A, 2.4KW) heaters in Aus? Official advice for homes here is that you should inspect and maintain power boards, not that you should never use them for heaters.
Also, my local fire board did a review of cheap imported power boards a few years ago, and didn’t find anything important enough to make the news.
And what plastic would you suggest for that? People tend to get touchy about making things from asbestos. I suppose there might be some silicones that would work, but I don’t know if they’d have the right mechanical properties.
Many plastics can be made fire-retardant, but that tends to increase the cost. Some information here.
You live in a country with electrical service with a nominal voltage of 230 volts RMS or often called 240V peak to peak. This choice was mostly made for reduced distribution costs because you can use thinner wire for the same energy content.
In the US we had a battle between Edison who was advocating DC and Westinghouse which used AC.
Edison pushed several high profile campaigns claiming that DC was safer. Edison actually held public “executions” of cats and dogs and e he even secretly financed electric-chair as a publicity stunt against Westinghouse and AC.
Due in part to publicity like this the US standardized on 120v service.
So 1500w with 120v will pull 12.5A, and 14 gauge wire like used on some less expensive devices can only handle 15A. It is rare for devices to use 12 gauge wire that would support 20A due to cost.
Your 10A has a far greater safety margin than 12.5A and your socket is more robust with safer spacing due to the offset angle. Basically if the central portion breaks down inside the socket of a NEMA 1R or 5-15P plug the parallel edges will need to move less to arc. Due to the voltage differences this isn’t exactly equivalent but newer NEMA plugs use a similar design.
So basically we are pulling more amps, and thus running hotter under the same wire sizes. The old style 1-15R receptacles haven’t been legal to install and post 1974 all plugs were required to have ground, but I am in a house that is full of them.
I try to replace some every every year, looking at the plastics and a few I have pulled have been very crispy and appear to have been close to catching fire a few times. Note I am in an old house that still only has knob and tube wiring to a large portion of the house.
In the area of the house where I have my computers and TV plugged in I actually ran 20A circuits which have a plug that is exceedingly rare in the US, but it was the only way I could figure out how to buy power strips that had thick gauge wire.
My parents owned a Motel/RV park when I was growing up and I saw way too many people “upgrade” their RV’s battery chargers then use a 20 to 30 A adapter on their old 20A cable and have it melt like nacho cheese while pulling max current.
On a side note, cars also moved from 6 volts to 12 volts, not because it was better but because it allowed them to use a lot less copper in the wiring.
I just checked an old space heater that I haven’t used in years but kept around “just in case”
It is rated at 12.5 amps and uses 16 gauge cords are rated for 13 amps, which is a razor thin safety safety and not enough to pop the breaker.
Yet it is UL listed…grrrr
A 1500 W heater in the U.S. will draw 12.5 A[sub]RMS[/sub] of current. Which means there will be 12.5 A[sub]RMS[/sub] of current through each of the plug/receptacle contacts.
A 1500 W heater in the Europe will draw 6.25 A[sub]RMS[/sub] of current. Which means there will be 6.25 A[sub]RMS[/sub] of current through each of the plug/receptacle contacts.
If we assume the contact resistance is the same for U.S. and European plugs/receptacles, then the contacts in the U.S. connectors will dissipate 4X the power of the contacts in the European connectors.
In other words, if we assume all else is equal, U.S. plugs/receptacles dissipate 4X as much heat as European plugs/receptacles. This may explain why it’s a bigger problem in 120 VAC countries vs. 240 VAC countries. Though it could also be due to the design of the plugs and receptacles. I’m not sure.
This is an old thread so poor Habeed probably was unaware of them, but Bitcoin mining rigs come pretty close to 1500w.
“Power Consumption: 1375W + 7% (at the wall, with APW3 ,93% efficiency, 25C ambient temp)”
I think you misunderstand.
A 13A-rated cord won’t melt or burst into flames if it is shorted, and that short will pull 100’s of amps, and trip the breaker. Why would you want a heavier cord?
Before this discussion I hadn’t really though about the USA being limited to 1K5 for normal use, nor the secondary effects of that. That’s actually quite interesting for me.
quibble: AUS in nominally 230V RMS, often closer to 250 RMS. 240V RMS (the old Aus standard) is about 345 Vpeak, 670V peak to peak.
You mean like the relative unpopularity of tea due to the lack of fast electric kettles?
How fast are 230v electric kettles? I have a 110v one from Hamilton Beach and it can heat a full liter in about 90 seconds.
It depends on the wattage of each.
If the wattage of the 230 V kettle is the same as the wattage of the 110 V kettle, they will take the same amount of time (all else being equal).
If the wattage of the 230 V kettle is greater than the wattage of the 110 V kettle, the 230 V kettle will take less time.
If the wattage of the 230 V kettle is less than the wattage of the 110 V kettle, the 230 V kettle will take more time.
I don’t have any in my house yet either, but given that they’ve been required in new homes or re-wires for several years now, I suspect they handle vacuum cleaners just fine. The internal micro controller probably can tell the “signature” of a motor from that of internal arcing in a squashed extension cord under the carpet.
A dead short isn’t the problem, heat and fire while within the load of the break is the issue.
You can avoid extension cord fires by investing in heavier gauge extension cords due to simplified Joules Law (H = I^2 x R)
Where:
I = Amps
R = Resistance
(Time is ignored to avoid confusing ascii math)
To over simplify, smaller gauges have less cooling capacity, yet have a higher resistance.
10’ of 12 gauge solid wire ~ 0.016 ohms
10’ of 18 gauge solid wire ~ 0.064 ohms
12 guage diameter 0.104" is around 78.48 square inches.
18 gauge diameter 0.0403" is around 30.4 square inches of surface area.
10’ of 12 gauge wire (15^2) * 0.016 = ~ 3.6 Watts
10’ of 18 gauge solid wire (15^2) * 0.064 = ~ 14.3 Watts
12 gauge needs to dissipate ~0.045 Watts per square inch to avoid heating up
18 gauge needs to dissipate ~0.47 Watts per square inch to avoid heating up.
Note that seems pretty safe, but that is for a perfect cord made of pure copper in free air. As resistance is inversely proportional to the cross sectional area of the wire if you step on it, kink it or if it corrodes the resistance goes way up and the cooling area goes down.
The RV reference above was because people would take a light duty 50’ cable with 16 guage wire, coil it up in an small enclosed compartment, pull out maybe 5’ and put on a 30A adapter and pull a full 30A.
Also note this.
Right, and 13A is fine for 12.5A load.
The problem is people who use a cheesy 6A rated extension cord to run their 12.5A space heater.