PRR said:
> I figured a little too long, too skinny, line cords would just heat the room a little more evenly.. I didn't think I'd need to heat sink a plug in connection...
The wire is rarely a problem. Connectors are.
Maybe you've lost the hindsight you must have gained working in the Big Amp factory? Or maybe these problems don't happen until after warranty. In the far field, we never see much burnt wire, often find bad contacts with heat stains.
Perhaps I've been lucky to avoid experiencing many seriously bad mains contacts.
I did experience a miswired extension cord (I borrowed from a neighbor?) with hot and ground reversed... Yup, no ground fault interruptor to prevent me getting a serious shock out in my wet yard (shock could have been worse. I was putting a sump pump into a water filled hole. i generally respect mains electricity so I wasn't in the hole, but wet enough feet to get shocked. )
My contact/current experience in amplifiers was mostly things like trying to push a couple kW out a 1/4 T-S speaker jack. Spacial 1/4" jacks with two tip contacts and higher contact force, make that work (mostly). Some out of tolerance offshore speaker plugs could get hot, but I don't know of fires.
Also dealt with line cord/outlet limits in the context of how much amp power UL would let us get from a basic line cord/outlet.
I doubt you had less than #18. As you say, that won't get hot at 7A. And the connectors are sample tested at high current by UL. But reality is different.
Backstab and Al are different.
indeed
If you have 3-hole outlets, it's certainly in the backstab era.
Thanks, I was guessing, since grounded outlets have been around for a while.
I have seen back stab when replacing light switches and ignored it, when I replaced the ballast in my fluorescent (with a higher efficiency version) that was back stab only, and the fixture for my DIY UVc lamps were stab only.
You can poke #14 or #12 into a hole and a spring grips it. Kinda. These gave SO much trouble they were banned. And then the mass-housing lobby rose up and got a #14-only exemption.
The push-in connector *can* be good. There's a whole line of standalone push connectors which compete with WireNuts, and are supplied on Halo recess fixtures which are very fire-conscious. But that's not what you get in outlets.
There's also Back Wire, hole in the back, but then you must screw it. Just a captive screw-clamp instead of screw-wrap. Excellent connection.
I think I've seen that but don't recall where, perhaps not mains wiring.
But when you get the connector to the wire, then you face the crappy connector design. "Design" may be too strong a word. The origins of the 2-blade plug are murky. There were several competing products, rarely used at first, and NEC/UL declined to get involved picking a Standard. When appliances were few, OK, but the market exploded. And price pressure cheapened the sockets and plugs. There IS a UL standard, hanging a weight on the cord. IMHO most connectors fail such a test after a few insertions. You can change a plug (who does?) but nobody changes wall-outlets until they HAVE to.
Yup, I have only dealt with this in passing in context of how much current. FWIW, outlets and plug current ratings are continuous and many loads are not (well my heater and incandescent light bulbs may be continuous), but amps and the like are not. As modern high current consumer products move to use more power factor correction the load current is more evenly spread out, more average. A good thing for high current applications because there is less voltage drop due to wiring. Back in the early days of high power audio amps, UL limited amp size, as if amps were full rated power 24x7, but they shifted gears back in the early 90s to allow higher power from Edison outlets.
Extension cord outlets are often worse.
"Electrical Fires" happen a lot. CPSC asked for suggestions. The industry bonded behind "Arc Fault". Though it is not clear that arcing causes many fires. Or how you could tell a steady connector arc from a vacuum cleaner. Or that the AFCI standard we got is actually effective against anything except an artificial UL test.
I have mixed feelings about UL, but warmed up to them a little more when they stood with us in court when peavey got sued because some muso got killed by a miswired hot outlet ground while playing two Peavey guitar amps. Our products were correct, the outlet was the killer, but it was appreciated that UL had our back in court.
The more likely fault is "glowing contact". With poor pressure and the least oxide, plus a few jiggles, our plugs are likely to make a microscopic contact. The current density, and oxides, can become a hot negative resistance. Because the load is positive resistance, this is stable. And the glowing contact can dissipate near constant power over a range like 1A to 10A. Since it is thermal, you can't see it in the load waveshape (what AFCIs monitor). Some AFCIs also have GFI action, and it turns out that some thermoplastics leak more when hot, and *this* may break the glowing contact. But by the time this happens the socket is all out of shape. And it's the wrong way to detect heat. And the better outlets use a thermoset which doesn't break-down and leak, but crumbles instead.
I've experienced the occasional warm plug.. Again a little surprising they work as well as they do.
You don't see such problems in rationally designed connectors. The Schuko is better, perhaps with a little hindsight from US plugs. The BS(UK) connector grips much better. (Also generally lower current and enough voltage to punch oxide.)
Not to change the subject back to my heater, but last night it worked as designed and programmed. I need to tweak the temperature targets. It was too warm after I was in bed, and I need more time to ramp up from 60' to 66' or so target with only a small 800W heater. More than enough to maintain a constant temp, but it struggles to heat up a cold room.
I will try to resist the temptation to apply windage. I know what the room temp is in real time, and know when and what I want the temp to be in the future, so I could do a simple approximation for when to start heating adaptively based on current temps.
I am trying to talk myself out of doing this (I need more data)., but it would also track with the seasonal changes outside since the cold room doesn't get as cold. The heat required to change the room temp will be roughly linear, but heat to maintain temp will vary with delta between inside/outside temp. Of course software doesn't even need to be linear, I can just do a step wise approximation in the software, even a crude linear approximation is better than nothing. Trade off for algorithm errors is that room heats to target temp perhaps a little too soon, vs not getting warm enough until later, so easy choice. If I had more heat power available, I could make that another adaptive variable, but I observed that it took hours to get up to temp last night so I don't have too much heat power (only 800W). Another thought that might be simpler to program. Just learn how long it takes to heat up, and use that data the next night. I could even measure the on vs off time after at temp to literally measure steady state heat loss (for given start temp that imputes outdoor temp). Interesting... somebody stop me... 8)
For a full house sophisticated Heat pump controller, I am tempted to detect outside temp also, so I could grab and bank a little more heat while the outdoor temp is higher and heat pump is most efficient, but this is contrary to optimal interior comfort. The in-wall heat pump unit already seems to heat less as outdoor temps rise, but this works OK for general comfort. I don't need to detect outdoor temp for small bedroom application. I can impute outdoor temp roughly from how cold room gets with heater off.
JR
[edit- well nobody stopped me... I figure I can do this simpler. I can start with a guess at capability to heat the room in degrees/time, and use this to work backwards to start heating the room early. Then I can literally measure how much the room heats up vs, actual true time the heater is on... This way I can update the actual capability-rate of heating on the fly, say updated every 15 minutes. If I miss and don't reach the temp target in time on a given night, the next night I probably won't miss as it learns capability over time. And can adjust the rate slowly as the seasons change. Damn, I've got real work I should be doing, but this is more fun. :-* [/edit]