They all have a ceramic rod or coil wrapped with nichrome wire that turn red hot. A vaccum forming table design I looked at used ceramic rods made the same way with reflectors to evenly distribute the heat. I believe all of the above (I did not verify if the table was) were UL marked.
1. A hot-neutral reversal will supply the 208/240V relay with 120V. It will make an angry buzzing noise but won’t close. Two hot-neutral reversals will supply it with 0 volts.
A properly wired, properly functioning dimmer switch can get hot to the touch. I’ve found that a 65-degree temperature rise is normal for a maxed-out dimmer. If the ambient temperature is 71 degrees and a dimmer switch is at 136 degrees, I’d be concerned, but I wouldn’t report the temperature as a problem. I would, however, take an extra minute or two to figure out how many watts the dimmer is rated for. I’d then make sure there wasn’t too much being controlled by the dimmer.
I am not going to go right into the above calculations as there are plenty of graphs and tables out the on the net that you can google for. Example – http://electronics.stackexchange.com/questions/22796/creepage-distance-for-pcbs-handling-line-voltage-ac, http://www.smps.us/pcbtracespacing.html
Bryan Orr is an HVAC and electrical contractor in Orlando, Florida. He is the founder of HVACRSchool.com and the HVAC School Podcast. He has been involved in technician training for 15 years.
Ive had a few shocks off 220vac but nothing that hospitalized me. But I do distinctly remember a shock recieved by a friend. He had a illegal cb with a zetagi 1kw valve linear amp, it tended to carbon up its changeover contacts and loose quality on ssb so I showed him how to turn it off, isolate it, drain it down and clean them up with contact cleaner. And I kept repeatedly stressing, dont do this without doing the whole isolation things as it will kill otherwise. Well, one day it went bad in the middle of a qso, and this was to some prized russian area, so throwing caution to the wind, he sprays contact cleaner at the relay while mid conversation, while holding a aluminium microphone in other end to talk it up. You guessed it, the valve hv field collapsed into the stream of contact cleaner, threw him across the room and into a wall and his glasses were blown off and twisted by the event. His girlfriend took him to hospital and it took a fortnight before they were happy with his vital signs to declare him fit to leave. All I could say when I visited him was “I bloody told you so” but his girlfriend was up for blaming me “for showing him”, and since then I’ve shied away from showing people things that if they ignore some of my warnings could kill them.
– Use isolated differential probes to measure high voltage. – Use current clamps or current transformers to measure current. – Put bleeding resistors in any big capacitor in your circuit. – Don’t change the position of the probes in the power circuit without power everything down. – Don’t work with high voltages alone. – If there’s more people involved in your experiment, block any circuit breaker, button or at least put some signs to prevent people from turning them on while you are messing with the circuit. Paranoids may even ground things while they are playing with the installation to direct the current to the ground in case someone makes a mistake.
The QD terminals I buy are not the crappy ones you get at Home Depot. I buy 10 gauge Molex AviKrimp ones from DigiKey. They’re ~33 cents each at Q:250. They are no joke. I use them in the high current path of OpenEVSEs that I build for up to 24A, and they perform perfectly.
All of this, if you suppose that you are taking a full hand of cable. Got shocked a few times with AC (and DC as well) and since I was just thouching, not handling, I had no trouble to get away with it (just swearing A LOT and throwing my screwdriver through the room).
For this application I would have used a contactor from a reputable supplier that breaks the connection on both legs of the 220V circuit vs a cheap ebay SSR.https://en.wikipedia.org/wiki/Contactor
I’d like to say that if a circuit breaker is X-degrees over ambient, it’s a problem… but there’s just no hard and fast rule for this. I can’t say this.
The controller board for the heat pump in our “3 Season porch” fried last January during a cold spell. All of the house plants we were keeping in there froze to death. SE Minnesota
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