He said "...have it plug into the wall. Is this inherently dangerous?" and the answer is yes. The reason is voltage. The location and action of plugging it into the wall IS the declaration of voltage and the introduction of the danger if there are exposed nodes and conductors..
Sure it is. Because at that level, their notion of AC IS the available source at the wall outlets, and he DID mention "plugging it in". So, for this thread, any mention of AC was an obvious reference to standard residential power service.
They do not have any low voltage AC sources to speak of in most high schools. Even in the best fitted schools. The only ones that do are those that have electronic technology vocational programs.
Also, most DC sources that are available to such educational systems are of a fairly low, safe voltage. It isn't like he would be hooking it up to a welder or a truck battery charger.
He can add a fuse in his circuit. Also, you got on me about ambiguity. What are "at high levels"?
DC at high voltages has a hard time being interrupted by contact type breakers, but low voltage DC acts no different than AC from the standard breaker's POV. Metal transfer from point contact to point contact is practically immeasurable. Bring up the voltage, and then you start seeing the anomalous artifacts of opening contacts when current is flowing in a DC circuit.
Should is right. However, what is typically available to such student groups at decent prices will be quite safe.
Both of which went without saying. Since he won't be hooking up any high current sources to the thing with any measurable degree of likelihood.
Actually, the project is simple enough that instead of supervision, the experiment would be an excellent opportunity to instruct, not merely supervise. If one has the wisdom to supervise such a setting, one would also have the wisdom to teach. The result would be far better than merely standing there making sure the kid or anyone else didn't start futzing around with it.
It had to be the same way you slipped through mensa's fingers.
The only difference is that I am a rising star, and you are on your way over the event horizon of the black hole of Darwinism.
No s*it.
However, in the setting he is in, with the things that are available to him, like the wall outlet, which is a fairly HIGH voltage source for this application, or a DC source, like a dongle from Radio Shack, which is most assuredly of a low enough voltage not to matter.
Unlike those of us with labs and all manner of voltage sources at hand, he has very few choices, so my mere mention AC over DC is valid due to the fact that the voltage for the AC is a given to be rather high, and the voltage for nearly any DC source he would use would be a given to be a fairly low number.
I guess if all I did was mention the type of light bulb to include, you all wouldn't be nit picking like this. I did mention a DC light bulb socket, and nearly all of those are low voltage as well.
And you also mentioned *low voltage DC* : " With low voltage DC, the most that can happen would be a hot wire causing a burn in the event of a short. Not really much else could happen."
It is clear that's what you were talking about. No need to identify the bulb.
Ed
You did mention low voltage DC and the implication in what you said is that AC is dangerous and DC is not.
Quote:
"Yes, AC can be dangerous. If there are any exposed contacts, then the
This is what you said and as it stands- is subject to interpretations that have been given. It may not be what you thought or intended to say but as it was expressed, left a lot for others (particularly the person who in following your advice, then lugs in an automotive battery ands finds that a short is anything but minor).
So, on the basis of what you initially said, not what you modified it to be, your mere mention is not valid as it is misleading.
Exactly! The person who asked the question doesn't know or he wouldn't have asked the question. I know what you meant even if you were incapable of stating it clearly, but he didn't and could make some dangerous assumptions.
My point stands. Have a good day
F*ck you. I am quite capable of detailing every little iota. I just didn't think it necessary to go beyond the quick observation I made at the moment, and I think he understood just fine.
Doubtful.
No. You mouthyness stands.
I will... laughing even.
On Sun, 09 Dec 2007 19:15:39 -0800 ChairmanOfTheBored wrote: | On 10 Dec 2007 01:13:33 GMT, snipped-for-privacy@ipal.net wrote: | |>Read the quoted text. It's saying something is dangerous because of the |>nature of the electrical system, rather than it's voltage level. I brought |>up 120VDC to show the misdirected statement about danger. | | | He said "...have it plug into the wall. Is this inherently dangerous?" | and the answer is yes. The reason is voltage. The location and action | of plugging it into the wall IS the declaration of voltage and the | introduction of the danger if there are exposed nodes and conductors..
What you said earlier is:
The first 2 paragraphs of that are what are in error. The 3rd is even a bit misleading. They should have been something like:
FYI, NEC permits low voltage lighting with exposed contacts when the voltage is under 30 volts. That would still be for professionally installed systems. For what students might build I recommend 12 volts AND limited current (e.g. no car/boat/cart batteries). A stack of 8 alkaline D cells should be enough. A wall wart with 12 volts and 2 amps (AC or DC out) should be enough.
| Sure it is. Because at that level, their notion of AC IS the available | source at the wall outlets, and he DID mention "plugging it in". So, for | this thread, any mention of AC was an obvious reference to standard | residential power service.
Only in reference to the original idea. WHen proposing ALTERNATIVES, then we are not talking about the raw power from plugging it in. We are then talking about things like transformer secondaries or batteries. So AC or DC are valid options.
| They do not have any low voltage AC sources to speak of in most high | schools. Even in the best fitted schools. The only ones that do are | those that have electronic technology vocational programs.
Radio Shack stores are nearby to most schools.
| Also, most DC sources that are available to such educational systems are | of a fairly low, safe voltage. It isn't like he would be hooking it up | to a welder or a truck battery charger.
The safety is in the low voltage and low current. That DC would be more commonly available in thst safe combination does not mean we should refer to "DC" to refer to that. I sure hope they are not using a welder or a battery charger, or even a car battery (it's DC, and unsafe for kids).
|> There is some degree |>of hazard for steady DC at high levels where common circuit breakers may |>not be able to break the current. | | He can add a fuse in his circuit. Also, you got on me about ambiguity. | What are "at high levels"?
A high available current sufficient to cause a flash arc with sputtering molten metal.
Limit voltage to 12 volts and available current to around 2 amps or so.
| DC at high voltages has a hard time being interrupted by contact type | breakers, but low voltage DC acts no different than AC from the standard | breaker's POV. Metal transfer from point contact to point contact is | practically immeasurable. Bring up the voltage, and then you start seeing | the anomalous artifacts of opening contacts when current is flowing in a | DC circuit.
Current is what is relevant to causing the breaker to trip, but voltage is what is relevant to extinguishing the arc. That's so even with a fuse. They use very special fuses on the 7200 volt power lines for a damned good reason. Fuses do have voltage ratings and that's not about the insulation (although that can matter, too).
|> But those are much higher levels than |>students should be working with. | | Should is right. However, what is typically available to such student | groups at decent prices will be quite safe.
Sure.
But that can be AC and/or DC.
On Sun, 09 Dec 2007 19:32:09 -0800 ChairmanOfTheBored wrote: | On 10 Dec 2007 01:20:18 GMT, snipped-for-privacy@ipal.net wrote: | |>On Sun, 09 Dec 2007 09:29:28 -0800 ChairmanOfTheBored wrote: |>| On 9 Dec 2007 17:21:44 GMT, snipped-for-privacy@ipal.net wrote: |>| |>|>On Sat, 8 Dec 2007 17:33:23 -0800 (PST) Bayou Self wrote: |>|>
|>|>| My son needs me to help him with a school project--a simple circuit |>|>| with a switch. He said he wants to use a light bulb, a switch, and |>|>| have it plug into the wall. Is this inherently dangerous? BTW, he's in |>|>| 9th grade and says he saw a setup like this on the teacher's desk. |>|>
|>|>I thought they quit using the Darwin effect to raise the average IQ. |>| |>| |>| So much for you thinking, Darwin boy. |>
|>OK, so they still use the Darwin Effect. How did you get past it? | | | It had to be the same way you slipped through mensa's fingers. | | The only difference is that I am a rising star, and you are on your way | over the event horizon of the black hole of Darwinism.
I avoided that foolish group by simply not going anywhere near them. So you stayed away from anything dangerous?
Stars are, by their very nature... dangerous. So are black holes. One is simply more fun than the other.
No s*it.
Not at the basic, lesson one, first learning experiment level.
On Wed, 12 Dec 2007 01:26:44 -0800 ChairmanOfTheBored wrote: | On 12 Dec 2007 06:02:11 GMT, snipped-for-privacy@ipal.net wrote: | |>At a safe voltage level, yes, DC is actually a very good choice to work with. |>But AC is not that bad, either. Both have their uses in experimental study. | | | Not at the basic, lesson one, first learning experiment level.
Not what? DC or AC?
So, how much is it going to take to just get you to say "I should not have said that DC is safer than AC ... I should have said low voltage is safer than high voltage right from the start ... I knew that, really I did"?
I would plug the setup into a plug strip with a breaker built in to it...
--------- You are right in indicating the importance of zero crossings
- however there is one point- it self extinguishes at current zeros- not voltage zeros which will only be the same if the load is purely resistive. If the voltage across the gap rises faster than the gap's withstand strength, it will restrike, otherwise not so the rate of rise of voltage across the contacts at the time of the current zero is important.
How about: "F*ck off... really you should..."?
I like breakers that drop big insulator flags in front of the contacts upon opening.
There are some the "blow out" the arc.
I like the big 400kV jobs that have to open up and span a 12 foot gap, and the arc continues as it opens until it gets nearly to that distance.
Everyone already knows about the video where they opened one leg of a three phase feed, and there is another where all three phases open on a similar breaker version. Neat stuff.
I wonder how the BCA DC Intertie has its breakers situated.
+500kV and -500kV 14 foot minimum clearance, Clarence.
ERrr... that would be BPA.
BCA is the Billiard Congress of America.
Have something to add? Share your thoughts — no account required.
Ask the community — no account required