dangerous student electricity project?

wrote: | snipped-for-privacy@ipal.net wrote: |> |> On Sun, 09 Dec 2007 00:02:25 -0800 ChairmanOfTheBored

|> | 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. |> |>Thanks. |> | |> | |> | Better off using a DC light bulb socket, bulb, and a switch. |> | |> | Yes, AC can be dangerous. If there are any exposed contacts, then the |> | AC will be available for human contact, and that is a bad thing. |> |> So 120VDC is safe? |> |> | 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. |> |> So 12VAC is dangerous? | | Edison vs Westinghouse, round 2.
My point is that, for the most part, it's not about AC vs. DC in terms of the safety factor for student science experiments. There is some degree of hazard for steady DC at high levels where common circuit breakers may not be able to break the current. But those are much higher levels than students should be working with. Lower voltage and lower current is where the safety is for this kind of application. That and appropriate adult supervision for the higher levels of this.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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On 10 Dec 2007 01:19:27 GMT, snipped-for-privacy@ipal.net wrote:

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.
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wrote:
| 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.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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On 12 Dec 2007 06:02:11 GMT, snipped-for-privacy@ipal.net wrote:

No shit.
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On 12 Dec 2007 06:02:11 GMT, snipped-for-privacy@ipal.net wrote:

Not at the basic, lesson one, first learning experiment level.
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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"?
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On 12 Dec 2007 15:15:18 GMT, snipped-for-privacy@ipal.net wrote:

How about: "Fuck off... really you should..."?
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wrote: | On 12 Dec 2007 15:15:18 GMT, snipped-for-privacy@ipal.net wrote: | |>On Wed, 12 Dec 2007 01:26:44 -0800 ChairmanOfTheBored
|>| |>|>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"? | | | How about: "Fuck off... really you should..."?
Sure, go ahead, say that. Then we'd know you a lot better. And more people would put your address in their kill file.
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I am curious. What kinds of shocks have readers of this newsgroup experienced.
I started high school toward the end of WWII. Some vacuum tubes were difficult to get. One technique to repair (usually very temporary) open heaters was called flashing.
In my case, I used an old Philco as my power source. It used a type 80 rectifier in a full wave rectifier circuit. About 750VAC from the power transformer was applied between the two plates.
To flash, I plugged test leads into the socket connections for the plates. The idea was to momentarily connect the leads to the opened heater's pins. Most of the time, it was possible to connect across the heater's break. With a little practice, it was possible to weld the heater's break.
Well, one time I got across the transformer winding.
Bill
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snipped-for-privacy@sbcglobal.net says...

When I was in high school I got nailed, twice, by the plate supply on my 100ish watt transmitter. That was 750VDC. It must have been on, idling, on the bench all day because I came home from school and was poking around - ZAP => OW! That *hurt*!

I was working in one of the labs in college (I was a tech working for the EE department) and got nailed by the 120VAC on one of the benches. Some idiot had wired the switch in the neutral side. I got tingled once and thought it was a fluke, then *WHAM*! I spent a while walking that one off, before I could get myself go in and figure out what was happening.
--
Keith

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Damn! Wasn't enough to rid us of your retarded ass though.
Keep poking.
One can only hope.
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snipped-for-privacy@crackasmile.org says...

Nah, I'm better than that.

Yep, unlike you, I've learned a lot by poking. You should try it sometime (learning something, that is).

Apparently even the hopeless have hope.
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Keith

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wrote:

I already related mine at 10kV. I'm sure it was a lot less with me as a load.
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On 12/14/07 6:18 PM, in article snipped-for-privacy@4ax.com,

I guess you were a dummy load.
Bill
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wrote:

No. I was smart before that event.
Now, (neck twitch)... I am the sanest (neck twitch) guy in the entire news(neck twitch) group. :-]
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says...

This is classic Dimbulb behavior. Killfile him and be done with it. ...or continue to poke it with a stick to see it flinch. It's all the same.
--
Keith

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You're the only "it" in this group, fuckhead.
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snipped-for-privacy@crackasmile.org says...

Why don't you go play in mommy's laundry some more, Dimmie?
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Keith

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----------------------------
wrote:

--------- 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.
--

Don Kelly snipped-for-privacy@shawcross.ca
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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.
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