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Author Topic: How NOT to work on mains  (Read 1805 times)

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Online Marco

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Re: How NOT to work on mains
« Reply #25 on: October 21, 2017, 11:42:56 AM »
The consequences are the outcome of a stochastic system, intelligence can't turn the illusion of control into actual control.
 

Offline steverino

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Re: How NOT to work on mains
« Reply #26 on: October 21, 2017, 01:45:50 PM »
What possible purpose was there in placing his finger on a live busbar is beyond me.  Matthias is a clever guy and his videos typically focus on his clever contraptions.  I can't help but think he thought it would be "clever" to show him touching a live busbar without getting shocked.
 

Online IanB

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Re: How NOT to work on mains
« Reply #27 on: October 21, 2017, 01:50:03 PM »
What possible purpose was there in placing his finger on a live busbar is beyond me.  Matthias is a clever guy and his videos typically focus on his clever contraptions.  I can't help but think he thought it would be "clever" to show him touching a live busbar without getting shocked.

Perhaps it shows how knowledge can keep you safe? If you know exactly where and what form danger takes, you are better able to avoid it. If you do not know how to recognize danger you are likely to be scared of everything, and at some point you will stumble into danger without seeing it.
I'm not an EE--what am I doing here?
 

Offline mcookieman

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Re: How NOT to work on mains
« Reply #28 on: October 21, 2017, 01:58:08 PM »
I'm not convinced behind his reasoning for sharing the neutrals in his additional 120v sockets as well.. If the power factors of the loads are different then it is possible to exceed the rating of the cabling.
 

Offline Jay_Diddy_B

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Re: How NOT to work on mains
« Reply #29 on: October 21, 2017, 02:36:06 PM »
I'm not convinced behind his reasoning for sharing the neutrals in his additional 120v sockets as well.. If the power factors of the loads are different then it is possible to exceed the rating of the cabling.

It is common practices to share the neutral like he did.

The worst case situation would be one load leading by 45 degrees (pf 0.707) and one load lagging by 45 degrees.

Under these conditions the maximum current in the neutral would be 1.41 x maximum phase current. For 15A circuits this would be 21A in the neutral lead. Each load would 1.16kW with a 0.707 pf.

These would be pretty special loads.

Jay_Diddy_B
 

Offline Gregg

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Re: How NOT to work on mains
« Reply #30 on: October 21, 2017, 02:50:51 PM »
I'm not convinced behind his reasoning for sharing the neutrals in his additional 120v sockets as well.. If the power factors of the loads are different then it is possible to exceed the rating of the cabling.
Sharing the neutrals is OK by the US National Electric Code and it makes sense because the neutral is connected to the center tap of the supply transformer.  Power used on one half of the 240 volt center neutral system is balanced out by power on the other half; same as a 240 volt load.  In other words if one half has a 10 amp load and the other half has a 10 amp load, the neutral is carrying virtually no current.
 

Offline b_force

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Re: How NOT to work on mains
« Reply #31 on: October 21, 2017, 07:43:49 PM »
I'm not convinced behind his reasoning for sharing the neutrals in his additional 120v sockets as well.. If the power factors of the loads are different then it is possible to exceed the rating of the cabling.
The proper way of doing this is therefore taking cables that are rated (much) higher than the fuse. Which makes a lot of sense and is even mandatory in most countries. The fuse should always and only be the limit, not anything else.
If you doing it well you also just standarize the fuses and wiring to a set value. (10, 16, 20 and 26A for example)

But I have seen many "safety codes" in some countries that are just simply dangerous.
For example, some countries don't work with a real earth/ground fuse/switch, but they only detect the imbalance of live and neutral. That is just asking for trouble. Not only is it possible to have accidentaly both shorted to ground (which means there is still nothing out of balans), it also doesn't care if there are any issies with the secundary side. Which can lead to very dangerous situations.
(I have even showed people these situations)
"If you can't explain it simply (or at all), you don't understand it well enough." A. Einstein

http://www.oneworldconcepts.com/
 

Offline jthomas

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Re: How NOT to work on mains
« Reply #32 on: October 21, 2017, 08:30:09 PM »

Not sure about the USA, but in the UK if you use a black wire for live you should mark it such at both ends, for example by putting a ring of red tape around it.  We don't use split phase supplies but the same situation arises with light switches where there is a switched live.

When I was in the trade for a short while, we used brown heatshrink sleeving, so at the point of termination it looked very obviously like a live wire (and it can't fall off, like tape). I've encountered quite a few suspicious-looking "is that meant to be live or not?" wires which required careful probing... and one of our goals when leaving a site was to make the next guy's job easier than ours was! If it looks like shit, it probably is.
 

Offline tautech

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Re: How NOT to work on mains
« Reply #33 on: October 21, 2017, 08:49:24 PM »
Until you've spanned a few generations and worked with sparkies that have "been around" it's far too easy to denigrate what was perfectly acceptable practices in other jurisdictions or from another earlier time.

Example
When power came to our part of the world in 1935 ALL installation was in steel conduit, the pitch and cotton covered conductors were drawn though from inspection cover to inspection cover that was mandatory at Tee junctions or 900 bends.
There were NO earth cables, instead the steel conduit was the earth.
I still have circuits like this in my house that give zero problems after all this time.
Aaaah, the good old days, it was all copper conduct here. 8)
Like, really, looking for the worst solutions EVER!  :-DD

I can also remember my grandma asking that everything she touched tickled, lol, jeeze.
And you well know that the circuits in that case should have been checked for the integrity of the earth bonding.  :P

Anyone that didn't rightly gets LOL treatment in return.
Avid Rabid Hobbyist & NZ Siglent Distributor
 

Offline Jay_Diddy_B

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Re: How NOT to work on mains
« Reply #34 on: October 22, 2017, 01:15:56 AM »
When I was in the trade for a short while, we used brown heatshrink sleeving, so at the point of termination it looked very obviously like a live wire (and it can't fall off, like tape).

Snip ...


Brown is the correct colour for hot in Europe.
Blue is the correct colour for neutral in Europe.

in USA and Canada

Black is the correct color for Hot
Red is used for a 2nd hot, split phase circuits and two-way switches
White is the correct color for neutral.

In three-phase circuits the phases are black wires marked with red, yellow and blue tapes.

Regards,

Jay_Diddy_B

 
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Online Jeroen3

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Re: How NOT to work on mains
« Reply #35 on: October 22, 2017, 01:31:04 AM »
Will this topic be going into :horse: about who's got the best wiring colors? Or why CAT ratings are super important because other people put their life in danger?
 

Offline Monkeh

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Re: How NOT to work on mains
« Reply #36 on: October 22, 2017, 01:31:23 AM »
For example, some countries don't work with a real earth/ground fuse/switch, but they only detect the imbalance of live and neutral. That is just asking for trouble. Not only is it possible to have accidentaly both shorted to ground (which means there is still nothing out of balans), it also doesn't care if there are any issies with the secundary side. Which can lead to very dangerous situations.
(I have even showed people these situations)

What on earth are you on about? RCDs? They all work by detecting current imbalance. Yes, shorting either side (.. well, neutral, line is going to have a whole different problem) to earth on the secondary side will cause an imbalance and lead to a trip. On the primary side, neutral and earth are already connected..
 

Offline T3sl4co1l

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Re: How NOT to work on mains
« Reply #37 on: October 22, 2017, 06:35:48 AM »
This thread is a better illustration of the lack of cultural relativism than of electrical wiring.  :horse:

Tim
Seven Transistor Labs, LLC
Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!
 
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