Electrical services

  1. I have been installing lighting from a 3 phase board. The wiring schematic has instructed me to place an l1 and l2 feed into the same switch box. Is this not bad practise? Would it be better to put 2 L1 feeds to it instead? Therefore there would only be 230v at the switch. Also , am i correct in assuming the potential across 2 L1 feeds would in fact be 0?
     
  2. jcsd
  3. davenn

    davenn 3,670
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    why are you dealing with these sort of electrical situations if you don't know what you are doing ??

    Have you not received training for such ?
    Why are you not under the supervision of some one qualified to work on these systems ?

    A forum like this ISNT the place to be asking these sorts of questions

    Regards
    Dave
     
    1 person likes this.
  4. dlgoff

    dlgoff 3,086
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    Yes. However it's difficult to run something across two lines with the same phase.
     
  5. Answer to first question is yes, i do know what i am doing.
    Answer to second question is yes, i have received training for such. This is why i am questioning what my engineer has instructed me to do.
    Answer to third question is no, i am not under the supervision of anyone because i am more than capable AND competent to do the job.
    Lastly, thank you for your response. I apologise for my apparent ignorance of my post and the wasting of your valuable time. Good day.
     
  6. sophiecentaur

    sophiecentaur 13,698
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    Before throwing the toys out of your pram, perhaps you should re-read your original question. It really doesn't look like it's from someone who knows as much as you claim to know. Imo, Dave's response was about right.
    Did you mean "2 L1 feeds" or One :1 feed and a neutral?
     
  7. jim hardy

    jim hardy 4,768
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    It might be okay if voltage between phases is less than 300 volts.

    See NEC 404-8(B)

    and here's a couple articles that might relate to your installation

    http://www.ecmag.com/section/codes-standards/voltage-between-adjacent-devices

    http://www.lutron.com/TechnicalDocumentLibrary/048148a.pdf

    It'd be worth spending a couple hours in the code book, maybe at home.

    A fellow named "Mike Holt" runs a site dedicated to answering practical code questions like yours.

    It's desirable to have lighting split among different phases so loss of one phase doesn't put everybody in the dark. But you haven't given much detail.


    old jim.
     
    Last edited: May 24, 2014
  8. To answer your first question, it's not bad practice, assuming you're using some kind of 2 pole single throw switch (DPST). The important thing is that a switch must de-energize a device. In cases where the device only uses a single phase and a neutral you only have the break the phase and can leave the neutral connected to the device since it should be at 0 Volts.

    It's perfectly normal to connect lighting to two phases because phase-to-phase voltage is higher than phase-to-neutral voltage. If you use a higher voltage the lights will draw less current. This saves energy from losses in wires as well as money spent on wire.

    Be safe and keep asking questions.
     
  9. sophiecentaur

    sophiecentaur 13,698
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    The lights must have the appropriate working voltage of course.
    Is the connection of lights across two phases standard practice? If so, which country? I don't think it's done in the UK.
     
  10. sophiecentaur

    sophiecentaur 13,698
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    You're talking here about redundancy (?): a good idea. You aren't talking about connection between phases - are you?

    I still don't get what the OP is actually describing in his statements about connections to phases.
     
  11. My first question would be, what voltage are the lights rated for?
     
  12. It's very common in the US sophie. Not in residential, which is single phase, but in commercial and industrial services that are 3-phase. Office and warehouse lights sold in the US tend to have ballasts (transformers) that can be tapped for 120, 208, 277, or 480V supplies.

    Basically you buy a ton of them and have some electricians go through them all and set them up for the correct voltage then go to town installing them.

    The circuit usually draws too much current for any kind of basic wall switch so you have to install a contactor that engages the lights. A basic wall switch can then turn the contactor on and off. Some people go the cheap route and just put a mini-switchgear in the electrical vault to turn the lights on and off.

    Brenfox is probably wiring up a contactor for his engineer.
     
  13. jim hardy

    jim hardy 4,768
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    Yes, redundancy. Myself, i'd only connect lights phase to neutral so as to avoid backfeeds when you lose a phase. Every room should have some lights from different phases.


    Nor do i.
    It'd be well for bren to brush up on the relevant sections of electrical code and educate his engineer, if necessary.

    Could be he just assumed engineering school teaches practical matters like NEC.
    I sure never had such a course.
    Young engineers new to industry need to be taken under the wing of an old hand. I had a most excellent mentor. Our electricians and mechanics were always happy to answer my questions about the practical side of things.

    old jim
     
    Last edited: May 24, 2014
  14. Before anyone goes jumping to conclusions here you don't even know if the OP is working with live wires or will even be the one doing the connections once the wires are pulled into the boxes. I have known electricians who send their teenage kids out to the job-site to pull wires into conduit. Guess what? There is no power on the site. Later on when all the wires are pulled in someone qualified makes the connections in each box.

    When the first response after the original post is this:

    Quite frankly I don't blame the OP for telling this forum to f*** off. It has always appeared to me that there are very few who post on here who have any real experience in actual electrician work. Oh yeah there are some of you who added an outlet or maybe even a whole circuit in their basement but compared to the project it seems the OP is handling you don't have a clue.

    Edit: That is not to say there is no one here that knows anything about it, just typically not the ones who yell the loudest.
     
    1 person likes this.
  15. I just had a thought that might help you on your second question Bren.

    A voltage measurement is always the difference between two points.

    At first that might seem like a subtle point but it's crucial.

    Consider this example:

    You're troubleshooting an outlet so you measure the voltage between the hot and neutral. You measure 0V so you think it's safe to open the outlet and inspect it. You get electrocuted. What do you think happened? The neutral was connected to the same phase as the hot! The difference between the phase and neutral is 0V because they're at the same potential but the difference from ground to neutral or hot was still 120V.

    That's a true story. Investigating this I found that an electrician had connected the neutral to a 3-pole breaker in the panel in order to make a special 3-phase outlet in another part of the building. The electrician either didn't know or didn't care that the neutral also connected to two regular 120V outlets. So one outlet had 0V from phase to neutral and another had 208V. That 208V outlet burned up plenty of tools before I was called to look at it.

    If I had measured the neutral to ground I would have immediately seen that it was energized. I could have used an NCV too (non-contact voltage tester). Keep one in your tool bag or your pocket. They only cost 10 to 15 bucks. It was totally my fault that I got zapped.
     
    Last edited: May 24, 2014
  16. sophiecentaur

    sophiecentaur 13,698
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    You could argue that this forum is not the vehicle for 'discussing' matters that are as clear cut as Wiring Regs. 'The Book' says it all.
     
  17. Not really. There are many places the 'book' is not that clear. Go here:
    -
    http://forums.mikeholt.com/
    -
    If everything was as clear cut as you claim then those message boards would not exist.
     
  18. sophiecentaur

    sophiecentaur 13,698
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    You have a point but your link is the sort of forum to post such specialist queries. PF will give you much better and reliable explanations than the purely practical groups (on which you can read total scientific rubbish).
    But don't expect PF contributors to know about part numbers and all abbreviations. That's not the Physics of the situation.
     
  19. I don't think I'd trust anyone to install lighting in my home or office who thought the lights would run with an electric potential of 0.
     
    1 person likes this.
  20. Then you would be really disappointed if you went to a job site and talked to the young apprentices.

    Electrical work isn't all Ohm's law and circuit theory. Apprentices start with making good pipe bends and pulling wire. Proper securement and good construction is every bit as important as knowing what conductance is. Apprentices learn as they go from their journeymen and masters who watch everything they do and answer all their questions.

    It's actually pretty hard to achieve a journeyman license. It takes four years of on-the-job training in many places. It also requires some night classes and a tough electrical code test around here. It takes about 6 to 10 years to achieve a good masters license (in a state with high standards).

    Believe it or not the system produces some pretty talented tradesmen and tradeswomen. It's well worth putting up with a few newbie questions.
     
  21. AlephZero

    AlephZero 7,300
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    There is no evidence here of the OP's qualifications. We have a question that (IMO, speaking as an engineer with no electrical training, but a lot of life experience reading between the lines and a BS filter that works pretty well) gives me the clear impression the OP doesn't understand the basics of what he/she is doing, otherwise the question wouldn't be necessary.

    And the OP's next post (again IMO) is the classic example of the well known engineering equation

    over-confidence in one's knowledge and ability + arrogant attitude = accident waiting to happen.

    I don't know what is the US equivalent of the UK expression "cowboy electrician," but I don't believe you don't have any on your side of the Atllantic.
     
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