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Thread: Connecting Neutral to PEG within equipment, justification for "NO WAY"!!

  1. #1
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    Connecting Neutral to PEG within equipment, justification for "NO WAY"!!

    Hello,

    please excuse me if this question seems too obvious. I am in an argument with a colleague over how we connect wires inside of some equipment we manufacture. In particular, we manufacture electrical measurement products housed in metal enclosures, for lab use, which typically sit on top of a lab bench. This product is about 30 lbs, steel box roughly 1' x 1' x 2'. The product has a standard fused/switched power inlet which accepts a linecord with an IEC320-C14 female on it. This line cord is intended to be plugged into a standard 120V/60Hz wall outlet (Line, Neutral, GND) in the USA. Our product consumes at most 300W.

    It looks like one colleague may believe it is OK to connect neutral and GND together within our product. I'm saying "no way". My justification for saying no way?
    1) General knowledge that the PEG conductor in the line cord is normally not supposed to carry any current. Connecting neutral to GND within our box will result in the PEG in the line cord carrying roughly half the load current. This is just one of several bad things which would happen.
    2) This section of IEC 61010:
    4.3.2.5 MAINS supply
    ...d) Equipment for single-phase a.c. supply shall be connected both with normal and reverse polarity.

    W/regards to IEC 61010 4.3.2.5 (d), my argument goes as follows:
    IF we connect PEG to neutral within our product, THEN a line-to-neutral short will result if our equipment is connected as specified in IEC 61010 4.3.2.5 (d).

    But...I would like a stronger argument, perhaps a reference to NFPA 70, NEC, etc? If someone can mention a document and specific location within the document, I can get that document and look it up myself. I just want something very short and sweet.

    Many Thanks, rtec

  2. #2
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    That is prohibited by 250.24(A)(5) in the NEC.
    (5) Load-Side Grounding Connections. A grounded conductor shall not be connected to normally non–current-carrying metal parts of equipment, to equipment grounding conductor(s), or be reconnected to ground on the load side of the service disconnecting means except as otherwise permitted in this article.
    Don, Illinois
    Ego is the anesthesia that deadens the pain of stupidity. Dr. Rick Rigsby
    (All code citations are 2017 unless otherwise noted)

  3. #3
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    Not only prohibited but makes me think very poorly of the makers of such equipment when I have to explain why GFCIs are tripping with this super expensive equipment. Not yours in particular, but you get the idea.
    Tom
    TBLO

  4. #4
    Join Date
    Dec 2007
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    NE Nebraska
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    Quote Originally Posted by rtec View Post
    Hello,

    please excuse me if this question seems too obvious. I am in an argument with a colleague over how we connect wires inside of some equipment we manufacture. In particular, we manufacture electrical measurement products housed in metal enclosures, for lab use, which typically sit on top of a lab bench. This product is about 30 lbs, steel box roughly 1' x 1' x 2'. The product has a standard fused/switched power inlet which accepts a linecord with an IEC320-C14 female on it. This line cord is intended to be plugged into a standard 120V/60Hz wall outlet (Line, Neutral, GND) in the USA. Our product consumes at most 300W.

    It looks like one colleague may believe it is OK to connect neutral and GND together within our product. I'm saying "no way". My justification for saying no way?
    1) General knowledge that the PEG conductor in the line cord is normally not supposed to carry any current. Connecting neutral to GND within our box will result in the PEG in the line cord carrying roughly half the load current. This is just one of several bad things which would happen.
    2) This section of IEC 61010:
    4.3.2.5 MAINS supply
    ...d) Equipment for single-phase a.c. supply shall be connected both with normal and reverse polarity.

    W/regards to IEC 61010 4.3.2.5 (d), my argument goes as follows:
    IF we connect PEG to neutral within our product, THEN a line-to-neutral short will result if our equipment is connected as specified in IEC 61010 4.3.2.5 (d).

    But...I would like a stronger argument, perhaps a reference to NFPA 70, NEC, etc? If someone can mention a document and specific location within the document, I can get that document and look it up myself. I just want something very short and sweet.

    Many Thanks, rtec
    This also results in stray currents flowing in every possible path that is connected to the EGC. Such currents will lead to voltage rise on those components also - which increases touch potential for users. When everything is in new and good condition there may not be much for noticeable problems, but when a path becomes interrupted that is where you have chances for voltage differences in what is otherwise not supposed to be current carrying components.

  5. #5
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    I doubt your UL listing would allow for such a connection as it would create a condition where line current would return on the green wire which is a no-no except in a fault condition.

    We don't call it "PE" here either, and in general IEC standards just don't apply here, although in many cases they are close enough that they are acceptable if one is careful in applying them.
    Bob

  6. #6
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    Well, now you have documented reasons as to why you can't do that. But what the heck is the matter with your "colleague"? Does he have a reason for wanting to do this or is he just that incompetent that he doesn't know any better? Has he never seen any equipment before that is line powered? Geeze, I didn't go to engineering school and I knew from probably age 12 that the green ground from a line cord doesn't get connected to the white neutral.

    -Hal

  7. #7

    IEC 61010

    Viewing the limited version available and looking at testing 4.3.5 under column shown as lab R required I get the rules used for IEC.
    I actually attached an index page that shows section 6 as the electrical safety concerns, would you or your team tell us how section 6 with regards to ' reverse polarity ' (normally encountered in FWR DC power supplies) is a requirement traditionally in EUR as 50HZ lines up with USA 60HZ , AC supplies?
    Attached Images Attached Images  

  8. #8

    IEC 61010

    Ok that was a bit awkwardly asked. There is such terms as straight polarity in the US and reverse in Europe.
    So in US the smaller slot on the plug matches up to the outlet terminated wire black and the larger slot on the plug to the white or neutral also termed straight polarity.
    In a rectifier DC the power supplies now kept from alowwing the electrons from wiggling forth and back although AC has no polarity how does plugs in the Europe keep my shaver from the U S from working?

  9. #9

    IEC 61010

    NEC 393.2 reverse polarity protection(backfeed protection,393.45(C) low voltage suspended ceiling power.

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