Switching neutral in 120v control
Switching neutral in 120v control
(OP)
Does anyone have experience with switching the neutral instead of the "Hot" conductor in control circuits except in motor starter buckets. I have encountered this practice on a DCS system in a chemical manufacturing facility.I am told this is a safer practice in that all conductors in the field are already a grounded conductor and any shorts to ground will only switch "on" the respective circuit. I would like some input on this concept if anyone knows some specifics. Thanks.





RE: Switching neutral in 120v control
The idea that switching on a circuit due to an earth fault is somehow safe is intriguing although in a system designed to fail 'safe' it is likely to be flawed.
When the switch is open there will be line voltage across the contacts, so it is foolish to regard it as a grounded conductor when in this state. It is very much live, and although the available current may be limited by the impedance of the contactor coil there will likely be enough current available to cause a fire or injury.
Where have you seen this scheme?
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If we learn from our mistakes I'm getting a great education!
RE: Switching neutral in 120v control
RE: Switching neutral in 120v control
The only application in relatively new AC control circuits where I see connection to neutral opened is where thermal protection sometimes is connected between 'lower coil' and neutral. But don't think that is done any more.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Switching neutral in 120v control
Switching a neutral is generally forbidden by the NEC unless the hot conductor is opened simultaneously.
I am sure that this practice will make trouble shooting more challenging.
Note that the intended operation of our grounding systems is to trip the supply breaker in the event of a ground fault, not unexpectedly start machinery.
You probably have serious safety violations with this circuit as well as code violations.
If management were aware of the possible legal and liability issues, they may over-ride the "Away from home" experts.
Despite that, be very careful approaching management. Such an action may be a career ending event in some workplace cultures.
s
Bill
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"Why not the best?"
Jimmy Carter
RE: Switching neutral in 120v control
The over-temp 'fuse' that was added (several years ago, part of a safety update) to my home's ventilation system was installed on the Neutral side of the motor. I thought it was a strange choice. For every rationale justifying that choice, it seems that there's probably two rationales for the Hot side.
RE: Switching neutral in 120v control
RE: Switching neutral in 120v control
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Switching neutral in 120v control
But I have done a ton of house wiring - usually without turning off the power... too big a hassle to find the right breaker, etc, etc
Anyway - imagine replacing a fan or light. Turn off at the swithc and you should be good to go. When somebody (usually my Dad) switched the neutral side I would grab the "black" wire thinking it was "dead". Well - I got knocked on my butt more than once!!
RE: Switching neutral in 120v control
Our house's previous owner was a fan of switching the neutral line... I thought I was safe killing the breaker (always do that anyways). Then I found some of his work where two circuits (i.e., two separate breakers) connected together through some odd patchwork of wiring in the attic. Now I have to trace everything back to the panel to make sure that breaker kills it completely.
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Switching neutral in 120v control
Unfortunately - when it doesn't beep - that does not guarantee its a dead wire. Learned that the hard way!!
RE: Switching neutral in 120v control
I wire my industrial enclosures the same way and I've never seen the standards contradict this... I'll review the standards that I have tomorrow and see if I can post a definition.
Z
RE: Switching neutral in 120v control
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Switching neutral in 120v control
Please tell me how to identify your enclosures. No offence but I never want one of them on our site - non-standard wiring practices which don't meet our national regulations just aren't worth the trouble, however good they otherwise are. Sorry.
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If we learn from our mistakes I'm getting a great education!
RE: Switching neutral in 120v control
You got that part right.
Bill
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"Why not the best?"
Jimmy Carter
RE: Switching neutral in 120v control
Opening the neutral at the switch means the socket is still live... that's always a bad thing. If I see a light go off when I flip a switch, common sense says that socket is dead, but that wasn't the case for my house (at least the stuff the idiot beforehand self-installed).
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Switching neutral in 120v control
So you guys are convincing me I'm wired backwards, but where is this documented? The only thing that I can find in IEC 601010 and NFPA 79 state that "all current carrying conductors" need to be disconnected. That makes sense for the power inlet, but not the switch. Maybe I'll learn a few more things by reading the right standard!
Mho, the engineer formally known as ZappedAgain
RE: Switching neutral in 120v control
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Switching neutral in 120v control
"Switches or circuit breakers shall not disconnect the grounded conductor of a circuit"
"...the grounded (neutral) conductor."
The world will be a safer place now.
Mho
RE: Switching neutral in 120v control
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Switching neutral in 120v control
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Switching neutral in 120v control
I did a web-search on this topic and it is amazing how much info pops up that switching the neutral is correct; scary. Luckily most of the entries also get corrected after a while.
Zapped
RE: Switching neutral in 120v control
RE: Switching neutral in 120v control