# Valid case for switching neutral?



## Rora (Jan 31, 2017)

I'm building a panel for an automation lab which has 120VAC coming in to feed a motion controller, 24VDC, and 5VDC power supplies. I'm adding a small disconnect box at bench level that makes it easier to cut power to the panel, this is connected to the L1 contactor input.

Conventional wisdom is to always switch the hot since the switch is less exposed than the load. In this case, the load (contactor input) is less exposed than the switch. I should also mention this is a solid state contractor, so I'm not even sure how much risidual voltage will be floating downstream of the input circuit, although it would still be a potentially dangerous electrical path.

Is this a valid case to switch the contactor on the neutral side? Don't think it will do anything in terms of reducing EMI (the cable to the switch runs out to the bench near sensitive instruments) considering the neutral is current carrying, but I figured it'd be safer and I need someone to tell me why I'm wrong.


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## CoolWill (Jan 5, 2019)

Switching the grounded conductor in controls is perfectly normal and done all the time. There are several control schemes that would be impossible, or at least way more involved, if you didn't switch the grounded conductor.


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## splatz (May 23, 2015)

I don't know if UL508A would apply but I don't think there's anything in there that prohibits switching the neutral. I could swear I have seen panels where the pushbuttons lights / switches on the door were switching the neutral but I can't remember. 

Motor overloads commonly interrupt the neutral, I can't think of another example. 

There may be something about a main disconnect for the panel, and that may be required to disconnect power to all the components in the panel. If the disconnect you're making is the main disconnect, I think the color codes would have you use a different color for power that's still hot when the main disconnect is open.


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## sparkiez (Aug 1, 2015)

There is nothing wrong with switching Line and Neutral. Just leave the EGC, of course.


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## Grounded-B (Jan 5, 2011)

The main issue with switching the grounded conductor (neutral), is that an un-intentional ground on the neutral conductor, will inhibit the action of the switching device.

Or, it could cause an un-intentional energization of the contactor.

Steve


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## sparkiez (Aug 1, 2015)

Wouldn't opening the line connection prevent that, though?


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## macmikeman (Jan 23, 2007)

You are allowed to switch neutral as long as you are breaking the connection to any associated ungrounded wire simultaneously . This is precisely because of sensitive environments , although I can't think of any such right off hand. Possibly in oxygen rich area's? It's still dark outside , early, and my tinkin ain't woiken up good yet.


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## Rora (Jan 31, 2017)

splatz said:


> I don't know if UL508A would apply but I don't think there's anything in there that prohibits switching the neutral. I could swear I have seen panels where the pushbuttons lights / switches on the door were switching the neutral but I can't remember.
> 
> Motor overloads commonly interrupt the neutral, I can't think of another example.
> 
> There may be something about a main disconnect for the panel, and that may be required to disconnect power to all the components in the panel. If the disconnect you're making is the main disconnect, I think the color codes would have you use a different color for power that's still hot when the main disconnect is open.


Here's what I found on it:

66.9.1 The following color coding shall be employed throughout the panel:
...
d) Yellow or orange – ungrounded control circuits or other wiring, such as for cabinet lighting that remain energized when the main disconnect is in the off position.
...
g) White with yellow stripe or white with orange stripe – grounded ac control circuit current carrying conductor that remains energized when main disconnect switch is in the off position.

So I believe A2 to switch should be yellow/orange since it's effectively hot if one were to touch it, and the switch to neutral white with yellow/orange. I guess technically the downstream side of the switch isn't "energized when the disconnect is in the off position" though.



sparkiez said:


> Wouldn't opening the line connection prevent that, though?


If I understand correctly, he's saying is that any short to ground on the A2 to switch will activate the contactor since the A1 connection has to be fed from the upstream hot, not downstream of the contactor, so it's always live/able to turn on the contactor if the switch is closed or that segment is shorted to ground. 

The same would apply if the switch was on the hot except in that case what's running out on the bench hasn't dropped across a load and any short will pop the breaker I'm putting in for this circuit. I think this identifies the real danger here--the A2 to switch, which could potentially ground through a person (with the the panel "off"/switch open) and not pop the breaker.

Solid state contactor inputs are fairly low current (the one I'm using is ~17ma?) so it should be easy to keep the breaker pretty small and I can use a fast blow characteristic since it's not an inductive load. If I understand correctly the input circuit impedance also limits the potential danger if users were to be a ground path on the downstream side, so I'm left to think it would indeed be safer.


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## joe-nwt (Mar 28, 2019)

macmikeman said:


> You are allowed to switch neutral as long as you are breaking the connection to any associated ungrounded wire simultaneously . This is precisely because of sensitive environments , although I can't think of any such right off hand. Possibly in oxygen rich area's? It's still dark outside , early, and my tinkin ain't woiken up good yet.


It's done in transfer switches, as an example.


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## gpop (May 14, 2018)

CoolWill said:


> Switching the grounded conductor in controls is perfectly normal and done all the time. There are several control schemes that would be impossible, or at least way more involved, if you didn't switch the grounded conductor.


Ive worked in many relay panels where the neutral was being switched. When i asked why they said that the relay contacts last longer in that configuration. No idea if that is true but it seemed plausible especially as the panels are old and the relays look original.


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## joe-nwt (Mar 28, 2019)

gpop said:


> Ive worked in many relay panels where the neutral was being switched. When i asked why they said that the relay contacts last longer in that configuration. No idea if that is true but it seemed plausible especially as the panels are old and the relays look original.


I'd sure like to see the rationale behind that one.


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## CoolWill (Jan 5, 2019)

joe-nwt said:


> I'd sure like to see the rationale behind that one.


Well, it's simple really. You see, it's grounded, and white, so... Magic. 

That's usually what old electrician wives tales about neutrals sound like.


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## Forge Boyz (Nov 7, 2014)

gpop said:


> Ive worked in many relay panels where the neutral was being switched. When i asked why they said that the relay contacts last longer in that configuration. No idea if that is true but it seemed plausible especially as the panels are old and the relays look original.


What's funny is that I was in a small control panel today and I noticed they are switching the nuetral. Can't say I have seen it before. I was upsizing a motor circuit and thought about changing it but decided to leave it be.

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## joe-nwt (Mar 28, 2019)

CoolWill said:


> Well, it's simple really. You see, it's grounded, and white, so... Magic.
> 
> That's usually what old electrician wives tales about neutrals sound like.


Ooff! <smacks forehead> Of course. I forgot.


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## gpop (May 14, 2018)

Decided to do a little research on why the neutral would be switched in a relay panel and all i could find was it's a European thing (not sure if they still do it that way panels were mainly Italian). 

The only thing worse is a relay panel with a isolation transformer which gives 2 lines at 60v. (i use to cheat and ground one side until i locate the problem as it makes troubleshooting easier)

I did find that on starters the OL used the neutral due to Y-delta starters this allows multiple starters to use the same OL block. (at least that's what google says)

Next week i have a panel to upgrade to a plc. That has OL, thermal protection, leak detection and a few other things on the neutral side. I will be changing them all to the hot side as that makes adding them to the plc easier.


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## sparkiez (Aug 1, 2015)

Rora said:


> If I understand correctly, he's saying is that any short to ground on the A2 to switch will activate the contactor since the A1 connection has to be fed from the upstream hot, not downstream of the contactor, so it's always live/able to turn on the contactor if the switch is closed or that segment is shorted to ground.



I must be misunderstanding this. When you say you are adding a "disconnect box", my understanding is that you are installing a local disconnect in order to mechanically isolate power to your motion controller and power supplies. That being the case, yes, cutting off the neutral and line together will completely open the circuit, as you should be tying that contactor into the load side of the disconnect.


Otherwise, at least according to OSHA, control voltages, are not an approved means of energy isolation. I'm sure that there are safety analysis that can be done in order to allow different levels of machine operation, but if you are simply opening a contactor as a means to safely isolate power in order for students to perform work, especially with a solid state contactor, it makes me pretty wary. Especially when the vast majority of solid state relays and contactors I have replaced failed in a saturated state.


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## Rora (Jan 31, 2017)

Not sure if I need to mention this, but this is only for the contactor control which is limited by the solid state input circuit (~17mA) and protected by its own breaker. The controlled side of the contactor is conventional, connecting L1 to the breaker for each device. The contactor 30A rating is beyond the 15A breaker in the building panel, not to mention the sum of the breakers being fed which is <10A.

Hypothetically the L1 for the control circuit would go through the contact A1/A2 then to it's own breaker, then the "disconnect". I figured by having all breakers after the contactor prevents any surges from bypassing breakers through the contactor (although unlikely as it's opto-isolated). The control circuit breaker can be sized restrictively since it's not a coil driven contactor, well below lethal current.



gpop said:


> Ive worked in many relay panels where the neutral was being switched. When i asked why they said that the relay contacts last longer in that configuration. No idea if that is true but it seemed plausible especially as the panels are old and the relays look original.


Interesting... maybe they're thinking if it always remains at L1 potential, the pulse from closing the switch won't travel through it or something?



sparkiez said:


> I must be misunderstanding this. When you say you are adding a "disconnect box", my understanding is that you are installing a local disconnect in order to mechanically isolate power to your motion controller and power supplies. That being the case, yes, cutting off the neutral and line together will completely open the circuit, as you should be tying that contactor into the load side of the disconnect.
> 
> 
> Otherwise, at least according to OSHA, control voltages, are not an approved means of energy isolation. I'm sure that there are safety analysis that can be done in order to allow different levels of machine operation, but if you are simply opening a contactor as a means to safely isolate power in order for students to perform work, especially with a solid state contactor, it makes me pretty wary. Especially when the vast majority of solid state relays and contactors I have replaced failed in a saturated state.


Yeah, I really shouldn't call it a "disconnect" that gives a false impression that it's mechanical or somehow related to safety. The bench this will be on is in a locked office and only used by me, so this is strictly for convenience... any work on the panel would of course require the plug to be pulled. I know this thing won't be winning any awards in the safety certification department, I have sunk about $1k on just AC components alone between the contactor, thermomagnetic breakers, other DIN mounted parts, etc. for just 3 devices... so I am taking it seriously and want to make it as practically safe as possible even if it won't meet industrial standard. Either way, figured it would make an interesting discussion on the spirit of the law behind the letter.


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## paulengr (Oct 8, 2017)

One of the biggest reasons for switching the hot is convention. Hard to get around the fact that it is far easier to troubleshoot anything that follows convention, especially when you don't have a print. Also it is really hard to troubleshoot neutral switching. On line-side switching, simply place one probe on something rounded (neutral or a ground) and the other at various places in your circuit. If you see voltage, it's energized. If not, it's not. On the neutral side it's not so easy because you don't get voltage since everything is close to 0.


I think you got the European wiring confused. Convention with control wiring is to wire one side of the loads to neutral and the other to the control wiring, feeding through the various relays, push buttons, etc.., and then to the "hot" conductor. DC is the same except that the DC negative is the neutral or common. European starter arrangements typically include the overload protection relays on the "hot" side of the loads as well. However North American convention is to put overload relays on the neutral side. Also North American convention is to put the power side of the overload relay on the load side of a contactor whereas European convention is to put it on the line side right after the short circuit protection, or integrated into it with manual motor starters.


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## sparkiez (Aug 1, 2015)

paulengr said:


> One of the biggest reasons for switching the hot is convention. Hard to get around the fact that it is far easier to troubleshoot anything that follows convention, especially when you don't have a print. Also it is really hard to troubleshoot neutral switching. On line-side switching, simply place one probe on something rounded (neutral or a ground) and the other at various places in your circuit. If you see voltage, it's energized. If not, it's not. On the neutral side it's not so easy because you don't get voltage since everything is close to 0.
> 
> 
> I think you got the European wiring confused. Convention with control wiring is to wire one side of the loads to neutral and the other to the control wiring, feeding through the various relays, push buttons, etc.., and then to the "hot" conductor. DC is the same except that the DC negative is the neutral or common. European starter arrangements typically include the overload protection relays on the "hot" side of the loads as well. However North American convention is to put overload relays on the neutral side. Also North American convention is to put the power side of the overload relay on the load side of a contactor whereas European convention is to put it on the line side right after the short circuit protection, or integrated into it with manual motor starters.



If I'm not mistaken, the NEC forbids switching neutrals in non-power-limited applications. And yea, it does. Check out 404.2.


That doesn't speak to the reason for 404.2, but I'm a simple guy. The code says to do it, so I do it. Also, when I throw a switch, I don't want voltage sitting there waiting for a path to Ground.


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## tates1882 (Sep 3, 2010)

46.2 Location
46.2.1 All operating coils of electro-mechanical devices and indicator lamps, including the transformer primary winding of an indicator lamp, shall be directly connected to the grounded side of the control circuit.
Exception: A switching device that is provided within the industrial control panel as specified in the exceptions to 45.3.1 is able to be located between the coil and the grounded side of the control circuit.


45.3.1 All control circuit contacts shall be arranged to open the ungrounded conductor to the coil.
Exception No. 1: Electrical interlock contacts on multi-speed motor controllers are not required to comply when the wiring to these contacts does not extend beyond the control enclosure.
Exception No. 2: Overload relay contacts are not required to comply when the wiring to these contacts does not extend beyond the control enclosure.
Exception No. 3: Contacts of multi-pole control circuit switching devices that simultaneously open both sides of the control circuit are not required to comply.
Exception No. 4: Ground test switching device contacts in ungrounded control circuits are not required to comply.
Exception No. 5: Solenoid test switching device contacts in ungrounded circuits are not required to comply.
Exception No. 6: Coils or contacts used in electronic control circuits are not required to comply.
Exception No. 7: ′′Run′′ pushbuttons for two hand operating are not required to comply when overcurrent protection is provided in each conductor.

Its pretty specific when you can do switching in the grounded circuit.


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## CoolWill (Jan 5, 2019)

tates1882 said:


> 46.2 Location
> 46.2.1 All operating coils of electro-mechanical devices and indicator lamps, including the transformer primary winding of an indicator lamp, shall be directly connected to the grounded side of the control circuit.
> Exception: A switching device that is provided within the industrial control panel as specified in the exceptions to 45.3.1 is able to be located between the coil and the grounded side of the control circuit.
> 
> ...


So, as long as you don't leave the control enclosure, pretty much whenever.


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## tates1882 (Sep 3, 2010)

CoolWill said:


> So, as long as you don't leave the control enclosure, pretty much whenever.


 pretty much there may be a few more requirements a little deeper in the standard that has to do with specific use control panels, this is for a basic industrial control panel. 

I break all my grounded conductors across ol contacts for almost all mags/contactors.


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## tates1882 (Sep 3, 2010)

This is why you see a white conductors in front of the msp’s.


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## Forge Boyz (Nov 7, 2014)

tates1882 said:


> This is why you see a white conductors in front of the msp’s.


Looks nice! Can we see the rest of that panel? 

Sent from my SM-G970U1 using Tapatalk


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## splatz (May 23, 2015)

tates1882 said:


> 46.2 Location
> 46.2.1 ...
> 
> 45.3.1 ...
> Its pretty specific when you can do switching in the grounded circuit.





CoolWill said:


> So, as long as you don't leave the control enclosure, pretty much whenever.





tates1882 said:


> pretty much there may be a few more requirements a little deeper in the standard that has to do with specific use control panels, this is for a basic industrial control panel.
> 
> I break all my grounded conductors across ol contacts for almost all mags/contactors.


Correct me if I am wrong, this is my understanding. 

For @tates1882 is complying with the UL 508A standard - he took the UL test, has the UL T-shirt, gets the UL inspection, so he's a legit UL panel builder. He makes a listed piece of equipment, the guts of which are outside the scope of the NEC. 

If you're not a panel shop, you are installing to NEC, building a control panel to article 409, different rules apply. As @sparkiez points out, it's simple; article 404.2 applies to all switches. 

Now if you're just building something for your workbench, I can not imagine you're subject to either, a man's contraption is his castle.


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## tates1882 (Sep 3, 2010)

splatz said:


> Correct me if I am wrong, this is my understanding.
> 
> For @tates1882 is complying with the UL 508A standard - he took the UL test, has the UL T-shirt, gets the UL inspection, so he's a legit UL panel builder. He makes a listed piece of equipment, the guts of which are outside the scope of the NEC.
> 
> ...


Well I think it would depend on your states rules regarding un-listed equipment, Idaho for example will allow for a qualified field evaluation body to certify equipment. The FEB doesn't have to be a NTRL to satisfy the state but does need to be to satisfy OSHA. I build listed, un-listed, and NEC based ICP's, some customers( I'm a multi-state, 2 country supplier) don't want the listed sticker or want components that UL won't allow so chose to use a FEB or AHJ. We require indemnification if they don't buy the listed version, as this removes a layer of protection for my shop. I normally won't build a panel under the NEC with more than 3 motors and simple controls as most AHJ's struggle to properly inspect and evaluate said panel.

What I'm getting at is if I was the OP, I would switch the grounded conductor, follow ul508a, and hire an FEB to certify the build.


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## JRaef (Mar 23, 2009)

macmikeman said:


> You are allowed to switch neutral as long as you are breaking the connection to any associated ungrounded wire simultaneously . ...



That. ^

Also, the ONLY reasons that the "neutral" was/is used in motor OL circuits is tradition, based on 1) an older practice that is no longer done (very much) and 2) the fact that originally, motor OLs were separate per pole, not one single 3 pole relay.

1) The older practice is from the fact that it USED TO BE very widespread practice to use the Line voltage as the control voltage (called "common control"). So if you had 480V power for a motor, you used 480V coils on the starters. In *that *case, the "other side" of the contactor coil was NOT actually a neutral circuit, *it was just as hot as the other side*.

2) Older starter assemblies used separate 1 pole OL relays, so the trip contacts were wired in series and up until 1978(?), three phase motors only required 2 OL relays.

So JIC and NEMA, in order to facilitate the simplest factory wiring that covered both of the above issues, put the OL relay contact(s) on the RIGHT side of the coil in a ladder diagram. It is ONLY when we use 120V coil that this BECOMES the "neutral" side of the circuit, but that was never the INTENT. 








Note that none of the above wires are white...

Since then, so much time has passed now that the vast majority of people in the industry have never even seen common control used, nor have they seen separate 1 pole OL relays wired in series. So they have created many different myths as to why the OL relay contact is on the "neutral" side. All of them wrong.

Side note: If SAFETY is your concern, you should not be using a solid state contactor as an isolation device. It does NOT isolate.


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