# Switching Neutral



## dronai (Apr 11, 2011)

Been struggling with a Latching relay, took it on my bench, and just realized, they were switching neutral using a momentary switch 3-way for the pulse. :blink: But, what threw me off, I was getting a *voltage reading 120V *on the switched side to ground, wtf ? still baffled by that one. unless it's an ungrounded neutral from a control transformer ? Help 
You guys in the field see this a lot ? 

Only time I have seen neutral switched is with PLC's and PNP transistor switching in controls.


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## dronai (Apr 11, 2011)

Question #2 How does a momentary switch hold a circuit like a contactor for the pilot to only go on with the pulse and stay on after the switch returns back to center ? The pilot lights pigtailed already, but only lights after the pulse ??


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## splatz (May 23, 2015)

dronai said:


> Question #2 How does a momentary switch hold a circuit like a contactor for the pilot to only go on with the pulse and stay on after the switch returns back to center ? The pilot lights pigtailed already, but only lights after the pulse ??


There is a very simple circuit that uses a relay so a momentary switch starts and another momentary switch stops / resets. 

http://www.electriciantalk.com/f2/latching-relay-circuits-202337/#post3811569


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## splatz (May 23, 2015)

dronai said:


> Been struggling with a Latching relay, took it on my bench, and just realized, they were switching neutral using a momentary switch 3-way for the pulse. :blink: But, what threw me off, I was getting a *voltage reading 120V *on the switched side to ground, wtf ? still baffled by that one. unless it's an ungrounded neutral from a control transformer ? Help
> You guys in the field see this a lot ?


If you are measuring either side of the *contacts* to ground yes they are both hot, think of it as the terminals on a switch. The coil is a load and you should see 120v across the coil terminals when energized, but the contacts are a switch, so when closed you'll see the same voltage on both sides.


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## Jeff B (Sep 30, 2017)

dronai said:


> Been struggling with a Latching relay, took it on my bench, and just realized, they were switching neutral using a momentary switch 3-way for the pulse. :blink: But, what threw me off, I was getting a *voltage reading 120V *on the switched side to ground, wtf ? still baffled by that one. unless it's an ungrounded neutral from a control transformer ? Help
> You guys in the field see this a lot ?
> 
> Only time I have seen neutral switched is with PLC's and PNP transistor switching in controls.


From where I sit, it does look like the control transformer *is not* bonded to ground at one end. I always bond to ground.

Is the "3-way" switch a selector with 1 N.O and 1 N.C. contact block?

Can you provide us an accurate drawing of your switch wiring and control transformer wiring as it is in the application?

As for PLC transistor switching you mentioned, I prefer to always "Source" inputs and outputs (I/O) rather than "Sink". "Sink" is popular when using different DC voltages within the same system (i.e. 5vdc, 12vdc, 24vdc) because it's just a simple path back to "0" (different from "ground"). For AC, there is no reason to "Sink" I/O. I want fuse/breakers to open when there is a short circuit. Only "Source" will do that and it eases troubleshooting.


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## dronai (Apr 11, 2011)

splatz said:


> There is a very simple circuit that uses a relay so a momentary switch starts and another momentary switch stops / resets.
> 
> http://www.electriciantalk.com/f2/latching-relay-circuits-202337/#post3811569


Well duh I know that now, I had the thing on my bench ripped apart and thought the coil was out. So I went direct with 120V



splatz said:


> If you are measuring either side of the *contacts* to ground yes they are both hot, think of it as the terminals on a switch. The coil is a load and you should see 120v across the coil terminals when energized, but the contacts are a switch, so when closed you'll see the same voltage on both sides.


Dude ! re read my first post

*NOT the latching relay*, but the 3 -way momentary toggle switch that is *switching neutral *is getting a reading to ground of 120V. When I first started troubleshooting this job, I was getting only 30V to ground, and Brian John nailed it, saying I was getting a ghost voltage. It was, because I switched to my Knopp, and presto, no voltage. That neutral wasn't getting across the poles, because that momentary switch is bad !

*
Also, the switched legs are power colors not white !*


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## dronai (Apr 11, 2011)

Jeff B said:


> From where I sit, it does look like the control transformer *is not* bonded to ground at one end. I always bond to ground.
> 
> Is the "3-way" switch a selector with 1 N.O and 1 N.C. contact block?
> 
> ...


"From where I sit, it does look like the control transformer *is not* bonded to ground at one end. I always bond to ground."

That's weird isn't it ? first one in a switching application I've seen, and I haven't located where that transformer is


The switch is not a selector, just a normal 3-way, toggle, but momentary action. I tested it on my bench last night, and it's not working properly.

Read what I wrote Splatz above ^ about the 30V, and the switched legs are power colors, and the common is off white, with the pilot light pigtailed ? I would think that needs a 2 pole switch to keep the pilot light on after the pulse is gone ? ODD ball for me


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## Jeff B (Sep 30, 2017)

dronai said:


> "From where I sit, it does look like the control transformer *is not* bonded to ground at one end. I always bond to ground."
> 
> That's weird isn't it ? first one in a switching application I've seen, and I haven't located where that transformer is
> 
> ...


The transformer is clearly *not* bonded to ground in your case. There will be about 90vac on one point of the secondary winding and 30vac on the other with and ungrounded transformer. That wiring scheme leads to troubleshooting headaches like you are experiencing.

Please locate the source of this voltage for your circuit. The fuse on the 90vac side may be blown which will still leave you the 30vac you have.

Please check this so we can better assist you.


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## dronai (Apr 11, 2011)

Jeff B said:


> The transformer is clearly *not* bonded to ground in your case. There will be about 90vac on one point of the secondary winding and 30vac on the other with and ungrounded transformer. That wiring scheme leads to troubleshooting headaches like you are experiencing.
> 
> Please locate the source of this voltage for your circuit. The fuse on the 90vac side may be blown which will still leave you the 30vac you have.
> 
> Please check this so we can better assist you.



Wouldn't the control transformers fusing just be primary and secondary, and be open if one fuse was blown ?


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## Jeff B (Sep 30, 2017)

dronai said:


> Wouldn't the control transformers fusing just be primary and secondary, and be open if one fuse was blown ?


Primary and secondary should be fused. That's how I design controls.

If at least 1 primary fuse were open, there would be no secondary voltage.

If the primary side is ok and the secondary fuse were open with an ungrounded winding, then you will absolutely see 30vac available on the unfused side. That is a fact.


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## John Valdes (May 17, 2007)

Jeff. You are going to be a valuable source of information on this forum. But I already knew that long before you joined.
Good to see you around.


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## sparkiez (Aug 1, 2015)

If there aren't any roaches, I can't help you.

Also, I don't bond the secondary of control transformers to ground , only at the ground tap on the transformer if provided. The measurements for the voltage should be referenced to X1, X2 etc and not ground. You can't assume an X2-ground bond. 

The only other take I have on this is that the neutral is often "switched " in a sense on overload devices on contractors. The overload contacts open, You will get voltage across the coil, but it will not pull in because the overload is breaking the neutral.


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## HackWork (Oct 2, 2009)

John Valdes said:


> Jeff. You are going to be a valuable source of information on this forum. But I already knew that long before you joined.
> Good to see you around.


Better than me, John?!?!?!?!?!?!


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## dronai (Apr 11, 2011)

Problem solved !!!! No control transformer at all, No ungrounded control transformer, No fuse blown, *The low voltage 30V , Brian John was right- Thank you * One call to the old Industrail boss, and he knew in 5 minutes what was happening. 
Thanks anyway guys


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## dronai (Apr 11, 2011)

sparkiez said:


> If there aren't any roaches, I can't help you.
> 
> Also, I don't bond the secondary of control transformers to ground , only at the ground tap on the transformer if provided. The measurements for the voltage should be referenced to X1, X2 etc and not ground. You can't assume an X2-ground bond.
> 
> The only other take I have on this is that the neutral is often "switched " in a sense on overload devices on contractors. The overload contacts open, You will get voltage across the coil, but it will not pull in because the overload is breaking the neutral.


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## dronai (Apr 11, 2011)

Jeff B said:


> Primary and secondary should be fused. That's how I design controls.
> 
> If at least 1 primary fuse were open, there would be no secondary voltage.
> 
> If the primary side is ok and the secondary fuse were open with an ungrounded winding, then you will absolutely see 30vac available on the unfused side. That is a fact.



This was not in the solution, because there was no control transformer, but...

I still don't see how you are getting the 90V and 30V on the control transformer secondary senario, there is no tap, so you aren't dividing the voltage. One fuse out, and you have no voltage on the secondary ungrounded or grounded. I would think the windings with no taps would be equal, unless there are taps


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## John Valdes (May 17, 2007)

HackWork said:


> Better than me, John?!?!?!?!?!?!


When it comes to industrial control and technology it would not be fair to compare you with Jeff as you are an electrician just like me.
Jeff was an industrial machine problem solver and is highly respected in this field. I know because he worked with me. Not for the same company, but we worked together on projects where I knew I would need him.

We cannot compare apples to apples because both of you guys do different work. I bet you know the code 99% better than Jeff. But Jeff knows controls 99% better than most electricians.
So the answer is its not an apples to apples comparison.

But I still love you and I am certain your good looks and smarts are very impressive. :thumbsup:


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## dronai (Apr 11, 2011)

Jeff B said:


> From where I sit, it does look like the control transformer *is not* bonded to ground at one end. I always bond to ground.
> 
> Is the "3-way" switch a selector with 1 N.O and 1 N.C. contact block?
> 
> ...


The answer to the problem "Sourcing to ground" I didn't get it, until I bench tested to prove his explaination


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## John Valdes (May 17, 2007)

dronai said:


> The answer to the problem "Sourcing to ground" I didn't get it, until I bench tested to prove his explaination


Dorian. I just got an unlock code from Dan Wade. If you have time, it seems like now would be a good time to hit him up.
I had to do it twice as I downloaded the regular version. Dan told me to download the pro version and he will provide my key. I bet its ready right now.
John


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## dronai (Apr 11, 2011)

Thanks John, but I hate bothering that guy. It's like i'm stealing his intellectual property, and I feeling like a mooch :laughing: For now I can just draw a simple ladder on paper


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