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Ryan SC

PLC AC Outputs Switching on LINE or NEUT

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I'm designing a valve control panel and we are providing contact closures for 115 VAC Valve Open/Close commands to an electric actuator and what we are used to is switching or closing these contacts on the LINE side and just connecting the neutral down to the actuator but our customer is suggesting we should be closing to the NEUTRAL back at the PLC, switching in the NEUTRAL path.

What is the most common practice for this type of control?

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There's another thread on here talking about the Overload contacts on motor starters interrupting the neutral side of the coil. That's one of the only instances I've ever seen using contacts to interrupt the neutral side. We have one machine built by an integrator that did that with 24VDC valve coils and PLC contact outputs. It's a royal pain to troubleshoot if you forget (or don't know) that they're switching the 0V side. It's the only thing I know of in our facility that does it that way.

Did your customer explain why they would prefer you do that?

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Maybe they prefer Lightning Damage?

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It's an actuator like this one and you can see they even show the Open/Close controls on the LINE side.  They still owe us an answer why they want to go that way.

Valve_Actuator.JPG

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To implement the customer's request you still need to to provide contacts to Open and Close.  Seems like they want you to provide one more dry contact to make or break the Neutral (contact closed for either opening or closing.  Be wary, by putting this "new" contact in the Neutral leg, you would be defeating the operation of the heater.  Regardless, you'll notice the overload is on the Neutral side.

Looks like you're in SC, so freeze protection might not be a concern.

Edited by pcmccartney1

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If it's South Carolina they may have picked up some bad habit from this one radio guy that thinks he can do controls without understanding electricity.
I've got some nice pictures of relays with the cover blown off the cube because he unbinds neutral from ground and won't install Lightning Arrestors on 80 foot antennas  because he swears they're a scam.

 

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It's the eternal battle of grounding and grounding loops.  Isolated ground bars for instrumentation vs. bonding grounding, etc...

Then throw in, on top of all of that, no protective (sacrificial) lightening or surge arresting devices.

It's not a scam when you have to go to a site and replace 300+ DNet Comms modules every other month, because you keep quoting them a lighten arrest system and they won't pull the trigger.

Edited by pcmccartney1

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One client lost three radios and two PLC's to that storm before the hurricane.
And a relay 

588611026.jpg

IMG_3729.jpg

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