# 220V AC And 24V DC don't mix



## just the cowboy (Sep 4, 2013)

We had a good one this week. We still did not find the smoking gun that caused the 220V AC control to go to the 24V DC. We have a machine with a 220v AC control system (pb, relays, starters all 220v) and the eyes on the machine are 24V DC. Somewhere we had a fault from 220v to 24 v. 
We had plenty of magic smoke, we lost a PLC, 3 axis motion controller, all 7 eyes and more. This is a German machine from 1995 and those voltages are mixed in the cables that run everywhere. We did find three bad cables but they did not have mixed voltage in them. 

It wasn't feasible to disconnect every wire in the machine and meg them to each other. We removed all DC equipment after doing allot of wire checks, and powered up again and had no AC voltage on the DC side. Don't feel good about it I know it is not fixed but what else could we do. 

This is a cable we found on another machine like it, this is why 220vac and 24vdc should not be in same cable. Must of been a low current burn that did not trip the breaker till the ac went to ground.


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## ampman (Apr 2, 2009)

It looks like the cable was against something that was hot and burned a hole thru the cable


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## just the cowboy (Sep 4, 2013)

No that cable was on an operator station, and that was where 8 ft of cable hung unsupported on a steel square stock. It came unsupported from the factory that way.


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## Big John (May 23, 2010)

Crap like that is why I love signal conditioners and interposing relays. Might've saved you the trouble of installing and reprogramming a new PLC.

It's possible there was a cable-to-cable fault, but the first places I'd look are obviously any components with both voltages connected: Power supplies, transducers, SSRs, whatever.


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## dronai (Apr 11, 2011)

So it's up and running with no fix ? When it shorts again, another new PLC, and sensors once more ?


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## just the cowboy (Sep 4, 2013)

Big John said:


> Crap like that is why I love signal conditioners and interposing relays. Might've saved you the trouble of installing and reprogramming a new PLC.
> 
> It's possible there was a cable-to-cable fault, but the first places I'd look are obviously any components with both voltages connected: Power supplies, transducers, SSRs, whatever.


The cables to the differant parts of the machine have mixed voltage, this may be where it is at but I can't find it.


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## just the cowboy (Sep 4, 2013)

dronai said:


> So it's up and running with no fix ? When it shorts again, another new PLC, and sensors once more ?


Yea it can go again, I want to pull new cables and get rid of the 220V control with a new PLC, but managment just wants it to run. Thats the way the world goes round.


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## Going_Commando (Oct 1, 2011)

I hate that. The hydraulic unit and solenoid valves have cables with 480v and 24vdc in the same cables for an Ossberger turbine we operate. I'll give you a hint on origin, Ossberger isn't Irish. :laughing:.


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## walkerj (May 13, 2007)

Dude trim your nails or wear gloves.


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## FlyingSparks (Dec 10, 2012)

walkerj said:


> Dude trim your nails or wear gloves.


I'm going to second this, not as an insult, but as a health concern. After working for a hospital I will never ever ever ever have long nails again.


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## sparkywannabee (Jan 29, 2013)

walkerj said:


> Dude trim your nails or wear gloves.


Leave him alone, He's the Cowboy.


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## macmikeman (Jan 23, 2007)

Add in a bit of low cost security to your system.


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