# Profibus cable with power cables in same raceway.



## Big John (May 23, 2010)

Might want to read 800.133(A)(1). Honestly, I think if you're running shielded cable it would probably work fine, but it appears to be a violation.

-John


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## CFL (Jan 28, 2009)

Big John said:


> Might want to read 800.133(A)(1). Honestly, I think if you're running shielded cable it would probably work fine, but it appears to be a violation.
> 
> -John


Based on everything I read today, it doesn't matter what the NEC says.


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## John Valdes (May 17, 2007)

When you say power do you mean input or output? Comm cables in conduit on the line side should see much less noise than Com cables on the output side.
It's not a good practice to mix these cables with power cables. The NEC does say something in regard to conductors in the same conduit being rated at the same voltage. But I am certain your concern is noise, right?


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## CFL (Jan 28, 2009)

John Valdes said:


> When you say power do you mean input or output? Comm cables in conduit on the line side should see much less noise than Com cables on the output side.
> It's not a good practice to mix these cables with power cables. The NEC does say something in regard to conductors in the same conduit being rated at the same voltage. But I am certain your concern is noise, right?


Yeah, noise was my concern. I asked the mfr rep today and he told me not to. So, regardless if it would have any effect or not, I'll do as they say. I was hoping you or another controls guy would tell me "no worries, we do it all the time".


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## Netree (Sep 3, 2011)

I'd not run your Profibus cable next to anything; strange things can occur, and the more complex the system... the more strange the things.


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## sparky105 (Sep 29, 2009)

It will keep u running for the rest of your life chasing dropped network issues profi is very very sensitive to noise. The issues are multiplied by induced voltages. Keep it seperate and keep it simple.


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## Jlarson (Jun 28, 2009)

CFL said:


> Based on everything I read today, it doesn't matter what the NEC says.


Now that you went and did your own thing it does.


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## JRaef (Mar 23, 2009)

Cable INSULATION in the same raceway must have the same voltage rating. The insulation rating for the jacket on most good quality Profibus cables is rated 600V, just like THHN. Just check to be sure.

Profibus cable is designed to be highly noise immune specifically for this reason. When people have noise issues, it's because they failed to pay attention to the terminations. They use cheap connectors or fail to pay enough attention to the shield connection methods etc. People tend to think of shielding connections as a minor issue because it's "just ground", but it is major. Terminating is the key, I used to work for Siemens, we conducted classes specifically on making up Profibus connectors to prevent this and it worked. Every one of the "noise" issues I investigated was due to poor workmanship on the terminations, and many of them involved the cables being run in trays along side heavy current power conductors. In every one of those cases everyone assumed it was from being next to the cables and we proved it was the terminations.


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## CFL (Jan 28, 2009)

Jlarson said:


> Now that you went and did your own thing it does.


All I did at this point was add a raceway, which still seems like the right thing to do.


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## CFL (Jan 28, 2009)

JRaef said:


> Cable INSULATION in the same raceway must have the same voltage rating. The insulation rating for the jacket on most good quality Profibus cables is rated 600V, just like THHN. Just check to be sure.
> 
> Profibus cable is designed to be highly noise immune specifically for this reason. When people have noise issues, it's because they failed to pay attention to the terminations. They use cheap connectors or fail to pay enough attention to the shield connection methods etc. People tend to think of shielding connections as a minor issue because it's "just ground", but it is major. Terminating is the key, I used to work for Siemens, we conducted classes specifically on making up Profibus connectors to prevent this and it worked. Every one of the "noise" issues I investigated was due to poor workmanship on the terminations, and many of them involved the cables being run in trays along side heavy current power conductors. In every one of those cases everyone assumed it was from being next to the cables and we proved it was the terminations.


So, would you completely frown upon my wishful install? I'm going to separate it since I was told not to. This is obviously not my area of expertise, but who knows, in the future I might be doing my own little design work and I'd like to know what the experts are able to get away with.


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## Jlarson (Jun 28, 2009)

CFL said:


> All I did at this point was add a raceway, which still seems like the right thing to do.


But you used your own conductors for power right? You should have left it as it came from the manufacturer and used all their cables.


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## CFL (Jan 28, 2009)

Jlarson said:


> But you used your own conductors for power right? You should have left it as it came from the manufacturer and used all their cables.


Well, I haven't pulled in those conductors. I changed my mind the other day and said I would pull their cables through my conduit. However, I spoke to the mfr rep yesterday and he told me to go ahead and run thhn ILO their cables if like. He was also under the impression that it was against code to run those cables through the ceiling and walls with no protection.


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## John Valdes (May 17, 2007)

CFL said:


> So, would you completely frown upon my wishful install? I'm going to separate it since I was told not to. This is obviously not my area of expertise, but who knows, in the future I might be doing my own little design work and I'd like to know what the experts are able to get away with.


Sometimes I do not agree with manufactures recommendations and sometimes they do not agree to cover it under their warranty. 
It is also is a good practice to keep signal cables in their own place. Why does every manufacturer warn the end user in this regard? That is the point.

I have always thought that shielded cable was just as susceptible to noise as any other cable. That shielded cable in some circumstances is more prone to noise issues. I am not sure, but that foil wrap sure seems like it would attract nuisance voltages more than it would repel them? I don't know for sure. But I am certain you can tell me.


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## Netree (Sep 3, 2011)

Proper terminating of the shielding is just as important as having good shielding.


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## BBQ (Nov 16, 2010)

John Valdes said:


> I am not sure, but that foil wrap sure seems like it would attract nuisance voltages more than it would repel them? I don't know for sure. But I am certain you can tell me.


The same way a Faraday cage works, http://en.wikipedia.org/wiki/Faraday_cage (In other words I can't explain it but I do know it works assuming proper termination as was mentioned. )

I would also point out that you can see just effective a shielded cable is by using non-shielded cables on an amplifiers input side.


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## Jlarson (Jun 28, 2009)

BBQ said:


> I would also point out that you can see just effective a shielded cable is by using non-shielded cables on an amplifiers input side.


Somebody made a youtube vid demonstrating that, let me see if I have it bookmarked.


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## bthesparky (Jan 23, 2009)

No matter how good the terminations are or how much the manf. says its ok. The first sign of trouble, the DCS guys will blame that in a heart beat. Couldn't tell you how many times we have had to take out conduit(that was grounded) and install basket tray because "Device net cables have problems with noise if they're ran through conduit".


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## LARMGUY (Aug 22, 2010)

CFL said:


> Yeah, noise was my concern. I asked the mfr rep today and he told me not to. So, regardless if it would have any effect or not, I'll do as they say. I was hoping you or another controls guy would tell me "no worries, we do it all the time".


Let me tell you something. Once a manufacturer says not to, and you start having problems with communication ie noise, they are through with you on technical support.

It may work fine for years then crap out. It may not work when you first power it up. Then you have egg on your face because you didn't follow specs. 

If you don't install according to spec, you are asking for problems.


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## Big John (May 23, 2010)

bthesparky said:


> ..."Device net cables have problems with noise if they're ran through conduit".


 Sounds like they should work with the IT guys who think everything needs an isolated ground. 

-John


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## LARMGUY (Aug 22, 2010)

Netree said:


> Proper terminating of the shielding is just as important as having good shielding.


And don't terminate both ends. If you do, you have created an antenna.


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## bthesparky (Jan 23, 2009)

Big John said:


> Sounds like they should work with the IT guys who think everything needs an isolated ground.
> 
> -John


Done that too. Had a piece of copper buss that we mounted on the wall to equo. ground all the DCS cabinets and clean power panels. Wanted the AC ground and ground for device net seperate, drew a line down the middle of the buss bar and wrote AC on one side and DC on the other. They didn't see the humor in it. Then proceeded to do there bidding and have a seperate piece of buss tied to the same ground grid outside.


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## Big John (May 23, 2010)

bthesparky said:


> ...Drew a line down the middle of the buss bar and wrote AC on one side and DC on the other. They didn't see the humor in it....


:thumbup: Nice. The stupid thing is the whole installation was probably a lot better the way you first installed it, because as soon as you get different ground impedances you end up with voltage gradients between equipment.

I remember a case where a RS-232 connection shunted ground differential current until it caught fire.

-John


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## Jlarson (Jun 28, 2009)

Big John said:


> I remember a case where a RS-232 connection shunted ground differential current until it caught fire.
> 
> -John


Speaking of RS-232, I want money for every time some CNC tech said the machine needed to be isolated from the EGC and have a separate rod installed.







I put a isolator in the RS-232 line and all is well.


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