PDA

View Full Version : PLC hard wiring


gawillia
April 5th, 2005, 03:05 PM
Is it ever permissible to run I/O wiring in the same conduit as 480 volt 3 ph motor wiring? I have a dispute going right now.

Ken Roach
April 5th, 2005, 03:09 PM
It's only permissible under two conditions:

1. Nobody is looking.
2. You don't want it to work.

Rick Densing
April 5th, 2005, 03:17 PM
I am assuming you mean 24V? I have had it work for short runs and small horsepower motors.


If you are using 120VAC, there should be no problem.

You must use 600V insulated or better wire for all conductors.

I don't believe there is an acutal law against it here. (local codes may vary)

darrenj
April 5th, 2005, 03:26 PM
Contrary to what Ken says it will work and as rick says there is no law against it...Is it a good idea..... no.

Analog signals would probably not work or would work intermittently. again as rick said all wires must be rated at the same voltage to meet code..

kamenges
April 5th, 2005, 03:42 PM
So on a totally different subject, can anyone explain the insulation level requirement that both Rick and darrenj refer to? It's OK to let a wire with 600 volt insulation lay against a grounded conduit but its NOT OK to let it lay against another wire that has 300 volt insulation. That just doesn't intuitively make sense.

Keith

Fred Floggle
April 5th, 2005, 03:55 PM
Not so much to do with insulation - how about cross talk caused by inductance . Big problem on many networks , railways included - flemings right hand rule - and his left hand one as well , you are making little current transformers , all set to upset your I/O

rsdoran
April 5th, 2005, 03:56 PM
Wire has 2 very important factors, voltage and temp. Voltage rating relates to the wall thickness and temp rating relates to the type of insulation.

Current thru parallel wires will create induction, this in turn will create heat. The idea is to have all wires rated at same voltage/temp etc to minimise the effects of the induction on the wire.

As far as wire laying against grounded conduit, the conduit should not have current flowing thru it and creating inductance.

I know I should be able to explain this better with more detailed facts but I seem to be brain locked.

Ken Roach
April 5th, 2005, 04:06 PM
I was being facietous, of course. I hope Ron Doran will chime in here, because his opinions are well rooted in both code and practice. I can only speak on experience because I don't have a background in the electrical trades.

I have experienced many installations in which 120 VAC and the output from a 480VAC variable frequency drive were run for a moderate distance (100+ feet) in the same conduit. We got a lot of induced noise on the PLC inputs from those 120VAC input points, causing false input signals. This is far less likely with "clean" 480VAC, but the longer the conduit the more likely that induced voltage will be a problem.

"Code-wise", I have only experienced problems when users get their hands on 300V insulated appliance wire. Typical "THHN" wiring that I see used in industrial applications has 600V insulation and can be installed in proximity to equally insulated conductors that are carrying 480VAC.

darrenj
April 5th, 2005, 04:22 PM
Ken i figured that!.and yes i have run into many situations with control and power from a drive causing problems. i have even had problems with main power and output from the drive in the same conduit cause problems...as i said it will work but is not a good idea





I was being facietous, of course. I hope Ron Doran will chime in here, because his opinions are well rooted in both code and practice. I can only speak on experience because I don't have a background in the electrical trades.

I have experienced many installations in which 120 VAC and the output from a 480VAC variable frequency drive were run for a moderate distance (100+ feet) in the same conduit. We got a lot of induced noise on the PLC inputs from those 120VAC input points, causing false input signals. This is far less likely with "clean" 480VAC, but the longer the conduit the more likely that induced voltage will be a problem.

"Code-wise", I have only experienced problems when users get their hands on 300V insulated appliance wire. Typical "THHN" wiring that I see used in industrial applications has 600V insulation and can be installed in proximity to equally insulated conductors that are carrying 480VAC.

TRACY H
April 5th, 2005, 04:29 PM
It's only permissible under two conditions:

1. Nobody is looking.
2. You don't want it to work.

I would stick with this answer. The variables to this question are many. A lot of yes`s and a lot of NO`S. The safe answer is NO the unsafe answer is yes.
My 2 pennies :argue:

:site:

rsdoran
April 5th, 2005, 05:22 PM
I will say this, code is a guideline for installation to mostly protect the wire/component/system...ie to prevent shock, fire etc.

Can they be combined...yes. Do you want to combine them? That you have to determine. If its strictly power wiring it shouldnt matter overall but if its any form of "signal" wire then its better not to.

NOTE: PLC discrete inputs are a "signal", analog, high speed, communication, etc are all "signal", induction, harmonics or noise generated from wire and/or field devices can interfere with the signal to or from any device.

I suggest you attempt to separate high voltage, especially motor leads from control voltage and/or signal wires. In the long run it may save you a lot of headaches.

stasis
April 5th, 2005, 07:18 PM
It's only permissible under two conditions:

1. Nobody is looking.
2. You don't want it to work.

actually, as long as all conductors share the same insulation, you CAN run them all together....that much is in the NEC.

In my experience, unless you are using crappy drives or analog (seen most on 4-20 mA) signaling, the noise won't affect controls operation in most 480 Volt systems as long as all wiring has the same insulation type...most 'engineers' will argue otherwise, and text-book answers back them up. But in a real-world setting, I have never encountered any problems running different voltages or AC/DC in the same panel/conduit....maybe I'm just lucky?

jolio ST
April 5th, 2005, 10:39 PM
I think that signal wirings are best not mixed together with power wirings.

My views are on the What Ifs:

- Poor insulation. Heat generated from power cables, especially high voltage supply, may affect the functionality of signal cables.

- Crosstalk. This may apply if you are running digital signal cables with analog signal cables. I experienced it once when I was doing a prototype multi-transmission box. my displayed images are totally distorted.

- And cables with very high voltage difference.. or current difference..a no no to me... unless you have good cables with good insulation. But it's always better safe than sorry.

My rookie input.

regards
Sherine T.

CaseyK
April 5th, 2005, 11:01 PM
It's only permissible under two conditions:

1. Nobody is looking.
2. You don't want it to work.

While Ken did comment further later on, this is still pretty much correct.

With some PLC's, operation would be very erratic. Safety wise, not a good idea, as a spike on the 480 could trigger something violent to happen.

In some local jurisdictions, that actually DO inspect, it is not accepted. It could nullify your companies insurance.

And on, and on, and on.

I have never tried this, but have had to correct problems cuased by it.

As previously stated, NOT RECOMMENDED.

regards.....casey

Spin
April 5th, 2005, 11:07 PM
It's only permissible under two conditions:

1. Nobody is looking.
2. You don't want it to work.

Thanks again for helping Emir today!!!

brucechase
April 6th, 2005, 06:28 AM
I have on many occasions run a motor circuit with the controls not only in the same conduit, but in the same cable. I would get a 9 conductor cable (usually for TC rated systems with a remote start/stop PB) and run 3 motors leads at 480 and the controls at 120 VAC. I never had problems. I usually would not run DC with the motor leads and like everyone else, never analog signal wire without having a shield. There is no rule that says you can not do this as long as the same insulation level of the wires are maintained. This is protect the circuits in case one of the 480 VAC wires has an insulation breakdown, the other wires will have the same insulation level and therefore not be breached.

my .015 cents

gary marano
April 6th, 2005, 08:16 AM
If you want to run the cinductors all in the same conduit you can

only if you color code the low voltage i/o wires. They should
not be brown,orange,yellow they are 480 volt colors. That is
nec code and electricans know this and they will be aware of
the fact that their are different voltages present in the conduit.
It is a good practice to run a seperate conduit for the i/o cables.
This way they come from the plc cabinet and the motor leads from
the mcc this way their is no confusion if you ever have to
trouble shoot the system in any way.

Unregistered
April 6th, 2005, 08:50 AM
The only person making any sense in Ken Roach - all the talk about colors and insulation thickness is real worrying - the major problem is inductance and cross talk , you have have peak currents in some of these cables hitting hundreds of amps , that is bound to have an effect is it not ?

rsdoran
April 6th, 2005, 10:09 AM
only if you color code the low voltage i/o wires. They should
not be brown,orange,yellow they are 480 volt colors.
This has been discussed before, NEC does not designate (BOY) those colors for 480.
The only person making any sense in Ken Roach -
Ken always makes sense but if you had fully read the thread you would see that all the talk was relevant AND that you have not said anything that has not ALREADY been said.

Rick Densing
April 6th, 2005, 10:14 AM
, you have have peak currents in some of these cables hitting hundreds of amps ,

Where did you get that data?

With regard to the rest of your response, I qualified my answer regarding low horsepower motors. Did you notice I cited actual experience?

You need the same insulation rating in case your higher voltage wire is damaged. If you have a paritially exposed 480V wire lying next to a 300V insulated wire, you are going to have a breakdown. Things can go boom. Like Ron said, NEC is to prevent fire and injury, not for nice clean I/O signals.

Also, it would be nice to hear from the original poster again.

snimra
April 6th, 2005, 10:54 AM
I don't remember all the Code and standards but I do remember having multiple machine shutdowns due to an AC cable (110VAC) laid across several signal cables (4-20mA, mV from TCs, mV from vibration probes, etc).
I don't care what's the reason but I'll stick to "No".

gary marano
April 6th, 2005, 12:43 PM
This has been discussed before, NEC does not designate (BOY) those colors for 480.

Ken always makes sense but if you had fully read the thread you would see that all the talk was relevant AND that you have not said anything that has not ALREADY been said.


Article 210.5C ungrounded conductors. being a electrician for
over twenty years pulls are done with a color code. I cannot
find the atricle with the color code in 2006 or 02 but it was
in earlier code books. I will look into earlier years, a gray color
was also used for a four wire 460 volt system.

rsdoran
April 6th, 2005, 01:20 PM
I know that BOY (brown, orange, yellow) has been used for 480vac wire color designation for many many years. The NEC Handbook example pictures even use those colors. They also use Red, Blue, Black for 240vac in an example.
BUT
They are not designated for those voltages.
Green or bare is ground
White or Gray is grounded conductor

Article 200.6 & 7 apply, also Article 310.12 Conductor Identification (C) Ungrounded Conductors. Conductors that are intended for use as ungrounded conductors, whether used as single conductor or in multiconductor cables, shall be finished to be clearly distinguishable from grounded and grounding conductors. Distinguishing markings shall not conflict in any manner with the surface markings required by 310.11(B)1.

Technically I am not an electrician but I do have a background in electrical work.

Unregistered
April 6th, 2005, 04:21 PM
Mr Doran , you mention that what I said is only what is said before , I have read and reread many of the post on this site , including yours , and notice that the number of posts saying the same thing are many , but nothing is said when it is between the "gang" - I also noticed you missed the point - disturbance is not a function of insulation thickness or efficiency (though this is a factor in capacitance , but rather in inductance caused distrubance - that is why it was repeated - people kept going on about colours and thickness of insulation - it didn't seem like they were understanding some of the other factors .

To the guy that "qualified" his answer re actual experience - the original post was a generalized question , therefore the generalized answer that peak current can hit hundreds of amps was correct and justified - I mean unless of course you are working on model railways - real life and industry is a bit different.

There does seem to be rather a "bullish" clan type attitude here - if you aren't gang , then we will just talk around your comments rather than acknowledge .

Please also understand that so called good "code" work is still not good practice even if allowed by code . Electrical codes should be improved upon where possible ( particularly in this case if they allow mixing signal with high current supplies ) ?

rsdoran
April 6th, 2005, 05:38 PM
This site and mine offers answers to questions that in "most" cases have many variables involved so there may be different approaches to the answer given. The other aspect is that answers provided may also provoke other questions that may or may not be specifically relevant to the subject but can be relevant in general so it is common to see tangents form within a thread.

I am not sure what you mean by "gang". I and many members have been on this forum for some time, years for some of us. The overall atmosphere attempts to keep things informative but at the same time have some clean humor and camaraderie. You dont always have to meet, socialize etc with people to consider them friends and be comfortable conversing with them. In some cases it may seem all others are excluded from the conversation but in general I do not believe that is the intent.

I am not a highly educated person but I have years of experience involving many aspects of the industrial field. I believe by now most know I attempt to provide accurate information on the subject in question, from time to time I may misinterpret something and provide the wrong information or possible state the information inaccurately. I think by now though most people understand I can/will/do provide resources to verify my information.

I state code as the minimum necessary, anything can be improved. I will correct statements pertaining to code or any subject I believe are inaccurate. The object is to obtain "accurate" information.

As for "bullish", I was born in May and that makes me a Taurus. I am hardheaded, stubborn and have been called a drama queen (didnt care much for the queen part though). I am many other things too, some may be bad and some may be good, just depends. What you call "bullish" is what makes me take the time to provide so much information, resources, pictures etc.

Think about this. You arent registered, you made one short post basically repeating what was already said. You have not provided resources, links, website or ?, so who knows if you have a clue?

CaseyK
April 6th, 2005, 05:42 PM
The only person making any sense in Ken Roach - all the talk about colors and insulation thickness is real worrying - the major problem is inductance and cross talk , you have have peak currents in some of these cables hitting hundreds of amps , that is bound to have an effect is it not ?

At some point in time, someone unfamiliar will work on the machine, and it probably will not have any documentation.

It would be nice if they followed some guidelines, if only common sense.

Insulation IS a factor, when you have your hand in there and it decides to leak through, or it cuases a machine to start up from leakage.

Back to a poll I once posted...


Should someone be registered to post?

regards, all.....casey

Rick Densing
April 6th, 2005, 05:54 PM
To the guy that "qualified" his answer re actual experience - the original post was a generalized question , therefore the generalized answer that peak current can hit hundreds of amps was correct and justified -

You did not say "can" in your first post.

Like I said, it would be nice if the original poster would chime in and get more specific.

Right now, the answer to his question is "it depends". We can squabble about semantics and this situation and that, but it won't change that answer.

Mr unregistered, please register and let us get to know you. A few people here have had much rockier starts than you. Don't assume that people talking amongst themselves are doing it to exclude you. It is just that they know each other and seek a comfort level.

I have been around here a long time and sometimes I feel that people are talking around me. It is just part of an online forum.

stasis
April 6th, 2005, 06:23 PM
Is it ever permissible to run I/O wiring in the same conduit as 480 volt 3 ph motor wiring? I have a dispute going right now.

the answer is yes, you can, under certain guidelines within the NEC.
As you can tell by most answers, it isn't common practice for several reasons.

And officially, there is no color code in the US other than those of grounded/grounding conductors. Most electricians use the old color code, but it's not law...again, common practice.

rsdoran
April 6th, 2005, 06:43 PM
And officially, there is no color code in the US other than those of grounded/grounding conductors. Most electricians use the old color code, but it's not law...again, common practice.

That isnt totally accurate, NEC doesnt specifically state anything but green, white, and gray. NFPA 79, which applies to machinery, does state colors for certaing things, my copy seems to be getting old so anyone that has a newer copy if its changed please correct this.
Black: Ungrounded line, load, and control coductors at line voltage.
Red: Ungrounded ac control conductors at less than line voltage.
Blue: Ungrounded dc control conductors
Yellow: Ungrounded control conductors that may remain energized when the main disconnect is in the OFF position.
NOTE: European/International standard requires the use of orange.
White or Gray (use to be natural gray): grounded circuit conductors
White with blue stripe: grounded (current carrying) dc conductors.
White with yellow stripe: grounded (current carrying) ac control circuit conductors that remain energized when the disconnecting means is in the OFF position.

I am not going to debate the issue of is it "law" or not, it is an accepted standard in the US.

Tark
April 6th, 2005, 08:27 PM
In case you wanted to know, there are 5 conductor colors stated in the NEC (I’m not counting bare as a color). A classic Master Electrician exam question. You have to list all 5 to get it right :)

Grounded conductor – White or Natural Gray
Grounding conductor – Green or Green w/ one or more yellow stripes
Delta High Leg – Orange

That’s it folks.

rsdoran
April 6th, 2005, 08:33 PM
Darn it, I always forget about that Delta high leg.
Article 215.8 Means of Identifying Conductor with the Higher Voltage to Ground
On a 4 wire, delta connected secondary where the midpoint of one phase winding is grounded to supply lighting and similar loads, the phase conductor shall be identified by an outer finish that is orange in color or by tagging or other effective means.

I knew this too, its one of my main marked pages.

kamenges
April 6th, 2005, 09:52 PM
Originally posted by Rick Densing:

You need the same insulation rating in case your higher voltage wire is damaged. If you have a paritially exposed 480V wire lying next to a 300V insulated wire, you are going to have a breakdown. Things can go boom. Like Ron said, NEC is to prevent fire and injury, not for nice clean I/O signals.

I know I risk winding some people up by continuing with a topic that is only loosely related to the original post, but in for a penny in for a pound, I always say.
Wouldn't you get that same boom factor if the bared 480 volt wire touched the grounded conduit it was running in? I guess that's my original point, which I DIDN'T express initially (sorry). What makes the grounded conduit so special that it isn't a concern for stray voltage but the other wires in the conduit are a concern?
I'm not trying to rock the boat (too much). Just trying to get a handle on the mindset of a document that is WAY too big and has too many exceptions.

Keith

tom_stalcup
April 6th, 2005, 10:41 PM
Well, say for example that you have a wire bundle that has a bunch of 24vdc wires in it, and also has a 240vac wire in it. If something happens to the insulation on the two wires, the poor bast--- that is disconnecting a prox expecting 24vdc gets hit with a 240v jolt....


(happened here last weekend..... gonna be doing some re-wiring on 7 different machines in the near future)

leitmotif
April 7th, 2005, 12:49 AM
I reviewed the whole thread.
FIRST can you put signal (or control or whtever you want to call it) wire in the same conduit as power conductors.
ANSWER It is a free world you can do what ever you like -- if you can live with the consequences.

SECOND would I do it ?? Resounding NO
I am just a maintenance electrician - the good thing about this is you learn how other people screw up cause you get to fix it. It is hard enough to pull in multi wire when they are the same type and size. Now you are going to mix in other type conductors or multi conductor cable??
WHY NOT ?? What will happen is the softer coverings will get more chafe. NOW you may get into a deal where you can have a fault in a power conductor that can cross over to the signal. I have heard the horror story of a phone guy who cut a phone cable that 13 kV on it.
THE OTHER REASON is of course the fields from the power conductors fouling up the signal in you signal conductors.
BUT it is your system and us maintenance guys need the work so go ahead if you want.

COLOR CODES
1. I agree with Ron Doran and Tark that the five colors white gray, green or green yellow trace and orange are the only ones required by NEC. The thing to remember is NEC is basically a life safety code and is not written to ensure a good job. YOu can wire to NEC and have a job that is not worth the powder to blow it to hell.

2. Ron thank you for BOY (Brown Orange Yellow) I always get confused on the common used colors for 3 phase 240 and 480. But then way back when in the Navy we were taught black white red ABC 123 for three phase DIFFERENT system because of no grounded neutral on ships. WHY oh WHY can I remember that and not the other and NOT confuse the two.
3. Yeah you are supposed mark the hi leg on delta when you center tap one phase and ground it for a neutral. That is orange. This circuit I think is falling by the wayside -- havent seen it in recent construction.

Dan Bentler

Rick Densing
April 7th, 2005, 05:36 AM
Wouldn't you get that same boom factor if the bared 480 volt wire touched the grounded conduit it was running in?

Not necessarily, it may just blow a fuse. (Proper design- it will blow a fuse) The conduit should have a much higher ampacity than the original wire. If you short to another wire, the completion path may be through a device that can't handle the current.

stasis
April 7th, 2005, 07:52 AM
3. Yeah you are supposed mark the hi leg on delta when you center tap one phase and ground it for a neutral. That is orange. This circuit I think is falling by the wayside -- havent seen it in recent construction.

Dan Bentler

no...the high leg is the one carrying a higher voltage (used to be called a '******* leg') than the other two conductors in the circuit. As stated, grounded (or neutral) is gray (high volt) or white (low volt) and green/bare is for grounding (ground). The high leg is quite common with Georgia Power, at least furthert away from the city. They like it because you can get away with less transformers on the poles.

leitmotif
April 7th, 2005, 12:58 PM
I mentioned the neutral connection to ensure everyone knew what I was talking about. The high leg would not be the neutral since the neut is grounded and at ground potential which I hope would not be that of a high leg.

Are they using 4 wire delta in Ga for commercial only? Here in Seattle for small stuff service seems to be 4 wire wye or 3 wire Edison and 3 wire Edison for residential of course.

Dan Bentler

stasis
April 7th, 2005, 01:10 PM
well, it's mostly seen in light industrial, like warehouses & the like. But, most of these warehouses end up with machinery installed in them so the owner doesn't have to make an addition to his building...the cheapskates.

leitmotif
April 7th, 2005, 01:20 PM
Well that was the whole idea of 4 wire delta - you get your lites and receptacles off the center tapped phase and you have the 3 phase for motors. Saw a fair amount in older school districts.

Dan Bentler

Tark
April 7th, 2005, 07:51 PM
In the end, you really need to check your local city ordinances, they are the authority having jurisdiction.

NEC 90.4 – The authority having jurisdiction may waive specific requirements in this Code or permit alternate methods….

Case in point – A city near me does NOT use orange to mark the high leg on a delta, I think they use orange for one of the conductors on a 480 Y.

Always check with the city you are working in to find out if they have any alterations or exceptions to the NEC

rubber ken
April 7th, 2005, 10:02 PM
I have run 120v descrete I/O in the same conduit with 3 phase motor feeders with no problems. I would not recommend using the same conduit space for 3 phase feeders and 24vdc or analog I/O.