Conveying conduit routing in electrical design pacakges

[mull982]

I often struggle with the best way to depict conduit routing on new electrical design drawings so I was hoping to hear other engineers and contractors on what they have found to work best for them.

Typically on most design packages there is a cable schedule which lists every cable for the project as well as a conduit size for each of these. The issues for me is how to represent the fact several circuits in the same area may end up being run in the same conduit and not in individual conduits per the cable schedule.

For example: I have seen a drawing and cable schedule which has control cables for three control devices that are literally right next to each other with their home runs all going back to the same control panel. The cable schedule lists each one of these control cables separately and assigns a 3/4" conduit to each. Seeing that these devices are all right next to each other and go to the same location I would think that in the field the contractor would just go ahead and route these all in the same conduit back to the control panel.

So my question is, how much directive to provide for conduit routing in the design package as opposed to giving the contractor the liberty to run the conduits as they see fit since that is their area of expertize.

Does the engineer typically list all cables and assign a conduit size for each with the understanding that the contractor may combine cables (talking about control cables) and run in conduit as they see fit?

This applies to overhead routing as I understand underground routing is more definitive in the design package.

Curious to hear others take on this.

 

[Strathead]

I often struggle with the best way to depict conduit routing on new electrical design drawings so I was hoping to hear other engineers and contractors on what they have found to work best for them.

Typically on most design packages there is a cable schedule which lists every cable for the project as well as a conduit size for each of these. The issues for me is how to represent the fact several circuits in the same area may end up being run in the same conduit and not in individual conduits per the cable schedule.

For example: I have seen a drawing and cable schedule which has control cables for three control devices that are literally right next to each other with their home runs all going back to the same control panel. The cable schedule lists each one of these control cables separately and assigns a 3/4" conduit to each. Seeing that these devices are all right next to each other and go to the same location I would think that in the field the contractor would just go ahead and route these all in the same conduit back to the control panel.

So my question is, how much directive to provide for conduit routing in the design package as opposed to giving the contractor the liberty to run the conduits as they see fit since that is their area of expertize.

Does the engineer typically list all cables and assign a conduit size for each with the understanding that the contractor may combine cables (talking about control cables) and run in conduit as they see fit?

This applies to overhead routing as I understand underground routing is more definitive in the design package.

Curious to hear others take on this.

I am cautious in this situation. I appreciate it when the Engineer spells out the allowance, and if he doesn't I will usually combine them as allowed by code, but specify that in my proposal. It shouldn't be too difficult to spell out guidelines in a couple sentences. For example, Cable runs may be combined in conduit as follows

Minimum conduit size is ...

Cable type such and such may not be combined with other cable types (if there is an example)
maximum fill ratios is 30%

Provide spare pull line in all conduits.

 

[Smart $]

What Strathead suggests is fairly common. IMO a lot depends on the project or perhaps certain portions. I've worked on some power plant projects where every conduit run, no matter its length, each condulet, junction box, etc. had an alphanumeric designation and got labeled.

I guess the first question to ask is: how specific do you want to get? Do you want to carry the same level of specificity across the entire project or express varied levels of specificity?

 

[charlie b]

I do mostly buildings, and I never do control wiring. So I don't generally give any details for the conduit routing. I have a list of equipment that I build using an Excel file that takes the voltage, number of phases, and some measure of the load (e.g., KW, FLA, HP, etc.), and calculates the breaker rating, the conduit size, and the wire size. I include a general note that allows the EC to combine home runs in a single conduit, but puts the responsibility of following the NEC rules (e.g., derating and conduit fill) into the EC's hands. I might show a feeder type as, for example, a "90NG," and I will include a table that explains what that means.

I have seen some designs that will have individual tags for each feeder, even if many of them have the same conduit and wire size. For example,

• Feeder #1 is a 20 amp breaker, 1/2 inch conduit, and 5 #12 conductors, and is run from panel LP-1 to motor CP-1.
• Feeder #2 is a 20 amp breaker, 1/2 inch conduit, and 5 #12 conductors and is run from panel LP-1 to motor CP-2.
• Feeder #3 is a 20 amp breaker, 1/2 inch conduit, and 5 #12 conductors and is run from panel LP-2 to motor CHWP-1.
• Feeder #4 is a 20 amp breaker, 1/2 inch conduit, and 5 #12 conductors and is run from panel LP-2 to motor CHWP-2.

I don't like that method. I will call each of them by the same tag, "20NG." The table will tell you that that means it is a 20 amp circuit with a neutral and ground wire (i.e., 20 amp breaker, 1/2 inch conduit, and 5 #12 conductors).

 

[Fitzdrew516]

Conduit routing and combining are two different things. As far as routing goes... that's a means and methods issue for me. I do not specify where to run the conduit on my drawings; that's a little ridiculous. Combining wires into shared conduit is different - If the EC wants to do it I have no issue with it (unless I'm planning on future growth). At that point the liability and code compliance lies with the contractor - that's how my specs are written.

 

[petersonra]

used to be that engineers would often go to elaborate means to show where conduits were physically routed. it always seemed like more work than it was worth to me.

most times these days it seems that what you get is a spreadsheet, and the contractor just figures out where to physically route the conduit out in the field.

 

[gadfly56]

I am cautious in this situation. I appreciate it when the Engineer spells out the allowance, and if he doesn't I will usually combine them as allowed by code, but specify that in my proposal. It shouldn't be too difficult to spell out guidelines in a couple sentences. For example, Cable runs may be combined in conduit as follows

Minimum conduit size is ...

Cable type such and such may not be combined with other cable types (if there is an example)
maximum fill ratios is 30%

Provide spare pull line in all conduits.

I'm not so sure anymore that this is a good idea. In a multi conductor pull, very frequently the conductors corkscrew as they get pulled along. This neatly wraps up the pull line as well, making it useless for a future pull. Better to run spare conduit if you think it's really going to be needed.

 

[petersonra]

I have never been a big fan of having someone run an extra string in a conduit. seems to me you won't ever need a string for anything other than to try and pull a conductor so why not just run a spare conductor?

I have seen a number of times were maint guys have used a ground wire in metallic conduit to pull in new wires.

 

[Smart $]

...
Provide spare pull line in all conduits.

I'm not so sure anymore that this is a good idea. In a multi conductor pull, very frequently the conductors corkscrew as they get pulled along. This neatly wraps up the pull line as well, making it useless for a future pull. Better to run spare conduit if you think it's really going to be needed.

I have never been a big fan of having someone run an extra string in a conduit. seems to me you won't ever need a string for anything other than to try and pull a conductor so why not just run a spare conductor?

I have seen a number of times were maint guys have used a ground wire in metallic conduit to pull in new wires.

Perhaps a slight change in sentence structure...

Provide pull line in all spare conduits.

 

[Strathead]

I have never been a big fan of having someone run an extra string in a conduit. seems to me you won't ever need a string for anything other than to try and pull a conductor so why not just run a spare conductor?

I have seen a number of times were maint guys have used a ground wire in metallic conduit to pull in new wires.

I don't disagree, about the potential efficacy of a pull string. However, I have used one effectively more often than it has been a problem. In this scenario, your solution is not likely viable. This is a controls run. There is no telling whether the spare needed would be a K type thermostat wire, 2 conductor, or 4 pair, twisted overall shield or any of dozens of different cable requirements. A spare would be useless. Either put the string in and try it, or leave it out and live with it. Either way, my statements were not intended to be absolute or complete. The OP's Engineering firm must decide what and how they want to place conditions on their projects.

 

[Cow]

Unless the conduit has to be routed a specific way, there isn't a reason to show routing on the prints. Let the electrician in the field make that call.

 

[midamericairon]

As the electrician I have seen it done several ways by the engineers. Most of the time it depends on the size of the job, or how complex the systems are. Hospitals are very complex, and usually the engineering is very detailed because they have the availability of all the prints for all of the systems and can overlay them to make sure there is no conflict with others. Smaller jobs, like a tenant finish, the prints/specifications will be less detailed. I feel, as the electrician/installer that it the engineers have a conduit/cable schedule that the responsibility should lay on them to tell me what size conduit, how many conductors in the conduit, and conductor size to use. They are usually privy to the cut sheets of all of the equipment attached to the conductors and can size accordingly. As far as conduit routing goes, if it's not specified by the engineer I'll run the conduit as I see fit.


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[ron]

Unless the conduit has to be routed a specific way, there isn't a reason to show routing on the prints. Let the electrician in the field make that call.

Agreed. If I need something specific, I call it out. Like don't combine critical "A" and "B" UPS circuits in common boxes or raceway.

Our schedule calls out feeders and circuits as if they were by themselves. If the EC wants to combine, they need to follow NEC for derating and fill (as mentioned by Charlie), and that's it.

 

[mull982]

I have seen some designs that will have individual tags for each feeder, even if many of them have the same conduit and wire size. For example, [/FONT][/SIZE]

• Feeder #1 is a 20 amp breaker, 1/2 inch conduit, and 5 #12 conductors, and is run from panel LP-1 to motor CP-1.
• Feeder #2 is a 20 amp breaker, 1/2 inch conduit, and 5 #12 conductors and is run from panel LP-1 to motor CP-2.
• Feeder #3 is a 20 amp breaker, 1/2 inch conduit, and 5 #12 conductors and is run from panel LP-2 to motor CHWP-1.
• Feeder #4 is a 20 amp breaker, 1/2 inch conduit, and 5 #12 conductors and is run from panel LP-2 to motor CHWP-2.

• 
  
  This is typically how I see it listed in cable schedules. If CP-1 & CP-2 are right next to each other for example and they are both being routed back to LP-1 is it best to typically list them separately like this and let the contractor combine them into a single conduit if it makes sense?
  
  

  Our schedule calls out feeders and circuits as if they were by themselves. If the EC wants to combine, they need to follow NEC for de-rating and fill (as mentioned by Charlie), and that's it.

  
  So it sounds like you size and list all conduit as if they were by themselves not matter how close the routing is or even if they go between same equipment. I would think that that keeps things cleaner and more organized on the engineers end of things and lets the contractor combine as necessary.
  
  Do you typically put a note somewhere that contractor is responsible for de-rating, fill calcs, etc... if they choose to combine in same conduits? Where is this note, on cable schedule, or elsewhere?

 

[Strathead]

This is typically how I see it listed in cable schedules. If CP-1 & CP-2 are right next to each other for example and they are both being routed back to LP-1 is it best to typically list them separately like this and let the contractor combine them into a single conduit if it makes sense?



So it sounds like you size and list all conduit as if they were by themselves not matter how close the routing is or even if they go between same equipment. I would think that that keeps things cleaner and more organized on the engineers end of things and lets the contractor combine as necessary.

Do you typically put a note somewhere that contractor is responsible for de-rating, fill calcs, etc... if they choose to combine in same conduits? Where is this note, on cable schedule, or elsewhere?

As an electrician, I wouldn't expect the plans to be cluttered up with the responsibility note you are referring to. I am responsible as a licensed contractor to follow those codes. It is when you accidentally draw something below code that the area gets gray. That said, in my opinion, you only need to make notes that tell them when you aren't allowing the combining of circuits. For example many Engineers don't want circuits larger than 20 amps combined. Or one control system with another, or 0-10v dimming with the power conductors. etc.

 

[ron]

Do you typically put a note somewhere that contractor is responsible for de-rating, fill calcs, etc... if they choose to combine in same conduits? Where is this note, on cable schedule, or elsewhere?

Immediately below the feeder schedule

 

[ggunn]

For my designs I usually call out conductor and conduit sizes and let the electrician decide how to run the conduit. Typically the rooftops where we are placing solar modules can be very complex topographically (especially for residential systems) and usually I have never been on site, so the guy with boots on the roof is better suited to make the call. Occasionally an owner will stipulate that the wiring be run in the attic; in those cases I just show the runs point to point from where the owner wants the penetration to be. Combining is another issue; with the summer heat and rooftop adders if they combine they could exceed the ampacity requirement of a run. They have to check with me first, and usually I have already considered it and combined runs if it's possible.

 

[Ingenieur]

I usually only show the homeruns
let the contractor lay the work out
he's better at it

the exception is work that may have conflicts like pharma
lots of ductwork and piping
and that can be avoided by layers
clg - 3' duct
clg -3 to -4.5 piping
clg -4.5 to -5.5 conduit

 

[JoeStillman]

I'm not so sure anymore that this is a good idea. In a multi conductor pull, very frequently the conductors corkscrew as they get pulled along. This neatly wraps up the pull line as well, making it useless for a future pull. Better to run spare conduit if you think it's really going to be needed.

That's why the telecom guys use innerduct. There's a woven cloth-type available that takes up almost no room and lets you pull things in and out.

 

[JoeStillman]

For jobs with a lot of control wiring, I'll layout the conduit and junction boxes. It saves the electrician the trouble of sizing conduits and saves the owner the cost of a lot of redundant pipes.