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A question about wiring boilers

Chuck_7
Chuck_7 Member Posts: 71
NEC 300.3(C)
120V and 24V can be run in the same conduit if they have the same insulation rating. E.G. #12 120V can be run with #14 24V if the same 600V wire is used. The wire should be well identified (color etc.).

Comments

  • I know you shouldnt run

    low voltage wires in the same conduit with line voltage . But can you run line voltage gauge wires , using them for low voltage , in the same conduit with line voltage carrying wires ? What Im trying to do is neaten up wiring by running all the wires down a conduit - if I can run 2 - 12 gauge wires up in the conduit to connect to a low volt thermostat wire - wire nut outside the juction box , of course , it would look better than running a low voltage wire outside the conduit with handy ties . Any code issues going that route ? Thanks
  • J.C.A.
    J.C.A. Member Posts: 349
    Ron Jr.

    Not in Ma . . As long as the wires are switched outside a box and brought in . I've worked with lots of electricians that do it just for that reason . My understanding is that as long as the wires are rated for the same voltage , they CAN be run in the conduit with simalar gauge wires . Chris.
  • Mad Dog
    Mad Dog Member Posts: 2,595
    Hi Ron Jr..........

    I believe Long Island is the same.....absolutely cannot have them in same conduit - regardless of wire size or type. That's what i was always told and what I do. Mad Dog

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  • Yep

    You go through all the trouble of getting every pipe level and square , and then you have to deal with a mess running down the conduit . A helper we once had a great time running electrical tape up the conduit like it was a baseball bat . Made the job look like hell . Have fun Chris . I gotta go get a few cold ones , its been a rough week . Take care .
  • Matt , do you know who would have jurisdiction

    over the code for it ? I took an Oil Burner 1 class , and my teacher , who said he was a boiler inspector in the city , thought that it was ok , as long as the wire gauge was all the same , and the connections for low voltage were outside the box .

    I remember a discussion about this here a long time ago , and someone said that the low voltage might pick up some stray current from being so close to the line voltage . Or some sort of induction might occur. One thing is though , say in a multiple zone relay , you got line and low voltage wires all over the place in one relay , and that works .

    Oh well , its time I got going for my beer or 2 ,maybe get rid of the backache , in trade for a headache tomorrow Take care Matt .
  • Boilerpro
    Boilerpro Member Posts: 410
    NEC

    While taking a tekmar training course, the instructor brought this issue up. NEC only requires that at least one set of wires is rated for 600V (I believe). It is okay to run low and line voltage in same conduit. Talked to an electrician recently about this too, he said the same thing, however the local inspectors ignores this portion of the code and insists that the wiring be run separate.

    Boilerpro
  • Dave Yates (PAH)
    Dave Yates (PAH) Member Posts: 2,162
    several

    times I've had the displeasure of finding out the hard way that what should be low voltage wiring, acording to wire gauge sizing, is actually line voltage! Zzzzzzzzzaaappp. Gives you that tingly sensation all over and a numb arm for a while.

    If you're going to change commonly accepted voltages associated with wire gauges, please label them prominently. 18/3 is not meant to be utilized for 120v!

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  • John T_2
    John T_2 Member Posts: 54
    I don't believe gauge

    > While taking a tekmar training course, the

    > instructor brought this issue up. NEC only

    > requires that at least one set of wires is rated

    > for 600V (I believe). It is okay to run low and

    > line voltage in same conduit. Talked to an

    > electrician recently about this too, he said the

    > same thing, however the local inspectors ignores

    > this portion of the code and insists that the

    > wiring be run separate.

    >

    > Boilerpro



  • John T_2
    John T_2 Member Posts: 54
    Wire guage

    I don't believe is important but rated voltage is. We will run line and low together as long as the low is 600v rated. However, we use a smaller wire size so they are easier to identify as low voltage and it's easier connecting to those small terminal strips in most of the modern controls.
  • Good reason to not mix voltages

    several years ago I was involved with an investigation at the sight of a fire. The area of the thermostat on the wall was determined by the fire inspector to have been the cause. There were several condos that had the same hookup of 14 gauge wire to thermostats and 24 volt low voltage circuits in the same conduit with 14 gauge 120 volt AC. The electrical inspector and myself along with the fire department determined that 120 volts had feed over into the low voltage circuit causing the anticpator on the thermostat to over heat and set the thermostat on fire. I have also seen this happen with dust accumulation in 24 volt thermostats. I do not recommend mixing voltages but I am aware that most codes do allow it. We do it with relays and aquastat controls but even they have in recent years been seperated by an insulated shield.
  • ScottMP
    ScottMP Member Posts: 5,884
    Not the problem

    I dont believe this is really a code issiue as it is a wiring problem.

    I may be wrong, but I believe the concern is cross over of voltage, as Tim said, or effecting the 24 volts. The more electronic equipment can be a service nightmare if the voltage gets spikes and drops.

    Scott


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  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    RFI amd EMI

    That stands for radio frequency interference and Electro Magnetic Interference. We discovered it long ago as it pertains to solid state controllers. If you have a low voltage line run parallel to a high voltage high, amp draw line, the high VA line generates a field of electricty that gets transferred over to the low voltagae line via induction. Wreaks havoc with low voltage control logic microprocessors. Kinda scrambles their brains.

    As far I know, it IS legal to run both low and high volt lines in the same pipe provided they have 600 volt ratings. Not recommended, but approved.

    Be safe, run the low outside of the conduit, and avoid paralleling high and low volt lines..

    ME

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  • Mad Dog
    Mad Dog Member Posts: 2,595
    I suppose the National Electric code would

    prevail there Ron....I'll ask around.... Mad Dog

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  • Paul Cooke
    Paul Cooke Member Posts: 181
    Cleaning up Low Voltage Wiring

    I've been using this plastic wiring chase lately. Found it at the local electric supply house. Gives you a place to gang all your low voltage connections...snap the cover on...done.
  • Would you have any info on how much

    of an amp draw will cause problems ? Say an oil burner is going at 5 amps , 3 circs at .7 amps , and controls and such not amounting to much more , would you think 7 amps would cause an induction , if we used , say 12 gauge wire for the supply and for the low voltage ? Thanks .
  • Boilerpro
    Boilerpro Member Posts: 410
    Avoiding interference problems

    When running sensor wiring for my Tekmar controls, all of it is run with shielded wire to avoid interference from other wiring, and other things such as flourescent ballasts. If run in metal conduit and conduit is grounded standard stat sire is okay, I've been told. As to creatin a magnetic field and inducing current from a high voltage line to a low voltage one, haven't run into it yet, even though I know it can happen.

    Boilerpro
  • volts vs amps

    Don't think the amps matter as much as the voltage.
  • Reasons to keep wires seperated...

    in my over 40 years of wiring thousands of systems it has been my experience that even if the code allows it do not mix wires for line and low voltage.

    1. Possible electrical interference (others have covered that)

    2. Difficult to troubleshoot electrical problems later

    3. It does not make it easy for someone who does not know what you did when they follow you on the job.

    4. If you are real good at wiring the low voltage wire can be twisted into some pretty professional looking set ups.

    5. Some electrical inspectors have there own code about it.

    6. Easier if I have to replace wire or add controls later on

    7. As much as I can avoid them I do not like wire nuts
    I also do not like junction boxes. Prefer electrical strips with individual connections. Junction boxes I call jack in the box, when you open them everything jumps put.

    8. My rule of ONE WIRE TO EACH CONNECTION-NO MORE THAN ONE!!!

    9. Possible mistaking low volt and line volt when same size wire is used.

    10. It is a fact that no matter what voltage or amperage you use electrical interference can occur.

    11. All of these new micro-processor controls with Data piggybacked on voltage signals go crazy. This is why many integrated conrol boards used mated plugs and miswiring compliant connections.

    12. I think the code should be changed to not allow voltages to be mixed. I think probably we are behind the times on many codes that need to catch up with technology.

    Other than that help yourself just do not do it in my territory.

    Oh yes, all the pretty piping everyone shows on this site if wiring is done professionally it looks just as pretty.
  • Big Ed
    Big Ed Member Posts: 1,117
    Running Wire

    What I like to do when dropping a voltage on a thermo line in a quick retrofit job is pull the wire out of the box and cut and splice it to a 18 gauge thermo wire up in the ceiling. Then run the 18 gauge either along the out side of the line conduit or strap a second "open" low voltage conduit for neatness.

    For wire neatness and having the circulators high when pumping away , mounting the relays high near the bank of circulators is the way to go. Which usually means a wall control board . Which I know is near impossible in a price conscious retrofit..........
  • tcutler
    tcutler Member Posts: 6
    low voltage

    I run the low voltage in its own conduit this keeps the job nice & neat . I have had a computerized control show a fault caused by the electrical contractor running the low voltage wire with the line. I allways have the eletrical contractor run schielded low voltage wire now.
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