Determing wire size

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  #1  
Old 10-24-10, 12:50 PM
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Determing wire size

I have a 200 amp main panel that feeds a sub panel in a barn thru a 125 amp breaker in the main panel by a "triplex" overhead wire run. The "triplex" (a colleague advised this is what this type of wire is called) consists of two heavy insulated (black) conductors & a stranded aluminum ground all twisted together. I am suffering from bad voltage sag at the barn end & the ground is very corroded & has actually broken in a couple of places (ground was spliced / repaired). I tried grounding the sub panel to a water pipe earth ground, & while that helped it didn't solve the problem.
My dilemma is that I have no idea what the triplex wire size is as it isn't stamped into the insulation & any printing on the plastic isulation is long gone. I need to replace this so I need some guidance on how to size this wire or what size wire will suit my needs. The run between the two panels is about 175'.
 

Last edited by TexasFire; 10-24-10 at 01:52 PM.
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Old 10-24-10, 01:53 PM
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Have you considered running underground? So much neater, not subject to falling limbs. Would require about 4 hours of a ditch witch.
 
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Old 10-24-10, 04:19 PM
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First of all, if you want to replace the overhead you can't use triplex any longer, quadplex is what you will need (3 insulated and 1 bare ground). Second, the bare in a triplex is not a ground, but a neutral. Third, you'll need to do a load calculation in the barn to determine the proper overhead aluminum wire size.
 
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Old 10-24-10, 04:27 PM
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By current code you can no longer use triplex. You must use quadplex. This may or may not be required by your local code. 1/0 aluminum should be large enough for 125a at 175 feet. You will need to separate ground and neutral at the subpanel. This will probably entail removing the bond strap or screw from the neutral and adding a ground bar. You will also need one or two ground rods.

Joe beat me to the post. Please answer his question on loads first. I assumed the 125 amp breaker was large enough but we need loads to be sure.
 
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Old 10-24-10, 05:47 PM
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I currenly only have about 15 - 20A load in some lighting but ultimately would like at least 100A capability. I have a good ground at the barn as there is a 1" metal water pipe from the ground through the concrete near the sub panel. I currently have 1 ought wire grounding my panel from this pipe. There is also a ground rod right outside the barn by the panel. I'm wondering if I can get away with triplex since I have a good ground at the barn...
I'm also on the Texas Gulf Coast!
 
  #6  
Old 10-24-10, 07:21 PM
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There is an exception in the code that allows not having a seperate ground to detached structures as long as there are no metallic components connecting the 2 buildings together. Bascially the detached building is treated as a main service being fed from the other building. Grounds and neutrals would stay together, 2 ground rods would need to be installed as well as your water pipe ground. Of course this whole idea is done if that 1" pipe is going from the barn to the house..
 
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Old 10-24-10, 08:33 PM
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ElectricJoe it is my understanding that Texas is on the 2008 cycle for all non-exempt wiring so it must be 4 wire.

Answer for code cycle based on http://www.license.state.tx.us/elect.../flash1208.pdf
 
  #8  
Old 10-24-10, 08:56 PM
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I don't hve a problem with running quadplex, I just need to know what size needed to suit the 125 breaker. The sub panel is reated for 200A but I'll never have that load on it.
 
  #9  
Old 10-24-10, 09:37 PM
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For aluminum conductors you need a minimum of 1/0 for the current-carrying conductors and a minimum of #4 for the equipment ground. This does not allow for any voltage drop due to distance however the chances of you actually pulling a load of 125 amperes is rather small so voltage drop can probably be ignored.
 
  #10  
Old 10-24-10, 10:51 PM
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I am with other guys in here you will need 55mm˛[1/0 AWG ] Alum quadplex overhead cable and keep the netural and ground at the subpanel and yes you will have to sink two ground rods and you have to bond the water pipe with bonding conductor { 16mm˛ (#6 awg )} as long you have either steel or copper water pipe over 10 feet but if all plastic underground it will not be really effetive.

All 120 volts circuit are have to be on RCD {GFCI } no extemps unless it written in local codes.

Is your Barn is used for workshop or part of it will be livestock { animails } ???

That part it may change on codewise so let us know what your plans in this one.

Merci.
Marc
 
  #11  
Old 11-05-10, 09:06 AM
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The barn is basically a workshop & a band practice area with a stage & lighting, no livestock. I have purchased 200' of 1/0 quadplex & plan to hang it this weekend. There are 3 strain reliefs in the system that anchor via insulators & "grab on" to the ground wire via a cam-lock type device. My old wire is smaller than 1/0 so not sure if these "wire grabs" are suitable or if I should replace them with bigger ones.
I have a great 1" water pipe ground as well as a separate ground rod with a separate tie-wire. Do I STILL need a 2nd ground rod?
Thanks for all of the help & info!
 
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Old 11-05-10, 09:32 AM
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No the water pipe plus ground rod should be sufficient.
 
  #13  
Old 11-05-10, 01:22 PM
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OK.... My current sub panel has grounds & neutrals all tied together. If I understand correctly, it was stated in an earlier post that my tie bar must be removed & grounds & neutrals separated. My MAIN panel that is feeding this has grounds & neutrals together, so what good would it do for me to separate them at the sub panel when they are tied together at the main panel? That's still a path. Doesn't make sense.... I need to understand how to tie this quadplex wire in that is replacing triplex. Wire is pulled & ready to connect!
 
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Old 11-05-10, 01:30 PM
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If the ground and neutral are tied at any point but the main dangerous voltages can be present on the ground. That could make touching the metal case of a device with a ground dangerous. You could create a voltage difference between earth and the ground wire.
 
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Old 11-05-10, 02:21 PM
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Originally Posted by TexasFire View Post
OK.... My current sub panel has grounds & neutrals all tied together. If I understand correctly, it was stated in an earlier post that my tie bar must be removed & grounds & neutrals separated.
Correct. The neutral bar must also be insulated from the panel box, which usually means it's the one mounted on plastic stand-offs.

My MAIN panel that is feeding this has grounds & neutrals together, so what good would it do for me to separate them at the sub panel when they are tied together at the main panel? That's still a path. Doesn't make sense
The ground and neutral are bonded only at the panel which contains the main disconnect for the service. The problem with bonding them again after the main is that it would cause current to flow on exposed metal surfaces between the main panel and the downstream bond. In an extreme case where the subpanel's neutral wire is compromised, it can result in voltage on metal surfaces in the barn high enough to shock a person. When the ground and neutral are improperly connected you can get all sorts of dangerous and hard to trace problems like getting shocked by touching plumbing, aluminum siding or metal conduits.

This is not really a safety issue, but you can also get bad humming or interference on radios, TVs and amplifiers when the ground and neutral are bonded incorrectly.

I need to understand how to tie this quadplex wire in that is replacing triplex. Wire is pulled & ready to connect!
Separate your ground and neutral bars. Before hooking up the feeder wires, set your multimeter to the lowest resistance (ohms) scale, put one probe on the ground bar and one on the neutral bar. You should get infinite ohms (no continuity). If you get a reading of zero then there is still a ground/neutral bond you have missed. Once verified the two are isolated, the neutral wire goes to the neutral bar, and the bare to the ground. The GEC to the ground rod and water pipe go to the ground bar.
 
  #16  
Old 11-06-10, 12:38 PM
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My quadplex is labeled Phase A, Phase B & Phase C. Does it matter which one is the neutral? I was thinking A & B would be my two 110 phases & C would be my neutral.
 
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Old 11-06-10, 12:51 PM
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I was thinking A & B would be my two 110 phases & C would be my neutral
You have no 110v phases. You have two 240v legs and the neutral which is the grounded center tap. If they are all the same size and none have a stripe or raised rib it doesn't matter. If one is smaller or has a raised rib or stripe it should be used for the neutral.

Tech notes: You are using single phase power therefore you only have a single phase. The power comes from a 240v secondary center tapped transformer. You are running the two legs of the secondary plus the center tap. The center tap is known as the grounded conductor or less formally the neutral. You have 120v between the center tap and either of the 240v secondary legs.
 

Last edited by ray2047; 11-06-10 at 01:48 PM. Reason: Clarify terminology
  #18  
Old 11-06-10, 12:54 PM
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Being technically proper you do not have any A, B or C "phases" but do have A and B "legs. You may use whatever arrangement you desire to label your individual conductors but common usage will be to use the color black for the left-hand leg, the color red for the right-hand leg, the color white (this one is required) for the neutral connection and the color green (required) for the equipment ground. Plastic tape is the common method of identifying the different colors. I like to tape the entire visible length inside the panel but all that is required is a one-inch wide band at the point of connection.

Be certain that you use the same colors on each end of each individual wire in the cable.
 
  #19  
Old 11-06-10, 12:59 PM
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Originally Posted by ray2047 View Post
You have no 110v phases. You have two 240v phases and the neutral which is the grounded center tap. If they are all the same size and none have a stripe or raised rib it doesn't matter. If one is smaller or has a raised rib or stripe it should be used for the neutral.
C'mon Ray, you know better. The 240 volts is not two phases but only a single phase and if only one of the four conductors in the cable is smaller then that smaller conductor is the equipment ground conductor.

Okay, I see that Texas is using quadplex and that probably means three insulated conductors with a bare suspension/equipment ground conductor. If of the three insulated conductors one is smaller in diameter Ray is correct that would be the neutral conductor. The bare is the equipment ground and the two larger conductors would be the "hot" conductors.
 
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Old 11-06-10, 01:38 PM
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C'mon Ray, you know better. The 240 volts is not two phases but only a single phase
Yes, but didn't want to confuse the poster more. I will amend my post. My guess is he has quadplex intended for three phase.
 
  #21  
Old 11-06-10, 08:54 PM
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I asked for 1/0 quad plex & got three black 1/0 insulated conductors labeled Phase A, B & C plus an uninsulated 1/0 twisted ground. I plan to mark them black, red & white as suggested. I completely rewired 16 circuits in the sub panel today to separate neutral from ground & plan to terminate & finish hanging the quad tomorrow. Again, I appreciate all of the input. Everything run on this system with be 110V except for a Lincoln AC/DC crackerbox welder once in a great while. It takes a 50A breaker with a 220V 3 prong plug.
 
  #22  
Old 11-06-10, 09:04 PM
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Sounds like you have everything under control.
 
  #23  
Old 11-06-10, 09:46 PM
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Everything run on this system with be 110V except for a Lincoln AC/DC crackerbox welder once in a great while. It takes a 50A breaker with a 220V 3 prong plug.
Actually almost everywhere in the US for the last several decades nominal voltage single phase residential has been 120 and 240.
 
  #24  
Old 11-07-10, 06:11 AM
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110, 120, whatever it takes! hehe
 
  #25  
Old 11-10-10, 05:35 PM
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Back in my 1st original post I stated that this power was fed to the sub panel via a 125A (dual) breaker in the main panel. I have run the 1/0 quadplex as suggested but there's no way this 1/0 wire will fit into the original 125A breaker. Should I install a larger breaker big enough to take the 1/0 wire or should I splice it down to a smaller size?
 
  #26  
Old 11-10-10, 05:56 PM
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Splice down to smaller size. Just enough to fit the breaker. For the neutral and ground you can buy adapters that fit in two holes on the neutral/ground bars.
 
  #27  
Old 11-10-10, 06:58 PM
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Roger that - thanks! I never was able to verify what wire size I had before, I think it might have been #6.
 
  #28  
Old 11-12-10, 08:25 PM
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Thanks!

Finished the job & powered up the system today, works GREAT!
Thanks to everyone on this thread who provided all of this excellent advice!
 
  #29  
Old 11-12-10, 10:02 PM
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Excellent. Thanks for letting us know.
 
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