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Author  [Modern View]

08-02-2013 03:11:33

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Is there a reson not to use outdoor overhead type tri-plex in a atic ? Need to feed a new service box on a new porch and have alot of tri-plex . Maybe run it in plastic conduit . The run is about 80 ft. and service cable aint cheap . Just want to use what I got if I can .

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dr sportster

08-04-2013 08:40:42

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 Re: Tri-plex in reply to TGIN, 08-02-2013 03:11:33  
These old arthritis hands have never done it but good luck landing the steel leg in the panel lugs.

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08-03-2013 20:08:38

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 Re: Tri-plex in reply to TGIN, 08-02-2013 03:11:33  
When using triplex, let's also talk about a tingle voltage filter between the neutral and ground.


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08-03-2013 23:38:40

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 Re: Tri-plex in reply to buickanddeere, 08-03-2013 20:08:38  
Interesting reading.

"The most common source of stray voltage in Canada and the U.S. is neutral current generated by normal power consumption in the grounded neutral electrical distribution system. Electrical distribution in Europe is phase-to-phase and with the rare exception of electric shock from ground faults there is no stray voltage on European farms."

OK, so how does a "tingle filter" work?

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08-03-2013 05:24:41

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 Re: Tri-plex in reply to TGIN, 08-02-2013 03:11:33  
Thanks for the replys , you guys more or less told me what I already knew . I worked wiring houses when I was 17 & 18 and I am not going to do somthing wrong , 18yro was a long time ago so just thought I would ask . As for mkirsch it is people like you that keeps the poster that really needs help from posting because they dont want to be belittled by people like you . You must be a very small person to have to talk so big !!

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david - OR

08-02-2013 09:04:17

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 Re: Tri-plex in reply to TGIN, 08-02-2013 03:11:33  
This is unlikely to meet code because overhead triplex is not listed for use in raceways (conduit). If you plan to get the work inspected, you need to ask the inspector first.

Overhead triplex uses a bare "messenger wire" (ACSR) which is a multi-stranded aluminum conductor wrapped around a single steel strand. The steel strengthens the messenger wire so that it can support the entire cable assembly. Running it in conduit presents several practical problems, whether you care about inspections or not. The most immediate practical one is that the cable assembly is bulky and stiff. You'll need a large diameter conduit to be able to pull the wire through it, especially with a 4th neutral conductor added. You are going to have to make at least two 90 degree bends to get from the service entrance to the sub panel. This is going to require some long gentle sweeps to pull such stiff wire. There may not be room in the attic to get the sweeps in place. Getting out of the service entrance and up the wall won't be fun either. You really don't want to make the turns with junction boxes and splices, as aluminum wire is demanding about keeping oxidation out, and every splice is one more hidden fire hazard in your house.

The ampacity of the wire is based on free air at a reasonable temperature (40 degrees C), not a hot attic in a raceway. You can be conservative about the actual ampacity and get around this.

The wire insulation is thinner than typical indoor wire, and may not be able to stand up to the friction of being pulled through conduit. This would be harder to get around.

An 80 foot run of PVC conduit in an attic is going to need an thermal expansion joint of some sort.

Because you will need to buy the conduit, and supply the 4th wire, the savings aren't as big as you might have first thought, even though the wire is "free".

The installation you propose is so much more trouble than using SER cable without conduit that the savings don't seem worth it.

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John T

08-03-2013 05:33:42

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 Re: Tri-plex in reply to david - OR, 08-02-2013 09:04:17  
"You are going to have to make at least two 90 degree bends to get from the service entrance to the sub panel. This is going to require some long gentle sweeps to pull such stiff wire."

INDEED, where my buried triplex comes up out of the ground to enter into the rigid conduit riser up to my meter base THAT WAS A PRETTY TIGHT/TOUGH TURN........

I NEVER in all my years as a design engineer specified it for INDOOR USE, but have seen it inside (Rigid or IMC as I recall) conduit where it comes up out of the ground to a meter base and would otherwise be exposed. It was always buried or an aerial drop from the utility to the service entrance in all my years of experience.

Again, I have no NEC reference regarding its suitability for use in conduit, mines sure that way inside conduit and passed inspection, but thats outside of course and the codes may have changed since then????

If the poster chooses its use, it will indeed "WORK" Well DUH it will still conduct the current, even if legal or not. His choice

Love sparky chat,,,,,thanks for your inputs

John T

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George Marsh

08-03-2013 17:18:18

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 Re: Tri-plex in reply to John T, 08-03-2013 05:33:42  
A union electrician wired my pole barn with 4 plex. In the basement he ran it in conduit, about 30 ft. Used an LB outside the house to go under ground. Then the rest was under ground to the barn. When it came out of the ground conduit again. Inside the house he pulled wire in only one section of conduit at a time. Glued after it was all pulled. Would have been impossible is he hadn't done it that way. I'm sure someone will find issue with it. I really don't care. Job is done and no sparks.

Don't see what the issue is running 4 plex or 3 plex in conduit.

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08-04-2013 15:47:27

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 Re: Tri-plex in reply to George Marsh, 08-03-2013 17:18:18  
And there lies an example of the problem. If the light goes on when switched, the operator isn"t shocked and there are no sparks. Thus the wiring and methods must be perfectly fine........

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david - or

08-03-2013 23:41:36

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 Re: Tri-plex in reply to George Marsh, 08-03-2013 17:18:18  
There is a big difference between overhead rated (ACSR) triplex and underground-rated triplex or quadplex (typically type USE).

It"s not the triplex/quadplex that"s the issue; its the overhead-rated nature of the triplex the original poster posited.

Overhead rated triplex has thin insulation befitting use in free-air and a steel center wire on the messenger that makes the wire strong enough to hang from poles. Underground rated triplex/quadplex has thick insulation for use in continuously wet locations (not to mention direct bury) and a plain-vanilla aluminum ground/neutral.

Underground triplex is still bulky, but it is much more flexible, and can be pulled through (big enough) conduit. Most of my objections to using "triplex" in an attic (or in conduit) disappear if we are talking wire not rated for overhead use. It"s entirely possible that the installations described by John T and George Marsh were completely code compliant (I"m a little unsure on the code compliance of USE inside buildings for a building to building feeder application.)

But it is clearly fine to enclose it in conduit for a service entrance emerging from the ground, and there may in fact be no other way to do it (it must be protected from physical damage inside buildings.)

But the original poster was pretty clear that his triplex was overhead-rated, and it would be pretty wrong to say that there"s no issue with that.

One more note: electric utilities are regulated by their own code; NOT the National Electrical Code. It is assumed that utilities employ electrical engineers to supervise the processes that they use for distribution.

No such assumption is made for commercial/residential wiring, and the NEC is more conserviative.

The dividing line between utility rules and NEC rules is the "service drop" for an overhead installation (basically the drip loop and splices up on the roof). For an underground installation it is the electric meter or service disconnect means.

In general, overhead-rated triplex is stuff used by utilities, and that"s one reason there"s not much (if any) discussion of it in the NEC.

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Bus Driver

08-04-2013 14:58:56

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 Re: Tri-plex in reply to david - or, 08-03-2013 23:41:36  
The POCO uses the National Electrical Safety Code, a different code.
Using the bare messenger in underground conduit is asking for quick failure. Underground will get condensed moisture or standing water and the bare conductor will corrode quickly-- no doubt about it. All conductors of Type UF will work well in buried conduit. Or those with "W" as the last letter on the Type designation, such as THW or THHW. THHN is not suitable for buried conduit.

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08-02-2013 16:57:15

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 Re: Tri-plex in reply to david - OR, 08-02-2013 09:04:17  
All the replies so far have really been top notch, really like yours David.

Unusual for such solid replies to an electrical question. :)

I think it comes down to the insulation not really suited for use in a conduit due to thinness and heat buildup, as well as the possible need for a 4th wire to be safe. It would probably all work out probably more or less, but it might not be easy nor really safe nor really all that cheap, and doubtful it would be to code for any future considerations.


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John T

08-02-2013 20:10:19

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 Re: Tri-plex in reply to Paul, 08-02-2013 16:57:15  
"Unusual for such solid replies to an electrical question. :)"

YOU CAN SURE SAY THAT AGAIN LOL As a retired electrical distribution design engineer Ive tried for 15 years on here to help educate the posters the best I can, but the lay uneducated Billy Bobs of the world figure the way they did it WORKS and thats all there is to it grrrrrrrrrr Youre soooooooooo right, you sure dont often get solid replies

John T

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08-02-2013 07:47:00

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 Re: Tri-plex in reply to TGIN, 08-02-2013 03:11:33  
Of course you can go ahead and do whatever the h*ll you want because there are no electricity police lurking in the bushes waiting to pounce on you when you do something "illegal."

The only times you have to worry about it is, if you do it wrong and it burns down your house, or if you or your children ever have to sell the house.

Triplex indoors won't pass inspection.

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08-02-2013 07:41:49

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 Re: Tri-plex in reply to TGIN, 08-02-2013 03:11:33  
I've got about 100 feet of it inside my shop, running from the breaker box over to my Lincoln tombstone stick welder. That set-up has been in place for more than 10 years and in that time the welder has burned up several pounds of welding rod. No problems ever. It just simply works.

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John T

08-02-2013 06:26:15

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 Re: Tri-plex in reply to TGIN, 08-02-2013 03:11:33  
I didnt look this up in the NEC, I advise you to CONSULT WITH LOCAL AUTHORITY OR YOUR UTILITY PROVIDER AND PROFESSIONAL ELECTRICIANS AND ENGINEERS (versus lay Billy Bob and Bubba untrained opinions or my rusty opinion) however here are my thoughts as I best recall... NO WARRANTY

1) First thing is you have to compute the load and overcurrent protection devices and know if your wires ampacity is sufficient.

2) Next, if your enclosing that triplex in conduit (I have no heartburn with that but see my final safety disclaimer) ascertain its ampacity in that environment, because its often used in free air and the more common known and advertised ampacity is for free air NOT enclosed. i.e. it may be rated say 100 amps in free air but less if its enclosed.

3) Is it copper or aluminum?? If aluminum use connectors and lugs and terminations rated for such and any necessary anti oxidant coating

4) FINALLY as we have preached on here for years, is this for a main panel or a sub panel fed by a circuit breaker in your homes main panel, and is it 120/240 volt????

If its 120/240 volt and its a sub panel fed by a breaker in your main panel YOU NEED 4 NOT THREE (Triplex) CONDUCTORS. Two UngrounDED Hots L1 & L2,,,,,,One Grounded Neutral Conductor,,,,,,,One Equipment GroundING Conductor

As always, I'm sure I missed something and hope the electricians and engineers can add to this as needed and correct any errors, I'm never too old to learn I figure.

Sorry to give you a complicated answer, but that just the way I'm wired and experienced and trained.

SHORT ANSWER sure run triplex in conduit provided its ampacity is properly computed and sufficiemnt and you may or may not have enough conductors???? See the above.


Ive seen triplex in free air and buried mostly as a service feed from utility transformer to the residence, but NOT familiar with its use indoors I HAVE NO IDEA IF SUCH IS PERMISSIBLE OR NOT and I'm too busy and lazy to look it up lol SURE Billy Bob and Bubba it will "work". Its your home and life and safety and money and decision, not mine, do as you wish.

John T

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08-02-2013 05:36:50

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 Re: Tri-plex in reply to TGIN, 08-02-2013 03:11:33  
I may get beat up, but my house (built in 2003) is fed by tri-plex underground within the grey plastic conduit. I had better not discuss what is inside the plastic conduit feeding my shop (very short run from power company pole/panel to building). I guess I never thought anything about tri-plex buried in conduit, and in my mind if it is protected from the elements in conduit it would hold up better than out in the elements and ran overhead, and in an attic it would not be exposed to any elements and should hold up fine. The 4th conductor would be an issue if running to a sub panel, but if you have the materials why not just twist in a 4th conductor off another section. This is just my thoughts, and probably what I would do if I had it laying around vs. purchasing.

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08-02-2013 05:16:14

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 Re: Tri-plex in reply to TGIN, 08-02-2013 03:11:33  
I am no electricitian but I know tri-plex is only rated for outside overhead use. The bare conductor has a steel wire or something other than aluminm in for strength on long spans. I know if I was an inspector it would not pass. There is no way you could get the ends hooked up properly. Also it is rated for exposure to air only. I have installed enough and more to go and I know how it is supposed to be used.

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08-02-2013 04:38:19

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 Re: Tri-plex in reply to TGIN, 08-02-2013 03:11:33  
New service panel on the porch....does this mean the panel for your whole house? Or a sub panel. Tell more about your project. What size is your triplex, and how many amp panel are you installing?

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08-02-2013 03:46:01

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 Re: Tri-plex in reply to TGIN, 08-02-2013 03:11:33  
By "service box" do you mean a subpanel? It's been discussed to death here that you'll need four conductors. I think the triplex is OK inside conduit, but you need to add another insulated conductor so you have separate ground and neutral. The neutral conductor needs to be the same gauge as the other two insulated conductors.

Installing a large conduit in an attic seems like a lot of aggravation to me. But it's your time and money.

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