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Tool Talk Discussion Forum

Re: Tri-plex

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david - OR

08-02-2013 09:04:17
208.67.204.213



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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
216.249.76.176



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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
50.104.212.180



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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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buickanddeere

08-04-2013 15:47:27
209.240.127.193



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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
184.76.14.88



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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
66.226.53.18



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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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Paul

08-02-2013 16:57:15
66.60.223.232



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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.

Paul

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John T

08-02-2013 20:10:19
216.249.76.176



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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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