What is FOUR wire Triplex for?

[homeowner]

A large store downtown has a heavy FOUR wire triplex feeding the building. 3 wires are black insulated, the other is the bare neutral.

The thing that caught my attention to it, is that the 4th wire is not connected to anything. All the triplex I've ever seen is 3 wire, two are insulated, one is bare. That's for a standard 240V single phase system.

Im thinking that this cable was intended to be for three phase wiring. Three hot, and the neutral. Is this right? Maybe that building once had 3 phase service, or they just had that cable on hand when they wired it, and used what they had...

[Dean Hoffman]

Triplex to me means three wires, not four. I would call that wire quad. The bare wire would be for the equipment ground, not the neutral. The neutral is current carrying and is supposed to be insulated. There have been some code changes regarding single phase wiring in the U.S. Electric stoves and clothes dryers are what I'm thinking of. It was acceptable long ago to wire them with three wires. The equipment ground and neutral were permitted to be combined. That is no longer permitted in new wiring. The current carrying neutral and the normally non current carrying equipment ground have to be separate.

[trader4]

If it's not connected to anything, why are you identifying it as the neutral? You have 3 wires that are apparently current carrying conductors and one that is bare, not connected. Assuming this is overhead, ie going from the pole to the building, sounds like the bare wire is for support only and you have a 240V service, with two hots, one neutral.

[gfretwell]

That says "3 phase". Three hots and a neutral. You can verify it by looking at the transformers. If you see 2, one perhaps bigger than the other, it is 3 phase center tapped delta. (AKA red leg or wild leg)

If you see 3 equally sized transformers it is usually 3p wye

[trader4]

Did you read the part where he says the "neutral" is not connected to anything? Sounds like a support wire to me.

[gfretwell]

The bare wire on the pole is the neutral.

leg)

>

wye

[dpb]

On 1/13/2013 9:20 AM, [e-mail] wrote: ...

...

Iff'en it "is not connected to anything" how can it support anything?

I'd not think that would be how OP would have written the description if it were the support cable he was speaking of.

--

[George]

Likely you mean it has a drop using quadplex aerial cable?

[trader4]

I would assume by "not connected to anything", he means it is not electrically connected to anything. He doesn't say anything about whether it's physically connected to the building, pole, etc

From what he wrote, a lot isn't clear. Hopefully he will clarify it.

[George]

The version on the newsserver I use does not mention anything about the "neutral" being unconnected.

leg)

>

wye

[trader4]

But again, he says the neutral wire in the service cable that he is talking about is not connected. It can't be a neutral if it's not connected.

[George]

The original post mentions describes the "four wire triplex" with one wire unconnected. "trader" introduced the idea of it being the "neutral"

[trader4]

Hide quoted text -

No, I didn't introduce the idea that it was the neutral. The OP stated that in the first sentence:

"A large store downtown has a heavy FOUR wire triplex feed "The thing that caught my attention to it, is that the 4th wire is not connected to anything. "

So he's saying he has 3 black insulated, the other is the bare neutral. The 4th wire is not connected to anything. I took that 4th wire to be the bare neutral. But it's not clear what exactly he means by the 4th wire. If it's one of the 3 blacks, I would think he would just say one of the blacks is not connected.

[trader4]

The c There are 3 blacks, one of them is unconnected and there is a bare neutral. That is the way the rest of you seem to be interpreting it. Hopefully he'll clarify.

[John Grabowski]

*It could be a 3 phase delta service. How many transformers are on the pole?

[gfretwell]

That is why I said "look at the transformers"

The topic is called "what is FOUR wire Triplex for? and the answer is "3 phase" I bet if he posts a picture, you are going to see that bare wire connected to the strand on the pole and one might believe that is not connected to anything but that is the neutral.

[bob haller]

around pittsburgh many aerial drops use a bare wire not connected to anything but the pole and building mechanically... no electric connections....

[gfretwell]

They have a messenger on service conductors that is not bonded?

They must have a different spin on wiring services there. The NESC even requires bonding messengers on low voltage.

[trader4]

Yes, I agree, IF they are all in fact connected. But that sure isn't what he's saying. And as I've said, from the confusing post, it's not clear exactly what the 4th allegedly unconnected wire is, ie the bare or one of the conductors.

[George]

They must have a different take on things. Standard practice is to bond bare wires than can become energized for any reason even if unused.