I still get amuzed by the number of electricians I meet on the job that don't realize you can't run seperate phases to the same three phase load in seperate conduits.
I've had to explain the concept of building a "choke" to more guys than I can shake a stick at.
It's almost as bad as the concept of splicing copper to aluminum in a split-bolt without the divider.
Anyone else have anything to add about this?

Lamplighter, actually you can do this if you are using non-ferrous wiring methods and the conditions of 300.20(B) are met.

Roger

I wasn't aware of that but, I've never been in a position where that would come into play either.
I have seen the effects of trying to do it in rigid metal conduit and it wasn't pretty.

There is nothing wrong in learning something new, we all do this from time to time. With me the times in between are real short.

One of the hardest things that I had to learn when starting out as a green horn was just where I was at.

It seemed that I was never just where I was supposed to be and was getting yelled at due to this fact.

Well one day I just ask the boss, “Just where am I supposed to be?”

He answered me with this.

If you are not here and you are not there then you have to be somewhere else. Now get over yonder where you are supposed to be. That was thirty seven years ago and the truth be know, I am still lost.

The company I work for recently repaired a job that the feeders for large RTUs where run in an isolated phase fashion. From the guys there they said it was quite an impressive meltdown.


A large underground service run in PVC is not unusual in my area.

Any chance they took some pics?

One of the best melt downs I've ever seen was in a holiday in that we had as a customer.
The maintanance man for the hotel was supposedly going to tighten the lugs on the main, he threw the switch to "off", opened the door, and stuck his bare metal allen wrenck into the lug.
The mechanism supposedly allowed him to open the door without actually shutting down the power.( most likely he used his screwdriver to trip the latch and hadn't really shut it down.)
The lugs were hot, he took a 480v hit, dropped the wrench into the gear and ended up blowing a 3'x5' hole in the F.P.&L. vault wall.
We showed up and overnighted a new switch in from Alabama or someplace. striped the old out, installed new and got the 400 unit hotel back on line in 36 hours.
Damn I was tired!
The maintanance guy survived but,last I heard, was starting to have digestive problems and trouble walking.

>>The maintanance man for the hotel was supposedly going to tighten the lugs on the main, he threw the switch to "off", opened the door, and stuck his bare metal allen wrenck into the lug...<<

no wiggy check? stupid is as stupid does...

... Sounds like a candidate for the Darwin Award to me.... I feel bad for the poor yutz!!
Russ

Any of you guys hear about the guy who tried to check a 13.2 line with his wiggy a year or so ago?
He didn't live to learn his lesson.
May have only been broadcast on local news.

I have a picture that is perfect for this thread , But I am too new to figure out how to add it to the conversation

Togol, if you email it to me, I can host'n'post it for you. You can find my email address by clicking on the icon on my post.

Ok Larry, ... I just did !

We would prefer to put pictures up that are loaded on the ECN servers. That way they don't get "lost" in the future.

Please e-mail them to me, another of the moderators, or e-mail them to webmaster@electrical-contractor.net

Thanks

[This message has been edited by electure (edited 10-20-2005).]

......ok,
it should be in your mail box

Here are togol's pics
He can explain what's happened here






Thanks, guys!

Thanks electure
well , these are examples of separate phases in individual raceways, there is an aluminum bus supported inside of the Aluminum pipes . referred to as Iso-Phase.
these were running at 13.8KV.
Incidentally ,this unit is adjacent to the unit that experienced some....electrical problems ....
Those are in the Photos folder ....titled ***FIRE***

togol

IIRC, aluminum has no magnetic properties, so you shouldn't get any inductive heating of the aluminum conduits.

Even though aluminium is not ferromagnetic, you will still see magnetic flux in the space between the conductors, and thus current flow induced in the enclosing conduit. The flux is stronger when the conduit is ferromagnetic; think 'iron core transformer versus air core transformer'. Clearly the separate conduit approach works; I'm curious as to the details of the engineering to prevent inductive heating.

I encountered this sort of conduit on a tour of the 'Glen Canyon Dam'. This was a standard open tour group, not some sort of special event. At one point the walkway has a very good view of the distribution transformers. Google images found this photo:

You can't see it in the above image, but at the end of the row of transformers (the side nearest to the viewing area), the ductwork is vertical; three _large_ pipes side by side. There was a horizontal rail near the ductwork.

Someone had arranged what appeared to be a coffee can, inverted and free to spin on a spindle, just sitting on the horizontal rail near the ductwork. The can was spinning merrily away. I believe that the can was essentially the rotor of an air core induction motor with two half turn stator windings. I suppose that it could have been wind, but I don't recall much wind at the time, and the can was smooth, so the wind should not have caused any torque.

-Jon

(edited to add image to ECN server)

[This message has been edited by electure (edited 10-22-2005).]

It seems to me that the bus arrrangement inside the "conduit", was comprised of four separate flat bars that were welded into a box shape, the sections were coupled together with flex links .and then the joint was covered and seam welded !

I recall tthe final connections on the transformer taking three days to complete,

togol

Aluminum is considered paramagnetic.

....is that anything like .....paranormal?

togol

Abby someone.