ECN Forum Forums General Topics of the Trade General Discussion Area Ok theorists, help me out

The 3ph delta with a center tap between a&b we call the wild leg sys its still in use I've seen it in florida and here in indiana many of times and boy if you dont check your panel voltages it can dammage alot of equiment.

Hello & Welcome!

Are these systems still being installed in new commercial buildings in Indiana, or are we just talking about old services still in use?

I think it was Scott (Electure) some time ago who reckoned that in his area (so. Cal.) all new services in the past 30 years or so were straight 120/208 or 277/480 Y.

I havent seen any utility install any but I have seen the power co hook up a new service to an existing one that was already there. even after my protest

Is the possibility of accidentally connecting to 208 thinking that it's 120 the main problem with the 4-w delta?

Are there any other drawbacks that you come across regularly with this system?

Hi Paul, Welcome back!!!

In regards to the Delta thingee, the major concern was as you stated - some one mistakingly setting up an L-N circuit between the high voltage to ground line and the grounded center tap [AKA "Neutral"], with the intentions of driving a 120 VAC load.

This will result in two things:

<OL TYPE=1>

[*] 208 VAC impressed upon the load,
and

[*] Smoke leaving said load.
</OL>
<Just wanted to add some humor! >

Anyhow, there are still many 4 wire Deltas in our area [I live near Scott "Electure"]. They can mostly be found in the older Commercial / Industrial areas, along with the areas zoned with Residential and Commercial / Industrial [again, older areas]. These systems are both flavors of Open and Closed configurations.

Funny thing is that the new company I work for, very few people have heard of - let alone worked on - a 4 wire Delta. I get some weird looks when mentioning them! Even weirder when I show the results of the "Orange Line To Ground" on my Wiggy.
P.S. a "Wiggy" is a Solenoid / Neon lamp type voltage tester which is usable from 120 to 600 Volts - AC or DC. They are the most common volt meters in the field. They have low accuracy [208 falls above the "240 VAC" markings!] and have a low input Impedance - which makes them useful as GFCI testers and when you run across an ungrounded Delta!

Lastly, my thinking on the 310 VAC [+/-] was that the tester is "Bridging" between two coils [one of 277 VAC potential, one of 120 VAC potential]- creating an Autotransformer / Reactor setup, similar to an HID Ballast.

I have seen readings like this. First was by use of a Wiggy, just to see what the voltage between Lines of 2 different panels [one 480Y277, the other 208Y120], the other[s] were with a DVM. I shunted the leads with a 22K Resistor to lower the input Z.

Felt nice to ramble again! Been really BZ [busy].

I'll be flying to San Fransisco on Monday, to do some surveys - then back to So Ca for a few days of work and colation, then back on Da Plane! again.

Scott S.E.T.

P.S.S. Looks like maybe next thursday our E-Mail address will change.
We are shooting for "stat113" at pac bell dot net. That will be confirmed later...

Scott

Safe to say that in most parts of the US, the only likelihood of being able to even request 4W&#8710; would be for small loads in older overhead areas.

Con Ed [the electric utility in New York City] lists 2-phase and DC available {for older elevators} for as long as their serving equipment lasts, and then you gotta update. [Imagine somewhere there is an apartment building with 90-year-old tenants that has a motor-generator set in its basement…that probably won't restart after the next power outage.]



[This message has been edited by Bjarney (edited 05-18-2002).]

Hey Scott,

Long time no hear!

On the 4-w deltas, didn't somebody here come up with the idea of painting the phase B blanking plates on the panel orange as a warning? Can't remember who it was, but I guess it could save the next person to work on that panel a lot of trouble.

It could be worse I suppose. Just imagine a (non-technical) U.S./Canadian tourist coming over here, buying a simple plig adapter and hooking up to our 240V. Even more smoke than on 208....

Off-topic....
"BZ" reminds me of the people here who look at U.S. software with something like "EZ Install" on it and ask what the "ee zed" means. Cue explanation that in America it's pronounced "ee-zee."

BJ,
Does Con-Ed still actually distribute DC or 2-phase, or do they just own/maintain conversion equipment at the customer's premises to convert? I assume we're talking about real 2-ph (90 deg.) here and not just two legs of normal 3-ph.

paul-- There used to be a link to an older {but still in service} New York turnstile bridge that used two 2-phase motors, but the link seems to have dried up.
http://www.coned.com/documents/elec/018-024.pdf See: §III. 2. (D and (E) for DC and 2-phase servce.
http://www.powerlineman.com/pictures/2001/march/g_good/good.htm Poster refers to it as “scotts system.” It looks like it is a true utilty-owned Scott-Tee transformation. A rare bird I’m sure.

Sometimes referred to incorrectly as 2-phase—a 3-wire 208Y/120-volt utility-furnished service tapped from two phases and a neutral is correctly called “Network Service” in the US.

Lastly, I have no idea why, but Table 430-149 in the 1999 NEC deals exclusively with 2-phase motors. I once mentioned in an IAEI chapter code-change session that it may be of limited use and possibly time to request its deletion, but the suggestion was not on the agenda so maybe I should use proper parliamentary decorum; wait 3 years and resubmit it for the next code cycle. [Unbelievably but sadly, I lost interest.]

Even Farther Off Topic...

www.ci.nyc.ny.us/html/dot/html/bridges/bridges/macombs.html mentioned being powered by two 2-phase motors, but link is dead.

www.nycroads.com/crossings/macombs-dam/ doesn't talk about motors.

Looks like many 2-phase motors were 4-wire, nominally 220-240 volts across opposite phases {for 90° displacement.} Probably usually grounded at the neutral point for “5-wire”...but there were likely ungrounded versions, too. Can you imagine floating pairs of voltages to ground, and maybe even pairs of connections floating with respect to adjacent terminals, too?

Musta' been cool! <What this has to do with 2-gang boxes and 310 volts I'll never know.>








[This message has been edited by Bjarney (edited 05-20-2002).]

Interesting about the bridges even if nothing whatever to do with power! One of the links reports "being revised," so I'll take another look sometime soon.

Re the floating adjacent terminals, just imagine if high-impedance DVMs had been around when these systems were being installed. That could have provided hours of amusement for someone trying to figure out what was going on!

Is there any particular reason for the "network service" designation? It seems a rather vague term to me, although I suppose it's shorter than "two phases from a three-phase service."

Another totally unrelated query, but as we're talking about Con Edison, do they still distribute their waste steam under NYC's streets for heating?


[This message has been edited by pauluk (edited 05-20-2002).]