[Top] [All Lists]

[AMPS] Re:230 /115 volts QUIZ.

To: <>
Subject: [AMPS] Re:230 /115 volts QUIZ.
From: (Tom Rauch)
Date: Mon, 9 Apr 2001 10:31:43 -0400

> Who knows about a "high leg" on a three phase system?

Wild-leg three-phase is common, and the configuration can be a 
Wye or Delta. 

Where the configuration is a delta, one 240 v transformer 
secondary is connected the normal way.

Each of the two hot phases have an additional full 240 volt primary 
to a common wild leg (or high leg). The center taps are not used. 

You get normal single phase 240 (with a 120 neutral reference, 
which is what you checked) plus 208 more than 120 on the wild leg 
connection. You also have 208 from phase to phase on all phases.

In Wyes, it is more common for you to have three 120 volt 
primaries with the common point grounded. You'd have three 120 
volt circuits to neutral and 208 from phase to phase. (.866 times 
leg voltages are summed, so you have 103.92 volts times two from 
phase to phase).

This gives you a 208 three phase than can be used for normal 
lighting, and it has no wild leg.

If you have a wild leg with a Wye, it can have three 240 volt 
primaries with the CT of one grounded. It is unlikely you have this 
setup, since only very special high demands would require three 
phase voltages over 400 volts.
> Have this at my shop.
> Three phase (4 wire plus ground).
> One of three phase is marked "high leg".
> Between the other two phases and neutral, I see 120VAC.
> Anyone know what I should be seeing between the "high leg" phase and
> the other wires?

73, Tom W8JI 

FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>