Delta xfrmr secondary: Line to Neutral Relationship
Delta xfrmr secondary: Line to Neutral Relationship
(OP)
What is the line to neutral mathematical relationship in a delta connected transformer secondary? As in, why is the "wild leg" voltage 208 volts, when the line to line voltage is 240 volts?






RE: Delta xfrmr secondary: Line to Neutral Relationship
RE: Delta xfrmr secondary: Line to Neutral Relationship
If the high-leg is at the mid-tap connection between phase A & B the vector relation could be as follow:
Vred-leg = Vcn = Vbc<60o – Vbn<0o = 1.73|Vbn|<90o
NOTES:
- Single pole breakers should not be connected to the high leg.
- Must be permanently market permanent per NEC 215-8.
- Red-leg is also known as wild leg, odd leg, high leg, and delta mid-tap.
REFERENCES:
- IEEE std 142- 1.5.2
- NEC 1999 and previous version: 210.4(D), 215-8, 230.56, 240.83 (E), 240.85, 250-5 and 384-3(E)). 408.3(E), FPN
- For 2002 NEC version: 200.6, 250.119, and 310.12.
RE: Delta xfrmr secondary: Line to Neutral Relationship
Illustrations at http://home.att.net/~benmiller/elecsys.htm