Why is the high leg higher than the other two?

Only one transformer winding is center-tapped to create the neutral, so two legs read half the line-to-line voltage. The third leg sits at the apex of the delta triangle and measures line-to-line times the sine of 60 degrees to that center-tap neutral, which is higher.

What is the high-leg voltage on a 240 V delta?

It is 240 × sin(60°), which equals 240 × 0.866, or about 208 V to ground. This is why the high leg is nicknamed the 208 V wild leg, stinger, or bastard leg on a 120/240 V delta service.

Which phase must be the high leg?

NEC 408.3(F) requires the high leg to be the B phase in panelboards and switchboards where the neutral is present. It must be durably marked, conventionally with orange, so no one mistakes it for a normal 120 V phase.

Can I land 120 V loads on the high leg?

No. A 120 V single-pole load connected to the high leg sees roughly 208 V to neutral and will burn out. Only the two normal legs supply 120 V; the high leg is used only for three-phase loads or 240 V line-to-line connections.

Does the high leg affect three-phase loads?

No. Line-to-line voltage between all three phases is the same 240 V, so three-phase motors and 240 V loads operate normally. The elevated voltage only appears between the high leg and the grounded neutral.

High-Leg Delta Voltage Calculator

A 120/240 V high-leg delta service hides a trap: two legs give a clean 120 V to neutral, but the third — the wild leg — sits at about 208 V to ground and will destroy any 120 V load wired to it. This calculator shows exactly what that high leg reads and reminds you of the NEC marking rule that keeps it safe.

How it works

The center-tapped winding sets the neutral halfway across one phase, leaving the opposite apex of the delta elevated:

normal legs to neutral = V_line-to-line / 2
high leg to neutral    = V_line-to-line × sin(60°)
                       = V_line-to-line × 0.866

For a 240 V delta that is 120 V on the two good legs and 207.8 V on the high leg. The three line-to-line voltages remain equal, so three-phase equipment is unaffected — the elevated reading appears only between the high leg and neutral.

Example and notes

On a 240 V delta the high leg reads about 208 V to ground. NEC 110.15 and 408.3(F) require that conductor to be phase B in the panel and marked orange so no one lands a 120 V receptacle on it. If you enter a single-pole device rating, the tool confirms whether it can survive the high-leg voltage, but the correct practice is never to connect 120 V single-pole loads to the high leg at all.