corner ground
- Thread starter kimrichi
- Start date
- Status
iceworm
Curmudgeon still using printed IEEE Color Books
- Location
- North of the 65 parallel
- Occupation
- EE (Field - as little design as possible)
Here are a few reasons:
Eliminates overvoltage caused from arcing ground faults (480V)
Outside, overhead, ungrounded systems are more suspectible to overvoltages from non-striking lightning.
Eliminates need for ground fault detectors.
A lot of the older, light industrial, were put in that way cause they only had to have 2 overloads (1960s stuff).
I'm sure there are plenty more. These are just the ones that come quickly to mind.
ice
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
It is a less common practice than it used to be. Lower voltage to ground is probably main reason.
Reason to ground a phase - if there is no need for a neutral conductor why run one? Grounding a phase still accomplishes the task of providing a grounding reference for creating low impedances for clearing ground faults.
It does not change the fact that once past the service equipment you still have to run an equipment grounding conductor separate from the grounded (phase) conductor for branch circuits and feeders.
Reason to ground a phase - if there is no need for a neutral conductor why run one? Grounding a phase still accomplishes the task of providing a grounding reference for creating low impedances for clearing ground faults.
It does not change the fact that once past the service equipment you still have to run an equipment grounding conductor separate from the grounded (phase) conductor for branch circuits and feeders.
meternerd
Senior Member
- Location
- Athol, ID
- Occupation
- retired water & electric utility electrician, meter/relay tech
As stated, corner grounding insures a low impedance path for fault current if either of the other two ungrounded phases go to ground. That will increase the likelihood that the breaker will trip on a ground fault. For 240 Delta, voltage to ground is 240 on the ungrounded phases. Code and safety guidelines use 250V to ground as a cutoff for numerous safety requirements. But at 480V, you are way over that, and if you've ever seen a 480 fault compared to a 240 fault, you'll know why it's a bigger deal. Twice the voltage, four times the power of the arc. NFPA has found that a 480 V fault can be the most dangerous arc fault of any commonly worked voltage, due to the tendency of 480 to sustain the arc. At least that's what taught in our safety meetings.
- Status