I've read through several posts about this but couldn't find a good reason as to why this is even used. In 2001, the company installed a Delta Delta 13.8/480. Later grounded the B phase. No problems encountered. One of the buss ducts it fed had all the equipment grounded with ground rods. That same ground from the B phase is ran to the buss duct as well. If I wanted to remove the corner ground, what type of problems should I expect if any. And the main question is, WHY have a corner grounded Delta to begin with?
Corner grounded delta
- Thread starter hurt33
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Hopefully the equipment is grounded by an equipment grounding conductor as well.
Back in the dinosaur days I was taught that the corner ground became "popular" when a nationwide industrial complex used it to reduce cost
on gear by not having to protect the grounded phase.
Back in the dinosaur days I was taught that the corner ground became "popular" when a nationwide industrial complex used it to reduce cost
on gear by not having to protect the grounded phase.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
I noticed the way you mentioned that the buss duct was grounded by ground rods, first I want to explain that grounding electrodes do not provide a low impedance path for fault current, nor are they allowed to, without having a low impedance path a fault to a grounded piece of equipment would not cause a breaker or fuse to operate to protect a person from a shock hazard, having a phase or a center tap such as in a WYE bonded to all equipment grounds provides a low impedance path back to source, Electricity does not want to flow to Earth, it wants to return back to source, this maybe a transformer or generator, or other means of supply but not Earth.
Now there are ungrounded systems allowed in certain circumstances but not without a phase monitoring system in place, these are allowed only where having the system go down would provide more of a danger then having a phase go to ground, this is to provide redundancy so the first fault goes to ground and sounds an alarm to allow time to schedule a shut down to repair it without taking the whole system down, it also only creates a grounded system on the first fault, the second fault will still take out the OCPD.
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
A sputtering ground fault is your worse case. One particular industrial complex with an ungrounded system had over 600 motors destroyed by a sputtering ground fault before anybody knew what was going on. 
ATSman
ATSman
- Location
- San Francisco Bay Area
- Occupation
- Electrical Engineer/ Electrical Testing & Controls
Sematics
Sematics
SG-1,
Let's clarify this for threst of us.
By "sputtering" I take it to mean "stricking ground fault" as the intermittent contact to ground of an ungrounded conductor?
TT
Sematics
A sputtering ground fault is your worse case. One particular industrial complex with an ungrounded system had over 600 motors destroyed by a sputtering ground fault before anybody knew what was going on.
SG-1,
Let's clarify this for threst of us.
By "sputtering" I take it to mean "stricking ground fault" as the intermittent contact to ground of an ungrounded conductor?
TT
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
Sputtering means re-striking. The fault from the ungrounded conductor only strikes during part of the AC cycle.
OK, so a faulted bus duct will have a metallic path for return current, but if the grounding electrode conductor does not follow the same path as the phase conductor, you may still have a high fault impedance. If there is no EGC to the equipment fed from the bus duct, then this is a problem also.
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