Corner ground

[liquidtite]

I'm trying to understand the different electrical systems between wye and delta and the variety of voltages that these system can derive . I recently have worked in a factory were the system was a corner-grounded delta , a phase to ground read zero so that has to be the grounded leg . Phase to phase read 240v, b, c , phase to ground read 240. so if you neaded to supply a piece of equipment with 240 could you only bring phase b or do you still have to bring both phases. What is the advantage of having a corner grounded delta ? Do they still supply corner grounded deltas? Is a center tap delta the system with the high leg? Can someone please list the voltages of wye and deltas so I can study and recognize each system. Thank you for your time

 

[jumper]

Mivey, another member, posted this recently:

3 Services
3.1 Types of Service Furnished
Available electric service includes 60 hertz, alternating current, single-phase or three-phase. See Section 3.10, Load Requirements. The nominal secondary voltages are provided below.

Underground Service
The following underground service may be provided:
* Single-phase, 120/240-volt, three-wire, grounded
* Single-phase, 240/480-volt, three-wire, grounded
* Single-phase, 120/208-volt, three-wire, grounded
* Three-phase, 208Y/120-volt, four-wire, grounded, wye
* Three-phase, 480Y/277-volt, four-wire, grounded, wye
* Three-phase, 240/120-volt, four-wire, grounded, open-delta1
* Three-phase, 480/240-volt, four-wire, grounded, open-delta1

Overhead Service
The following overhead service may be provided:
* Single-phase, 120/240-volt, three-wire, grounded
* Single-phase, 240/480-volt, three-wire, grounded
* Three-phase, 208Y/120-volt, four-wire, grounded, wye
* Three-phase, 240/120-volt, four-wire, grounded, delta
* Three-phase, 480Y/277-volt, four-wire, grounded, wye
* Three-phase, 480/240-volt, four-wire, grounded, open-delta (motor loads are limited to 40 hp or less unless equipped with ASD)

If other service voltages are required - such as three-phase, 480/240-volt, grounded, delta - the Customer must request and PGE must approve these voltages before services can be provided.

 

[kwired]

I'm trying to understand the different electrical systems between wye and delta and the variety of voltages that these system can derive . I recently have worked in a factory were the system was a corner-grounded delta , a phase to ground read zero so that has to be the grounded leg . Phase to phase read 240v, b, c , phase to ground read 240. so if you neaded to supply a piece of equipment with 240 could you only bring phase b or do you still have to bring both phases. What is the advantage of having a corner grounded delta ? Do they still supply corner grounded deltas? Is a center tap delta the system with the high leg? Can someone please list the voltages of wye and deltas so I can study and recognize each system. Thank you for your time

You can ground any point on any system. NEC does require a particular point on some systems to be grounded, like the neutral of a wye or the mid point "neutral" of a single phase system.

A corner grounded delta is simply a delta system with no mid point of any phase available to possibly be a system conductor to ground. If you want to ground this system pick a corner and ground it, otherwise set it up as an ungrounded system and provide ground fault detection and indication devices.

It is not a question of if you want to supply a piece of equipment with 240, because 240 is all you have, any other voltage must be transformed somehow. If the equipment is three phase then you need all three conductors, if it is single phase you only need two conductors, may or may not include the "grounded phase", but it is still 240 volts either way. The grounded phase is also bonded at the service or first disconnecting means and the equipment grounding conductor is created from this point on. It is no different from keeping neutrals and grounds separated in other systems, the "grounded" conductor is a current carrying conductor and must be separated from equipment grounding conductors beyond the service or first disconnecting means.