Corner-Grounded Delta System

[thebigmt]

Hello. I am new to the forum as far as posting, 'been reading for quite some time there are some very knowledgeable people here!

I would like to know more about the corner-grounded delta system and the dangers of working on one and why a lot of people don't like them.

Thanks!

 

[augie47]

I will offer a comment:
One "danger" as such is that you have a greater potential to "ground" than you would on a "neutral" grounded system. With 1 phase grounded on a 480 system the potential is obviously 480 to "ground" rather than 277v.
Offhand, I do not know the advantage of such a system other than a possible cost savings in one phase not needed OCP, etc.
With an ungrounded system you have the advantage of maintaining an operating system if one phase goes to ground.

 

[kwired]

Biggest danger is people that don't know what they are working with. This applies to all voltage/phase systems.

The most basic rules are really no different than any other system with a grounded conductor. Once you are past the service equipment you have separate grounded circuit conductors and equipment grounding conductors. You do not place switches or overcurrent devices in grounded conductors unless the device opens all ciruit conductors.

These systems are quite safe if properly installed and maintained, it is the unqualified that get into trouble with them - they often have no clue that such systems exist and really don't know what is going on with it.

 

[thebigmt]

I was in a class last weekend and the guy teaching the class said that exact thing. He said it was people that don't know what the hell they are doing that get into trouble with them.

I have never had to work on one but I would like to know more.

 

[kwired]

They are typically used where no 120 or 277 volt loads will be used, like on a site where there is only one load or very limited loads, like a pumping station.

All they do is ground one phase conductor instead of the mid point of a phase or the center of a wye. This will only require 3 conductors run to the service instead of 4. Will also work on open delta primary configurations to save POCO on equipment cost for limited load applications.

As I mentioned before the grounded conductor is treated just like a grounded conductor in any other system, it must not have switches or overcurrent devices installed in it unless they open all poles, and grounded circuit conductors and equipment grounding conductors must be separated after the service equipment.

The grounded phase has no voltage to ground (at the service) and 240 or 480 volts to the other two phases. There is no 120 or 277 volt lead, you will need to derive these voltages with a separate transformer if they are needed.

 

[LarryFine]

As I mentioned before the grounded conductor is treated just like a grounded conductor in any other system, it must not have switches or overcurrent devices installed in it unless they open all poles, and grounded circuit conductors and equipment grounding conductors must be separated after the service equipment.

The grounded conductor should also be colored as one.

 

[kwired]

The grounded conductor should also be colored as one.

As well as equipment grounding conductors.