Wye or Delta serving motor loads

[Smart $]

I have never seen a 3 phase corner grounded system that used a white wire....yes I am well aware that code requires that, but have never seen it in the real world.

May well be. I've only run across one in my lifetime and it was so long ago I don't remember if the GC was white, gray, or not. Nevertheless, from here I have to go on the assumption the system is up to Code.

BTW, there are also CG3WΔ systems that switch the GC, some OCPD the GC, per Code. I'm just pointing out the worst case scenario.

 

[drcampbell]

That would be code compliant even today. ...

Sure, as long as it remains CGΔ. Otherwise, we're right back to "you certainly cannot just hook up this new system to the existing without a major change".

I have never seen a 3 phase corner grounded system that used a white wire ...

If I recall correctly, the one I saw used one-color cotton-over-rubber, and the individual phase conductors were identified with filth. But whatever the colors, the potential for a nasty surprise -- one phase energized with 277 volts after being switched off -- is still there.

 

[kwired]

So let's make up odd situations that won't happen in real life just to give reason to nit pick.

:lol: Looks like you picked the wrong day to take that one-in-a-million chance...

Not so odd of a situation at remote single load applications.

Following comment applies for a simple motor controller and motor installation and assuming that the grounded conductor was run through circuit breakers and not run straight through unswitched at branch circuit switces.

Aside from issues with identification of previously grounded conductor as well as possible overcurrent protection issues on the former grounded conductor, the only other major issue that comes up is the need for an additional (grounded) service conductor. Beyond the service disconnect everything would otherwise work as is as long as phase rotation stayed the same.

Beyond the service disconnect if the corner grounded system were done properly there should be separate grounded and equipment grounding conductors. Many old installs did not properly identify the grounded conductor, but it still should be isolated from EGC, so simply changing from corner ground to wye should not present much issue other then conductor identification which is a code issue - physically it would work fine as the electrons in the conductors don't discriminate when it comes to color.

 

[Smart $]

Not so odd of a situation at remote single load applications.

Stating it as a one-in-a-million chance was me being exaggeratively nice.

Following comment applies for a simple motor controller and motor installation and assuming that the grounded conductor was run through circuit breakers and not run straight through unswitched at branch circuit switces.

That's the thing. I would dare to say the odds of CG systems running the GC through OCPD are not that great... especially where fusing in a fused disconnect is the means of OCPD. Yes, it would be great for whoever is flopping the system over from CG to Wye to have a 3-pole fused disconnect... but weigh the odds that someone putting in a CG-compliant disconnect is going to install a 3-pole with one "bypassed" fuse rather than a 2-pole disconnect... :angel:

 

[kwired]

Stating it as a one-in-a-million chance was me being exaggeratively nice.


That's the thing. I would dare to say the odds of CG systems running the GC through OCPD are not that great... especially where fusing in a fused disconnect is the means of OCPD. Yes, it would be great for whoever is flopping the system over from CG to Wye to have a 3-pole fused disconnect... but weigh the odds that someone putting in a CG-compliant disconnect is going to install a 3-pole with one "bypassed" fuse rather than a 2-pole disconnect... :angel:

One of the area POCO's got rid of all their corner ground systems back in the 1990's. You primarily saw them on irrigation services on the farms. They did have to run an additional conductor on all of those systems, and some likely were not grounded/bonded properly to begin with as most of those were never inspected. The problem was 480 to ground and untrained people that commonly had their hands in these things was not a good combination and is why they converted them to wye systems in the first place. Still dangerous with 277 to ground but is more forgiving then 480.

Also was common on those applications years ago to use three pole fused disconnects and put a slug (usually something makeshift and not intended for the purpose) in the grounded phase position of the disconnect. I once recall one farmer that got tired of replacing a fuse that kept blowing and thought it would work to swap the slug with the fuse that kept blowing. I remember him saying that he swapped them back to where they were when he called the POCO to tell them there was a fire on the pole:slaphead:

If you want my opinion - we need to somehow keep the untrained hands out of either system. Then if we can accomplish that the corner ground is safe and uses less conductor on a 1000-1500 foot service lateral. There is never anything on these installations that needs a 277 volt neutral.

But you are not going to keep the untrained hands out of irrigation equipment. Maybe you will at an oil well, municipal pumping station or something of that nature but not on a irrigation well.