Transformer xo bonding

[electrofelon]

Oh "must go" gotcha, misinterpreted that. Definitely agree. I had a wye delta transformer once where they had landed the supply neutral. Lost a utility phase and that imbalance caused the supply conductors insulation to fail and blew a big hole through the 2 inch emt.

 

[mbrooke]

Oh "must go" gotcha, misinterpreted that. Definitely agree. I had a wye delta transformer once where they had landed the supply neutral. Lost a utility phase and that imbalance caused the supply conductors insulation to fail and blew a big hole through the 2 inch emt.

Its ok, I frequently end up with my posts saying the exact opposite of what I mean. That would be my fault not yours



Yahhh, a wye delta will definitely wreck havoc. Would not be surprised in the least if that blown fuse (lost leg) was caused by the wye delta in the first place.

 

[romex jockey]

So ground detectors in 250.21 aside, how does one corner ground?

Is it simply making say H3 a double lug,and off to building steel and GEC's?

And what of the 480 secondary disco? I thought a 'dummy fuse' was required?

~RJ~

 

[LarryFine]

So ground detectors in 250.21 aside, how does one corner ground?

Is it simply making say H3 a double lug,and off to building steel and GEC's?

And what of the 480 secondary disco? I thought a 'dummy fuse' was required?

Basically, yes, or just use a 2-pole disco

 

[romex jockey]

Thx Larry

So the grounded phase really could not pass through a 3ph breaker then?

It's have to be a fused disco ? with either a dummy fuse, or passing the grounded leg right on through a 2pole disco?

Sorry to confuse the issue, but i'm a wee bit lost, probably need another cup 'o joe

~RJ~

 

[kwired]

Thx Larry

So the grounded phase really could not pass through a 3ph breaker then?

It's have to be a fused disco ? with either a dummy fuse, or passing the grounded leg right on through a 2pole disco?

Sorry to confuse the issue, but i'm a wee bit lost, probably need another cup 'o joe

~RJ~

Grounded conductors can pass through common trip breakers/multipole switches as they simultaneously open all conductors. If you blow a fuse in the grounded conductor you may still have closed circuit in ungrounded conductors, so you must somehow bypass fuses in grounded conductor for such an application.

 

[JFletcher]

Are those breaker panels inside a secondary cabinet? It looks to me that one cant operate the 208V breaker w/o lifting the deadfront (the 480V breaker doesnt appear to have a deadfront at all). If so, that's somewhere near the corner of Sketchy Lane and Deathtrap Highway. Good thing it's all getting ripped out.

eta: is the primary neutral hooked straight to the secondary to make 277V?

 

[kwired]

Are those breaker panels inside a secondary cabinet? It looks to me that one cant operate the 208V breaker w/o lifting the deadfront (the 480V breaker doesnt appear to have a deadfront at all). If so, that's somewhere near the corner of Sketchy Lane and Deathtrap Highway. Good thing it's all getting ripped out.

Both appear to me to have provisions for attaching a deadfront. One just has little tabs with a hole for screw the other has a lip most the way around the perimeter with some holes for screws.

 

[JFletcher]

Both appear to me to have provisions for attaching a deadfront. One just has little tabs with a hole for screw the other has a lip most the way around the perimeter with some holes for screws.

see my edit re: the neutral. also, even if they both had working deadfronts, wouldnt the panel being located inside a second panel be a working space violation?

 

[kwired]

see my edit re: the neutral. also, even if they both had working deadfronts, wouldnt the panel being located inside a second panel be a working space violation?

OP said there were no loads utilizing a neutral in his OP.

work space violation - maybe, maybe not, depends on how strict you read into it. If the outer enclosure is no more then 6 inches deeper then the inner enclosure, I think it is even harder to say there is a violation.

 

[LarryFine]

Thx Larry

So the grounded phase really could not pass through a 3ph breaker then?

It's have to be a fused disco ? with either a dummy fuse, or passing the grounded leg right on through a 2pole disco?

Sorry to confuse the issue, but i'm a wee bit lost, probably need another cup 'o joe

As stated above, the grounded conductor could be opened as long as not by itself. Plus, that conductor would have been white.

 

[electrofelon]

So ground detectors in 250.21 aside, how does one corner ground?

Is it simply making say H3 a double lug,and off to building steel and GEC's?

And what of the 480 secondary disco? I thought a 'dummy fuse' was required?

~RJ~

Last time I did one, was a 600 volt delta for an older elevator. I used a 2 pole safety switch and bonded there. White wire off one of the phases, gec and sbj to the "neutral terminal" in the safety switch. There's a joke that on every electricians first corner grounded system, they turn away the first time they throw the switch, having just "grounded out" one of those "hot" phase conductors

 

[jumper]

Last time I did one, was a 600 volt delta for an older elevator. I used a 2 pole safety switch and bonded there. White wire off one of the phases, gec and sbj to the "neutral terminal" in the safety switch. There's a joke that on every electricians first corner grounded system, they turn away the first time they throw the switch, having just "grounded out" one of those "hot" phase conductors

Well, I have never did a corner grounded delta but I certainly would not be turning my head away....

I would be in another room hiding, then yelling to some noobie on the crew “Go ahead!”

 

[jumper]

Thx Larry

So the grounded phase really could not pass through a 3ph breaker then?

It's have to be a fused disco ? with either a dummy fuse, or passing the grounded leg right on through a 2pole disco?

Sorry to confuse the issue, but i'm a wee bit lost, probably need another cup 'o joe

~RJ~

Look at 240.22.

 

[ActionDave]

Last time I did one, was a 600 volt delta for an older elevator. I used a 2 pole safety switch and bonded there. White wire off one of the phases, gec and sbj to the "neutral terminal" in the safety switch. There's a joke that on every electricians first corner grounded system, they turn away the first time they throw the switch, having just "grounded out" one of those "hot" phase conductors

It took a little bit thinking about it time for me before I got my head around corner grounds. When I tried explaining it to my workmate he kept insisting "You can't ground a HOT!" And the thing about it was he was a really good electrician, it just tore him up that something he had never considered possible his whole life could be true.

 

[kwired]

It took a little bit thinking about it time for me before I got my head around corner grounds. When I tried explaining it to my workmate he kept insisting "You can't ground a HOT!" And the thing about it was he was a really good electrician, it just tore him up that something he had never considered possible his whole life could be true.

That is what confuses people. It isn't "hot" if it is grounded. You still have 240 or 480 volts to other corners of the delta though.

But at same time you can't have it plus another point of the system grounded

 

[nickelec]

So I'll try to explain a little further.

Sent from my SM-G950U using Tapatalk

 

[nickelec]

What we have is that Transformer that is being fed via 120 208 wye from the utility.

the feed goes into an 800 amp 3 phase disconnect the neutrals from the feed a splice straight through do not land on anything as you can see from the pictures
then to the Transformer.

Inside the Transformer the XO is not hooked up and the neutrals are just floating in the cabinet safed off with tape .

coming out of the Transformer on the secondary side are all three ungrounded conductors traveling about 200 ft to feed some vfd to control some motors.

The grounds you see inside the 800 amp switch are bonded to the neutral inside the CT cabinet the only thing they land on inside the Transformer is a lug that's bolted to the case and the ground going out on the secondary side to the motors

Sent from my SM-G950U using Tapatalk

 

[GoldDigger]

Note that under [2017] the transformer whose nameplate is shown is designed as a step down transformer (voltage changing taps are on the H windings) and cannot be used as a step-up transformer (using X as primary) unless the manufacturer explicitly states that it can be used in either direction.

 

[jumper]

Note that under [2017] the transformer whose nameplate is shown is designed as a step down transformer (voltage changing taps are on the H windings) and cannot be used as a step-up transformer (using X as primary) unless the manufacturer explicitly states that it can be used in either direction.

Agree, but the rule, 450.11(B), also applies to 2014. It was adopted in that cycle.