Breaker size to reverse feed a 30 kva transformer?

[kingpb]

In other words, the disconnect with fuses would not work. Gotcha.

Not sure what type of ground detector to get and how I would connect it. I guess I could just ask the supplier and it would probably connect to the disconnect.

Check "Bender" ground detection devices.

Also, be prepared in the future to get a call back when the 80A breaker trips; eventually. The issue is that the inrush is independent of load. It is a characteristic of the core saturation. The curve indicates even a 100A breaker may not be sufficient. You could turn it on and off 100 times and it works fine, on the 101 it will trip, or you could turn it on once and it trips, then 30 more times it won't. Just depends on where the zero crossing end ups when it was de-energized.

 

[iwire]

Retrofit should be possible.

For what reason?

 

[victor.cherkashi]

The 208 volt side is rated 83 amps so not that surprising a 60 is having trouble.

The code would allow up to 250% of that 83 amps as an overcurrent device rating. (212 amps) I would think a 100 amp would do it but I am really guessing so wait for someone more knowledge on that.

Is there overcurrent protection on the 480 volt side?

How are they dealing with the 480 volt side, corner grounded delta or ungrounded with ground-fault indicators?

Agree. Note: 250% allowance if you have also protection on secondary side of transformer. Also see note 3 in table 450.3(B) required overload protection from manufacturer

Sent from my Nexus 5 using Tapatalk

 

[Smart $]

With a zigzag transformer and a resistor, okay?

Ground detector is much easier.

 

[Smart $]

Also, be prepared in the future to get a call back when the 80A breaker trips; eventually. The issue is that the inrush is independent of load. It is a characteristic of the core saturation. The curve indicates even a 100A breaker may not be sufficient. You could turn it on and off 100 times and it works fine, on the 101 it will trip, or you could turn it on once and it trips, then 30 more times it won't. Just depends on where the zero crossing end ups when it was de-energized.

As long as the facility is aware of this possibility, it shouldn't be a problem and there should be no call back.

If it is set up like most machinery, the only time the transformer gets de-energized is on power loss or during maintenance shut downs.

And more often than not, when a breaker trips turning it on, the operator usually tries a second, even a third time, before getting really suspicious... and odds are that it will energize without tripping on one of those attempts. :happyyes:

 

[zinsco]

As long as the facility is aware of this possibility, it shouldn't be a problem and there should be no call back.

If it is set up like most machinery, the only time the transformer gets de-energized is on power loss or during maintenance shut downs.

And more often than not, when a breaker trips turning it on, the operator usually tries a second, even a third time, before getting really suspicious... and odds are that it will energize without tripping on one of those attempts. :happyyes:

Yes, and I explained all of this before I did the job and they understood and wanted me to do the job.

If I ground H2 in the transformer am I still required to replace the fuseable disconnect that is outside the machine with a breaker when, as you can see, there is a breaker inside it?



Why does my digital meter read voltage to ground but my knopp tester does not? http://www.knoppinc.com/tools.htm

 

[GoldDigger]

Why does my digital meter read voltage to ground but my knopp tester does not? http://www.knoppinc.com/tools.htm

The voltage you read on your digital meter is a "ghost" voltage coming from capacitive coupling. The Knopp tester has a low impedance and does not get enough current through the capacitance to indicate a high voltage.
See this thread for more details.

 

[Smart $]

If I ground H2 in the transformer am I still required to replace the fuseable disconnect that is outside the machine with a breaker when, as you can see, there is a breaker inside it?

All the field wiring would have to be brought up to Code. You wouldn't necessarily have to replace the disconnect, but you would have to defeat the fusing of the grounded conductor. Some use a dummy (aka no-blow) fuse. The grounded conductor must be be re-pulled because it is smaller than #4 and must be white, gray, etc.. Having to do this, I'd probably just pull through the fused disconnect and not use B-pole (no connection, no fuse).

 

[zinsco]

All the field wiring would have to be brought up to Code. You wouldn't necessarily have to replace the disconnect, but you would have to defeat the fusing of the grounded conductor. Some use a dummy (aka no-blow) fuse. The grounded conductor must be be re-pulled because it is smaller than #4 and must be white, gray, etc.. Having to do this, I'd probably just pull through the fused disconnect and not use B-pole (no connection, no fuse).

I should say that the picture with the breaker inside is some kind of control cabinet or something and is outside and is feed from the disconnect located inside next to the machine. The machine is then powered from that control cabinet thing located outside.

Does this change anything?

 

[Smart $]

I should say that the picture with the breaker inside is some kind of control cabinet or something and is outside and is feed from the disconnect located inside next to the machine. The machine is then powered from that control cabinet thing located outside.

Does this change anything?

View attachment 13608

No, it does not. All the wiring up to the control cabinet is field wiring. Technically, the wiring between the control cabinet and the machine is field wiring if not furnished by the manufacturer as part of the machine. All field wiring must be brought to Code if you ground H2 at the transformer.

 

[zinsco]

All the field wiring would have to be brought up to Code. You wouldn't necessarily have to replace the disconnect, but you would have to defeat the fusing of the grounded conductor. Some use a dummy (aka no-blow) fuse. The grounded conductor must be be re-pulled because it is smaller than #4 and must be white, gray, etc.. Having to do this, I'd probably just pull through the fused disconnect and not use B-pole (no connection, no fuse).

So the fuses are fine in the disconnect except for B phase (B phase must not be lost unless all lines are killed) and this is because of the breaker in the cabinet would trip if there was a short and kill all lines?

Also, I couldn't take out the disconnect altogether because it has to be with-in site and the breaker is outside. Right?

 

[Smart $]

So the fuses are fine in the disconnect except for B phase (B phase must not be lost unless all lines are killed) and this is because of the breaker in the cabinet would trip if there was a short and kill all lines?

Correct. The entire load must be disconnected any time the grounded conductor is disconnected... and a blown fuse inline with the grounded conductor would not do that.

Also, I couldn't take out the disconnect altogether because it has to be with-in site and the breaker is outside. Right?

Quite likely. You did not elaborate on the parts or operation of the machine... but I like to think that if any of it has electrically-powered moving parts that there be an emergency disconnect nearby.

 

[zinsco]

Do you think it is possible that grounding "B" phase could effect how the machine works? I see all those fuses inside that control cabinet and it just makes me wonder.

 

[Smart $]

Do you think it is possible that grounding "B" phase could effect how the machine works? I see all those fuses inside that control cabinet and it just makes me wonder.

Shouldn't affect machine operation at all.

As I said earlier, ground detector is much easier.