Service 480v 3ph or straight 480 ?

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Part-Time

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I am reading the voltage at the meter and getting
480v leg to leg and
L1 to ground is 510
L2 to ground is 484
L3 to ground is 252
Is this normal ?
The machines are blowing fuses
 
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Part-Time said:
I am reading the voltage at the meter and getting
480v leg to leg and
L1 to ground is 510
L2 to ground is 484
L3 to ground is 252
Is this normal ?
The machines are blowing fuses
Click to expand...

I'm not familiar with the term "straight 480? What is that?

ice
 
Straight 480 is two 480v legs the 3rd transformer goes to ground
Really strange but have worked on it and really eat my lunch till I found out that was
Normal
 
Part-Time said:
I am reading the voltage at the meter and getting
480v leg to leg and
L1 to ground is 510
L2 to ground is 484
L3 to ground is 252
Is this normal ?
The machines are blowing fuses
Click to expand...

Did you get the line to line voltages?

When you say "ground", is there a neutral and it is bonded to ground? Or, there is no neutral and you are infact measuring Line to Ground?

And no, the voltages you list don't fit any known "normal" I know of.

ice
 
Part-Time said:
I am reading the voltage at the meter and getting
480v leg to leg and
L1 to ground is 510
L2 to ground is 484
L3 to ground is 252
Is this normal ?
The machines are blowing fuses
Click to expand...

Part-Time said:
480v line to line
Having problems with power to control transformers in the machines blowing fuses
Neutral and ground bonded at service
Click to expand...

Here's my translation of what you are saying:
1. There are three phases and a neutral.

2 The neutral is bonded to the ground at the service.

3. You measured the line to line voltages and got 480v (Nominal)

These three tell me the service is 3 phase grounded 480V Wye.

4. You measured the line to ground (neutral?) voltages and got:
L1 to ground is 510
L2 to ground is 484
L3 to ground is 252

I don't any systems that would react like this to any faults I know of. This is true even if the system is not grounded 480 Y.

The first thing I would do is go measure the Line to Neutral voltages again and make sure I was connected to a system neutral for the measurement.

ice
 
Part-Time said:
480v line to line
Having problems with power to control transformers in the machines blowing fuses
Neutral and ground bonded at service
Click to expand...

I don't doubt that since the control transformers are likely connected line to line.

Added note to previous post:

Take the line to line reading again as well. if the Line to ground(neutral?) readings are correct, the the utility is feeding you:
L1 to L2 860V
L2 to L3 642V
L3 to L1 672V

And that would certainly ruin control transformers as well as motors, light bulbs, probably not the computers. Any surge suppression will be blown or CPC open.

I'd definitely check the readings again.

ice
 
I have measured it at the meter and through out the plant I get the same reading at every disconnect in the plant the only machines not have problems are strictly 480v no low voltage or control transformers no servo drives just 480
 
Part-Time said:
I have measured it at the meter and through out the plant I get the same reading at every disconnect in the plant the only machines not have problems are strictly 480v no low voltage or control transformers no servo drives just 480
Click to expand...

Just because I have not seen it before dosen't mean it doesn't exist. Is this something that just started? Or is this: All was fine and working well yesterday - today all is fubar?

Is there even a system neutral out in the plant that you can measure too.? Most (okay - actually every one) industrial plants I've been at don't carry the neutral past the first disconnect. Everything is connected 3 phase 480 with an equipment ground. I'm baffled on how you could get those readings.

Doesn't look like I can help. From my side of your monitor I'm not seeing how the symptoms could be connected.

ice
 
Can you see the bank? Look up at the fuses and see if one is out.
 
Part-Time said:
... And it is only a 480v system no low voltage at all
Click to expand...

I don't know what that means. Are you saying this is not 480/277 grounded Y.

Cause that is not consistent with your previous answers. Perhaps you could ask the utility exactly what the customer side system is.

ice
 
iceworm said:
I don't know what that means. Are you saying this is not 480/277 grounded Y.

Cause that is not consistent with your previous answers. Perhaps you could ask the utility exactly what the customer side system is.

ice
Click to expand...

It sounds like a center tap(on 1 pot) grounded 480 delta. The voltages read like a fuse was out, or as he stated, a bad pot.
 
the Utility Company is supplying only 480v NO low voltage at all
the guy that came out said that a transfomer is bad the next guy who came to change is
said it is not bad HAHAHA now who is right he said he is getting 477 line to line and that is good
which is. but inside side the plant i get the odd voltage
 
Part-Time said:
the Utility Company is supplying only 480v NO low voltage at all
the guy that came out said that a transfomer is bad the next guy who came to change is
said it is not bad HAHAHA now who is right he said he is getting 477 line to line and that is good
which is. but inside side the plant i get the odd voltage
Click to expand...

Then check the fuses at the disconnect. Ask him if it is a center tap grounded bank or a corner grounded bank. Even better, look up and see for your self.
 
Hv&Lv said:
It sounds like a center tap(on 1 pot) grounded 480 delta. The voltages read like a fuse was out, or as he stated, a bad pot.
Click to expand...

I thought of 480V "Hi-Leg". I've never seen one and have only head of one. But, I thought could be. So I had sketched the vectors figuring both a Y primary and a D primary, with a D secondary, one center tapped and grounded.

I didn't see any failure modes that would give 510, or 484 to neutral/ground. 240V, 415V - yes. A bad transformer if it were not completely out, maybe it could. - that I don't know. A transformer that were completly out would look like an open delta. So help me out here. How does an open primary fuse give 510V to ground on a 480D, centertapped? How does an open transformer give 510V or 484 to neutral/ground?

An un-grounded delta can - but this ain't that.

I'll chalk this up to another one of the many things I have not seen. But if you have time to explain - I'm listening.

ice
 
fuses are good
i am getting good voltage LINE to LINE
but to neutral or ground one leg is 510v and the other 250v is this normal for a corner ground delta ?
and they are the legs i blow fuses that supply the control transformers in the machines
the 480v line is fine
Does anyone have a schematic of this type of 480v grounded system ?
 
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