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#### jbfan

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I have a machine that is rated at 460
Input voltage is 495
Machine label
460V 34A 3Phase
Icc 10KA

Not sure what Icc means.

I need to buck this down to 460.
Some online calculators can't give me an answer.

This is one I got.

http://fpbbcalc.com/default.aspx

Can this be done with 2 transformers or do I need 3?

#### micromind

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##### Bilge Rat
motors and controls.........
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Icc = Interrupting Current Capacity, or something like that. Basically it means is don't hit it with a circuit that can come up with more than 10,000 amps during a short-circuit.

Use two B/Bs, not 3.

If you use 3, and the neutral is not present, you'll have a closed delta. A closed delta will try to balance voltage at the expense of current. This is good, but only if the transformers have the capacity to actually change the voltage on the system. B/B are small, and when they try to balance voltage, they don't have enough capacity, so they burn up.

2 B/Bs with 480 volt primaries and 32 volt secondaries connected open delta will do exactly what you want.

#### jbfan

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Thanks.
Will either of these work?

SB24N1.5F
SB24N1F

Both are federal pacific, and the only online calculator that gave me model numbers.

#### BBQ

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A 460 volt machine is designed and intended to be connected to a 480 volt source.

495 is within the range for a 480 volt supply.

#### jbfan

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BBQ, I should have said the machine is from Italy, so not sure that will make a difference.
It is connected to the 495 volts now, but seems to skip a beat at times.
I only have second hand knowledge right now, so I was exploring alternatives.

Any and all comments are welcome, so I can learn more about B/B transformers.

#### BBQ

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BBQ, I should have said the machine is from Italy, so not sure that will make a difference.
Neither do I.

Micro has given you some good info, I install a fair amount of BB trans typically to raise 208 up to 230.

The wiring diagrams, the sizing and conductor sizes will all seem strange.

Is there something particular you are looking for?

#### captkirk

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##### Bababoee
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are you sure its not a 415 y machine..? 380/415 how are you getting almost 500 volts..?? what does the machine do..?

#### BBQ

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how are you getting almost 500 volts..??
495 is acceptable on a 480 volt service and I have seen as high as 525 volts.

#### Southeast Power

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I have a machine that is rated at 460
Input voltage is 495
Machine label
460V 34A 3Phase
Icc 10KA

Not sure what Icc means.

I need to buck this down to 460.
Some online calculators can't give me an answer.

This is one I got.

http://fpbbcalc.com/default.aspx

Can this be done with 2 transformers or do I need 3?
You will need two small transformers.
Get in touch with your favorite wholesaler and find out what gear they have an use their on line calculator.
Its seems complicated but when you get it all setup, you will be a hero.

#### Southeast Power

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495 is acceptable on a 480 volt service and I have seen as high as 525 volts.
He probably called tech support and the first thing they said was the voltage was too high and call back when they have it fixed.

#### captkirk

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##### Bababoee
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495 is acceptable on a 480 volt service and I have seen as high as 525 volts.
no kidding...??? never seen that much..

#### Ultrafault

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no kidding...??? never seen that much..
It is only 3 percent high. If you saw 123.5 volts you wouldn't blink.

#### jbfan

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Captkirk, it is a straight 460 v.

BBQ, I agree that the motors will have no problems, but what about control boards and such?

jrannis, yes, tech support sated as much.

I'm getting prices now, and let you know what is happening.

I'm not sure what the machine is doing or not doing.
It was just installed this week, and I believe they are just testing.

The machine is a router used in a cabinet shop.

#### jbfan

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You will need two small transformers.
Get in touch with your favorite wholesaler and find out what gear they have an use their on line calculator.
Its seems complicated but when you get it all setup, you will be a hero.
We decided to go with the 1.5 kva transformers.

The online calculator listed the output current at 34.4 amps for the 1 kva, which I thought was just a little too close to the 34 amps the machine pulls.

I will let you know what happens.

Thank for the input.

#### captkirk

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##### Bababoee
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Take the amount you are trying to buck and multiply it by the amperage of tge machine...so in your case its 35 x 34 which is 1100 or something. 1.5 kva is plenty for your application..

#### EBFD6

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He probably called tech support and the first thing they said was the voltage was too high and call back when they have it fixed.
I had a customer with a VFD issue a while back, the vfd would go out on an over voltage fault occasionally. We checked voltage at the line side and it was high at around 495ish, but within acceptable links we thought. We couldn't figure out what was going on. Replaced the drive with a new one, same problem. Called tech support, they confirmed that the voltage was ok. Finally we put our recording meter on the line to monitor for a few days, we notice voltage going to >500 volts occasionally and that coincided with the drive shutting down. Called tech support back and they told us that those drives were designed to shut down when the voltage goes over 500 volts. We were able to get the poco to come out and change the taps to lower the voltage into the building. My point in all of this is, just because the voltage isn't too high percentage wise, doesn't mean the equipment will tolerate it.

#### jbfan

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Ok, here is the big day.
Connected the transformers per federal pacific diagram, and lo and behold, got 545 volts output.

Rechecked connections and web site, same thing.
I am at a loss right now to get this thing working.

#### Big John

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Sounds like they're connected backwards. Your lower-voltage tap should be between your two high-voltage connections, if it's not, it's going to boost the voltage instead of bucking it.

What diagram did you use?
http://www.federalpacific.com/literature/drytrans/IN-7900.pdf

Also, what conductors did you take measurements between? If you do L-G you can get some unexpected voltages.

#### jbfan

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#### Big John

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I don't know why it tells you to use Connection G, because that is definitely a boosting connection: The high voltage is only connected to half the winding, and your LV winding tap is outside of that meaning that winding is added to the 495V supply.

If I use the table in the link I posted, I think "Figure H" is gonna get you closest. Look at that diagram. It looks similar, but the difference is that the high voltage is connected across the whole winding.

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