Good trick

[petersonra]

I was looking at the AB manual for a 200 HP drive.

The manual says the drive is rated for 232.8 A input continuous, and 248 A output continuous.

That ought to solve our energy crisis.

Yea - I know it is a PF thing.

So let me pose this question. Can I use the 232.8 number for sizing the feeder to a box that has 4 of these things in it?

232.8 * 4 + 25% of 232.8 is just a hair under 1000A.

240*4 + 25% of 240 is just a hair over.

 

[jim dungar]

The NEC says to size based on the input of the drive.

 

[petersonra]

The NEC says to size based on the input of the drive.

The input to each VFD gets sized by the input current.

But these are still motor circuits. Do the feeders look at the drive input or the motor current from the table?

 

[iwire]

The input to each VFD gets sized by the input current.

But these are still motor circuits. Do the feeders look at the drive input or the motor current from the table?

:huh::huh:

The feeders are sized per the speed control name plate input current. What am I missing?

 

[petersonra]

:huh::huh:

The feeders are sized per the speed control name plate input current. What am I missing?

the feed to the individual VFD gets sized according to the VFD current.

However, what I have is four of these things in a box. What I am asking is about the feed to the main CB of the box. It seems to me that even though the direct input is to the VFDs that they are still motor circuits, and would need to be calculated accordingly.

 

[Cow]

Did you read 430.122(A)?

I read it as 232.8 x 4 x 1.25=1164 amp feeder ampacity, which looks like a 1200 amp breaker. Then individual OCPD before each drive.

 

[petersonra]

Did you read 430.122(A)?

I read it as 232.8 x 4 x 1.25=1164 amp feeder ampacity, which looks like a 1200 amp breaker. Then individual OCPD before each drive.

It does not say anything in this paragraph about the feeder breaker. Only about the conductors.

 

[Smart $]

It does not say anything in this paragraph about the feeder breaker. Only about the conductors.

That is correct. Part X does not cover feeder SC&GFP. Motor Feeder Short-Circuit and Ground-Fault Protection is covered in Part V. However, none of the references in 430.62 & 63 say anything about conductors sized per Part X... :?

 

[Jraef]

That is correct. Part X does not cover feeder SC&GFP. Motor Feeder Short-Circuit and Ground-Fault Protection is covered in Part V. However, none of the references in 430.62 & 63 say anything about conductors sized per Part X... :?

Under the basic "intended use rule", you should use what the unit says you should use as the SCPD, it's right there in the same chart where you found the current ratings. In this case, each drive would need a 700A TM breaker. If you are using fuses, you can use anywhere from 300-550A dual element time delay.

As to the main that's going to feed them all, that would not follow the motor circuit rules, you are back to it being a main breaker in a cabinet because there are BRANCH breakers below it. In that case the issue of conductor size from 430.122 doesn't come into play. If it were me, I would go with the 700A CBs on each drive and as big of a MCB as I could afford ahead of them, because at 1000A you are flirting with a nuisance trip that will take out all 4 drives if just one of them has a problem. There will not be that much difference in the Inst. setting ranges between an 800AF and a 1000AF (assuming you found one*) MCCB.

* I deal mostly with Eaton breakers, they go from 800AF to 1200AF, so with them, there is no difference in price between a 1000A or a 1200A breaker anyway, it's just a different rating plug.

 

[petersonra]

I have 400A CBs on each VFD right now.

Can't say I ever had one on a VFD trip on me before at all, but with a large VFD like that, maybe making the breakers larger is a good idea. I will have to give that some thought.