Choosing the right VFD protection

[Alexal]

Hi,
I need to choose the right protection for VFD and motor according to UL standard.

Motor: 30kW, 480VAC, In=46.8A

Drive: Sinamics G120P with Power Module PM230 (6SL3223-0DE33-7AA0) - LO 37kW (output 75A, input 70A), HO 30kW (output 60A, input 56A).

I have two questions:

1. According to the manual, Siemens recommend 100A Type J fuses for UL. Is it ok to use 80A protecion? Input current (HO) 56A x 1.25 = 70A.

2. Can I use UL Circuit Breaker instead of Type J Fuses?


Appreciate your help,

Thanks

 

[infinity]

We typically use what the manufacturer recommends. Why do you want to use 80 amp fuses instead of the recommended 100 amp fuses?

 

[Alexal]

Because the main CB is 100A, if I use 100A for VFD I will need to change the main breaker to 125A min.

 

[petersonra]

Because the main CB is 100A, if I use 100A for VFD I will need to change the main breaker to 125A min.

if you have a 100A main, you don't need one on the VFD as well.

 

[iceworm]

...

1. According to the manual, Siemens recommend 100A Type J fuses for UL. Is it ok to use 80A protecion? Input current (HO) 56A x 1.25 = 70A.

2. Can I use UL Circuit Breaker instead of Type J Fuses?


... Because the main CB is 100A, if I use 100A for VFD I will need to change the main breaker to 125A min.

Couple of questions:
What is mandating changing the feeder CB to 125A if you use 100A fuses?

Type J fuses are available in both fast acting and time delay? Which is Siemens specifying?

I understand you don't want to change out the feeder CB. That requires time and money. And I think I understand (but, maybe not) you want the CB/fuse to coordinate.

So, recommend: Personal opinion (see signature line)

Lay out the TCC curves see exactly where they overlap. You don't have to have ETAP or SKM. Just tape them up on a window. This way you will know what you are dealing with as far as the coordination goes.

It wouldn't matter which opened first, the VFD fuse or the feeder CB. If either open, you have a problem to T-Shoot. Ease of resetting a CB over replacing $150 in fuses doesn't matter. With the information we have, I would tend to leave the feeder at 100A, and use the 100A type J ( TD or fast acting, as specified)

 

[Alexal]

But the main breaker is for the panel (besides VFD I have other loads / branch circuits). The main breaker is part of feeder circuit... am I wrong?

 

[iceworm]

But the main breaker is for the panel (besides VFD I have other loads / branch circuits). The main breaker is part of feeder circuit... am I wrong?

Okay, you left me confused.
Draw out the one line.

Panel with 100A main
Panel CBs feeding other loads on panel
Panel CB - feeder to VFD (we don't know what this is)

conductors to VD
Type J fuses in VFD (MFG specified as 100A type J)​

You are adding 50 to 75A load on a 100A panel
Highly recommend a load study on the panel loads, panel feeder. From what you are saying, there may not be enough headroom to feed the VFD.

 

[Alexal]

Okay, you left me confused.
Draw out the one line.

Panel with 100A main
Panel CBs feeding other loads on panel
Panel CB - feeder to VFD (we don't know what this is)

conductors to VD
Type J fuses in VFD (MFG specified as 100A type J)​

You are adding 50 to 75A load on a 100A panel
Highly recommend a load study on the panel loads, panel feeder. From what you are saying, there may not be enough headroom to feed the VFD.

Changed main CB to 125A

 

[iceworm]

That looks pretty good
Curiosity Q: Does the drive get the Type J fuses? If so, does Siemens specify fast or TD? Doesn't matter much - just curious.

Caution note - if you are under the NEC:
430 Part X, 430.122, conductors supplying power to the drive have to be sized at 125% of the rated drive input. Even if the motor load is smaller that the drive rating - size the conductors for the drive.

 

[Besoeker3]

Hi,
I need to choose the right protection for VFD and motor according to UL standard.

Motor: 30kW, 480VAC, In=46.8A

Drive: Sinamics G120P with Power Module PM230 (6SL3223-0DE33-7AA0) - LO 37kW (output 75A, input 70A), HO 30kW (output 60A, input 56A).

I have two questions:

1. According to the manual, Siemens recommend 100A Type J fuses for UL. Is it ok to use 80A protecion? Input current (HO) 56A x 1.25 = 70A.

2. Can I use UL Circuit Breaker instead of Type J Fuses?


Appreciate your help,

Thanks

I'd have been happy with 80A fuses.

 

[Alexal]

That looks pretty good
Curiosity Q: Does the drive get the Type J fuses? If so, does Siemens specify fast or TD? Doesn't matter much - just curious.

Caution note - if you are under the NEC:
430 Part X, 430.122, conductors supplying power to the drive have to be sized at 125% of the rated drive input. Even if the motor load is smaller that the drive rating - size the conductors for the drive.

Siemens does not specify FA or TD, just type J and value.
Anyway, I will use circuit breaker for VFD protection instead.

Regarding conductors size, I chose 2AWG for VFD LINE and 4AWG for VFD LOAD.
Thanks

 

[infinity]

With an input current of 46.8 amps you could use #6 conductors to feed the drive. (46.8*125% = 58.5amps)

 

[Alexal]

With an input current of 46.8 amps you could use #6 conductors to feed the drive. (46.8*125% = 58.5amps)

46.8A is a motor's rated current.
Input current of the VFD is 70A (70*1.25=87.5A) - 2AWG

 

[infinity]

46.8A is a motor's rated current.
Input current of the VFD is 70A (70*1.25=87.5A) - 2AWG

Oops, yes you did say that in the OP. Sorry for the mix up. :ashamed1:

#3 THHN is good for 100 amps.

 

[Jraef]

If the drive says that you need Class J fuses per their UL listing and does not say you can use circuit breakers as an alternate, using the CB alone means you are not using it in the manner intended by the manufacturer and therefore violating the NEC.

Looked at the other way, the only way you can use a CB alone is if the drive mfr specifically states that this is an approved option. Some drive mfrs do, some do not. Almost any drive will pass the UL SCCR listing requirements when protected by current limiting fuses, but not all designs will pass with CBs alone, and some mfrs are unwilling to do the expensive destructive testing only to find out they will not pass. So they “bury the lead” in their installation/technical documents by simply stating that fuses work. As a general rule, if a mfr has gone to the risk and extreme expense of getting their drive UL listed behind CBs alone, they make that very clear because it gives them an advantage in the market over those that do not.

If you don’t feel this is stated clearly enough for you in the Siemens instruction manual, you should ask them for a specific response in writing to clear it up.

 

[Alexal]

If the drive says that you need Class J fuses per their UL listing and does not say you can use circuit breakers as an alternate, using the CB alone means you are not using it in the manner intended by the manufacturer and therefore violating the NEC.

Looked at the other way, the only way you can use a CB alone is if the drive mfr specifically states that this is an approved option. Some drive mfrs do, some do not. Almost any drive will pass the UL SCCR listing requirements when protected by current limiting fuses, but not all designs will pass with CBs alone, and some mfrs are unwilling to do the expensive destructive testing only to find out they will not pass. So they “bury the lead” in their installation/technical documents by simply stating that fuses work. As a general rule, if a mfr has gone to the risk and extreme expense of getting their drive UL listed behind CBs alone, they make that very clear because it gives them an advantage in the market over those that do not.

If you don’t feel this is stated clearly enough for you in the Siemens instruction manual, you should ask them for a specific response in writing to clear it up.

Got it,
Thanks