VFD line side fuse or bkr

[hhsting]

Attached sketch shows 800A fdr bkr feeding 800A bus duct. At 5th floor the bus duct ends however before it ends 5th floor their is Disco #1. The Disco #1 feeds 3#2/0 + 1#6 Gnd feeder which feeds VFD controller and then to 3 phase chiller more than 25 feet away. Disco #1 is non fuse.

Following questions:

1. Disco #1 should it be fuse or non fuse? I suspect fuse due to feeder taps but not sure.

2. Disco #1 if fused then line side of VFD should it be fuse or bkr?

3. What size fuse Disco#1 on VFD MOCP or feeder size?

4. Would feeder to VFD from Disco #1 require neutral?

 

[Besoeker3]

We fed ours with a fused switch, usually an ABB OESA

https://library.e.abb.com/public/a684eea27ecc6a2ec1256c5500269533/OESA2DIN%20GB%2099-12.pdf

 

[petersonra]

Attached sketch shows 800A fdr bkr feeding 800A bus duct. At 5th floor the bus duct ends however before it ends 5th floor their is Disco #1. The Disco #1 feeds 3#2/0 + 1#6 Gnd feeder which feeds VFD controller and then to 3 phase chiller more than 25 feet away. Disco #1 is non fuse.

Following questions:

1. Disco #1 should it be fuse or non fuse? I suspect fuse due to feeder taps but not sure.

2. Disco #1 if fused then line side of VFD should it be fuse or bkr?

3. What size fuse Disco#1 on VFD MOCP or feeder size?

4. Would feeder to VFD from Disco #1 require neutral?

1. Its a tap so needs ocpd.
2. Can be either. in most cases not required at all if disc 1 is fused and selected appropriately.
3. Look in manual for vfd.
4. No. Unless there is some piece of info you left out.

 

[Jraef]

1. Its a tap so needs ocpd.
2. Can be either. in most cases not required at all if disc 1 is fused and selected appropriately.
3. Look in manual for vfd.
4. No. Unless there is some piece of info you left out.

I think #2 should be look in the VFD manual as well, it should tell you the maximum size OCPD required for the VFD. If it is less than 800A, you would need to add another OCPD at the VFD. If not, you might be able to use the NF disconnect if the bus duct is just being used as a substitute for wire, meaning nothing else is tapped off of it (maybe).

... Unless the VFD has another set of Branch OCPD rated fuses inside (some larger VFDs may have fuses inside, but they will tell you that they are NOT listed as Branch OCPDs).

But side note to that disconnect #1, without the fuses most NF disconnect switches have a maximum SCCR of 10kA and on an 800A feed, it's likely that your available fault current is going to be higher than that. So it may all be moot, I would just put in a Fused Disconnect with fuses sized as per the VFD manual and be safe.