Diagnosing overcurrent error on VFD

allamateur · Jun 18, 2023

I have a box powering three 3-phase motors off of one 240V single phase line, NEMA 10-30. In the picture you can see a wiring diagram. The original wiring I had was one box containing all those components. It would cause over-current errors on the right-side (1 HP) VFD when I didn't have fuses installed, and when they were installed it would always pop them as soon as the box was hooked up to the NEMA 10-30 plug.
I have a suspicion that the reason is a ground loop or something similar but I can't see any such loop in the diagram. The common ground is attached to the enclosure box itself.
What's going wrong in this design, and how can I determine that and test it to be sure?

Not being able to see a loop, I decided to add line reactors because they are sometimes recommended to prevent VFDs in parallel from sending each other interference. I also added a MCCB and contactor with control switch so I would have a master on/off at the box. The new components are in a separate box. Does the new design have a ground loop as well? There is an intentionally placed loop in the middle because I am using 10/3 wire and the first box has 2 of those wires going to the 2nd box. If I connect both white/neutrals from the 2 cables to the common ground in the 2nd box, I'll have that loop. If I only connect one, I shouldn't have that. This is a separate question to the main "what's going wrong in the first design?" but does this trivial loop matter?
Thanks.

LeeH · Jun 18, 2023

Looks ok to me, reactors up front (line)
are used if you are very close to the supply transformer, not because you have 2 in parallel so that will not solve your issue. Basically adding impedance. Only used them once where the panel was sited 50m away from the HV/LV supply.

What size and type of fuse does the manual of the VSD state you need?

You need a common ground to the chassis of the VFD from the supply ground. Nothing special required.

allamateur · Jun 18, 2023

LeeH said:
What size and type of fuse does the manual of the VSD state you need?

You need a common ground to the chassis of the VFD from the supply ground. Nothing special required.

The manufacturer of the line reactors (MTE) mentioned they could be used for this type of thing too, but yeah you're right, I knew they weren't strictly necessary (to be fair, neither is most of what's here aside from maybe the fuses). Figured it couldn't hurt.

The fuses are exactly the size and even brand that the VFD calls for, BS88-style British fuses from Eaton-Bussmann. 50FE 50-amps on the large side and 20CT 20-amp fuses on the small VFD side. The system had a common ground when last tested, the test resulted in the usual fuse-popping on the smaller VFD's input side, before the VFD had a chance to power up (neither VFD was ever run, the pop is on start-up).

Could the problem be powering from a NEMA 10-30 and using neutral as ground?

LeeH · Jun 18, 2023

allamateur said:
Could the problem be powering from a NEMA 10-30 and using neutral as ground?

What country are you in? This sound odd.

Edit - I not familiar with your code and I did not fully digest the wiring at 0400 but that would not be allowed here.

W - is this N or your ‘ground’. If the latter it’s switched. If it’s N you should not be connecting that to the chassis.

LeeH · Jun 18, 2023

Drives are 3 phase or 1 phase plus N over here. Never seen a 2 phase input.

allamateur · Jun 18, 2023

LeeH said:
What country are you in? This sound odd.

Edit - I not familiar with your code and I did not fully digest the wiring at 0400 but that would not be allowed here.

W - is this N or your ‘ground’. If the latter it’s switched. If it’s N you should not be connecting that to the chassis.

I am in the U.S. using a grandfathered-in NEMA 10-30 plug, no ground only neutral. I thought such circuits were meant to use the neutral as ground (even though this is very sub-optimal and stopped being code in 1996, I'm stuck with the 10-30 plug).

The VFD manual, https://www.tecowestinghouse.com/Manuals/L510_instruction_manual.pdf, on page 3-11, calls out the input to the VFD as L1 (L) and L3 (N) but I believe the (L)/(N) labels are for 120V models, not 240V as it wouldn't be possible to hit 240V using the neutral on split-phase (I don't have "true" 240V input on one wire, just standard U.S. split-phase) since this would be 120V.

Sorry for my bad labeling, the wires were labelled by color. Black (B) is hot, White (W) is neutral (N), and Red (R) is hot. It may indeed be that these VFDs are meant to be powered by one hot 240V and a neutral, but whenever I've powered one stand-alone VFD from this manufacturer from split-phase power, it has worked perfectly fine.

Megawatt · Jun 18, 2023

allamateur said:
I am in the U.S. using a grandfathered-in NEMA 10-30 plug, no ground only neutral. I thought such circuits were meant to use the neutral as ground (even though this is very sub-optimal and stopped being code in 1996, I'm stuck with the 10-30 plug).

The VFD manual, https://www.tecowestinghouse.com/Manuals/L510_instruction_manual.pdf, on page 3-11, calls out the input to the VFD as L1 (L) and L3 (N) but I believe the (L)/(N) labels are for 120V models, not 240V as it wouldn't be possible to hit 240V using the neutral on split-phase (I don't have "true" 240V input on one wire, just standard U.S. split-phase) since this would be 120V.

Sorry for my bad labeling, the wires were labelled by color. Black (B) is hot, White (W) is neutral (N), and Red (R) is hot. It may indeed be that these VFDs are meant to be powered by one hot 240V and a neutral, but whenever I've powered one stand-alone VFD from this manufacturer from split-phase power, it has worked perfectly fine.

My friend never use the neutral as an equipment ground. Yes all your enclosures should be grounded but never with your neutral. You should be able to go to the source of power feeding your VFD and pull a ground from there. I would think that this is your biggest problem. Good luck

Megawatt · Jun 18, 2023

allamateur said:
I am in the U.S. using a grandfathered-in NEMA 10-30 plug, no ground only neutral. I thought such circuits were meant to use the neutral as ground (even though this is very sub-optimal and stopped being code in 1996, I'm stuck with the 10-30 plug).

The VFD manual, https://www.tecowestinghouse.com/Manuals/L510_instruction_manual.pdf, on page 3-11, calls out the input to the VFD as L1 (L) and L3 (N) but I believe the (L)/(N) labels are for 120V models, not 240V as it wouldn't be possible to hit 240V using the neutral on split-phase (I don't have "true" 240V input on one wire, just standard U.S. split-phase) since this would be 120V.

Sorry for my bad labeling, the wires were labelled by color. Black (B) is hot, White (W) is neutral (N), and Red (R) is hot. It may indeed be that these VFDs are meant to be powered by one hot 240V and a neutral, but whenever I've powered one stand-alone VFD from this manufacturer from split-phase power, it has worked perfectly fine.

You need to replace the 3 prong plug and receptacle to a 4 wire and your problem should go away. Pull a ground wire to your plug and your receptacle.

allamateur · Jun 19, 2023

Megawatt said:
You need to replace the 3 prong plug and receptacle to a 4 wire and your problem should go away. Pull a ground wire to your plug and your receptacle.

Thanks. This may be the entire problem but I can't tell. Should I assume that this wiring scheme (2 VFDs on one 240V line) is impossible to get running without a 4-wire plug? Just for the sake of argument, if I did have a 4-wire hookup, where would the neutral go? The VFDs take hot/hot/ground, same with all the other components. Would I just leave the neutral unconnected in the wire?