Sizing 400V Equipment Help

M

mikev86

Member
Location
Easton, MD
Occupation
Electrical Designer
Hello,

I am looking for some guidance in sizing conductors for a piece of equipment coming from overseas. Main switch for the equipment is rated at 400A at 400V. (integral control panel with fuses).

There is a 480V Square D QED style switchboard that feeds a terminal box on a piece of bus duct (800A breaker in the MSB). Terminal box will go to a zig-zag transformer with a primary voltage of 480V delta and a secondary voltage of 400V zigzag + neutral (see attached photo). I am being asked to help size the terminal box, conductors from terminal box to transformer, and conductors on the secondary side of the transformer to the new equipment control panel.

Terminal box to transformer will be ~15' and transformer to equipment will be ~5'.

My thoughts below:
  • 350A terminal box.
  • (2) sets of 2/0AWG CU phase conductors + 3AWG CU grounding conductor to the transformer in 2" conduits (assuming worst case since we do not have MCA on equipment).
  • Customer supplied 280kVA transformer.
  • (2) sets of 3/0AWG CU phase conductors, (1) 3/0AWG CU neutral, + (1) 2AWG CU grounding conductor in 2" conduits.
Any input and direction would be greatly appreciated as I have not worked with this equipment before.

Thank you,
Mike
 

Attachments

  • 280kVA ZigZag.jpg
    280kVA ZigZag.jpg
    83.1 KB · Views: 14
Besoeker3 said:
Hi Mike. If the kit is from 400V it may intended for 50Hz - possibly for EU.?
Click to expand...
Thank you! I will ask for additional clarification. Our warehouse in MD does have a converter to change from 60Hz to 50Hz for some equipment, so I will check and see if the warehouse in AR has (or needs) something similar.
 
For purposes of OCPD and grounding, treat this transformer as a standard delta-wye unit.

The 'zig-zag' in this case is just a different relative phase shift from primary to secondary. I'm curious why a zig-zag was used, but it might simply be a case of 'what we had on the shelf'.

Remember that each conduit in a parallel set must be electrically similar, meaning the same number and type of phases and neutral in each conduit.

Are you treating the 800A breaker as the transformer primary OCPD? And the 400A in the equipment as transformer secondary OCPD?

-Jonathan
 
mikev86 said:
Hello,

I am looking for some guidance in sizing conductors for a piece of equipment coming from overseas. Main switch for the equipment is rated at 400A at 400V. (integral control panel with fuses).

There is a 480V Square D QED style switchboard that feeds a terminal box on a piece of bus duct (800A breaker in the MSB). Terminal box will go to a zig-zag transformer with a primary voltage of 480V delta and a secondary voltage of 400V zigzag + neutral (see attached photo).
Click to expand...
I am just curious why a zig zag transformer and why the 400V?
Just like here we have 460V motor nameplates (or even 440 if you go way back) and use a 480V transformers we call it a 480/277V nominal system,
for a 380 - 400V motor (or other load) I'd just use a delta/wye 416V transformer and call it a 416/240V nominal system.
For the 400V side color code I'd suggest using blue / yellow / red for the phases and white neutral as the IEC colors require special permission.

mikev86 said:
I am being asked to help size the terminal box, conductors from terminal box to transformer, and conductors on the secondary side of the transformer to the new equipment control panel.

Terminal box to transformer will be ~15' and transformer to equipment will be ~5'.

My thoughts below:
  • 350A terminal box.
  • (2) sets of 2/0AWG CU phase conductors + 3AWG CU grounding conductor to the transformer in 2" conduits (assuming worst case since we do not have MCA on equipment).
  • Customer supplied 280kVA transformer.
  • (2) sets of 3/0AWG CU phase conductors, (1) 3/0AWG CU neutral, + (1) 2AWG CU grounding conductor in 2" conduits.
Any input and direction would be greatly appreciated as I have not worked with this equipment before.

Thank you,
Mike
Click to expand...
So is the 350A terminal box protected by a 800A breaker? If yes presuming the terminal box can be considered a feeder tap under 360.17(C) Exception No. 1 the phase conductor sizes look ok and If the other tap rules in 240.21(B)(3) like the 25' limit are met that seems good to me.
But if these are tap conductors I believe your #3 EGC with the tap conductors needs sized according to the 800 amp OCPD as a 1/0 CU, per 250.122(G) and (F)
 
The equipment manufacturer is not from North America. They are probably using power systems and transformers that are local to them.

Wye transformers are great for when you need L-N loads.
Zig-Zag transformers are great for L-G fault management where L-N loading is not used.
 
The voltage does not matter when sizing conductors. There are rules about sizing feeders in the code. Likely the ampacity required won't exceed the 400 Amp rating of the switch being supplied so no reason not to plane on something like 400 Amp of ampacity

Two 3/0 copper should cover it.
 
winnie said:
For purposes of OCPD and grounding, treat this transformer as a standard delta-wye unit.

The 'zig-zag' in this case is just a different relative phase shift from primary to secondary. I'm curious why a zig-zag was used, but it might simply be a case of 'what we had on the shelf'.

Remember that each conduit in a parallel set must be electrically similar, meaning the same number and type of phases and neutral in each conduit.

Are you treating the 800A breaker as the transformer primary OCPD? And the 400A in the equipment as transformer secondary OCPD?

-Jonathan
Click to expand...
Hi Jonathan,

Thank you for your response, it is appreciated. My thoughts were to treat the terminal box as the primary OCPD (but I am not very familiar with using bus duct) and correct, the 400A in the equipment as the transformer secondary OCPD.

-Mike
 
tortuga said:
I am just curious why a zig zag transformer and why the 400V?
Just like here we have 460V motor nameplates (or even 440 if you go way back) and use a 480V transformers we call it a 480/277V nominal system,
for a 380 - 400V motor (or other load) I'd just use a delta/wye 416V transformer and call it a 416/240V nominal system.
For the 400V side color code I'd suggest using blue / yellow / red for the phases and white neutral as the IEC colors require special permission.


So is the 350A terminal box protected by a 800A breaker? If yes presuming the terminal box can be considered a feeder tap under 360.17(C) Exception No. 1 the phase conductor sizes look ok and If the other tap rules in 240.21(B)(3) like the 25' limit are met that seems good to me.
But if these are tap conductors I believe your #3 EGC with the tap conductors needs sized according to the 800 amp OCPD as a 1/0 CU, per 250.122(G) and (F)
Click to expand...
Thank you so much for the quick response, it is appreciated. Regarding the zig zag transformer, I was only recently brought into conversations and given a photo of the nameplate. I can't speak as to why that was chosen, but it is my understanding it is already on site.

Please see attached for a nameplate for the equipment that I just received.

I will need to request additional information on the bus duct. I have asked for clarification if the 800A breaker in the MSB feeds the bus duct and if there are just multiple taps. Please see attached for what I was given.

Is there any harm in providing a 1/0AWG CU EGC if the terminal box is a feeder tap? I don't necessarily want to oversize, but I have a feeling I will be hard pressed to get all of the information.

Thank you,
Mike
 

Attachments

  • Nameplate.jpg
    Nameplate.jpg
    77 KB · Views: 7
  • BusDuct.jpg
    BusDuct.jpg
    77.6 KB · Views: 7
mikev86 said:
Hello,

I am hoping 60Hz. As far as I can tell from the nameplate, the new equipment can operate at either, but I am still awaiting confirmation.

Thank you,
Mike
Click to expand...
The reply I just received said we are good at 60Hz and we can run without a frequency converter.
Thank you!
 
mikev86 said:
Hello,

I am hoping 60Hz. As far as I can tell from the nameplate, the new equipment can operate at either, but I am still awaiting confirmation.
Click to expand...
Thanks Mike. Yes. a lot of equipment can be dual voltage. Motors, not always....
 
You must log in or register to reply here.
Top