Power feed to machinery

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Hello.

I design electrical systems for robot cells. The robot is provided with a 30A breaker that was based on a 200V system. When we get the robot, we add a transformer for use here in the USA. Generally the transformer would be a 10kVA, 480 or 240: 208/120. I will add fuses to the secondary based on the kVA of the robot and a 10A fuse for the single phase secondary. The 30A breaker becomes the primary disconnect for the transformer.

The customer will supply the 480V to the 30A breaker that is on the robot controller. The question is, how is the supply determined? Would I tell the customer to supply 480V suitable for the 10kVA transformer or something else?

The reason for this: We have three different transformers we would supply in a cell based on the size of the robot/external axis. There is a 4kVA, 10kVA, and 18kVA. The 30A breaker does not change. I am tasked with developing a spreadsheet that the salesmen can use to tell the customer what size bus plug or breaker and conductors to install for their robot cell based on robot size, etc.

Thanks for the responses.
 
The robot is 3 phase.

The transformer is installed in a fabricated cabinet that the robot controller sits on top of. Wiring from the outlet of the 30A breaker to the primary of the transformer is 3' max. Wiring from the secondary to fuses is 1' max, and from the fuses it goes back up into the robot controller's high power unit.

120VAC single phase comes from a different secondary winding on the transformer, through a fuse at the transformer and ran out to another enclosure for use for control, etc on the system.

We have been creating the machine label to show the load as the transformer. If it is a 10kVA transformer, the label shows the system as being a 10kVA load.
 

don_resqcapt19

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Illinois
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retired electrician
For the 10 or 18 kVA transformers, just tell the installer that you need a 30 amp, 3 phase, 480 volt circuit. That is assuming that you have transformer secondary overcurrent protection rated at no more than 125% of the transformer secondary current.

It looks like you will need to provide primary overcurrent protection in your equipment if you use the 4 kVA transformer and have the installer provide a 15 amp circuit.

I am a bit confused on what type of transformer you are using based on your statement:
"120VAC single phase comes from a different secondary winding on the transformer,"
 
Thanks for the reply.
All three transformers are custom built and have two secondary windings. So on the 10KVA transformer, 3 phase is supplied in wye configuration - 208 VAC 9KVA. We don't bring the neutral out of the secondary. The terminals are X0, X1, X2, and X3. Nothing connected to X0.

There are two more terminals on the secondary, Y1, and Y2. Y2 is grounded. It is 120V at 1KVA

On the 4KVA I did the calculations awhile back:
Primary current - 4.8A at 480VAC
Secondary current (3KVA) - 8.3A at 208VAC

I am using primary and secondary protection. The 30A breaker on the primary, and we add fuses to the secondary. Based on the table in 450.3(B) I can go to 250% of rated current on the primary and 167% on the secondary.

So 15A standard size ocpd on the primary and 15A on the secondary?

If the customer uses a bus plug for service to the 30A breaker, the fuses in that plug should be 15A? I have no choice on the 30A breaker. That is what comes with the robot.
 
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