Control Transformer Secondary Fusing

[fifty60]

I have a 3KVA transformer that will step a 460V primary down to a 115-230V secondary. Does the NEC limit the number of fuses I can have on my secondary?

I have 2 actuators that will require 10Amps (@ 12VDC derived from a power supply on the secondary), a 230V motor that will draw 3A, and the remaining 115V control circuit which will draw around 5A.

How do I derive the maximum amps for fusing on a mulitple tap secondary? If I use 115V as my secondary I get 26A * 1.25 = 35A CC fuse. But, the entire load of the secondary is not on the 115V tap because I have the motor at 230V. Can I have a 9A fuse for the 115V control circuit, 15A fuse for the actuators, and a 5A fuse for my motor?

 

[augie47]

You need to consider two aspects. As far as transformer protection, look at Art 450.3(B).
If you size the primary protection per the chart (167% of FLA, I believe) , you need not worry about the size of the secondary protection as far as transformer protection.
You also need to take Art 240.21(C) into consideration and protect your conductors as their ampacities.

 

[fifty60]

That's very helpful. Thanks.