Wiring questions on 240 - 480 Transformer

Hi,

I have a new Martin shaper coming that requires 480 - 3ph power for a 7.5kva motor. From what I am reading the Martin has L1, L2, L3 and Ground, whereby the L1-3 are where I connect the 480v 3-ph power to.

I purchased a new Maddox 3 - Phase 240V to 480 Y 277 Step up transformer and have a couple of quick questions. SKU MIT-DRY-139

I'm stepping up power from a Phase Perfect unit, so I have 3 hot leads and 1 ground from the PP unit to connect to the transformer at X1, X2, X3 and the Case ground.
The input voltage reported by the Phase Perfect is 246v and the output on each of my phases is 246/244/246.

Questions:

1. Regarding ground to the machine, the Transformer has H0, H1, H2, H3. Should I connect the ground wire from the Martin to the H0, and then add another wire from the case ground to H0? Reading on a variety of posts it is not clear on this item. I understand that I would connect H1,H2 and H3 to their respective L1/L3/L3 on the Martin.

2. The voltage from my phase perfect is slightly high i.e. 246. Should I move the transformer taps from #3 240v to #2 246v? Not sure if this is even necessary or just leave the taps at their current #3 position.

3. I have a spool of 10ga 4 conductor wire I use for my 240 - 3Ph machines, if I am reading my amp conversion formula's right, I should not draw more than 30A from the transformer to the machine at 7.5kva so that wire I'm assuming would be fine. I'll use a higher gauge to connect the transformer to the Phase Perfect unit.

Here are pictures of the unit and the label.




Thanks for any help.

Isolation transformer grounding.

Your transformer case should be grounded with the equipment ground wire from your Phase Perfect, for starters. This will will provide a fault current path back to the 1Φ source, should a fault develop in your transformer input or supply wiring.

The input of your transformer requires overcurrent protection at 125% of it's input rating, 15KVA = 36A @240V x 1.25 = 45A. #6AWG @ 60C or #8 @75C wire size.

The secondary 480V side is an isolated coil and also needs to be grounded. The XO terminal should be connected to the case ground. And the NEC requires a grounding electrode system, this could be two 8' ground rods connected with a #6AWG Cu, or structural steel of the building, or underground metallic cold water pipe, 5' from where it enters the building. Can also use the existing grounding electrodes (rods) that serve the existing service. But it needs to be connected to the earth, for you and your machine safety, as well as meet the NEC standard.

The output of the transformer should have overcurrent protection as well. 15KVA @ 480V = 18.04A, 18 x 1.25 = 22.5A, so it should be protected at the next size up @25A. A 30A 600V fused switch, would be a good choice.

On adjusting the tap voltage. if your 6V high on the input, likely you will be 12V high on the output. Most equipment should operate OK on +/- 10%, 480 x 1.1 = 528V as an upper limit. I don't know anything about your shaper.

For the wire size, 18A is your 480V maximum output, so your #10 AWG is sufficient.

SAF Ω

If the H0 is not connected to ground at the transformer then ground it to the case someplace. Also connect the Green wire of the line leading to your planer and connect the green wire to the frame. You can use it for single phase but understand it will be 277VAC. But if you do use the "ground" to operate lights you can't use the ground (green wire)and will have to run a 4th wire (Grey)for a neutral. Ground can not be used to carry current!
10 seems a little lite for the 240 side. Not sure where you see 30A but I see 36Amps! How far are you running the 240vac connection?
Old code used brown, yellow and orange and 480VAC wire color and Gray as the neutral. Green is always ground. But new code lets you choose the color code.

To recap:

Ground from Phase Perfect to Transformer Case and then Ground HO terminal to the case as well.
Ground from Transformer Case to the Martin Shaper.

6avg is what I was planning from Phase Perfect to the Transformer.
10avg from the Transformer to the machine as the 7.5kva should not draw more than 30A.

The output from the Phase Perfect actually goes into a separate panel, and I have an available 50A circuit breaker in that panel ready to wire to the Transformer, this is where I'll use the 6avg wire to connect to the transformer.

I'll look into another fuse panel after the transformer with a 30A fused switch, I'm assuming something along the lines of Square D HU361RB 3 Pole 600V safety switch will work.

You didn't mention anything about an earth reference ground, on the output side of the transformer.

It's a NEC code requirement, and in the lightning capitol state, you may one day wish you had.

SAF Ω

I saw the extra grounding requirement you listed. My shop is located in an area with underground electric. Next to my shop is a big green metal box from the utility company with wires directly to my 400A service along with a ground wire...

Do I still need another grounding source besides that which is provided by the electric company?

All ground should be hard wired, it just can't be used to carry current. 240VAC supply to the transformer should be 4 wire, one being ground and attach it to the frame. Old school used either rigid or EMT as a ground but that has been ended. Bare wire is OK but you should have continuous wired ground. If anything for your protection. So just because the power company has a ground connection you should also connect a ground. Simply put if you have a ground yet it becomes disconnected as I'm sure you have seen EMT pulled out of the connector (when conduit was considered ground) and someplace a short happens connecting the "Hot" line to ground the entire ground circuit will become hot up to that disconnection. The main disconnect on the building should have a ground rod and connected to the ground buss. You can simply connect grounds to that buss/terminal strip