Wiring a transformer

[anthracitedub]

I have 3 phase power and I have a transformer. I took two lines from the disconnect to a fuse block to feed my transformer. My secondary lines from the transformer are labeled X1 & X2. I have my desired voltage at this point and I wish to run a small blower motor ([email protected]). I have my X1 going to a fuse before the motor. My question is about the neutral.... all the drawings I find show the Neutral being grounded and then goes on to complete the circuit.

Where do I ground it? To the frame or what. I have my normal earth ground for the motor going back to a ground bar inside the machine panel. Just not sure what/where to tap this neutral to. Anybody know for sure? I know there are a few electrical guys on this site.

FYI this motor is being started by relay logic, so the 120 feeding the motor goes through a relay and not directly to the motor, that way it can be started by control.

[OB Bus]

[jwold]

I'm kind of assuming you're doing some kind of furnace wiring? Perhaps you're wiring a motor that will finally defrost a VW window?

[anthracitedub]

I work in a small shop and there is a piece of equipment that I wanted to install a blower/vac on. The machine is 3 phase and I want to run this blower along with the machine. I don’t want to have to just plug in this vac when using the machine, I want it to come on when the machine turns on. I’ve already wired the control circuit and the transformer, it works... I just don’t have the neutral right. Currently the X2 from the trans just goes to the motor... I don’t think it’s right. I don’t have the circuit in use until I get it sorted though. Every print or diagram I look at shows the neutral being grounded, but I can’t find clear info on where to tap it... I’ve never messed with transformers before.. just need some clarity on the ground/neutral thing.

[cbeck]

Call a real electrician before you electrocute yourself by energizing the equiptment with the nuetral side.
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[PD41]

What is your voltage input ?

277/480 ?

220/440 ?

[PD41]

You can ground it to the xfmr frame depending on the size.
Larger xfmr's sometimes require a ground rod bonded at the xfmr and ground wire running back to the panel. Is the wires in conduit. They also require a small stripped section going through ground bushing where the conduit enters the xfmr.

You want to do it correct for safety. Not just for somebody getting zapped or killed but also fire. No permit and there could be a problem with insurance co if you have a fire.


My buddy lost a huge shop due to a fire. Motorhome, Seadoos and a original Porsche Speedster. Not sure what he was paid for the Speedster but they go for $250,000

According to the U.S. Fire Administration, there are 28,600 electrical fires per year.

I did commercial/industrial electrical for 25 years. I googled the above stats, it is for houses.

[anthracitedub]

It’s 277/480 in and it’s just a small GE 9T55Y55...3kva. I appreciate your input.

[gt1953]

I stuck with low voltage in my career. Glad I did too. That kinda voltage and current will burn and it hurts to.
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[anthracitedub]

I’m using low voltage to turn everything on. I have the 480 going through a disconnect. Two legs are going into a fuse block inside the main panel. These feed the trans which is mounted in an enclosure outside the panel. The reduced single phase 120 then goes back inside to its own fuse. From there it goes into a contactor which has a 24vdc coil. This coil is fed from the machines safety circuit (banner safety). The 120 is then fed from that contactor into another relay that has a 24 vdc coil which is turned on through a timed plc output.

The machine should be turned on, after the safety latch comes in, plc output starts the motor after a programmed 5 seconds... I did this because I plan on running two motors for vacuum. The second motor will come in through its own relay in 5 seconds after the first output times out. I’m staging the start up of these motors because if I turn everything on at once, the amp draw is crazy...about 20. If I start one and let it spool up and then start the other... they only pull about 10 amps running.

Edit... I think I may have figured it out. I went looking at other machines and found one with the same trans installed... the previous guy just ran a ground right from X2 to the back plate of the enclosure...so I may have been over thinking this whole thing.

[PD41]

Good news, most guys never heard of 277/480 but it is very common in the industry. We used to put in many 75 KVA xmfrs. Output on those is 120/208 V.

What kind of shop ?

[anthracitedub]

It’s a small production shop..: just about a dozen pick/place assembly machines for building pressure relief valves. I’ve worked in skilled trades for 20 years... not a licensed electrician, I’m more into control/automation but I tend to do it all. I left the big grinding automotive jobs to hang my hat in a low stress small shop... just easier to balance life this way.

[anthracitedub]

Just wanted to say that I got my circuit all sorted out and it works perfectly. Motor inrush current is ridiculous but I was able to get the proper fuses and everything looks good.

[nsracing]

[anthracitedub]

I got it man 😁... circuit checks out and the neutral is terminated properly. It’s running now and there’s no issue... everything is done properly as far as wire size, terminals and fusing.