Wiring a 220v to 460v step up transformer for HLV-H

Hi, I am in the process of wiring up my HLV-H and it is a 460v machine. I have opted for the set up transformer since it was the cheapest and easiest route. The transformer will be hard wired to the machine and I will run the machine off my rotary phase converter.

I am having a bit of trouble understanding how I am supposed to wire the transformer properly and I have not been able to find an explanation on the internet.

For the input, I have wired my three phases to X1, X2 and X3 and have also attached the #3 wire since it is a 220v input. I believe this is correct.

I however am not sure on how to wire the three outputs. At the moment I have connected the three output wire to H1, H2 and H3 but I am not sure what to do with the H0 wire if it is even needed or what else I need to do. I also am not sure what I means by Line-Line for 460V and Line-Neutral for 266v.

Any help is appreciated and I hope I was able to explain this well enough. I have attached a picture of the transformer tag.

Thanks,

-Chris

I need to do the same thing for a Haas lathe I got today. Sorry I cant help you with the correct wiring but may I ask where you got your transformer?

Neutral on your output would be H0. I believe just tape this off. You don’t need it. Connect your machine to H1,H2,H3. And it’s good to check the voltage at the machine to make sure you got what you want before turning anything on.

Thank you for the replies! I figured that I probably would not use the H0 since the previous user had just taped it off. I will also make sure to check voltages.

Special thanks to Thermite for the info! Seems like you reply to every one of my posts

I purchased the transformer from HGR industrial in Ohio. The thing weighs 100 lbs and I paid $70 for it so I paid less than shipping would have been. Took me a bit of searching for it since most of their transformers and 110v output or single phase transformers.

thermite said:

So for my one, the "re-derived" or local Neutral IS Earthed.
....

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This is an isolation transformer, so by code the secondary is a 'separately derived service' and as such, the H0 center point on the windings needs to be bonded to ground.

jim rozen said:

This is an isolation transformer, so by code the secondary is a 'separately derived service' and as such, the H0 center point on the windings needs to be bonded to ground.

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That is true if you are supplying a "branch circuit". If the transformer is part of a machine, there is no such NEC requirement. UL may have requirements on construction of a transformer used that way, but not the NEC.

However, the NEC DOES have requirements on a transformer used "in reverse" as this one is going to be. The transformer has to be "identified for that use" by the manufacturer, and be either so marked, or have a published declaration of that. Many are, but not all.

That requirement is widely ignored, but it exists. Again, it only applies if the transformer is used in an NEC controlled installation, meaning hard-wired to building wiring (and in the USA). If plug-connected, it is not covered by the NEC.

JST said:

... If the transformer is part of a machine, there is no such NEC requirement. ....

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It's common (good IMO) practice for machine manufacturers to bond secondaries of isolation transformers. One reason is to prevent the secondary circuit from becoming live with respect to ground in the event of a fault with the primary wiring in the machine, or for that matter, if there is a fault *in* the transformer itself. In this case the secondary could become overall live at 460 volts with respect to ground.

jim rozen said:

It's common (good IMO) practice for machine manufacturers to bond secondaries of isolation transformers. One reason is to prevent the secondary circuit from becoming live with respect to ground in the event of a fault with the primary wiring in the machine, or for that matter, if there is a fault *in* the transformer itself. In this case the secondary could become overall live at 460 volts with respect to ground.

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Sure.

However, in some cases it is desirable to NOT have the particular winding hard grounded, as part of the design of the device. In that case, it is possible to monitor the winding so as to detect it becoming grounded, which then can shut the machine off.

Otherwise, it may be necessary to use a double-insulated (special) transformer which is accepted as an isolation transformer.

Any product which has a two pin plug (there are a vast number of them) uses such a transformer if there are any accessible parts. The common "wall wart" power supply is one such that is commonly seen.

There are machines which require isolated windings as well.

JST said:

However, in some cases it is desirable to NOT have the particular winding hard grounded, ....

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In this *particular* application, should it be bonded or isolated, as best practice?

Those low voltage supplies are, well, extra low voltage. And double insulated or with an earthed screen between the primary and secondary. They meet the requirements of SELV.

Yes, some mains-voltage gear uses an isolated/floating supply. Generally only very critical stuff with ground-fault monitoring. PV arrays typically are floating as this allows you to detect earth leakage from any point, along with things like distribution systems on ships. But again, with ground-fault monitoring.

For everything else, bond something.

jim rozen said:

In this *particular* application, should it be bonded or isolated, as best practice?

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It's an option, as it is not a branch circuit. If you can, then ground it. There is no particular reason not to, here.

It would not be the end of the world if it were NOT grounded. The motor is comfortably rated above the source voltage. So there is no bad thing that we know of to happen if one side were grounded or the primary shorted through. The wires are insulated, they and the motor can stand the voltage to ground, no whoopee.

But, with no reason not to, just do it. Basically because most will expect that.

Why is it done?

The normal assumption with a transformer supplying mains power, is that the output voltage is less than the input. In that case, the devices connected to that output almost certainly are not rated for the primary side voltage to ground. They may be damaged, and are probably unsafe, if the primary side voltage breaks through to the secondary. That is the main threat.

Here, the motor will laugh at 230V, it is rated for 575V. So is every other part of the machine. It can take 350VAC to ground (Hot to neutral for 600V class machinery).

Your house has 240V, which is 120V to ground. All the powered things and wiring in the house is rated for that. The voltage on the other side of the transformer is likely to be 4160V or 7200V. If that gets through the transformer, bad things will happen. I have seen them, they were bad.

Grounding the secondary may help keep that from being really very bad. It should pop the transformer fuse quickly, and the grounding (connection to grounded neutral) is intended to keep the voltage from being the full 4160V, etc.

.

JST said:

.. The voltage on the other side of the transformer is likely to be 4160V or 7200V. ...
.

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Around here it's 13.8 KV.

alcro1998 said:

For the input, I have wired my three phases to X1, X2 and X3 and have also attached the #3 wire since it is a 220v input. I believe this is correct.

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Measure your input source. I would have to use #2 wire because in sunny Kaliforniya it's 230V and sometimes higher. That's just the 230V single phase input utility.

What is actually coming out of your RPC setup might be a little different depending on your balancing. I would think using #3 is not going to be correct.
I measured my incoming 230V single phase and it is a hefty 249V at this time in the morning.

(Maybe it will stabilize to around 230V when all the other neighbors turn on their machine control centers)

alcro1998 said:

I however am not sure on how to wire the three outputs. At the moment I have connected the three output wire to H1, H2 and H3 but I am not sure what to do with the H0 wire if it is even needed or what else I need to do. I also am not sure what I means by Line-Line for 460V and Line-Neutral for 266v.

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Give H0 a study. I would probably not connect it. But I would have a good reason not to. You can look at other transformer hook-ups on the internet
and decide how much of the code you can take.

Line-Line - the two potential points being measured are "this line" & "another line". H2 & H1, or H1 & H3, or H2 & H3.

Line-Neutral - Any one of H1 or H2 or H3 as one point. The second point is H0 (Neutral).

thermite said:

Is there any pressing reason to NOT Earth it? No? Then Earth the sumbich! How hard WAS that?

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You're not paying attention:

===================
This is an isolation transformer, so by code the secondary is a 'separately derived service' and as such, the H0 center point on the windings needs to be bonded to ground.
======================

Maybe you were too busy cleaning the brown off your nose to see what was posted above....

jim rozen said:

You're not paying attention:

===================
This is an isolation transformer, so by code the secondary is a 'separately derived service' and as such, the H0 center point on the windings needs to be bonded to ground.
======================

...................

Click to expand...

True for a branch circuit. Not a "requirement" for an individual machine, but certainly no reason not to do it in general.

Arnold S. in Predator... "DO IT, DO IT NOW".

Over-protect and over-kill, if it is not going to be a great expense. Only live once. But a burnt up project can be done over and over again until it's right.

Unless you have a voltage-operated ground-fault relay, there are basically no reasons to want an isolated secondary.

There are plenty of reasons to want a grounded secondary.

Grounding the secondary is going to take two lugs and a foot of cable (if that).

Seems like a no-brainer to me.

Once you get it wired up turn on the power and stand by your machine with bare feet on the DRY concrete floor.
Turn on power and touch the machine with your hands. If you feel a slight tingle in your feet then some current is moving.
Happened to me, reason the green ground wire was not attached.

Yeah I’ll make sure to ground everything properly. I pretty much have it all figured out at the moment and just need to finish up a little bit of wiring this weekend.

I checked the voltage of my supply to the RPC a bit ago and if I remember correctly it was a real 220v but I’ll check again. I will also check the output of the RPC since I have not done that before.

Thank you for all the replies!