Single Phase Transformer Secondary Options

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westgbazo

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Location
MI
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EE
Hello, I'm specifying a single phase, dual-secondary, 480-120/240V 1000VA transformer in a control panel.

We have a 240V heat exchanger and a 120V convenience receptacle to power. Can we serve both from this transformer? Looking at a SquareD catalog #: 9070T1000D31.

Thanks in advance!
 
What are you powering? At 1000VA , you have a little more than 4A at 240V and a little over 8A at 120V. That transformer can give you both voltages but little useable current.
 
BillyMac59 said:
What are you powering? At 1000VA , you have a little more than 4A at 240V and a little over 8A at 120V. That transformer can give you both voltages but little useable current.
Click to expand...

And on top of this, for the purpose of the OP, your _total_ load is limited to about 4A; meaning that if the 240V heat exchanger uses 2A, you will only be able to plug in a 2A load on that convenience receptacle. Perfectly fine if the heat exchanger only needs a couple of amps and the receptacle is used for powering a laptop, problematic if an HVAC tech plugs a vacuum pump into that receptacle. I recommend labeling the receptacle with the maximum load it can serve.

(If the receptacle is actually a _duplex_ receptacle, you could put each opening on a separate leg of the transformer to distribute the load, but you still have the limit of 4A total, meaning the sum of the 240V load plus the larger 120V load.)

So to the general question of 'can this transformer power both 120V and 240V loads at the same time?' Yes.

To the specific question of 'is this transformer large enough for the loads I wish to power?' You need to describe what loads will be powered.
 
The transformer sizing was not my main concern but the 240V heat exchanger will only draw 0.14A. The receptacle will be limited to light loads for programmers laptop, etc.

Schneider Electric's tech support is telling me 120V AND 240V is not possible due to the jumper configurations that are required.

In their catalog, this is what they're referring to:
1743685822231.png
But to the point a few of you have made, if you jumper X2 and X3, this is essentially the same as a single phase 240V panel. Which means I could connect to X1 or X4 and X2/X3 to derive 120V.
 
westgbazo said:
But to the point a few of you have made, if you jumper X2 and X3, this is essentially the same as a single phase 240V panel. Which means I could connect to X1 or X4 and X2/X3 to derive 120V.
Click to expand...

Exactly. You connect X1-Hot, X4-Hot, X2/X3-Neutral/Ground, and you get a 120/240V supply.

Perhaps they were trying to communicate that connected this way you can only have a maximum of 500VA 120V load, not the full 1000VA to a _single_ 120V load.
 
westgbazo said:
The transformer sizing was not my main concern but the 240V heat exchanger will only draw 0.14A. The receptacle will be limited to light loads for programmers laptop, etc.

Schneider Electric's tech support is telling me 120V AND 240V is not possible due to the jumper configurations that are required.

In their catalog, this is what they're referring to:
View attachment 2576531
But to the point a few of you have made, if you jumper X2 and X3, this is essentially the same as a single phase 240V panel. Which means I could connect to X1 or X4 and X2/X3 to derive 120V.
Click to expand...
There is a problem in their table, it does not included any of the load connections, so it is hard to see that a neutral point does exist when X2 is jumpered to X3.

The ANSI voltage connection shown in columns 2 and 3 show single voltage connections as an "X" and multiple voltages as a "/". So their voltage code D31 provides 3-wire outputs, while D55 only provides 2-wire ones.
 
Last edited:
The industry standard convention is:
An 'X' means either of the single voltages is available based on the winding configuration. In your example 120V or 240V 2 wire
A "/" means either or both of the voltages are available based on the winding configuration. In your example 120V or 240V 2-wire or 120/240V 3-wire.

It appears the bottom half over the table was repeated verbatim in the top half.
 
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