120 to 480??

[Praedatus1]

Hi, I work in the oilfields and my boss wants us to use a 480-120 transformer, wire it backwards and feed a cathodics testing box. He wants us to use 120v feeder to secondarys and get 480 to power the cathodics testing receptacle. Will this work? I need 2 phases 480 to work the cathodics. I was thinking it wont work since I am only starting with 1 phase (120)...? Also, is this safe?? Our cathodics load is very small, like <.2a
Thank you!
Tim (journeyman)

 

[haskindm]

If you have 120-volts available, do you also have 240-volts available?
240 to 480 volt transformer should be easy to find.

 

[Praedatus1]

The only one we could find was 120 secondary and 240-480 primary

 

[kingpb]

This should work using a 480 -120/240V transformer

 

[Joethemechanic]

I need 2 phases 480 to work the cathodics.

Please clarify,

You need 2-phase?

you need 2 phase conductors off a 3-phase 480 source?

 

[Praedatus1]

Yes, I know its called single phase 480, but I wanted to clarify that its not 3 phase 480. Thank you for all your input!

 

[Joethemechanic]

If all you need is single phase 480, as long as your transformer, and whatever cord you are using is of enough capacity, you are fine

 

[infinity]

Just curious as to how or if you would ground the 480 volt secondary?

 

[Besoeker]

Just curious as to how or if you would ground the 480 volt secondary?

Tie one side to ground and call it the grounded conductor?

 

[Joethemechanic]

Tie one side to ground and call it the grounded conductor?

No worse than a corner grounded 480V delta

 

[kwired]

If the transformer has 240/480 capabilities I would likely ground the center tap and therefore lower voltage to ground.

Grounding one line is your only choice for a two wire output.

 

[Besoeker]

No worse than a corner grounded 480V delta

And probably better than having no ground at all.
Maybe an earth (ground) leakage detection system using a core balance CT would be another option but more complex and more costly.

 

[rbalex]

While Besoeker's option is permissible, which condition in 250.20(B) would you apply to require it? It is a separately derived system, so 250.30 (B) applies but it doesn't require either of the 480V legs to be grounded.

 

[Joethemechanic]

Yeah, if this is a 120 V control transformer that he is backfeeding it most likely is 240/480 on the higher voltage side and would have a center tap.

 

[templdl]

As I read all of the post one thing that appears to have been oveerlooked was the VA required. Smaller MT type transformers do not have a exact 4:1 winding ratio but a slightly higher secondary ratio, that is a bit highter than 1. If 480v is applied you will get a slightly higher than out. This is because of how a MT transformer is applied and the way if is loaded to provide better regulation. As such if you input 120 in the LV side the HV out will be less than 480v.

 

[Joethemechanic]

As I read all of the post one thing that appears to have been oveerlooked was the VA required. Smaller MT type transformers do not have a exact 4:1 winding ratio but a slightly higher secondary ratio, that is a bit highter than 1. If 480v is applied you will get a slightly higher than out. This is because of how a MT transformer is applied and the way if is loaded to provide better regulation. As such if you input 120 in the LV side the HV out will be less than 480v.

440,,,,,,,,,,,,460,,,,,,,,,,,,,,,,,,,,480,,,,,,,,,,,,,,,,481, most times it really don't matter much, `Long as I'm getting my money come friday

 

[Besoeker]

As I read all of the post one thing that appears to have been oveerlooked was the VA required. Smaller MT type transformers do not have a exact 4:1 winding ratio but a slightly higher secondary ratio, that is a bit highter than 1. If 480v is applied you will get a slightly higher than out. This is because of how a MT transformer is applied and the way if is loaded to provide better regulation. As such if you input 120 in the LV side the HV out will be less than 480v.

It's a valid point and one that has been made in previous threads.
I suppose the ensuing question is how accurate does the 480V need to be for this particular application.

 

[rbalex]

It's a valid point and one that has been made in previous threads.
I suppose the ensuing question is how accurate does the 480V need to be for this particular application.

An impressed current cathodic protection system is basically current regulated and the voltage only needs to be "close."

 

[Praedatus1]

So will grounding the center tap on the 480 side be a safer install? It will help the fuses blow faster in the event of a ground short? Also, it seems to me that the other downside to single phase 120480 makes only single phase 480? Whichever wouldn't work for a motor...right?

 

[Joethemechanic]

So will grounding the center tap on the 480 side be a safer install? It will help the fuses blow faster in the event of a ground short? Also, it seems to me that the other downside to single phase 120480 makes only single phase 480? Whichever wouldn't work for a motor...right?

Unless you had a 480V single phase motor. Not common, but no reason it can not be done.


In reality, there are no single phase motors. There are just motors with built in phase converters, and universal motors which are really DC machines.

Single phase induction motors are really two phase motors. The most common ones use a capacitor to shift the phase 90 degrees in order to produce the second phase. Some only use this second phase for starting, and some use it the whole time they are operating.


There are some exceptions to this, such as "shaded pole" motors, but these are mostly small very fractional horsepower devices used in small ventilation fans, clocks,,,,,,,,,,,,,