Parallel transformers with common primary voltage but different secondary voltage and different loads

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hamza_arif777

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Hi everyone,

I have a query related to transformers. I have existing transformer at a facility which is having 480V primary to 220V secondary (3-phase). I want to connect another transformer with same voltage at the primary and 380V at the secondary side with different load from the same source. Will it have any impact?
 
How else would you connect the primary's?

If connecting to a supply circuit that has no ability to handle the added load would be the main thing to take into consideration
 
It will look something like this
Protection is not drawn in this SLD as it is a general one. The transformer highlighted in red is the new one which will connect to the 2 loads as shown while the transformer in black is the existing one which will stay connected to other loads in the panel.
 

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hamza_arif777 said:
It will look something like this
Protection is not drawn in this SLD as it is a general one. The transformer highlighted in red is the new one which will connect to the 2 loads as shown while the transformer in black is the existing one which will stay connected to other loads in the panel.
Click to expand...
Hopefully not on the same 600 amp disconnect as shown.
 
hamza_arif777 said:
It will look something like this
Protection is not drawn in this SLD as it is a general one. The transformer highlighted in red is the new one which will connect to the 2 loads as shown while the transformer in black is the existing one which will stay connected to other loads in the panel.
Click to expand...
You are connecting the load or outputs of each transformer to the same bus?
I don't think that will work out well at all.
 
ptonsparky said:
You are connecting the load or outputs of each transformer to the same bus?
I don't think that will work out well at all.
Click to expand...
Even if the transformers don't try to melt down, what voltage do you get at the connected equipment? Maybe you get smart equipment that can select which voltage it wants to use? :unsure:
 
Hv&Lv said:
Hopefully not on the same 600 amp disconnect as shown.
Click to expand...
No
ptonsparky said:
You are connecting the load or outputs of each transformer to the same bus?
I don't think that will work out well at all.
Click to expand...
No not doing that
Both transformer will be serving different loads not the same. The 380V output will be used for AC units while the 220V output will be used for Lighting loads
 
No problem with that but you do need to make sure each transformer is properly protected. If you aer under NEC, 450.3
 
hamza_arif777 said:
Both transformer will be serving different loads not the same.
Click to expand...
Then they are not paralleled.
They are simply two transformers supplied by a common feeder.

As others have mentioned you need to protect these following the rules in 450.3.
I would typically put a fused disconnect in front of each transformer so they, and their loads, can be removed from service individually.
 
The drawing does show the two transformers wired in parallel, which can not be done.

Each transformer should have its own supply circuit, sized to suit the primary requirements.

Each secondary feed a separate load panel, complete with a connection to a GEC system.
 
There is a lot of information missing from your drawing, and incorrectly drawn.

As others have stated 450.3, and 240.21, GES/GEC, conductor sizing, etc.

What you describe is just multiple transformers in an installation.

What exactly are you trying to figure out?
 
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