Transformer Hot, 3 phase supplying a 1 phase panel

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brother

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There has'nt been an infared done on this transformer, but first glance to me it seems a little unusually hot. Too hot to leave your hand on. It's an old install.

What I did notice it was a 3 phase transformer, 15kva, 480 primary to 208/120 secondary. The transformer is fed froma 3 phase panel. The panel it feeds aparently is only a 3 wire, single phase, 120/208. It's only using 2 of the phases of the 3 phase transformer secondary. Could this 'imbalance' cause the extra heating.???? I do not know why they installed this way, or why they just didnt use a 3 phase panel.

Maybe this is normal heat, but its the first Ive seen(felt) this hot in a while.
 
Even a "low temperature rise" transformer can have surface temperatures which are too hot to touch.
 
I don't see how the install you describe would cause any undue amount of heat.

It could be quite hot to the touch and still be OK. If you get 3rd degree burns from leaning on it, then it's a problem. :)
 
what color orange is it ?

(dried cut on my hand red, fresh cut on my hand red, traffic cone orange, sunny-D)

if its any color but transformer green, its probably too hot.
 
I "played" with numbers in reference to this post and confused myself (eassy task).
If we have a 15kva 3 phase 208 transformer out outpurt current should be
15000/208 x 1.732 or 41.6 amps thus calling for a 52 amp secondary OCP
(upped to 60).
If we feed a single phase panel, our usable output on a 3 phase 15kva transformer would be 10 kw or 10000/208= 48 amps still a 60 amp OCP.

But is my math correct as far as the outputs ?
 
augie47 said:
I "played" with numbers in reference to this post and confused myself (eassy task).
If we have a 15kva 3 phase 208 transformer out outpurt current should be
15000/208 x 1.732 or 41.6 amps thus calling for a 52 amp secondary OCP
(upped to 60).
If we feed a single phase panel, our usable output on a 3 phase 15kva transformer would be 10 kw or 10000/208= 48 amps still a 60 amp OCP.

But is my math correct as far as the outputs ?
Click to expand...

Another way to look at it is:

41.6A * 208V = 8.65KVA
or
41.6A * 2 *120V = 9.98KVA (or 1.15 x the 208V calculated connection)

1.15, hummm, isn't that the number in the discussion of the Oregan Fudge Factor?

EDIT: Just for the record, I hate serving a single-phase panel with 2 phases of a 208Y/120V transformer.
 
hurk27 said:
yep because the neutral will always be a current carrying conductor in the wire counts:roll:
Click to expand...

That is a reason, but the biggest one for me is I hate serving 240V equipment with 208V. Yea yea, I know, get the HO to buy 208V rated equipment. Well, they shouldn't have to do that, my opinion, and it's staying that way. :)
 
augie47 said:
I "played" with numbers in reference to this post and confused myself (eassy task).
If we have a 15kva 3 phase 208 transformer out outpurt current should be
15000/208 x 1.732 or 41.6 amps thus calling for a 52 amp secondary OCP
(upped to 60).
If we feed a single phase panel, our usable output on a 3 phase 15kva transformer would be 10 kw or 10000/208= 48 amps still a 60 amp OCP.

But is my math correct as far as the outputs ?
Click to expand...

how you get 10kw for the secondary out put??
 
brother said:
how you get 10kw for the secondary out put??
Click to expand...

I stand to be corrected, but I was taught a 15 kva 3 phase transformer was like having (3) 5 kw coils..if your load is only single phase, then you only have 10 kva capacity
 
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