transformer

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snjeza

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Is this OK to do: Feed (protect) 75kVA transformer on the primary 120/208V, 208A from/with 200A fused disconnect?
I'm checking the project and found that. I never done that but I see there is no space for larger source.
Thank you.
 
Re: transformer

I don't follow your question. Can you please clarify:
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  • <font size="2" face="Verdana, Helvetica, sans-serif">What is the primary voltage?</font>
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  • <font size="2" face="Verdana, Helvetica, sans-serif">What is the secondary voltage?</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Will you have both primary and secondary protection?</font>
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Re: transformer

Allowed - yes, Smart - no.

The primary protection for a transformer can be a maximum of 125% FLA, in your case 260A.

By sizing the primary at effectively 100% you are not providing the ability to accommodate the transformer inrush currents.
 
Re: transformer

I agree with Jim. However, it might not be an issue if you keep the load below 80% of the transformer?s rating. If you effectively de-rate it to a 60 KVA transformer, then you might not be plagued by nuisance trips of the primary OCPD.
 
Re: transformer

Hello Fellas, I am new so bear with me. Your post caught me attention. Would'nt the scenerio as presented be limited. In MOST but not all cases isn't overcurrent required on the secondary side as well?
 
Re: transformer

Technically the transformer secondary never needs protection. However the conductors on the secondary do need to be protected, by an OCPD or by adherence to the "tap rules". Of course a lighting and appliance branch circuit panelboard connected to the secondary would also need protection.
 
Re: transformer

Thas where I was going with that... The panelboards themselves in most cases.. I should have been a little more specific.
 
Re: transformer

Charlie: the loads should not effect the inrush current. Should They?

As for nusiance tripping of the OCP he did state this was a fused disconnect and it may be possible (too lazy to look sorry) to find a fuse with sufficient clearing time, with a standard MCB it would be harder to overcome this issue.
 
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