OK what do you say?

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e57

e57

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PEE turns you on to contract with plans for 480/277 input 30KVA UPS with 208/120 output and #4's in and out, 100A OCP both sides straight through. What do you say? (Job notes to follow applicable codes.)
 
Something sounds wrong with the numbers. I would ask to see the cut sheets on the equipment so I could see the manufacture's specs on the unit. Depending on what is in the specs, it may be just fine.
 
The following is a link for a Liebert UPS 30kva. They call for a 50A OCD on the primary with 480 in and 120/208 out. Doing the calcs for a transformer 30kva/480x1.73= 36A x 125%=45.2A round up to 50A OCD. Seems that the secondary is OK since you can go to 250% OCD if you have primary OCD at 125%, 30kva/208x1.73=83.3Ax125%=104A round up to 125A.

The input current may be larger to allow for the battery charging circuit, depending on the arrangement of the system.

That being said, if you go with the listed manufacturer's specs I don't see how you could go wrong. Just watch the wire size on the secondary, #4 AWG I believe is too small. Assuming you do not have a large harmonic load on the unit and do not have to count the grounded conductor, you would be at #2AWG or you would have to go with 1/0 if you have a majority of harmonic loads.


http://www.liebert.com/product_pages/ProductTechnical.aspx?id=79&hz=60
 
KevinVost said:
The following is a link for a Liebert UPS 30kva. They call for a 50A OCD on the primary with 480 in and 120/208 out. Doing the calcs for a transformer 30kva/480x1.73= 36A x 125%=45.2A round up to 50A OCD. Seems that the secondary is OK since you can go to 250% OCD if you have primary OCD at 125%, 30kva/208x1.73=83.3Ax125%=104A round up to 125A.

The input current may be larger to allow for the battery charging circuit, depending on the arrangement of the system.

That being said, if you go with the listed manufacturer's specs I don't see how you could go wrong. Just watch the wire size on the secondary, #4 AWG I believe is too small. Assuming you do not have a large harmonic load on the unit and do not have to count the grounded conductor, you would be at #2AWG or you would have to go with 1/0 if you have a majority of harmonic loads.


http://www.liebert.com/product_pages/ProductTechnical.aspx?id=79&hz=60
Click to expand...
Now your speaking my language... And how you nearly nailed the make and model is well - just scarey.... ;) So now the question - should I RFI and call out the EE on the OCP? And IMO as well as the wire size? Or just go with it - with no real opprotunity to change in contract?
 
e57 said:
Now your speaking my language... And how you nearly nailed the make and model is well - just scarey.... ;) So now the question - should I RFI and call out the EE on the OCP? And IMO as well as the wire size? Or just go with it - with no real opprotunity to change in contract?
Click to expand...

Without a code ref. If the conductors are sized to the load it might be ok. , so you may want to check first.
 
IMO I would RFI or inquire of the EE and show him your calcs for the equipment, then ask his recomendation or have him sign and seal it the way it is. If you get called on it at inspection you can hopefully request a change order since it is his design. I personallly hate to do it this way, but if he insists on his calcs, all you can do is document, document, document.
 
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