Three Phase Transformer 600V to 120/208V

[powerplay]

In an electrical drawing with an calculated Load of 27KW is the transformer supposed to be sized to 125%, or is an Three Phase step down 30kVA Transformer from 600volt to 120/208volt rated to handle an commercial load of 27KW? Thanks for your feedback! I am hoping 30KVA works to reduce the wieght to suspend off an Concrete wall and some money too! The 30KVA is probably around 220 lbs.

 

[petersonra]

I think we have been over this a bunch of times. There does not appear to be any NEC requirement that a transformer be sized in any particular way.

 

[iceworm]

In an electrical drawing with an calculated Load of 27KW is the transformer supposed to be sized to 125%, or is an Three Phase step down 30kVA Transformer from 600volt to 120/208volt rated to handle an commercial load of 27KW? Thanks for your feedback! I am hoping 30KVA works to reduce the wieght to suspend off an Concrete wall and some money too! The 30KVA is probably around 220 lbs.

Calculated load should include 125% continuous plus 100% non-continuous load. If you did that, loading the transformer to 100% of it's rating will work fine. It meets the NEC requirement of 90.1.B for "essentially free from hazard, but not necessarily effecient, convenient, adequate for good service, or future expansion" .

Two curiousity questions - just for my own education: 220 lbs is really light for a 30kva xfm. Most 150C rise, 30kva, are in the 260 lb - 300 lb range.

1. Are you looking at a one with >150c rise?

2. What brand/model are you looking at that is that light?

ice

 

[Besoeker]

In an electrical drawing with an calculated Load of 27KW is the transformer supposed to be sized to 125%, or is an Three Phase step down 30kVA Transformer from 600volt to 120/208volt rated to handle an commercial load of 27KW?

I can't answer on code compliance. But note that the transformer is rated 30kVA. How that translates to a kW rating depends on load power factor.

 

[powerplay]

Calculated load should include 125% continuous plus 100% non-continuous load. If you did that, loading the transformer to 100% of it's rating will work fine. It meets the NEC requirement of 90.1.B for "essentially free from hazard, but not necessarily effecient, convenient, adequate for good service, or future expansion" .

Two curiousity questions - just for my own education: 220 lbs is really light for a 30kva xfm. Most 150C rise, 30kva, are in the 260 lb - 300 lb range.

1. Are you looking at a one with >150c rise?

2. What brand/model are you looking at that is that light?

ice

It's an Engineered drawing calculated to 27kw. The load will be 10 spa chairs and LED lighting, LED exterior signs and table lamps and tools for Manicure Stations... not a big load. It may be better to go to 45KVA, but I really don't see it being used up outside the calculations.

1) I don't know, but will find out more variables.

2) Commercial Electric I believe is the brand....asked for an 30 KVA transformer, and he guessed it weighted around 220...I shall see..

 

[Smart $]

I can't answer on code compliance. But note that the transformer is rated 30kVA. How that translates to a kW rating depends on load power factor.

It's an Engineered drawing calculated to 27kw. ...

Load calculations under the NEC are done in kVA. Are you just saying kW when it's kVA, or is it really kW? If the latter, I have to wonder if the engineer is U.S.-based or from abroad...???

Unless a high percentage of that load is motor(s), you should be good with a 30kVA, provided the calculated load is actually 27kVA. However, you will have to take into account any unbalanced loading, which may push you up to the next available size.

 

[kingpb]

Is the 27kW running or connected load.

Does the drawing or specs say the EC has to figure out what size transformer to use? If so, I would use a 45kVA.

Is this in the Bid stage? If so, contact the Owner, ask what size they want the transformer to be; and make engineer issue an Addendum to the bid documents.

Have you already won the job, and you are trying to save? If so, then issue an RFI asking for detailed load information so you can properly determine the continuous and non-continuous load. If you bid a 30KVA, and the loads change, and that requires you to use a larger size then you can issue a CO.