load calculations

[thorn949]

have a meter base that has a 100amp service disconnect below the meter itself and feeds a 30 circuit panel 277/480 volt 3 phase with 225 amp main lugs.transformer 45KVA primary side feeds a 120/208 volt panel 3 phase and the secondary side feeds a 70 amp breaker for the transformer.I am going to install a 42 circuit panel since we need more room 277/480 volt 3 phase with 225 amp main lugs. will the current set up be sufficient to handle the extra loads or do I need to pull bigger wire so that breakers will not be tripping? any help would be greatly appreciated!!

 

[Little Bill]

have a meter base that has a 100amp service disconnect below the meter itself and feeds a 30 circuit panel 277/480 volt 3 phase with 225 amp main lugs.transformer 45KVA primary side feeds a 120/208 volt panel 3 phase and the secondary side feeds a 70 amp breaker for the transformer.I am going to install a 42 circuit panel since we need more room 277/480 volt 3 phase with 225 amp main lugs. will the current set up be sufficient to handle the extra loads or do I need to pull bigger wire so that breakers will not be tripping? any help would be greatly appreciated!!

I am confused about this, especially why would you feed anything from the primary of a transformer other than the secondary? You also failed to mention what size conductors you have now. Hard to know if you need larger or not without more info.

 

[S'mise]

Your question confuses me. "transformer 45KVA primary side feeds a 120/208 volt panel 3 phase and the secondary side feeds a 70 amp breaker for the transformer" ?

Do you mean to say; You have a 100 amp service 277/480 panel with a 70a breaker that feeds the primary of the 45kva xformer, then the secondary feeds the 120/208? A 70 amp breaker is OK to protect transformer primary at 480.

"will the current set up be sufficient to handle the extra loads or do I need to pull bigger wire so that breakers will not be tripping?

I don't know, You need to know what your loads are to do a calculation.

 

[thorn949]

load calculations

Sorry about the confusion guys!! The 480 volt feeds the panel coming from the meter base at the electrical room and there is the transformer that feeds the 120/208 volt panel and out to 480 volts for the transformer.Looks like they fed the 480 volt panel with1/0 or 2/0.250 MCM from the 120/208 panel to the transformer and out to feed a 70a 480 volt breaker for the transformer.The fuse block on the meter base said it was rated at 100 amps.Hope this helps and thank you!

 

[Smart $]

Sorry about the confusion guys!! The 480 volt feeds the panel coming from the meter base at the electrical room and there is the transformer that feeds the 120/208 volt panel and out to 480 volts for the transformer.Looks like they fed the 480 volt panel with1/0 or 2/0.250 MCM from the 120/208 panel to the transformer and out to feed a 70a 480 volt breaker for the transformer.The fuse block on the meter base said it was rated at 100 amps.Hope this helps and thank you!

Still confusing!!!

Let's take it one step at a time... and direction from utility to load

First is the meter then this 100A fuse block. Is there also a disconnect switch in between the meter and fuse block??

Then we have the fuse blck feeding the 480V panel, right?

Now here is where I lose you...

What feeds the transformer?

What feeds the 208/120 panel?

Typically the 480V panel feeds the transformer and the transformer feeds the 208/120V panel...

 

[Little Bill]

Sorry about the confusion guys!! The 480 volt feeds the panel coming from the meter base at the electrical room and there is the transformer that feeds the 120/208 volt panel and out to 480 volts for the transformer.Looks like they fed the 480 volt panel with1/0 or 2/0.250 MCM from the 120/208 panel to the transformer and out to feed a 70a 480 volt breaker for the transformer.The fuse block on the meter base said it was rated at 100 amps.Hope this helps and thank you!

Still confusing!!!

Let's take it one step at a time... and direction from utility to load

First is the meter then this 100A fuse block. Is there also a disconnect switch in between the meter and fuse block??

Then we have the fuse blck feeding the 480V panel, right?

Now here is where I lose you...

What feeds the transformer?

What feeds the 208/120 panel?

Typically the 480V panel feeds the transformer and the transformer feeds the 208/120V panel...

You're right, still confusing. I can't tell by the statement in red above if he has 1 or 2 transformers.
thorn949, please look at your set up again, draw yourself a diagram, and give us a more simple, helpful description. Look close because the order in which they are arranged is not necessarily the order in which they are wired.

 

[kingpb]

From a terminology standpoint it is better to use HV and LV when discussing transformers, because primary and secondary can be confusing. Case in point, a step up transformer primary is the LV winding, and the secondary is the HV winding.

My gut feeling is that the OP may be attempting to describe a set-up where a transformer is being used to provide 480V at some location where only 208Y/120V is available.

 

[Dennis Alwon]

Sorry about the confusion guys!! The 480 volt feeds the panel coming from the meter base at the electrical room and there is the transformer that feeds the 120/208 volt panel and out to 480 volts for the transformer.Looks like they fed the 480 volt panel with1/0 or 2/0.250 MCM from the 120/208 panel to the transformer and out to feed a 70a 480 volt breaker for the transformer.The fuse block on the meter base said it was rated at 100 amps.Hope this helps and thank you!

Sounds like you have a 480 volt service. Meter to first panel is 480V-- from first panel you feed a transformer that is 480V primary and 120/208 secondary. That trany feeds the 120/208 panel.

From the meter you feed the 480volt panel with either 1/0 or 2/0 assuming copper... Yes?

A 70 amp breaker feeds the 45kva transformer from the 480V panel. From the secondary side of the trany to the 120/208 panel it is fed with 250KCM.

The meter is rated 100 amps.

Is this correct????

 

[Little Bill]

Sounds like you have a 480 volt service. Meter to first panel is 480V-- from first panel you feed a transformer that is 480V primary and 120/208 secondary. That trany feeds the 120/208 panel.

From the meter you feed the 480volt panel with either 1/0 or 2/0 assuming copper... Yes?

A 70 amp breaker feeds the 45kva transformer from the 480V panel. From the secondary side of the trany to the 120/208 panel it is fed with 250KCM.

The meter is rated 100 amps.

Is this correct????

Depends on the load, but doesn't the 70A breaker sound low for that transformer?


Never mind-bad math!

 

[S'mise]

70a is right on the money

OK, I wont show my math

 

[Little Bill]

70a is right on the money

OK, I wont show my math

Me either, but after I redid my math (and Edit Post) I came up with 67.66. That's right at on the money!