load adding to existing

[Toros]

Hi, I was walking a commercial project, a big print shop, to assess the existing condition or the existing 600A, 3phase, 4w delta, to see if Owner can install a new press machine on line and no need for service upgrading. This is how and what I concluded; The existing loads per peak demand (worst) from local utility company (SCE) is, 150 KW and the new load (press machine) is, 160 KW @240v,3ph. 150 KW + 160 KW=310 KW plus P.F 370 KW or, 896A @ 240V, 3phase Overloading????? But my Alternat. way, 896A / 3 (Above calculated devided 3 legs)=298A draw from each leg not-overloading????? Also , Note this, That I jumped to the roof and measure one of the ungrounded conductor while every 3phase equipments were on and it was 150A . since all loads on that service are 3phase, balanced and I was not sure all loads really were on ,(may be some motors in machines were off) I would says 190A draw avarage each leg . Plus, 128A each leg of new 160 KW machine Plus, safety factor, 28A total: 190+128+28=346A not overloading?????? Thank you

 

[bob]

the existing condition or the existing 600A, 3phase, The existing loads per peak demand (worst) from local utility company (SCE) is, 150 KW and the new load (press machine) is, 160 KW @240v,3ph. 150 KW + 160 KW=310 KW plus P.F 370 KW or, 896A @ 240V, 3phase Overloading?????

370 KVA/(0.24 x 1.73) = 891 amps. You do not divide this by 3. You have 891 amps on all 3 phase conductors.

Also , Note this, That I jumped to the roof and measure one of the ungrounded conductor while every 3phase equipments were on and it was 150A . since all loads on that service are 3phase, balanced and I was not sure all loads really were on ,(may be some motors in machines were off) I would says 190A draw avarage each leg . Plus, 128A each leg of new 160 KW machine Plus, safety factor, 28A total: 190+128+28=346A not overloading?????? Thank you

You have checked with the utility and found that the max load is 361 amps. So you must have been measuring on a slow day.
You say you measured the load on one phase conductor. How many conductors make up each phase? 2,3 or 4 maybe.

Looks to me like you will have to increase the main ampacity.

 

[Toros]

370 KVA/(0.24 x 1.73) = 891 amps. You do not divide this by 3. You have 891 amps on all 3 phase conductors.


You have checked with the utility and found that the max load is 361 amps. So you must have been measuring on a slow day.
You say you measured the load on one phase conductor. How many conductors make up each phase? 2,3 or 4 maybe.

Looks to me like you will have to increase the main ampacity.

I measured one of four legs, on that time, all 3phase loads were on for testing .......

 

[bob]

I measured one of four legs, on that time, all 3phase loads were on for testing .......

How many conductors per phase? A 600 amp service probably has parallel conductors. If the conductors are parallel,
you need a reading on all conductors per phase.

 

[Toros]

How many conductors per phase? A 600 amp service probably has parallel conductors. If the conductors are parallel,
you need a reading on all conductors per phase.

There are four giant conductors I think 700 mcm minimum

 

[charlie b]

Here is another error in your math:

Plus, 128A each leg of new 160 KW machine

The 160kW machine will draw 385 amps, not 128. That assumes a unity power factor. Here again, you don't divide by 3 to get 128 amps. The current leaving the source on phase A will return to the source on phases B and C. It is the same amps. At some moments, phase A is at its peak, and phases B and C are at lower values and in the opposite polarity from A. At other moments, phase B or phase C will be at their peak values. But it is still the same amps.

Now back to the original question. At 240 volts, a three phase 600 amp service has a capacity of 240 KVA. You are adding 160 KW to an existing 150 KW load. That is too much. Period!

 

[Toros]

back to my Load Adding

back to my Load Adding

How many conductors per phase? A 600 amp service probably has parallel conductors. If the conductors are parallel,
you need a reading on all conductors per phase.

Hi Bob, About that issue, where an existing print shop wants to add a new 3phase, 160kw press machine. Existing service which is 600A, 3phase, 124/240v, 4w delta, overhead fed through 700 mcm or larger (not parallel), 600A fused disc. sw. as main to be modified to accomo....... here is my calculation of total load or, final.... existing loads; 150 kw (per utility company bill-maximum peak demand) plus , new load: new press machine 160kw or385A @ 240v, 3phase so, total loads: 310 kw 0r, 746 A @ 240V, 3ph. {746 A running through each leg, smell of overloading the service drop or main OCPD.} Now, The Owner says, he is going to bring that new press machine regardless and if the system gives hard time such as , blow of any main 600A fuse or all three of them, than he will consider upgradig the exist. service to 1000A. " A large print machine in the shop that has the nameplate stating 30kw, 72 A @ 240v, 3ph. But why it draws 16A each leg" he wonders??. What is your thought, Bob??????