Sizing Panelboard for 240V/3-ph Generator

[Johnhall30]

How should I size a panelboard coming from a 150 kW 240V/3-Phase high leg delta configured generator.

This system will provide power for various 240V/3-ph loads, as well as various 120/240V / 1-ph loads.

Load calculations say that 150 kW can provide 625 Amps at 120/240V / 1-ph
Also 150 kW is 360 Amps at 240V-3-ph

Would a 600 Amp three phase panelboard be sufficient to get the most out of this generator

 

[jim dungar]

This system will provide power for various 240V/3-ph loads, as well as various 120/240V / 1-ph loads.

Would a 600 Amp three phase panelboard be sufficient to get the most out of this generator

You would need a 3-phase panel if you plan to have 3-phase loads.

 

[Jpflex]

You would need a 3-phase panel if you plan to have 3-phase loads.

Although I have seen single phase loads powered from individual breakers in a 3 phase panel I’m not sure which would be most code compliant this way or feeding 3 separate single phase panels from AB, BC and AC out of the 3 phase panel. However, in his case he has a high leg delta so B phase would have to be orange and probably wouldn’t apply here?

 

[Jpflex]

How should I size a panelboard coming from a 150 kW 240V/3-Phase high leg delta configured generator.

This system will provide power for various 240V/3-ph loads, as well as various 120/240V / 1-ph loads.

Load calculations say that 150 kW can provide 625 Amps at 120/240V / 1-ph
Also 150 kW is 360 Amps at 240V-3-ph

Would a 600 Amp three phase panelboard be sufficient to get the most out of this generator

For 3 phase maximum ampere secondary output I get 150,000 VA / 240 / 1.732 = 360.85 i amperes

For others here would he get a main breaker at next standard size at 400 I amperes?

Can someone explain how this 360.85 secondary is split between 3 phases?

 

[LarryFine]

The traditional setup has been a 3ph panel a 1ph panel with neutral.

 

[Jpflex]

The traditional setup has been a 3ph panel a 1ph panel with neutral.

Yes but if you only have a single 1 phase panel then you can only load up 2/3 phases of the 3 phase system? Balance?

 

[topgone]

Yes but if you only have a single 1 phase panel then you can only load up 2/3 phases of the 3 phase system? Balance?

It should be made clear what those single-phase loads are. If it's all 120V, only the center-tapped phase can provide the 120V. That means you only availed of 1/3 of the transformer capacity (120-0-120V). 120V breaker will be 50.000/240 X 1,25 = 260.84 ~ 300A.
Things get complicated if there are 240V single-phase loads spread across the other phases. It would be best to investigate what loads will be placed on the transformer and take it from there.
All in all, the secondary 3-phase breaker should be sized for a line current of 150,000/(1.732 x 240) x 1.25 = 451 ~ 500A. The phase currents of the delta secondaries will be = 208A.
The usual thing I do is install the 500A 3-phase transformer secondary main breaker (240V, 3-phase) and then take off two phase conductors from the load side of the 500A breaker, pair them with the center-tap conductor, and install the 300A for 120-0102V loads. That way, you don't overload the transformer.

 

[jim dungar]

Although I have seen single phase loads powered from individual breakers in a 3 phase panel I’m not sure which would be most code compliant this way or feeding 3 separate single phase panels from AB, BC and AC out of the 3 phase panel. However, in his case he has a high leg delta so B phase would have to be orange and probably wouldn’t apply here?

You cannot supply 3-phase loads from a single phase panel. 'Delta' breakers have not been code compliant for 50 years.

Yes you can feed a panel with a 240/120 3ph 4w delta source, and the NEC does not require the center B phase bus bar to be identified by color. Many electricians prefer to use a dedicated 3-phase 240V panel and a second 120/240V single phase panel.

 

[Jpflex]

You cannot supply 3-phase loads from a single phase panel.

This is not what I said

However, there is a code requiring the high leg from a delta secondary to be phased orange as far as I recall

 

[jim dungar]

However, there is a code requiring the high leg from a delta secondary to be phased orange as far as I recall

The code requirement is for your field installed conductors, it does not apply to the bus bars inside of Listed equipment.

 

[Jpflex]

The code requirement is for your field installed conductors, it does not apply to the bus bars inside of Listed equipment.

You don’t tape or color buss bars where did you come up with this?

 

[jim dungar]

You don’t tape or color buss bars where did you come up with this?

Look at the Listing requirements for panelboards and switchboards. The NEC does not apply to the internal wiring of Listed products.

Of course, you are free to make a design decision including your own requirements.

 

[Jpflex]

Look at the Listing requirements for panelboards and switchboards. The NEC does not apply to the internal wiring of Listed products.

Of course, you are free to make a design decision including your own requirements.

We are not talking about internal wiring done by manufacture and when i say you cannot tape or color a buss is because doing so would create insulation resistance between contacts. Paint must be removed if conductors are to be bonded

 

[kwired]

Keep in mind that 1/3 of the total capacity is not capable of supplying 120 volt loads, without additional transformation. So you really need to do load calculation, not just a total VA calculation but a per phase calculation. Three phase loads will split up by square root of 3 factor between all three lines, 240 single phase loads split up by factor of 2 per line and 120 volt lines are full load on the line they connect to.

 

[Jpflex]

Three phase loads will split up by square root of 3 factor between all three lines

Is this computed mathematically at

KVA / secondary voltage x 1.732

Then how is each line to neutral max current available calculated again?

 

[kwired]

Is this computed mathematically at

KVA / secondary voltage x 1.732

Then how is each line to neutral max current available calculated again?

What I said actually would apply more directly to a wye source A delta with a midpoint tap is basically the same thing as you have with 120/240 single phase source. If you had a 150 kVA generator you have 50 kVA available across that center tapped winding, 25 kVA per half of that winding.

Balanced three phase load capacity in amps would be kVA / volts / 1.732. If you multiplied by 1.732 you would get 1082.5 amps for 150 kVA.

 

[topgone]

Is this computed mathematically at

KVA / secondary voltage x 1.732

Then how is each line to neutral max current available calculated again?

You will max the line to neutral current when half of the winding is unloaded, that would be 25,000/120V = 208A.

 

[Jpflex]

You will max the line to neutral current when half of the winding is unloaded, that would be 25,000/120V = 208A.

With half the winding unloaded do you mean L to L or A to B legs winding so that only A leg to N has a load and the other B to N does not have a load?

 

[topgone]

With half the winding unloaded do you mean L to L or A to B legs winding so that only A leg to N has a load and the other B to N does not have a load?

How else do you compute for the neutral current going into the center-tapped neutral?