SIZE MAIN OCPD for a panel with motor

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binwork91

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new york
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electrical engineer
Hi, i am confuse with the motor OCPD.
I want to verify if I make any mistake. see picture below. All of these are in the panelboard.
I want to size the main fuse of this panelboard.
So 477*1.75=834.75, next size up=1000A.
1000+302+40+60+60+77+200+300=2039, next size down=2000A. so the main fuse for this panel is 2000A. am I correct?
what about the load for this panel? I think we use load to size the panel, but for the motor, it is different.
1622668637516.png
 
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jim dungar

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Isn't it 1.25x the largest motor current plus all of the other currents at 1.00x?

You do not round up to the next size device until after you have developed a total current.
 
augie47

augie47

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For the OCP device, IMO, you are on the right track. Considering fusible, 175% of the largest + the FLA on others with no provision for next size up (I'm basing it on 430.62).
If you go larger you will need to size your service/feeder conductors on the OCPD.

(I come up with 1800A allowable but I imagine you will want to go with 2000 as that is a standard)
 
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jim dungar

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augie47 said:
For the OCP device, IMO, you are on the right track. Considering fusible, 175% of the largest + the FLA on others with no provision for next size up (I'm basing it on 430.62).
If you go larger you will need to size your service/feeder conductors on the OCPD.

(I come up with 1800A allowable but I imagine you will want to go with 2000 as that is a standard)
Click to expand...
The motor protective devices would be done using 1.75x, but the combined load would be done by: summing all of the full loads current + .25x the largest motor current.

I like the idea of a 2000A service.
 
kwired

kwired

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Any loads that will/can not run at same time?

How many the motors are soft started or on VFD's? That will reduce the need to go with 175% in the calculations.
 
Dennis Alwon

Dennis Alwon

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If the freeze pump is a refrigerant pump which falls under art 440 then you are correct

430.62 Rating or Setting — Motor Load.
(A) Specific Load. A feeder supplying a specific fixed motor
load(s) and consisting of conductor sizes based on 430.24 shall
be provided with a protective device having a rating or setting
not greater than the largest rating or setting of the branchcircuit
short-circuit and ground-fault protective device for any
motor supplied by the feeder [based on the maximum permitted
value for the specific type of a protective device in accordance
with 430.52, or 440.22(A) for hermetic refrigerant motorcompressors],
plus the sum of the full-load currents of the
other motors of the group.
Where the same rating or setting of the branch-circuit shortcircuit
and ground-fault protective device is used on two or
more of the branch circuits supplied by the feeder, one of the
protective devices shall be considered the largest for the above
calculations.
Click to expand...
 
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binwork91

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new york
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electrical engineer
one new question.
is the 2000A main fuse the max size I can use for the panel?
Can I have larger size main fuse? for example 2500A main fuse for future expansion. or 2000A main fuse is the maximum.
 
mikeames

mikeames

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Gaithersburg MD
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binwork91 said:
one new question.
is the 2000A main fuse the max size I can use for the panel?
Can I have larger size main fuse? for example 2500A main fuse for future expansion. or 2000A main fuse is the maximum.
Click to expand...

Of course you can. You can make it as large as you want. The fuse or breaker protects the panel, not the motors. The calculations give you minimums so the motors can start without tripping the main in the panel.
 
Dennis Alwon

Dennis Alwon

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You would have to upsize the wire. If the panel is just motors then you could size your conductor at 125% of the largest motor and then add the sum of the other motors. That is for conductor sizing yet you can still have an overcurrent protective device rated at what you calculated.

I thought the 175% that you used was for refrigerant type pump..
 
mikeames

mikeames

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What Dennis wrote was an assumption I made. I assumed you would also increased the feeder size.
 
Dennis Alwon

Dennis Alwon

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Imo, if you go above the calculated load for the overcurrent protective device then you need to size the feeder to match the overcurrent protective device .
 
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jim dungar

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binwork91 said:
View attachment 2556751
Click to expand...

You are correct my reference to the 1.25x applies to sizing the feeder conductors per 430.24 not to a motor feeder protective device rating.

430.62(A) requires you to have a feeder device with a rating not greater than the largest motor branch circuit protective device plus the sum of the other motor full load currents.
But the OP has a list of both motor and non-motor loads and VFD loads as well as a possible chiller/compressor load so 430.63, with its less restrictive not less than rating, is more probably the appropriate reference.
 
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