What size OCPD for 2 motors (200hp, 20hp)?

[carryyourbooks]

I have been tasked with installing 2 machines. Each of these machines will have (2) motors: (1) rated at 200hp @ 480v/3ph and (1) rated at 20hp @ 480v/3ph. For one of the machines, I have an availble 800a, 480v panelboard availble. For the other machine, I will need to build a new service. With the new service, I want to leave room to add other circuits if needed.

So, first, is the 800a panelboard adequate? IMO, I would prefer to put both machines on the same breaker, bring my feeders to the outside where the machine will be located and install (2) fusible disonnects for each machine.

For the second, what size service would you recommend? Should an 800a service be adequate?

TIA.

 

[GoldDigger]

I have been tasked with installing 2 machines. Each of these machines will have (2) motors: (1) rated at 200hp @ 480v/3ph and (1) rated at 20hp @ 480v/3ph. For one of the machines, I have an availble 800a, 480v panelboard availble. For the other machine, I will need to build a new service. With the new service, I want to leave room to add other circuits if needed.

So, first, is the 800a panelboard adequate? IMO, I would prefer to put both machines on the same breaker, bring my feeders to the outside where the machine will be located and install (2) fusible disonnects for each machine.

For the second, what size service would you recommend? Should an 800a service be adequate?

TIA.

Look at the NEC sections for multiple motors on a single circuit.
with that big a difference in current, even with the smaller motor having a separate overload protection device you will need to carefully consider the ampacity of the wires feeding that second motor to avoid violating tap rules.
Even if you use the same size wire to both motors, there are additional conditions laid out in the NEC for this type of circuit.

 

[carryyourbooks]

Look at the NEC sections for multiple motors on a single circuit.
with that big a difference in current, even with the smaller motor having a separate overload protection device you will need to carefully consider the ampacity of the wires feeding that second motor to avoid violating tap rules.
Even if you use the same size wire to both motors, there are additional conditions laid out in the NEC for this type of circuit.

OK.

I can install a breaker for each motor. What size should be used for each motor?

 

[augie47]

Excuse my bluntness this morning but I feel like I'm reading a DIY thread. Have you spent any time in Art 430 researching this ? Please do so !
There are so many factors involved here a short answer could easily be misleading
(a) Are any of the motors supplied by drives or are they all Across The Line starting ?
(b) Is the facilty large enough that adding 400 HP will have little effect on POCO ? If not,
do they have an approach for motors of that size. They may not accept ATL starting.
(c))Do they have overload protection and you are supplying only SCGF protection ?
You state "OCPD" .... from the question, I assume you are wanting to size the feeder short-circuit protective device for two motors. If so, as Golddigger mentioned, go to Part V of Art 430.
Your follow-up question concerns "a breaker for each motor".. again are we discussing overload or short-circuit/ground-fault protection.
This sounds like your first rodeo with a project this size. if so I would suggest on-site advice rather than advice from the Forum.

 

[Dennis Alwon]

There is no way for us to know if the 800 amp panelboard is adequate without knowing the loads on the panel. You will have to do a load calculation for the building

 

[Smart $]

Are you talking identical machines? Are these manufactured machines, i.e. assembled complete off site? Does each machine have a power and control panel for the entire machine? Does it have a main ocpd/disconnecting means? Does each machine have nameplate data? Is there documentation?

A lot of required facts not yet in evidence...

 

[kwired]

Any other load on this 800 amp panel or just the four motors mentioned?

 

[petersonra]

I have been tasked with installing 2 machines. Each of these machines will have (2) motors: (1) rated at 200hp @ 480v/3ph and (1) rated at 20hp @ 480v/3ph. For one of the machines, I have an availble 800a, 480v panelboard availble. For the other machine, I will need to build a new service. With the new service, I want to leave room to add other circuits if needed.

So, first, is the 800a panelboard adequate? IMO, I would prefer to put both machines on the same breaker, bring my feeders to the outside where the machine will be located and install (2) fusible disonnects for each machine.

For the second, what size service would you recommend? Should an 800a service be adequate?

TIA.

generally the machine nameplate will tell you the FLC of the machine. you can use that to figure out if you can add that load to the existing panelboard.

I do not think you are really going to add another service for the second machine. You may add a panelboard but it probably is not a service. But again, the machine nameplate should point you in the right direction.

I don't see that you need an 800A service or an 800A panelboard to feed 220Hp worth of 480V motors.

 

[Smart $]

...

I don't see that you need an 800A service or an 800A panelboard to feed 220Hp worth of 480V motors.

Probably not the only load of an 800A panel... but it will likely be insufficient for 440HP worth of 480V motors simply because the OCPD may be undersized for starting current (~534A FLC).

 

[petersonra]

Probably not the only load of an 800A panel... but it will likely be insufficient for 440HP worth of 480V motors simply because the OCPD may be undersized for starting current (~534A FLC).

The OP is kind of confusing. In one paragraph it seems like he wants to have a separate 800A PB for each machine and then later on it seems like he wants a single 800A feeder to supply both machines.

I don't see why an 800A PB could not supply both machines, especially if nothing else is on that PB.

As another poster mentioned, it is unlikely he is going to be allowed to start a 200HP motor (or at least problematic to do so) across the line so the starting current is less of an issue.

 

[don_resqcapt19]

...
As another poster mentioned, it is unlikely he is going to be allowed to start a 200HP motor (or at least problematic to do so) across the line so the starting current is less of an issue.

Around here it is common for industrial sites to start 200 hp 480 volt motors across the line.

 

[carryyourbooks]

Any other load on this 800 amp panel or just the four motors mentioned?

No, not at all. Only 2 motors will be added to this panelboard potentially: a 200hp motor and a 20hp motor. The other (2) motors are going in a different area of the facility and will not be connected at all to the 800a existing panelboard. In my OP, I suggested that we will be building a new service due to the lack of available power in that area.

 

[petersonra]

Around here it is common for industrial sites to start 200 hp 480 volt motors across the line.

I can't recall the last time I had an actual starter for a motor of that size. VFD or soft start.

most times the specs we see allow ATL starting upto about 50 HP.

 

[carryyourbooks]

The OP is kind of confusing. In one paragraph it seems like he wants to have a separate 800A PB for each machine and then later on it seems like he wants a single 800A feeder to supply both machines.

I don't see why an 800A PB could not supply both machines, especially if nothing else is on that PB.

As another poster mentioned, it is unlikely he is going to be allowed to start a 200HP motor (or at least problematic to do so) across the line so the starting current is less of an issue.

To clarify, I have 2 systems to install. Each systerm has (2) motors: a 200hp motor and a 20hp motor. These systems will be located on opposite side of a facility.

One system (2 motors) will be connected to the 800a PB. I usually don't work with motors this large, so I am wanting to know what size breaker to feed this 200hp motor with. I already know what to feed the 20hp motor with (since it will be on its own breaker). Once I know what is necessary for this 200hp motor, I can install a new service for the other system.

I have no choice but to install a new service for the second system because the facility won't be able to sustain both loads. Also, they have no power in the secondary location available, so a new service is inevitable.

 

[don_resqcapt19]

I can't recall the last time I had an actual starter for a motor of that size. VFD or soft start.

most times the specs we see allow ATL starting upto about 50 HP.

The biggest I hooked up was a 4,500 hp across the line at 5kV.

 

[don_resqcapt19]

...
One system (2 motors) will be connected to the 800a PB. I usually don't work with motors this large, so I am wanting to know what size breaker to feed this 200hp motor with. I already know what to feed the 20hp motor with (since it will be on its own breaker). Once I know what is necessary for this 200hp motor, I can install a new service for the other system.

...

How did you find out what breaker you need for the 20 hp motor? The process is the same.
You will find what you need to know in 430.52.

 

[carryyourbooks]

How did you find out what breaker you need for the 20 hp motor? The process is the same.
You will find what you need to know in 430.52.

That is the whole purpose of my questions. According to 430.52, I'd use a 600a inverse time CB. I am unsure of myself and wanted to check with others.

 

[petersonra]

That is the whole purpose of my questions. According to 430.52, I'd use a 600a inverse time CB. I am unsure of myself and wanted to check with others.

That would be the maximum rating allowed. I don't recall that there is any minimum rating, although there are some practical factors that limit you on the lowest rated breaker you could use.

 

[augie47]

That is the whole purpose of my questions. According to 430.52, I'd use a 600a inverse time CB. I am unsure of myself and wanted to check with others.

Thats a whole lot easier to answer than the first post. As petersonra noted above that is the "maximum: allowed by 430,52 but note, as always, there are exceptions.
Note that might not be the case if there are drives involved... is the motor starter an "across the line" starter ?

 

[Cow]

First things first, how are these motors starting? Starter, soft start, etc? Or does this machine come with a large control cabinet you simply hit with a feeder, a single point connection?