Advice on pulling 800 amps.

[Smart $]

Let me throw another one at ya- The breaker we have installed is a standard 80% breaker. Meaning I should not load it beyond 640 amps, right?

No, that is not right. You can load to 100% with noncontinuous loads. You can only load to 80% if your loads are all continuous—figured in at 125% loading on breaker and conductors. It amounts to you can go to 100% of the rating after applying the 125% headroom allowance for continuous load portion.

Also, just because a machine is on more than three hours does not make it a continuous load. It has to operate at the calculated load amperage for more than three hours to be a continuous load. For example, you can operate an electric oven for more than three hours preparing some meals, but the heating elements are usually efficient enough that thermostatic control cycles the elements on and off during that time. This is not a continuous load.

Have some chores to do, will comment on rest later if not already commented on (properly) by others...

 

[Smart $]

...
Basically what this looks like to me is that this breaker will only serve this one press line. There won't be enough left over to do much else.

And if this is true, then isn't the 500 cable at 760 amps (75*) sufficent for the calculated load(640 max)?

It depends on how close you are to 800A with noncontinuous plus 125% continuous and your adjustment and correction factors. 760A is the crossover point if there are no adjustment and correction factors. A calculated load of 640A that is all continuous would require sizing at 800A and would put you undersized with 500's. However, if some of that calcualted load is noncontinuous, it reduces the value to somewhere between 800A and 640A.

FWIW, calculated load per Article 220 does not include 125% for continuous loads. That is under 215.2(A)(1) for feeder and OCPD sizing

Here is what I have worked out so far: The press, straightener and feeder are fused at a combined 387 amps (200+175+12). If they are continuous and/or motor loads then x 125%= 484 amps.

640-484=156 amps left avalible.

Way off base so far? Let me know what you think. Thanks guys.

Ultimately, you will have to use refined calculation methods rather than using a basis of all loading being continuous... especially if you want to use 500's.

Determine your motor loads, add 25% for the largest, add noncontinuous non-motor loads, then add 125% of continuous non-motor loads. That will give you your sizing value. There may also be some nuances if a large part of your load is from motors, but we'll get into that if need be... but in the meantime you need to determine the motor load to see if we have to consider those nuances.

PS: the calculator I provided a link to earlier may help with your sizing issues.


***PPS: You cannot base loading on the sum of fuse or breaker ratings.***

 

[milemaker13]

Interesting. I need to get after my bosses to come up with more info. My company always seems to be lacking in the planning dept. :slaphead: Anyway, I really appreciate you all bringing these things up. I want to get this one correct. I will check out the calculator you posted.

 

[Smart $]

... I will check out the calculator you posted.

FWIW, I discovered a problem with my calculator, but nothing major... at least it errs to the safer side. :roll:

If 0 is entered for continuous load, the calc's return a #NUM error.

Also, rounding of continuous times 125% can push values higher than need be (I rounded up because it uses significant figures).

I'll fix and upload it when I get a chance. Subscribe to the linked thread if you want notified when that occurs. Oops, I guess that won't work because the thread is closed.

 

[milemaker13]

Good morning-
I'm not sure I am doing this conduit fill calculation correctly.

What would be the formula to find out if (3) 600mcm's plus the 1/0 ground wire will fit into 3" emt?

From the tables I find that:
3" emt @ 40% = 3.538 sq. inches
600 mcm cable = .8676 sq. inches
1/0 cable = .1855 sq. inches

Do I simply add (.8676 x 3) to .1855 to get 2.7883 sq. inches? Then, is that subtracted from 3.538?

3.538 - 2.7883 = .7497

What does FPN #2 mean? I don't understand how to calculate the ration of pipe to wire...

 

[infinity]

I didn't check you numbers but you appear to be on the right track. You found the area of the conduit at 40% which is for three or more conductors. Then you found the area of each conductor. Simply add the area of all the conductors together and it must be equal to or less than the 40% area of the conduit.

Which FPN are you referring to?

 

[milemaker13]

Well, here is what I figured for the ratio:
600mcm OD=1.051
3" emt ID=3.356
If I multiply 1.051 by 2.8 I get 2.94
If I multiply 1.051 by 3.2 I get 3.3632
So, that is right on the edge of 3.356, which tells me jamming may occur? Hmmm:huh:

 

[milemaker13]

Chapter 9, Table 1 FPN #2. "When pulling 3 conductors into a pipe, if the ratio between the ID of the pipe and the OD of the wire is between 2.8 and 3.2, jamming may occur"

 

[milemaker13]

I didn't check you numbers but you appear to be on the right track.

Cool. So its looking good for 600's in 3" so far... But what about the "jamming"? Of course, there is that 4th wire.. but being its smaller, will that just make it worse?

Also, the run will probably be shortened to about 150-190 feet. We are still discussing locations.

 

[GoldDigger]

Cool. So its looking good for 600's in 3" so far... But what about the "jamming"? Of course, there is that 4th wire.. but being its smaller, will that just make it worse?

Also, the run will probably be shortened to about 150-190 feet. We are still discussing locations.

The jamming problem gets harder to solve theoretically the more wires there are in the pull. And as a practical matter, the range of sizes which can cause jamming will be that much wider. When the wires are not all the same size it gets harder still. One way to look at it that may help is that you have to worry about any combination of three wires, so the problem area of conduit ID will include smaller sizes. Another way to look at it is that four wire jam combinations can include all four wires (duh), so the problem area will include larger conduit sizes as well. But any four wire combinations will tend to form a less stable jam and you might get away with it if well lubed.

 

[milemaker13]

Cpt 9, table 1 FNP #2 says that 4 wires is less likely to jam than 3. I plan to get the super slick "simpull" cable. That should help the lube situation.

I had a quick meeting with one of the bosses this morning. She seems onboard with saying that this service will only realistically be feeding this one press. Not the future planned sheeting line as well. Thats a load off.

She is trying to get more info, but I don't know what I'll see or when.

So right now, it seems like using the 500's will be ok, since the (assumed) max load will be closer to 500 amps, not near 760. And if it ever does run 24/7 like they envision (again, assuming its all continous), its still less than the 640 amps (breaker @ 80%).

Does anyone disagree with that so far?

I think I know the awnser to this next question: Why not just put this 800 amp panel next to the incomming service and run seperate lines over to the machines? (vs running the box about 200' then running seperate lines to the equipment)


1. Convenience
2. Voltage drop

I have yet to do any voltage drop calcs...

 

[milemaker13]

Wye vs Delta??

Wye vs Delta??

OK, I have a little more info on the press. I am looking up this info in the code book, but I have a quick meeting with my boss at noon and wanted to get you guy's opinions too..

Motors on press: Main drive 75HP
Slide adjuster 7.5 (used only during setup)
lube motor 2 hp

All I have on the leveler (straightner) and feeder is the fuse values. (175a & 12a)

Also, the info makes referance to the power supply being in a Y configuration. I don't fully understand how I would know what is being supplied to the building. Can you help me on that?

 

[GoldDigger]

OK, I have a little more info on the press. I am looking up this info in the code book, but I have a quick meeting with my boss at noon and wanted to get you guy's opinions too..

Motors on press: Main drive 75HP
Slide adjuster 7.5 (used only during setup)
lube motor 2 hp

All I have on the leveler (straightner) and feeder is the fuse values. (175a & 12a)

Also, the info makes referance to the power supply being in a Y configuration. I don't fully understand how I would know what is being supplied to the building. Can you help me on that?

If the service input to the building has a neutral, or you can see an X0 terminal on the secondary of the feed transformer, you pretty surely have a wye. Another indication is three equal phase-to-ground voltages.
If one of the phase conductors is grounded (either corner ground or high-leg), you have a delta.

If there is a mismatch between the service and the needs of the equipment, you will need to install a transformer.

 

[Smart $]

...

Also, the info makes referance to the power supply being in a Y configuration. I don't fully understand how I would know what is being supplied to the building. Can you help me on that?

In OP you said voltage is 480.... we assume 3?. The question is whether it is 4-wire... i.e. with a neutral, which would make it 480/277V 3? 4W if the Line-to-Line voltage is 480V, and the Line-to-Neutral voltage is 277V. That'd be a "Y" (wye) configuration.

 

[milemaker13]

Yes, that is correct. It is 480v/277v 3 phase, 4 wire. 480 phase to phase, 277 phase to neutral.

Based on wire costs, we have decided to put the large 800 amp panel on the wall close to the service and run individual lines to each machine.

Since I work here, my time isn't a huge cost factor:ashamed1:. We also have enough 2" pipe to make the runs, so it really just comes down to wire cost. And running just the press line power now and waiting to run the sheeting line later will help spread the cost out.

 

[jimC.]

It's been interesting reading this thread, we're putting an addition on our building for a slitter (slices large coil steel to size, and then recoils). I know what you mean about always needing more info......

 

[liquidtite]

Since you have only an 800 amp CB you will need to use taps. If they're at that end of the run then you would need to follow the rules for parallel conductors from the 800 amp CB to the tap point.

What's the tap rule

 

[infinity]

What's the tap rule

Take a look at 240.21(B).

 

[Smart $]

.... I will check out the calculator you posted.

FWIW, I discovered a problem with my calculator, but nothing major... at least it errs to the safer side. :roll:

If 0 is entered for continuous load, the calc's return a #NUM error.

Also, rounding of continuous times 125% can push values higher than need be (I rounded up because it uses significant figures).

I'll fix and upload it when I get a chance. Subscribe to the linked thread if you want notified when that occurs. Oops, I guess that won't work because the thread is closed.

For updated versions, start at the post linked below, and subscribe to the thread for notification...

http://forums.mikeholt.com/showthread.php?t=153415&p=1485789#post1485789