# 400 amp brreaker



## Morg12345 (Jan 22, 2016)

So please don't think that I'm crazy this isn't my idea it's just what I've been asked to help out with
I have a commercial building that has some 480 V equipment that they need to get running. The only service that they have right now is a 1000 amp service 208/120
Paco cant get the 480 service for a long time and they really want to get this piece of equipment going.

The unit consists of A DC motor that has a drive that is prtected with a 250 amp breaker.
There are some heaters involved that are on the same unit. They are protected with a 225 AMP breaker.
This equipment is 480 V 3 phase. They purchased a 275 KV transformer to step up from 208 up to 480 V
The 1st problem I have is the breaker panel for the 208 will not accept any breaker bigger than 400 AMP...Tag is above...
If anyone is willing to help I'm here with any answers that I can answer..
MORG


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## Forge Boyz (Nov 7, 2014)

That looks like a buss mounted MAINE breaker. If there is space above it you could add another one just as big as it is.

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## Awg-Dawg (Jan 23, 2007)

You could lug off of the buss and put a temporary ocpd ahead of the xfmr.


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## micromind (Aug 11, 2007)

Whatever you do, DO NOT TURN OFF THE MAINE BREAKER..........if you do, the entire state of Maine will go dark!

I agree with the above suggestions, if you can't get a big enough breaker in the panel, there's a good chance you can tap the busses and feed either a fused disconnect or more likely, a breaker enclosure with it. 800 amp will do.

I kind of hate to say this but the 208 current at 275KVA is 764 amps, that's not all that far from the 1,000 amp main; if it's absolutely guaranteed to be temporary, I would be very tempted to tap the busses and go directly to the transformer. Absolutely.....guaranteed......

In any case, if the transformer is 120/208 Y - 480 ∆, do not connect anything to X0. If it's grounded at the factory, get rid of the ground connection. X0 absolutely must be isolated from anything. If X0 is connected, you'll have circulating currents and it'll eventually burn up the transformer.


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## Morg12345 (Jan 22, 2016)

micromind said:


> Whatever you do, DO NOT TURN OFF THE MAINE BREAKER..........if you do, the entire state of Maine will go dark!
> 
> I agree with the above suggestions, if you can't get a big enough breaker in the panel, there's a good chance you can tap the busses and feed either a fused disconnect or more likely, a breaker enclosure with it. 800 amp will do.
> 
> ...


Now they want to try to energize the step up transformer and manipulate the equipment to see if they can get everything to run and if the 400 amp breaker holds or not... I'm working on getting the 480 service in to the building as soon as possible.. the owners are really desperate for this... Or this facility will be shutting down Everybody's probably thinking the same thing I am they didn't plan before they moved into the building
Morg


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## Almost Retired (Sep 14, 2021)

Your failure to plan and thus cause your self an emergency
does not extrapolate into being my emergency, but i will try to help if i can

when you fail to plan ..... you have planned to fail


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## kb1jb1 (Nov 11, 2017)

How much power does the equipment actually draw? I worked on equipment where the control panel said 90 amps, 480 volts. The total maximum draw was never more than 23 amps. Sometimes control panels are one size fits all. 
Are they reverse feeding a step down transformer or did they get a 208 volts Delt wired input with a 480/277 Wye output?
Also check the service feeders. Are they sized for 1000 amps?


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## Morg12345 (Jan 22, 2016)

kb1jb1 said:


> How much power does the equipment actually draw? I worked on equipment where the control panel said 90 amps, 480 volts. The total maximum draw was never more than 23 amps. Sometimes control panels are one size fits all.
> Are they reverse feeding a step down transformer or did they get a 208 volts Delt wired input with a 480/277 Wye output?
> Also check the service feeders. Are they sized for 1000 amps?


..hello 
It is a listed step up transformer 208 to 480 v
Y secondary....it's a 250 hp. DC motor...runs off a 90s vintage drive.... They tell me that after start up it only draws around 50 amps continuous and that's where it runs the whole run on the product(plastic sheet)

The 225 AMP side feed heaters, that they say after start up very little current just to maintain the heat for this plastic sheet.
They are willing to manipulate things to keep it running until the 480 V service is installed
The answer to your question is yes it's a 1000 anp main breaker on the 208 service..
Thanks for talking me about this.
MORG


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## Flashedout (4 mo ago)

Sounds like the money your company is shelling out to step up the service.. For a temp at that,, would it be feasible to convert the drive and element's of the equipment itself? You still need to dish out $$ for the 480 equipment yet..


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## CMP (Oct 30, 2019)

From the sounds of it, your biggest hurdle may be the transformer inrush current. If you could split the load in half and use two transformers and feeder breakers to supply the equipment, you might stand a better chance of getting it started on what you have to supply it with.

Just an avenue of thought, I didn’t see enough detail presented to make an informed decision, but the inrush current on that large of a step up transformer can be a bigger problem than the demands of the loads.

You would need to compare the worst inrush current of the transformer and compare that figure to the trip curve of the largest breaker you could get to supply the loads. Then work your way downward from there by dividing up the loads until you get to some sizes that will get you past the worst transformer inrush current demand. I would bet that getting your transformer started and running, would be a bigger challenge than getting the load started.


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## Morg12345 (Jan 22, 2016)

CMP said:


> From the sounds of it, your biggest hurdle may be the transformer inrush current. If you could split the load in half and use two transformers and feeder breakers to supply the equipment, you might stand a better chance of getting it started on what you have to supply it with.
> 
> Just an avenue of thought, I didn’t see enough detail presented to make an informed decision, but the inrush current on that large of a step up transformer can be a bigger problem than the demands of the loads.
> 
> You would need to compare the worst inrush current of the transformer and compare that figure to the trip curve of the largest breaker you could get to supply the loads. Then work your way downward from there by dividing up the loads until you get to some sizes that will get you past the worst transformer inrush current demand. I would bet that getting your transformer started and running, would be a bigger challenge than getting the load started.


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## paulengr (Oct 8, 2017)

Colin va little late to this…

Most heated coils are wired as two coils in series for 480 V. If you open them up it’s probably quite easy to convert to 230 which would be close enough. They will just fire a little longer at 208 and that removes a lot of 480 V load.

Second I would look hard at the DC motor. Many are rated say 250/500 V where again some simple jumper changes goes to 250 V. But in most cases it’s cheaper to just convert everything over to AC. You can easily get AC drives (if you know where to look. DC rebuild time and cost nearly always make AC conversion a good option.

That would put you in a pair of 400 A breakers, permanently if you wanted to. The problem is the full current on the primary side of that tranny is 763 A. An 800 A breaker or fuse will nuisance trip from inrush. NEC allows up to 1145 A. You can get molded case breakers that large but what it will likely be is a 1200 A frame breaker with an electronic trip unit that you set to 1145 A and that’s what we sell. Thermal-magnetic breakers are more expensive than electronic trip units at that size. You can usually even set a small delay on instantaneous then crank it down to 125% or 954 A which would provide secondary protection and make it legal to run without a main on the 480 V side. Especially when this is all temporary.

Keep in mind that your existing 1000 A main is likely to TRIP if it’s not set up for that transformer. And there is zero chance of coordination. Double tapping is of course illegal but if the POCO recommends it, I’d go for it.

Before you get too far into this I’d recommend doing one thing. See if you can get the magnetizing curve data from the tranny manufacturer. If you can’t get it, there are ways to estimate it. The trouble won’t be just the size of the load. You have a big problem with nuisance tripping.

Also is this both temporary and something that runs on and off? I have a couple customers with the same problem that found that it’s just cheaper to burn diesel instead of coal/gas. They just use a generator. No crazy questionable Code issues, no super expensive and hard to get parts. And you can most likely rent one and just plug it in for testing NOW and then deal with the other issues later.


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## Tonedeaf (Nov 26, 2012)

i would send it over to you supply house that is a Square D distributor.......MAYBE they can add to the existing MDP to give you another section with an 800 amp breaker.

you also gota check the loads too ask them for 12 months of electric bills to make sure you have the capacity to add the new load. You may need a larger service in this case your gonna change the MDP so you can order it with the space you need.


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## Morg12345 (Jan 22, 2016)

paulengr said:


> Colin va little late to this…
> 
> Most heated coils are wired as two coils in series for 480 V. If you open them up it’s probably quite easy to convert to 230 which would be close enough. They will just fire a little longer at 208 and that removes a lot of 480 V load.
> 
> ...


A lot of good things being discussed here I'm sure I could talk that man to putting an AC drive-in and replace the 250 dc system with a possible 250AC motor
This is driving a screw which puts hot plastic into a sheet, it really doesn't draw much. heaters once they heat up takes very little to maintain the heat
It would be great to run it at 208 without having to step up to 480 ,but like I said the biggest breaker I can put in the 208 cabinet is a 400 amp breaker.. matbe I can reduce the horsepower of the motor to decrease current


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## Morg12345 (Jan 22, 2016)

Tonedeaf said:


> i would send it over to you supply house that is a Square D distributor.......MAYBE they can add to the existing MDP to give you another section with an 800 amp breaker.
> 
> you also gota check the loads too ask them for 12 months of electric bills to make sure you have the capacity to add the new load. You may need a larger service in this case your gonna change the MDP so you can order it with the space you need.


 Any idea where I can get used AC drive equipment and AC motors?


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## Forge Boyz (Nov 7, 2014)

Morg12345 said:


> A lot of good things being discussed here I'm sure I could talk that man to putting an AC drive-in and replace the 250 dc system with a possible 250AC motor
> This is driving a screw which puts hot plastic into a sheet, it really doesn't draw much. heaters once they heat up takes very little to maintain the heat
> It would be great to run it at 208 without having to step up to 480 ,but like I said the biggest breaker I can put in the 208 cabinet is a 400 amp breaker.. matbe I can reduce the horsepower of the motor to decrease current


Are you positive you can't put a bigger breaker in? Looking at that buss mounted main it sure seems to me that you could. Do you not have space in that side?

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## sbrn33 (Mar 15, 2007)

Morg12345 said:


> View attachment 171050
> 
> So please don't think that I'm crazy this isn't my idea it's just what I've been asked to help out with
> I have a commercial building that has some 480 V equipment that they need to get running. The only service that they have right now is a 1000 amp service 208/120
> ...


That piece of equipment is going to draw more that 600 amps 480?


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## Morg12345 (Jan 22, 2016)

Forge Boyz said:


> Are you positive you can't put a bigger breaker in? Looking at that buss mounted main it sure seems to me that you could. Do you not have space in that side?
> 
> Sent from my SM-S908U using Tapatalk


That's what I was told ...hope I'm wrong
MORG


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## Morg12345 (Jan 22, 2016)

sbrn33 said:


> That piece of equipment is going to draw more that 600 amps 480?


Primary?


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## Forge Boyz (Nov 7, 2014)

Morg12345 said:


> That's what I was told ...hope I'm wrong
> MORG


Do you have a picture that shoes more of the panel?

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## micromind (Aug 11, 2007)

micromind said:


> Whatever you do, DO NOT TURN OFF THE MAINE BREAKER..........if you do, the entire state of Maine will go dark!
> 
> I agree with the above suggestions, if you can't get a big enough breaker in the panel, there's a good chance you can tap the busses and feed either a fused disconnect or more likely, a breaker enclosure with it. 800 amp will do.
> 
> ...


Now that I've looked at the transformer nameplate, ignore my last paragraph. This transformer is 208∆ to 277/480Y, my last paragraph assumes that it is 480∆ to 120/208Y.

In this case, H0 needs to be grounded.


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## kb1jb1 (Nov 11, 2017)

Morg12345 said:


> ..hello
> It is a listed step up transformer 208 to 480 v
> Y secondary....it's a 250 hp. DC motor...runs off a 90s vintage drive.... They tell me that after start up it only draws around 50 amps continuous and that's where it runs the whole run on the product(plastic sheet)
> 
> ...


I have been there before. The owner controlled and adjusted the machine until the proper service went in. Sometimes it takes months for the town and Utility to get their act together and they expect everybody to hold their lives and businesses and wait for them.


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## Morg12345 (Jan 22, 2016)




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## kb1jb1 (Nov 11, 2017)

Forge Boyz said:


> Are you positive you can't put a bigger breaker in? Looking at that buss mounted main it sure seems to me that you could. Do you not have space in that side?
> 
> Sent from my SM-S908U using Tapatalk


The last Square D I Line panel I installed had the left side using one frame size and the right side used another frame size. One side was empty while the other side was full.


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## Morg12345 (Jan 22, 2016)

Morg12345 said:


> View attachment 171164
> View attachment 171165
> View attachment 171166





Forge Boyz said:


> Do you have a picture that shoes more of the panel?
> 
> Sent from my SM-S908U using Tapatalk


Did you see?


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## kb1jb1 (Nov 11, 2017)

Now I understand what micromind said . The whole state of Maine could go down.


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## TEO (Jan 17, 2020)

I'm no I-Line expert but if that frame size breaker fits on the left side and you have the room above it for another then you should be able to fit another one of those. Unless there's no bussing up there. Have you opened it to look?


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## Forge Boyz (Nov 7, 2014)

Morg12345 said:


> Did you see?


I see no reason why you could not put an 800 - 1000A breaker right above the main unless the rest of the left side above the one filler I can see is full. There is should be bussing on the left side. Good luck finding one though. We waited months for an 800A on a project we are doing.

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## TEO (Jan 17, 2020)

We have been using used breakers for some emergencies but there pricey and it's hit or miss for what you need. Not sure were you are. But my local go to is Capial Enterprises in Tempe AZ


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## paulengr (Oct 8, 2017)

Morg12345 said:


> A lot of good things being discussed here I'm sure I could talk that man to putting an AC drive-in and replace the 250 dc system with a possible 250AC motor
> This is driving a screw which puts hot plastic into a sheet, it really doesn't draw much. heaters once they heat up takes very little to maintain the heat
> It would be great to run it at 208 without having to step up to 480 ,but like I said the biggest breaker I can put in the 208 cabinet is a 400 amp breaker.. matbe I can reduce the horsepower of the motor to decrease current


Maybe but it’s a tricky situation. The issue is that 250 HP is 186.5 kw, without considering efficiency. DC systems are not particularly efficient. But even at 100% efficiency if you run the motor at the peak power point (name plate torque and speed) 186.5 kw is 518 A. So we already exceed 400 A.

What I don’t know (don’t know enough about plastic injection molding) is there are two reasons to pick say a 250 HP motor. One is you need 250 HP. The other is that you need that amount of torque (torque = HP x 5252 / RPM) but not necessarily that much power. That’s where an AC system (or the DC system) could run under 518 A. But I don’t know enough about how these run to say that you can current limit it and still get it up to speed/power that you need.


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## Morg12345 (Jan 22, 2016)

paulengr said:


> Maybe but it’s a tricky situation. The issue is that 250 HP is 186.5 kw, without considering efficiency. DC systems are not particularly efficient. But even at 100% efficiency if you run the motor at the peak power point (name plate torque and speed) 186.5 kw is 518 A. So we already exceed 400 A.
> 
> What I don’t know (don’t know enough about plastic injection molding) is there are two reasons to pick say a 250 HP motor. One is you need 250 HP. The other is that you need that amount of torque (torque = HP x 5252 / RPM) but not necessarily that much power. That’s where an AC system (or the DC system) could run under 518 A. But I don’t know enough about how these run to say that you can current limit it and still get it up to speed/power that you need.


 I did find that a 500 anp breaker will fit in my 208 service panel
Now my choices are to use the 275KV transformer 208/4 80 V
Find A 208 volt DC drive to run that motor I am not sure if I have to change the motor out in that case
Go to A ..AC drive and change out motor and drive to 208 volt AC
MORG


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## paulengr (Oct 8, 2017)

Morg12345 said:


> I did find that a 500 anp breaker will fit in my 208 service panel
> Now my choices are to use the 275KV transformer 208/4 80 V
> Find A 208 volt DC drive to run that motor I am not sure if I have to change the motor out in that case
> Go to A ..AC drive and change out motor and drive to 208 volt AC
> MORG


On the AC side most motors are dual voltage. So finding a motor in stock is easy. A 250 HP, 208 V VFD is not as common but they are out there. You are cutting it close even at 500 A.

On the DC side check the name plate first. A common rating is 500 V armature, 300 V field. You are looking for a 250 V armature which is more rare. You will also need a drive twice as large.

As you have probably figured out this whole thing is stupidly expensive and marginal at best.

If I was going to do it first I’d park a big rental generator on site and let them test and work the kinks out. Then we’d get down to business. Reason being a couple things. This takes the pressure off doing things ASAP. It just becomes a cost savings. It gives everyone time to work things out, especially trying to get large drives and motors on short notice. Also the customer can start making (or losing) money right away which helps finance big changes down the road. Also you can collect data to find out what the real electrical power needs are, especially during startup.

Second if you really have to go to anything exceeding 400-500 A on one load, ideally you can install a large panelboard or switchboard with 3 1200 A breakers and a separate new MLO MDP for the building, all same brand so they all coordinate properly or are series rated or use ZSI on the big ones. Maybe extra expansion slots too. Less than ideal is maybe get two 1200 A frame electronic breakers and mount them yourself or get them prepackaged with bus bar extensions and either bus bar or Flexibar or 4 350s per phase. One is the “main”. One is the plastic machine “feeder”. Then reuse the existing “main” panel but convert to a subpanel (separate grounds and neutrals, move ground to new “main”), fed from the new “main”. Series combination won’t exist. Somewhere in the new “main” you will need three things. You will probably need to incorporate a new meter base?? You will need to have ground fault (easy) and arc flash “maintenance switch” (an extra selector switch connected to the main) to meet Code.


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## Morg12345 (Jan 22, 2016)

paulengr said:


> On the AC side most motors are dual voltage. So finding a motor in stock is easy. A 250 HP, 208 V VFD is not as common but they are out there. You are cutting it close even at 500 A.
> 
> On the DC side check the name plate first. A common rating is 500 V armature, 300 V field. You are looking for a 250 V armature which is more rare. You will also need a drive twice as large.
> 
> ...


I only have a 1000 amp 3 phase 208 service
MORG


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## paulengr (Oct 8, 2017)

Morg12345 said:


> I only have a 1000 amp 3 phase 208 service
> MORG


Standard frame sizes on breakers are typically 1200
A. You usually get 1000 A by either using a rating plug or setting it to 1000 A.

This is an example:



https://benshaw.com/downloads/catalogs/Molded-Case-Circuit-Breakers-Catalog.pdf



The 800 and 1200 A frames are electronic. You can adjust them to anywhere between the frame size and 50% of frame size.


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## kb1jb1 (Nov 11, 2017)

Morg12345 said:


> ..hello
> It is a listed step up transformer 208 to 480 v
> Y secondary....it's a 250 hp. DC motor...runs off a 90s vintage drive.... They tell me that after start up it only draws around 50 amps continuous and that's where it runs the whole run on the product(plastic sheet)
> 
> ...


1000 amp main breaker but what are the feeders to it? I have seen parallel 500 kcmls copper feeding a 1000 amp main lug panel and I always questioned that. I am sure it is correct but check it if you did not do the original installation.


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