125Hp to 200HP?

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Cody K

Senior Member
Location
Texas
My question is for a possible motor upgrade.

We now have an overloaded 125 HP 480v 3phase motor running (a centrifugal pump) around 175 amps. The FLA is 138amps with a 1.15 service factor.

My question is if I install a 200 HP motor (which is what this pump needs for future installations) what would I expect to see on amps. Would I run just over the 175 amp mark or would it pull closer to full load itself which would be in the neighborhood of 225 amps (i have a motor already picked out for use).

Thanks fella's:smile:
 

Cody K

Senior Member
Location
Texas
iwire said:
A single 200 HP motor at 460 volts is going to need conductors with an ampacity of over 300 amps.

Bob, I understand that, and maybe I am asking this question in the wrong place because there is not a NEC compliant way to fix our problem other than running new conduit, pulling much bigger wire ( we pulled 4/0 thwn-2 today to help with overheating issues), installing bigger motor, installing bigger soft start.

I know my soft start is good for a continuous 195 amps (it is in 60F climate all the time). I have already pulled 4/0 with EGC today, that is about max for my 2" rigid conduit. I am trying to see if I can get by with just upping the motor size for now, this installation will probably move in the next few years.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
200 Hp

200 Hp

Cody K said:
Bob, I understand that, and maybe I am asking this question in the wrong place ...............


"Duck & run" seems to be in order here... :)

stepping in these forums for suggestions on a non code compliant job, to me, is akin to the hen stepping into fox's den for directions.....
 

iwire

Moderator
Staff member
Location
Massachusetts
Just curious what would be your motivation to do this?

Wire it to code and make money for doing it.


Beyond that I agree with augie47, this is a NEC forum, not a 'git er done' forum. :grin:
 

Cody K

Senior Member
Location
Texas
your right about doing to code, but I dont write the checks.

The reason for this is they upgraded the pump to pump more than original installation required. Now we have a electrical installation that is too small. I can get by with the soft start and conductors and just change the motor.

My question is what would a 200hp motor pull if under same conditions as the 125 hp.
 

jtester

Senior Member
Location
Las Cruces N.M.
Cody K said:
.....My question is what would a 200hp motor pull if under same conditions as the 125 hp.

I think an underloaded 200 hp motor would likely pull slightly more than a loaded 125. However, as has been pointed out, regardless of the amp draw, you'd be in violation of 430.22 in most cases.

Jim T
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
200 Hp

200 Hp

Cody,
I think one of the problems here, is most of us deal daily with assuring installations are code compliant and daily with the liabilities associated with completing non-code compliant jobs or giving advice that would lead to such actions.
I'm not sure of your association with the "check writers" that need you to perform such an installation, but if you hold any type of professional license and murphy's law goes into effect, you might be the one left "holding the bag".
Most of us have had experiences with situations where someone is asked to do such intstallations, only to find that same individual in serious trouble if things go wrong. Somehow the folks that promote the "quick fix" diappear when disaster looms.
 

Bob Kraemer

Senior Member
Location
Ohio
augie47 said:
Cody,
Somehow the folks that promote the "quick fix" diappear when disaster looms.
Or they say when things go wrong, I don't know what he is talking about, I never told him to do that, I was told the install would be code compliant etc! you get the picture.
 

hardworkingstiff

Senior Member
Location
Wilmington, NC
New Contractors

New Contractors

augie47 said:
Cody,
Somehow the folks that promote the "quick fix" diappear when disaster looms.

New contractors need to heed augie's warning. We all are approached like this at some time. If you are hungry and not working, you might be tempted to do it. Advice: DON'T!!!
 

Cody K

Senior Member
Location
Texas
Thanks guys,

jtester, i think as you on the amp draw of the 200 hp. I believe it will be in the neighborhood of 200 amps (with the 125hp pulling 175 amps).

You are all right on doing this to code. Somehow I knew when I posted I was going to get hammered.:D I still dont know exactly how we are going to handle it. I work for the natural gas company that is wanting a solution to this problem. The bad thing is this installation will only be there at the most another 10 years so we dont want to spend a fortune. Otherwise on installations we always do our best to follow code.:smile:
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
temporary

temporary

Cody K said:
Thanks guys,

..... The bad thing is this installation will only be there at the most another 10 YEARS so we dont want to spend a fortune. Otherwise on installations we always do our best to follow code.:smile:

Oh! You didn't say it was TEMPORARY :)
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
the only answer I can come up with that is code compliant and does not involve redoing your conduit is to use a 550V motor. It might just sneak in at being code compliant with the size wires you have at the higher voltage and HP.

I wonder what the cost of a 460-550V xfnr is versus redoing the conduit?
 
Cody K said:
Thanks guys,

jtester, i think as you on the amp draw of the 200 hp. I believe it will be in the neighborhood of 200 amps (with the 125hp pulling 175 amps).

You are all right on doing this to code. Somehow I knew when I posted I was going to get hammered.:D I still dont know exactly how we are going to handle it. I work for the natural gas company that is wanting a solution to this problem. The bad thing is this installation will only be there at the most another 10 years so we dont want to spend a fortune. Otherwise on installations we always do our best to follow code.:smile:


Cody
This kind of response really ticks me off. I do not think you really care if it is code compliant. It would seem to me that you just want someone to tell you how it will work.

"only be there at the most another 10 years..." give me a break!
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
jtester posted the correct technical answer as far as adressing your specific question. Aside from some additional magnetizing current for the larger motor, the normal running current is going to be based upon the LOAD, not the motor. By the way, the soft starter only helps with regards to the starting current. It isn't going to make that 200HP motor look like a 125HP motor.

The issue everyone else is warning you about is, the NEC is mostly not about NORMAL conditions, it's about what happens if... So in your case, what happens if your 200HP motor seizes a bearing? The answer is, it is going to draw FAR MORE current that your 125HP motor would in the same circumstances. So with you having undersized conductors, you run the risk of starting a fire.

You can put circuit protective devices in line that are rated for the 4/0 wire, and that will help to provide that protection. However, said circuit protectives devices for that size wire are engineered using base assumptions regarding the load and that you are not going to attach them to something that is capable of trying to pull any more current than what the wire is truly rated for. Sure there are margins of error, but to dip into them is to remove them, so now you have NO margins for error. No matter what you do to try to protect the wires from being overloaded, the motor is a "dumb animal" and will effectively ignore your best efforts to keep it from working too hard if it needs to.

Bottom line, if the guys with the purse strings are trying to skimp on electrical costs, they are asking you to abet a crime. If a fire starts, and it is found that they / you ignored the code, they/you can be help accountable for gross criminal negligence. Put that in your pipe and smoke it a bit.
 

iwire

Moderator
Staff member
Location
Massachusetts
Jraef said:
So in your case, what happens if your 200HP motor seizes a bearing? The answer is, it is going to draw FAR MORE current that your 125HP motor would in the same circumstances. So with you having undersized conductors, you run the risk of starting a fire.

Exactly along the lines I was thinking.

Bad bearing, broken impeller causing a jam, foreign objects sneaking past intake screens etc.

This thread is now closed, we are not going to discuss how to circumvent the NEC at an NEC forum.:roll:
 
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