Motor Fuses

Hello Guest, Anthony

You will need to advise more details, so a proper answer may be given.

• Number of phases
• Mains Frequency
  
• RPM
• Type of Motor - Squirrel-cage, slipring(wound rotor) other- Advise please.
• Age of the actual motor - (Motors from the 1920's differ from recent motors)
• Type of fuses: wired, HRC etc.
• Type of load the motor is driving
  
• Other useful information
  

Reply here with the proper information.

Kind Regards....

Sparkstation, I am some what confused by your request for the information in your post.

You just stopped short of asking for the Guests date of birth and bank account number . Yes of course if all this information was supplied then it would be easier, however, this information is not needed for an educated guess and that's all we can provide since we don't actually have the motor nor do we know the installation conditions, load etc.

The details given by Guest is a 15HP (11.19KW), 230V, 40amp. Based on this information I would suggest that this is a three phase motor and not single phase since if it was a single phase motor then the absolute max HP would be approx 12HP (9KW) (ignoring pf and eff). My basis would be that if we assume a pf = 0.9, eff = 0.8 and three phase then this would work out at approx 11KW. Of course with single phase motors the eff would be lower.

However I could be wrong if this motor had pf = 1.0 an eff =1.2 .

Kind Regards

Mr. W.A Snow

Yes, your imagination is perfect as motor specs are

HP -15

Phase -3

Volts- 230/460

Amps- 40/20

Service factor- 1.0

RPMs - 3540

Hertz- 60

Code -G

But right now it is connected to 230 v three phase power supply.

Please reply

Anthony

But in most of district, 3 phases power supply is 380 or 420V. no 230 line voltage.

3p4w can be 220 or 230v between line and nutral line.

Do you mean, the 3phase power supply link to your motor 3 input terminals and your motor connects in Y ( star) ? so that the phase voltage of your motor will be 230V.

if there is 230V line voltage in your district, you will connect in delta. you will ue fuse of 40xV^-3 x1.2= *.

[hehe ask something while knowing the answer?---reply holeinthesnow]

cnpower, my japanese, (sorry I keep think that you and Epke are related , my fault) chinese friend I would like to suggest a couple of useful pointers to you that may assist you in your future endeavours:-

1. Read the previous posts before posting a reply and
2. Read the previous posts before posting a reply

If you follow these two pointers then it may actually make your posts more valuable.

"you will ue fuse of 40xV^-3 x1.2= *" - As far as I am aware you use the motor name plate current when sizing the motor overload and this will typically be either 115% or 125%. I am not aware of every regulation/requirement that exist through out the world so this is given as a general comment.

However, I would suggest that an overload set at 83A (by your calculations) would probably be a bit on the high side- true you would never get nusiance tripping , however it is highly unlikey that the overload will protect the motor which is the primary purpose of the overload. As stated previously (you would see this if you actually read the posts, but we have already mentioned this) the motor overload by my calculations and by others would probably be 50A.

Kind Regards

Your friend ()

Mr. W.A Snow

P.S not sure if I have mentioned this but you should read the previous posts before posting a reply !!!

Hehe, holeinthesnow, there are decimate countries in the europe, which one is yours matherland? North europe? Iceland? because pinguin lives there.

Dont bother Epike, because he is from sun country--Japan(es) always like to call it.-- when sun is shinning, snow will melt. and you will not find home.

You are active here, it seems to be your major field. but I can still put out some suggestion, however I think mine is quit right. I know its a not simple way to select fuse. but generally speaking, people like choice it according coeficient like you said 1.15-1.2, in fact, some motor can be from 1.2 -- to 2.2 depend on its start time. I choice 1.2 here to comport with yours'.

if there is 230V line voltage in your district, you will connect in delta. you will use (select) fuse of 40xV^-3 x1.2= *.

I say if the voltage between lines is 230V, not 380 or 420V. ( which is said else by the guess in his specification) then the motor will connect in delta method to suit to the line voltage. then how much current will be in the motor phases? how much current will be drawn in the lines?

you must know at this situation, line current will be 1.73 times phase current.

how much current in the line? 40 x 1.73 = *C;

ok then the fuse will be *C x 1.2 = *A. now you will not laugh at me.

Although I hvnt dealt with the electric for many many years, but the basic knowledge hasnt forgotten.

haha, like a pupile homework.

which district has such line voltage?

cnpower, Firstly thank you for concerning yourself with my well being, I won't visit Epke in the land of the Rising Sun.

Secondly, I would never laugh at you or anyone else (we only joke).

You, like myself, are more than welcome to put suggestions forward - that's what makes this site so good.

Now back to the issue at hand:-

The motor nameplate supplied by the Guest (Anthony) will be something like:

400/230 V, 15HP (11.19 KW), 60 HZ, 23.12/40 A - Star/ Delta, 0.9 pf, 0.8 eff. I have included a typical pf and eff.

If you have a 400V line voltage system then the motor would be connected in Star and the resultant line current would be in the order of 23.12 A. The overload would be sized (generally) at 23.12 A x 1.25 = 29A approx.

If you have a 230V line voltage system then the motor would be connected in Delta and the resultant line current would be in the order of 40A. The overload would be sized (generally) at 40 A x 1.25 = 50A

If you do the math for the power (KW):

Power = √3·V·I·cosφ.η, remember to use the line voltage and line current.

Star: Power = √3x400x23.12x0.9x0.8 = 11.5 KW

Delta: Power = √3x230x40x0.9x0.8 = 11.47 KW

The end result is the same for both, as you would expect.

So hopefully this clears up the "how much current in the line? 40 x 1.73 = *C;ok then the fuse will be *C x 1.2 = *A" issue.

This is my understanding and of course I could be wrong, if so can up please correct as necesary.

Kind Regards

Mr. W.A Snow

wow, I hope you will not angry with my words, different cultrue may has different amuse joke. sometimes may be misunderstand. but after checking up we should get use to it.

both of us are right at this point, I understand your meaning, but I still hope a joke.

I dont know where there is a 230v 3 phases system, I just play a game of math. I havnt done in practice.

----Delta: Power = √3 x230x40 x 0.9x0.8 = 11.47 KW

√3 x 40 = I, which is transmiting through lines. not going through motor windings.

thats why I said fuse should be √3 x 40 x 1.2 = fuse.

at the meantime ,there will be 40A rate current in the winding .(phase current).

anotherway, I dont agree to your using pfxeff in formular, becaue we conside input poer not output power or say efficient power.

Say again, dont be bothered by some of my words. All of our chinese love that nice penguin.

cnpower, I do not get angry at your words - no problem. Yes there is a difference in cultures but that does not affect physics/ engineernig laws etc. I somehow think that gravity and Ohms law also applies in China .

I think I now realise where our misunderstanding/ disagreement is.

We agree that the motor name plate data might be something like:-

400/230 V, 15HP (11.19 KW), 60 HZ, 23/40 A - Star/ Delta, 0.9 pf, 0.8 eff.

I am saying that the 400/230V are the line voltages and that 23/40A are the line currents associated with Star/Delta connection. You seem to be saying that these are the load voltages and currents - because you say "there will be 40A rate current in the winding .(phase current)"

When connected in Star the 23A is the load current but this is because the load current equals the line current in a star connected load (regardless of whether balanced or unbalanced), however in Star the load voltage is going to be 230V and the line voltage 400V (note that this will always be true in a WYE-WYE configuration but only true in a balanced Delta-WYE confguration).

If we were to follow your logic (by saying that the motor name plate voltages and currents were the load voltages and currents) then you would need a line voltage of 690V in order to connect the motor in Star. I am not ruling out this possibility, I just don't think it is correct (this is a polite way of saying that I think you are wrong ).

When connected in Delta the 40A is the line current and the load current will be 23A (only true in the case of a balanced load) and the load voltage will equal the load voltage (regardless of whether balanced or unbalnced), in this example load and line voltage will be 230V.

You can see from the above that in either case (Star/Delta) the voltage across each windings (load) is 230V and the current through each windings (load) is 23A.

Again, this is my understanding so please correct as necessary.

Kind Regards

Mr. W.A Snow

You wrote: which one is yours matherland? North europe? Iceland? because pinguin lives there.

I hope your knowledge of electricity is better than your knowledge of geography... Penguins live exclusively in the SOUTHERN hemisphere.

But few things are certain, you know absolutely nothing about human relations good manners and how to use a spell checker. Basic English grammar school could also help you a lot.

Wangito.

why so bother? take it easy. dont become the second G. Andy.

I appear to ignore your existing, because hvnt replied your thread above. dont angry with it. hehe. its not any thread need to return a reply.

another hand, you can read that good thread and ignore worst one, its not everyone who come here has as good english as you have. although you also made a mistake times. after all its chat, not composition.

people needs help each other. none is a specialist in every field. that why this cr4 is existing. as well as internet.

I wonder why some people here dont like help others with their languge skill, whereas cry out them to go to school? hehe

I think here is a fair place, I help others with their tech wheras others can repay us with their language knowledge. its equal exchange. none will suffer losses.

I said many times, Im a rather lazy, will not use word check function, this will not mislead others comprehension. unless occasionally, when I take seriously.

hehe, forget again reply your question, complement here;

Even chinese children know there was penguin in the north pole district. as well as even in equator district. its not exclusive right for penguin to live only in the shouth pole. although you cannt find any of them now in the north pole district. they are distributing vey widely in the world. once yoiu pay more attention to geography you will know you are as noive as a child.

from now on, you will not make this mistake again. hehe, you owe me a score.

besides, my electricity is as the worst as my chinese words. I can only write now less 3000 words, in fact. need endeavor. and learn from you all out there.

which is your major? you appear to less help others. hehe. try to be an entherism. haha.

because you hvnt read the guest's post, so you think my formula 230/40 w will equal to =^.~6 w (ohm).

not bad.

he said above:

But right now it is connected to 230 v three phase power supply.

Have you ever read it?

for 15 kW motor (3 phase) correct rating of fuse shall be 63 A.

rajesh.sharma, Yes I am sure you are correct but we are dealing with a 15HP motor not a 15KW motor.

Would you agree that the overload should be set at 125% of the motor name plate current or do you have a different method for selection ?

Kind Regards

Mr. W.A Snow

for 15 hp / 11 kw motor (consideraing 3 phase) fuse rating shall also be 63 A.

hope this is in line with our dealing.

Details of motor are:-

Model 5K254BL115 GE manufacturer

HP -15

RPM- 3540

Volts- 230/460

Amp- 40/20

Service factor- 1.0

Code -G

Right now it is connected to 230V power supply.

Please reply

Thanks

Anthony

Anthony, Thanks for the additional information. Your motor windings are connected in Delta (starts in Delta and runs in Delta). Regarding your initial question about the overload setting, my assumption is that you wish to size the overload for the motor. The overload would be set at 50A for such a motor, however (there is always an "however" with these types of answers) it does depend on how the system is wired i.e do you have a frequency inverter, softstarter, is it running at full load etc.

If you wish to get a specific answer then this information will need to be supplied, however it is probably not necessary given all the good advice/ information supplied by the different people on CR4 to this thread.

I think it is unlikely (not impossible) that a 15A olverload will suffice but as charsley99 pointed out it may be better to appease the hierarchy initially.

Kind Regards

Mr. W.A Snow

Anthony

Your voltage rating is not 3 phase standard. 230/460 v is a single phase doubler. Can you tell us what does the name plate read regarding phases, single or three. Check the voltage again, if it is three phase motor, the voltage will be 230/400 volts.

Good spot JMSK. I just also noticed that the current is given as 20/40. I would have expected something like 23/40.

GA from me.

Regards

Mr. W.A Snow

230/40 W motor uses 15A fuse?

he must be kidding !!!!! or your motor work only in a very samll output state. if so why dont change smaller one? 230/4 W

now you know how to select fuse.

Hello cnpower

<"....15 hp 230v/40 amp GE motor....">

It is not a 40 Watt motor.

The missing information really needs to be supplied bythe Topic writer "Guest", for a meaningful answer to be given.

Kind Regards....

close to 40A

oh, I see, you must think I write 230/40 W as 40W.

hehe, 230x40 = *W.

230x 4 = *W

Hello again, cnpower

The way you use standard electrical terms is confusing to those who know Ohms Law.

Nothing in your equations actually makes sense.

Perhaps you are typing on a Chinese character keyboard, and the results are quite different to what you type.

Kind Regards....

From this topic context, none will be confused.

chinese keyboard is not unique, its universal in the world.

have you ever seen this express of squre root?

V^- x+y+z ? its well ocured in some the west books. we can understand it presents as SQRT( x+y+z).

neeednt write as V^--------.

^{btw, are} you teaching in a middle school?

"230x40 = *W" - this is incorrect as you are not considering pf, eff or if this is a single phase or three phase motor.

Also when someone writes 230/40 as a mathematical formula I would consider this to mean 230÷40 and not 230* 40.

Kind Regards

Mr. W.A Snow

hehe, Snow, you can call Epike come here to see my fun.

Back to the right way.

You are quit right. I hvnt taken account of pf, eff etc. lets say its total power, not only pure useful power. if its 3 phase, multiply V^--3. in the engineering, we use to say its total power or say rate power, not useful power. pf and eff is a veriable, according to its site situation. besides, if you select fuse, yoiu cannt use the concept of useful power.

oh, I laze to write as 230V/40A, as we see at top thread. I explain it in #8, pls read it. I dont think there is any different meanings. if in other places, I would not write like this,

However, thank you and Sparkstaion, I wish I could become a bit industrious. and lose too lazy habitude.

You better read the thread more carefully,

Where did he say 230/40W? Read again.

Our guest was asking a legitimate question the best way he could. Maybe not sufficiently clear, but certainly not worthy of sarcasm.

An apology is due.

Wangito.

There should be a name plate with voltage, amps, speed and other information listed on it. What specs are these? What kind of starter will you be using? Will this be a smart motor controller or will it be a magnetic relay. These items also need to be taken into consideration.

If it says 40 amps you could always start with a slow blow 15 amp fuse and see what it spikes up to on your meter. Monitor your runtime amperage draw and see what the results are. If your manager thinks 15 will work and the wiring will handle the load it couldn't hurt to install them and tell him you'll monitor the equipment and inform him of whether or not the fuses are handling the load or not. If under normal run conditions they hold and all is well, you made your manager happy. If they blow you could always increase the rating to a higher fuse and continue to monitor. If the startup and run are much lower than expected you could decrease the fuse ratings and see how they hold. It all depends on the conditions and process that the motor will be used for. Constant stopping and starting could also require a higher amp fuse, but it's better to start low than high. Make sure all wiring is rated for load and protective circuits and monitoring for Jams and overloads are in place.

Good Luck with the manager. Sometimes it's better to appease the hierarchy.

15hp=11185.4981watts?

Is it a 3 phase motor? is 40 amps the running amperages or the maximum current?

and what is his calculation?

A 15 hp motor will pull approx 21 amps Full load current power output should be 11 kilowatts When purchasing fuses ask for motor start as they will take the extra amps on startup. 20 amps is a standard fuse size, if going for a circuit breaker a D curve would be suitable as it will also take the extra load on startup

15A was too low.... start by using 40A

50 amp fuse

A fuse can run at 80 percent with out overheating

yeah, that's what I would have said but now I'm really waiting to see what sparks comes up with...

If you are in the U.S., look at NEC electrical code Table 430.52. The table provides the maximum allowed protection based on motor type & fuse/breaker trip speed.

Good answer Speed. NEC has all the info you need.

JD

Hello Anthony,

A 15 HP motor at 230 volts draws 42 amperes at full load. Locked rotor current could be as high as 100 amperes.

The correct service amperes would be 100 amps. The motor starter heaters are sized according to full load amps. and HP. The motor starter and motor heaters are the components that protect your motor from overload or motor winding defects. The fuses protect the service feeders from overloads and shorts, in turn protecting the motor.

The best type fuse for motor disconnects are dual element time delay.

An excellent reference for motor control specifications and motor starter sizing and fuse applications is the NEC article 430. The charts and drawings will give you all the specs you might need.

Jerry D.

Gerard ESM Inc, my undertanding from the original post is that Anthony is looking for the size of overload for the motor.

The overload protection would typically be set at either 115% or 125% of the motor nameplate rating not the motor full load current rating. You make the selection between 115% and 125% based on the service factor and the temperature rise rating.

Therefore the size of the overload would be either 40x1.15 = 46A or 40x1.25 = 50A

Also, in general the LRC (Locked rotor current) can be as high as 5 or 6 times the running current and the starting current will typically be a minimum of 6 times the running current - these are typical values and of course there are exceptions depending on how the motor is connected.

Kind Regards

Mr. W.A Snow

Hi Snow,

Thanks. I was basing it on a simple motor application. The 115% and 125% overload protection is correct.

100 amp fuse protection would be ideal with properly rated overload protection in the motor controller. (starter)

JD

well since you dont want the motor drawing more than 40 amps...use a 40 amp fuse to protect it

Hi

230 V is a single phase distribution standard; 3 phase voltage will be 400 volts for those who are guessing whether it is a s/p or 3 ph application.

15 HP motor at 230 volts single phase will draw about 40 amps as the name plate says.

To select a fuse, you have to know the in-rush current which is a function of the type of load. Most loads will give rise to an inrush current of 10-20% higher than the full load current. 20% will give a 57A fuse; using a standard fuse of 60 amp will do the job.

Tell your plant manager that the name plate rating of the motor is 40 amp, you can not use fuse less than the rated current.

JMSK, "230 V is a single phase distribution standard; 3 phase voltage will be 400 volts for those who are guessing whether it is a s/p or 3 ph application" - this is incorrect. As an example to prove this point we have three phase motors rated at 400/230 V, 0.6/1.05 A, 0.18KW, pF 0.69 Star/Delta.

Also based on your post should we assume that the motor has η > 1 ?

Kind Regards

Mr. W.A Snow

400/230 v is a standard voltage configuration; 400v being the line voltage & 230 the phase.

You are right the motor could be wired in delta formation by connecting each phases independantly at the motor terminals (provided motor terminals are are wired that way). Not having that info in the first place lead to lot of assumptions.

Question in the post was whether 15 amp fuse is appropriate. The answer was no, it is more like 60 amp.

see Motor Data Calculator

http://www.squared.com/us/squared/corporate_info.nsf/unid/FBD5A5BCC7AA086385256A540060B879/$file/IECMotorDataCalculator.xls

For 230VAC, 3Phase, 15HP, Full Load =42Amps, The Fuses should be 60A Time Delay fuse rating.

considering standard rating of fuses 60 A fuses are not avialable commercially, we have to go for 63 A fuse. in general thumb rule for fuse selection is equals

rated current x 3 (in this case 11 kw motor implies 20 A full load hence fuse rating shall be more than 60 A , hence of 63A.)

If the motor is rated 40 AMPS full load, then a 50 AMP slo-blow is proper. Any short will instantly blow that fuse, while 10% overload is within motor capability, long term operation at or near 50Amps will blow the fuse. Starting the morot of course requires perhaps 150-200 Amps for a second or so, but the fuse will handle that short term overload.

I have read posts through #28.

The old rule 70 years ago when I first learned about motors and installations the info was 3 time the nameplate amps for loaded starting motors...

Before slow blow fuses......

Or, if breaker protected the suggested 125% of name plate amps..nearest breaker over that size.

It is the first revolution that blows fuses......obviously a fan blade loaded motor acts differently than any instant mechanically connected loaded work.

Modern design motors bring many other things into play but the above carries no penalty to design a system. Fits with 2..4...6..or 8 pole motors on 120 volt to 480 volt AC systems in the U.S.A.

MR. GUY

Here's a silly answer; disregarding all the provided motor data and looking at what his manager said, maybe his boss knows the wire is AWG14 which would be protected with a 15A fuse. Of course, the fuses would blow on motor start.

I'm waiting through the whole night for that so-called Wangito's response.

He might be one of proud of his limited southern hemishphere geographical knowledge. and I could image cool sweats he broke out after read the wild distribution. I know he read above thread and keep silence so far. of cause he will not make such stupid mistake. not bad.

I wish he would be one that like to help others, not speak only jibes and taunt . so that he can learn more electric skill from chinese workers. and dont act as a porter.

haha, assume ...

15Amp?????

How he calculated? you clearly mentioned that the motor is 40Amp, so fuses must be 40 x 1.25 = 50Amp. But why you are using fueses? I recomend to use Circuit breaker. If motor's speed is controled via an inverter then fuses are better as they can bllow fast as compare with MCB/MCCB. Any how, we have been using rather fuses or MCCBs.

I would simplify the whole thing to this--Size your conductors beyond what your FLA and motor circuit needs and size the breaker or fuses to protect the conductors legally.

Motor protection should come from the overload and I would size it for FLA and no more--I believe it is legal to "up size" overloads one size above FLA, but why would you?

If you use fuses for motor protection--The inrush current will have you over sizing them--Then if you blow a fuse in one leg and single phase the motor, the current may not blow the other two fuses and may let too high of current to the motor and damage or destroy it.

Just my opinion.

Kilgore Trout, When sizing the conductors, disconnects etc (NEC) you should use the FLC from the tables and not the FLA (there are exceptions to this I believe).

When sizing the motor overload protection you should use the FLA (motor name plate current rating).

I realise that you are saying this but it is important (I believe) to point out the subtle diffference.

Kind Regards

Mr. W.A Snow

Oh--excuse me. I read the post and thought it was a 3 phase motor. I have sized and set up may, but never any single phase--Disregard my previous post, please. OOOPS.

But I did find this and think it's worth a look:www.electrician2.com/calculators/motor_ver_1.html

Fuse manufacturers data recommend fuses for a motor taking from 28A to 45A FLC per phase with a gG characteristic (General purpose fuses) of 80A

Motor rated fuses of gM characteristic 63M80 are recommended for 28A to 45A motor FLC (This allows 63A physical sized fuseholders to be used)

All the tables I have show 11kw motor FLC at 220v as 40A or very close.

These fuses will allow 7 x FLC for at least 10 secs.

220v is a common European phase to phase voltage and most small motors are wound for 220v delta and 380v star connection. (220 x root 3 = 381)

Of course this assumes that the cabling etc is rated to supply the motor.

Apologies for stating facts in this light hearted thread.

<...plant manager suggested 15 amp...>

Aren't the <...fuse...>s supposed to protect the cabling, though? Details of it have been withheld from the forum!

Rather than the <...plant manager...>, consult a local qualified Electrician instead, who will be able to assess the design, complete the installation, test and certify its safety in accordance with a national standard, such as BS7671, should this be applicable,

However, the location of the installation has been withheld from the forum, and that will have a bearing on the standard used.

<...do not agree with this calculation....>

It's wise to be wary. Safety doesn't give a damn about agreement between people, though.