# Different Amp Fuses



## Mastertorturer (Jan 28, 2009)

Is there a reason someone would use different amp fuses in a three phase disconnect for motors? 

It seems to me like they didn't have the correct size and just used what ever they had. Perhaps someone who's had more experience with Mag-Starters could elaborate on this.


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## jbfan (Jan 22, 2007)

Mastertorturer said:


> Is there a reason someone would use different amp fuses in a three phase disconnect for motors?
> 
> It seems to me like they didn't have the correct size and just used what ever they had. Perhaps someone who's had more experience with Mag-Starters could elaborate on this.


If you are talking about two 15 amps an 1 20 amp fuse, or some other combo, then someone did not have the correct fuse in stock.


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## Mastertorturer (Jan 28, 2009)

That's what I'm talking about. The range differance is more than 5 amps which kinda makes me laugh when I see it. 

In more than one instance I've come across a differance of 20 amps or more. Then again the same building contained bridged fuses too so it's on par. 

Didn't want to jump to conclusions. 

I've found the Ontario Electrical Safety Code for not bridging fuse holders.

_Ontario Electrical Safety Code 14-210_
_Fuses and fuse holders_

_Only fuses and fuseholders of proper rating shall be used; and no _
_bridging or short-circuiting of either component shall be permitted. _


Still looking for the code that says not to mix fuses but it may be under correctly sizing the fuse to the wire. Or does that one kind of say what I'm thinking. Correct size fuses...

It still seems kinda grey to me for mixing them.


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## wildleg (Apr 12, 2009)

Mastertorturer said:


> Is there a reason someone would use different amp fuses in a three phase disconnect for motors?
> 
> It seems to me like they didn't have the correct size and just used what ever they had. Perhaps someone who's had more experience with Mag-Starters could elaborate on this.


1) too cheap
2) too stupid
3) too lazy


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## Mastertorturer (Jan 28, 2009)

That is very efficient elaboration.


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## mutabi (Jun 2, 2009)

I have to say I am guilty of this. Feel free to correct me if I am wrong. 

Fuses before a motor starter are designed to protect the wire, not the motor. If I am running a 5 amp motor using 10 guage wire, I would have no problem using two 15A fuses with a 20A fuse. All I am doing is protecting the wire, and a 20A fuse is still perfectly fine for 10 guage wire. Of course, for aesthetics more than anything I would like to have three 15amp fuses. But getting a machine running is more important than aesthetics in my opinion. As long as its safe. 

Now, to go a bit further down the line...what about using different size overloads on a motor starter? Lets say my motor starter uses overloads good for 5 amps to protect my 5A motor. And one of these overloads goes bad, and I have no identical replacement. Is it acceptable to replace that one overload with one good for say 8 amps? I have done this also in the past. And dont see a problem with this either. Thoughts anyone?

I am open to correction


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## wildleg (Apr 12, 2009)

the problem I have with different size fuses is that I am always afraid that a temporary overload could result in the motor getting fried from single phasing. Now, I have not seen it happen, but if anyone has a book on installing motors or fuses that says something like "when you get to installing fuses, just put any old size you want in - they don't have to match . . .etc" I would love to see it.


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## mutabi (Jun 2, 2009)

I have never seen a motor, whose only protection was by fuses. Like I said, in my opinion, fuses are only there to protect the wire feeding the motor. Not the motor itself. Some of the guys here with more experience may be able to say that it does happen. Its just I have never seen it. 

The motor starter should provide overload protection for the motor. And as long as there is at least one correctly sized overload in place, then the motor should be fine until the proper overloads can be installed. The reason being that if a starter has 1 five amp and 2 eight amp overloads, the five amp will trip first (before frying the motor), which will in turn, kill the power to the starter coil. Motor Protected. Time to go buy the correct parts.


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## Mastertorturer (Jan 28, 2009)

Well after reading a good portion code I've notice that the overcurrent protection is based off the motor load.

So in the Ontario Electrical Safety Code 2009 it does not base overcurrent protection on the feeder gauge but the motor and load itself. The ampacity of the wire is based on a percentage of the full load of the motor. The overcurrent protection is then based on the full load current aswell.

I imagine to keep things the same for clarity. 

So by code each overcurrent protection must be based off the motor and therefor cannot be of different ampacity. 

Or at least that's my understanding at this point in time.


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## mutabi (Jun 2, 2009)

> The ampacity of the wire is based on a percentage of the full load of the motor


Do you happen to have a percentage/table?


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## John Valdes (May 17, 2007)

mutabi said:


> I have to say I am guilty of this. Feel free to correct me if I am wrong.
> 
> Fuses before a motor starter are designed to protect the wire, not the motor.
> 
> ...


*I use the term "heater" as most NEMA contactors have interchangeable thermal devices ("heaters") and the OLR is a separate component. IEC OLR's are encompassed in one (1) component and are usually adjustable.*


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## John Valdes (May 17, 2007)

mutabi said:


> Do you happen to have a percentage/table?


NEC Article 310.16


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## mutabi (Jun 2, 2009)

Useful info guys and interesting discussion, thanks. 



> The NEC states in Article 430.52 you can use an inverse time breaker rated at 250% of the motor FLA. So you have a 5 amp motor.
> 5 x 2.50 = 12.5 amps. So the maximum breaker allowed is 15 amp. The minimum wire size would be #14.


So how does this fuse/breaker protect the motor? Ignoring the overloads, if that 5A motor starts pulling 12 amps, the 15A fuse/breaker will never interrupt the current. Motor gets fried. The wire will be protected, but the motor wont be. Or is that breaker/fuse designed for those occasions when a motor develops a direct short?


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## wildleg (Apr 12, 2009)

the breaker/fuse is for short ckt and ground fault protection for a thermally protected motor, the conductors, and the controller (430 part IV). otherwise you use heaters for overload protection.
(check out 430.31,.32)


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## InControl (Mar 20, 2007)

As has been stated, in a properly designed circuit, the fuse/breaker is to protect the conductors, while the motor should have its own overload protection. 

If that is the least of your worries, than you have it pretty good. I cant remember how many fractional HP DC drives/motors I have replaced because they come from the factory with 15A fuses and no one bothers to verify the fuse with the FLA.


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## RIVETER (Sep 26, 2009)

*Fuses*



Mastertorturer said:


> Is there a reason someone would use different amp fuses in a three phase disconnect for motors?
> 
> It seems to me like they didn't have the correct size and just used what ever they had. Perhaps someone who's had more experience with Mag-Starters could elaborate on this.


You size the conductors to the load...You protect the motor to it's current...plus 25%.


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## wildleg (Apr 12, 2009)

RIVETER said:


> You size the conductors to the load...You protect the motor to it's current...plus 25%.


lol. not exactly. You size motors, conduuctors, control panels, and overloads according to article 430. If it was as simple as what you wrote, studying for masters tests and sizing motor ckts would be a whole lot simpler.


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## Grimlock (Aug 4, 2009)

I disagree with some of the posts stating that its not an issue to have overloads of the incorrect rating as long as one is the correct rating. What happens when one of the windings shorts internally and begins to draw a higher current than the others? The motor overheats and potentially causes more damage than it would have otherwise. Never compromise on overload ratings they are there to protect the motor as well as safety.


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## chenley (Feb 20, 2007)

Grimlock said:


> I disagree with some of the posts stating that its not an issue to have overloads of the incorrect rating as long as one is the correct rating. What happens when one of the windings shorts internally and begins to draw a higher current than the others? The motor overheats and potentially causes more damage than it would have otherwise. Never compromise on overload ratings they are there to protect the motor as well as safety.


I agree with you Grim. I've seen motors do that and it usually always comes down to improperly sized heaters on the starter. I don't know how many times I've had to explain to maintenance "electricians" that the OCPD is just there to protect the conductors supplying the motor and that the heaters on the starter are there to protect the motor.


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## John Valdes (May 17, 2007)

Grimlock said:


> I disagree with some of the posts stating that its not an issue to have overloads of the incorrect rating as long as one is the correct rating. What happens when one of the windings shorts internally and begins to draw a higher current than the others? The motor overheats and potentially causes more damage than it would have otherwise. Never compromise on overload ratings they are there to protect the motor as well as safety.


I agree all thermal overloads (heaters) should be of the same correct size. However, at 2:00 am and you have one close but not exact I use it until morning when I can get the correct one. Its usually a good idea to replace all three anyway.



wildleg said:


> lol. not exactly. You size motors, conduuctors, control panels, and overloads according to article 430. If it was as simple as what you wrote, studying for masters tests and sizing motor ckts would be a whole lot simpler.


Well Said :thumbsup:



chenley said:


> I don't know how many times I've had to explain to maintenance "electricians" that the OCPD is just there to protect the conductors supplying the motor and that the heaters on the starter are there to protect the motor.


We are not dealing with a residential branch circuit here. This is a motor circuit and is addressed differently.
Article 430.52 describes how to size the OCPD of the motor circuit. This is determined by a percentage of motor FLA. The conductor size is determined by motor FLA. 
There are circumstances in a motor circuit where for example you could have a 70 amp breaker on #10 wire, and be perfectly code compliant. 

In my experience it is the maintenance/technical people that explain these things to the contractors. In my experience.


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## Mastertorturer (Jan 28, 2009)

So is there now general agreement that OverLoad protection for the feeders and motor windings is based off the FLA?

That's my current interpretation from this discussion and from my code book (even though it's an Ontario 2009) 

Our code on motor circuits is very similar in case you ever wondered.


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## chenley (Feb 20, 2007)

John Valdes said:


> We are not dealing with a residential branch circuit here. This is a motor circuit and is addressed differently.
> Article 430.52 describes how to size the OCPD of the motor circuit. This is determined by a percentage of motor FLA. The conductor size is determined by motor FLA.
> There are circumstances in a motor circuit where for example you could have a 70 amp breaker on #10 wire, and be perfectly code compliant.
> 
> In my experience it is the maintenance/technical people that explain these things to the contractors. In my experience.


I was thinking of one motor: OCPD -> conductors -> motor starter -> conductors -> motor

Sure, you could have a 70A breaker on 10 awg, say for instance if you're feeding a control panel for equipment using multiple motors. The feed and OCPD for the control panel is based on all the loads attached to the control panel and devices within the control panel. Then the conductors feeding the starter and motor are sized by that motors FLA. At least that is my understanding. 

I've never ran into maintenance/technical people at the places I work at. One place is completely ran by a guy who has am engineering degree and knows about everything you could possibly know about hydraulics, air systems, and that stuff. This same guy has also had a motor running in forward and manually depressed the reversing starter for it. Ever since then he calls us when he has an electrical problem.


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## John Valdes (May 17, 2007)

chenley said:


> I was thinking of one motor: OCPD -> conductors -> motor starter -> conductors -> motor
> 
> Sure, you could have a 70A breaker on 10 awg, say for instance if you're feeding a control panel for equipment using multiple motors. The feed and OCPD for the control panel is based on all the loads attached to the control panel and devices within the control panel. Then the conductors feeding the starter and motor are sized by that motors FLA. At least that is my understanding.
> 
> ...


_On a reversing starter/contactor there must be a mechanical interlock to prevent your customer from pushing in a contactor when the other one is closed. It also must have an electrical interlock, that prevents current from flowing into both contactors at once. Reversing contactors purchased pre-wired meet both requirements out of the box. You should check this for him asap. One day it will blow up in his face. Pushing in a contactor to see if a motor will start is also very dangerous. I worked in a plant where the mechanic pushed the contactor in and it blew up. The motor was shorted and the IEC contactor took the full hit. POW!_


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## chenley (Feb 20, 2007)

I replaced it with a mechanically interlocked reversing starter. I'm thinking is was electrically interlocked so going forward/reverse from the control panel was impossible, since he pushed it in manually he pretty much bypassed that safety feature. 

All the control panels that are at that manufacturing facility were built by this guy (trial and error) from parts left over from a Mattel plant that had moved to Mexico. 

This is the same building we installed a 480/277 service on and have been transferring equipment to that new service from the existing 240 3PH. Luckily he won't touch the 480 equipment and that it was just a reversing contactor connected to a 5HP motor on 240 that he depressed.


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## John Valdes (May 17, 2007)

He knows enough to be dangerous...lol. Good job on replacing that home made starter.
You can buy the starters and all the additional stuff to assemble reversing starters safely. If he likes to build stuff, maybe he just needs you to make sure its safe. 
If you are using IEC starters, PB's and relays try this link. http://www.weg.net/us/Products-Services/Automation/Controls Rebuildable starters to 75 Hp. Use a .50 multiplier to get your cost.


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## smeric28 (Nov 16, 2009)

wildleg said:


> the problem I have with different size fuses is that I am always afraid that a temporary overload could result in the motor getting fried from single phasing. Now, I have not seen it happen, but if anyone has a book on installing motors or fuses that says something like "when you get to installing fuses, just put any old size you want in - they don't have to match . . .etc" I would love to see it.


this can still happen even when all the fuses are the same size...... to protect from single phasing you need a 3phase CB (or iec starter) you guys should google UL508 and you'll find out more than you ever wanted to know about how to protect motors when using different devices.

EDIT: even a cb won't protect against what i find to be the most common kind of single phasing, when the plant looses 1 phase all together at the main or some distribution point somewhere.


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## John Valdes (May 17, 2007)

smeric28 said:


> this can still happen even when all the fuses are the same size...... to protect from single phasing you need a 3phase CB (or iec starter) you guys should google UL508 and you'll find out more than you ever wanted to know about how to protect motors when using different devices.
> 
> EDIT: even a cb won't protect against what i find to be the most common kind of single phasing, when the plant looses 1 phase all together at the main or some distribution point somewhere.


Heads up facilities will install phase monitors on any critical equipment. They don't cost much and pretty much anyone can install them. They can warn or turn off any load.


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## Mastertorturer (Jan 28, 2009)

I've found the information to answer my question in the code. To help anyone with the same issues or curiosity with OESC.

Appendix "B" page 527 of the Ontario Electrical Safety Code has a "Diagram of circuits, control, and protective devices for motors"

For my particular inspection and code violation found; this applied. 

Ontario Electrical Safety Code 28-200
Branch circuit overcurrent protection

Each ungrounded conductor of a motor branch circuit shall be protected by an overcurrent device complying with the following:

(a) a branch circuit supplying a single motor shall be protected, except as permitted by Item (c), by using an overcurrent device of rating not to exceed the values in table 29 using the rated full load current of the motor;

Thanks to the people who added their information to the thread because you steered me in the correct direction in my own code book.


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## chenley (Feb 20, 2007)

John Valdes said:


> He knows enough to be dangerous...lol. Good job on replacing that home made starter.
> You can buy the starters and all the additional stuff to assemble reversing starters safely. If he likes to build stuff, maybe he just needs you to make sure its safe.
> If you are using IEC starters, PB's and relays try this link. http://www.weg.net/us/Products-Services/Automation/Controls Rebuildable starters to 75 Hp. Use a .50 multiplier to get your cost.


Thanks for the link, that'll go into the bookmarks. I didn't know they sold starters, just thought they manufactured motors. Which I have installed a few saw arbor motors from them. Which they are about 1/2 the cost of the Himmel motor.


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## John Valdes (May 17, 2007)

Actually they are the GE of Central and South America. Thats where their plants are. They sell controls, power distribution and motors to the world. I represented them for a few years and got to see first hand what a top notch company they are. I spent a week in Brazil checking out their factories and women. Both were exhausting.

They are leaders in the US for big motors. Low and medium voltage. They have the respect of some large aggregate companies for motors. Vulcan and Hansen are two that come to mind. They (quarries) will not trust them on drives or controls yet, but when the old timers retire that will change.
The prices are so good and the quality is so high I had a hard time pushing any other manufacturer. Their IEC starters are 1/4th the price of AB. Siemens is close, but still a little higher.
The way I got customers to try Weg, was to ask them what motor in their plant took the most beating and had to be replaced the most. I would then put a Weg motor in that spot. Usually if they tried one they were Weg fans from then on.

Ps.....Did you know that they do not sub any work out except bearings? They have their own mining and foundry's for iron/steel and copper. They cast all their own motor frames and draw their own magnet wire and much more.


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## muhammadarshad (Dec 25, 2009)

Mastertorturer said:


> Is there a reason someone would use different amp fuses in a three phase disconnect for motors?
> 
> It seems to me like they didn't have the correct size and just used what ever they had. Perhaps someone who's had more experience with Mag-Starters could elaborate on this.


it seems to be a mistake. or they don't have in stock. what so ever it is not a standard. all the fuses should be of same ratings.


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## John Valdes (May 17, 2007)

muhammadarshad said:


> it seems to be a mistake. or they don't have in stock. what so ever it is not a standard. all the fuses should be of same ratings.


True. Welcome to the forum. :thumbsup:


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## Mr.C (Dec 20, 2009)

Here's the deal:
1. If any winding internally goes to gnd, boom there goes the ckt bkr.
2. You really want to protect that motor you put a motor saver on it to protect it from single phasing, overcurrents, current and voltage imbalances, over and under voltages, yada yada yada.
3. We would all like to have a magic box with every right size fuse ckt bkr and old in it but we don't and if fuses are mixed, yea make sure the wire is protected bit as far as relying on fuses to protect a motor forget about it unless were talking big DC motors but that's a different story and on electric shovels fuses are very effective and sizing makes a big difference. But again on 3 phase motors get yourself a 777 motorsaver.


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## Mr.C (Dec 20, 2009)

*777 motorsaver*

Here's the deal:
1. If any winding internally goes to gnd, boom there goes the ckt bkr.
2. You really want to protect that motor you put a motor saver on it to protect it from single phasing, overcurrents, current and voltage imbalances, over and under voltages, yada yada yada.
3. We would all like to have a magic box with every right size fuse ckt bkr and old in it but we don't and if fuses are mixed, yea make sure the wire is protected bit as far as relying on fuses to protect a motor forget about it unless were talking big DC motors but that's a different story and on electric shovels fuses are very effective and sizing makes a big difference. But again on 3 phase motors get yourself a 777 motorsaver.


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## John Valdes (May 17, 2007)

What!


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## Mr.C (Dec 20, 2009)

What?


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## htneighbors (Jan 23, 2009)

*3Ph 480V Motors*

Here's a little chart I made up years ago which I used. I modified the answers a bit - like my minimum wire size for the feeders was #10 - but it worked as a quick reference for me. I'll see if it posts correctly. 

OK - it didn't work. Disregard this post!


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## John Valdes (May 17, 2007)

htneighbors said:


> Here's a little chart I made up years ago which I used. I modified the answers a bit - like my minimum wire size for the feeders was #10 - but it worked as a quick reference for me. I'll see if it posts correctly.
> 
> OK - it didn't work. Disregard this post!


"like my minimum wire size for the feeders was #10". 

So a five amp motor had to be fed with number 10 wire? :whistling2:

I worked in many facilities in my career. Some very high tech and some not so high tech. There was always at least one guy that had all these made up rules in his head. Rules he decided were correct, but had no bearing on NEC compliance at all. In fact, most plant electricians could care less about compliant installations. Overkill was the answer to all the problems.


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