Motor Fuses

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kwired said:
I took his 3,5, and 7 to mean he has smaller motors in these instances and the fuse settings associated with them are in the 3-7 amp ranges. But I agree if that is the case that he likely has ground fault issues and not motor overload issues when it takes out those fuses
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Are we reverting dack to fuse protection of motors or fuse protection of motor circuits? Unless the motor control does include an OLR coordinated to protect the motor itself or the motor manufacturer specifies that fuse protection is required for their motor fuses protect the motor circuit from a motor failures. L-G, L-L etc.
 
templdl said:
Are we reverting dack to fuse protection of motors or fuse protection of motor circuits? Unless the motor control does include an OLR coordinated to protect the motor itself or the motor manufacturer specifies that fuse protection is required for their motor fuses protect the motor circuit from a motor failures. L-G, L-L etc.
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IDK, but fuses are an option and are still used for various reasons.
 
I am not a huge fan of fuses for various reasons.

One reason is the need to have a set of spare fuses on hand for every size and type of fuse in the plant so that when one blows, you can replace it. Often it seems like the rating you need is not available so you end up putting in whatever you can find that fits in the fuse block just to get back and operating, always with the intent of getting the correct rating, but it does not always happen.

As an integrator, another reason I don't like fuses is because over about 100A they usually cost more then a MCCB and take up more space. They also have more options for being able to be locked out that is less available with fuses. MCCB also have more/better options for lugs in many cases than fuse blocks do.

However, if you need a high SCCR, fuses are often a cost effective answer.

I find myself using fuses mostly 60A and smaller. That seems to be the break point for me where fuses become less practical and a MCCB starts to make more sense. I have gravitated toward class CC fuses for 30A and under and class J fuses for 60A sizes. One reason I like the class CC fuse blocks because you can now get 1,2, and 3 phase bus bars for them. Makes wiring a lot simpler.

Siemens and AB both have UL489 mini breakers now that have bus bar options, but they are only good for 10kAIC, so that limits their usability, even though they are rated for up to 480/277V. Even so they are pretty cost effective and take up very little space. Pretty good for small motors.
 
iceworm said:
Disclaimer: My experience is all medium/heavy industry. That will be my point of view. I don't do IEC motors, very little with combo IEC overload/contactor/disconnect/cb units. Everything I will refer to will be NEMA standard stuff.

There are some on here that do not agree with my design philosophy. So if you find yourself disagreeing - you are in good company - wrong, but in good company:roll:.

Assumption:
When you say, "every year we have buckets trip, and they are usually 3, 5, or 7 amp 480 volt buckets", you are refering to a bucket with separate CB, contactor, overload relay. The "3, 5, 7" is the number on the CB handle, and the trip was the CB. If not pitch the rest of the post.

The circuit breakers will be mag-only (instantaneous). The "3, 5, 7" doesn't have much to do with breaker setting. Most all of these I have seen will have three dials near the bottom, usually marked A -G (or so) These are what set the trip level. Using the chart that came with CB, one selects the setting that cooresponds with a suitable fault level, usually 8X to 17X the motor FLA. For example, for a CB marker "7', and the dials are set for a trip of 8X, the load can draw 50A for ever and the CB will not trip - yep, truth

Mag-only CB can only be part of a listed combination controller. This type ese should be part of a bucket that was purchased assembled (CB, Contactor, overload) and they should have a NRTL sticker. The sticker applies to all the parts, not just the CB.

So, if the CB is tripping on a GF of short Circuit and ovlds are not tripping, the devices are working exactly per plan.

This is short and there are a bunch of design and code issues that I didn't go into. I'm working today (someone is paying my bill) so all for now. Do a search. I've got some posts as well as others. There's plenty of detail.

later

ice
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yeah, I have to adjust the breaker pots usually to the max.

otherwise we get nuisance trips. And equipment and lines down.

I think it's setting H,

there is about, I want to say 10 letter settings on a single pot, for most of our MCC's.

we usually turn up the heat.

if it's shorted it will for sure trip it anyway.

but if it's a high resistance short, that is hard to detect with our testers, meggars, etc....

it will still run until the short becomes detectable.
 
kwired said:
I took his 3,5, and 7 to mean he has smaller motors in these instances and the fuse settings associated with them are in the 3-7 amp ranges. But I agree if that is the case that he likely has ground fault issues and not motor overload issues when it takes out those fuses
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actually the former poster hit it spot on.

These MCC's have a breaker per each bucket, as it's main.

and these buckets are rated by horsepower and intercheangable and upgradable to any horse bucket in the series.

they just stab in.

but the breakers are there, and typically there will be a starter with a overload.

and no fuses.

(so that was my other question, is why can't we have an overload/breaker unit.

The Sneider Electric GV2 series rotary, with lockout tab is the one we buy for new panel installs.

then the starter will not need a OL on the secondary, as it is inherent with combo, branch circuit protection and motor overload device:

https://www.schneider-electric.us/e.../684-tesys-gv2-manual-starters-and-protectors
 
godsquadgeek said:
actually the former poster hit it spot on.

These MCC's have a breaker per each bucket, as it's main.

and these buckets are rated by horsepower and intercheangable and upgradable to any horse bucket in the series.

they just stab in.

but the breakers are there, and typically there will be a starter with a overload.

and no fuses.

(so that was my other question, is why can't we have an overload/breaker unit.

The Sneider Electric GV2 series rotary, with lockout tab is the one we buy for new panel installs.

then the starter will not need a OL on the secondary, as it is inherent with combo, branch circuit protection and motor overload device:

https://www.schneider-electric.us/e.../684-tesys-gv2-manual-starters-and-protectors
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I know interrupt rating is an issue with transformers and main panels etc, and they may want fuses.

but so far there seems to be leeway to do away with fuses all together.

but what I don't know is if the above overload/breaker has ground fault protection, I assume not.
 
petersonra said:
I am not a huge fan of fuses for various reasons.

One reason is the need to have a set of spare fuses on hand for every size and type of fuse in the plant so that when one blows, you can replace it. Often it seems like the rating you need is not available so you end up putting in whatever you can find that fits in the fuse block just to get back and operating, always with the intent of getting the correct rating, but it does not always happen.

As an integrator, another reason I don't like fuses is because over about 100A they usually cost more then a MCCB and take up more space. They also have more options for being able to be locked out that is less available with fuses. MCCB also have more/better options for lugs in many cases than fuse blocks do.

However, if you need a high SCCR, fuses are often a cost effective answer.

I find myself using fuses mostly 60A and smaller. That seems to be the break point for me where fuses become less practical and a MCCB starts to make more sense. I have gravitated toward class CC fuses for 30A and under and class J fuses for 60A sizes. One reason I like the class CC fuse blocks because you can now get 1,2, and 3 phase bus bars for them. Makes wiring a lot simpler.

Siemens and AB both have UL489 mini breakers now that have bus bar options, but they are only good for 10kAIC, so that limits their usability, even though they are rated for up to 480/277V. Even so they are pretty cost effective and take up very little space. Pretty good for small motors.
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thank you for your input, I didn't see your post till now.

I agree fuses are pricy,

migets are what 10 bucks a piece or more?

and if you have two troublshooting calls you can blow 4-6 easy, if you are in a hurry and don't check stuff.

thats 60 bucks out the window!

and thats a fuse less than 35 amps!

Breakers are good because they open all phases, and reduce the possibility of single phasing.

but one thing I have seen and sort of have a question about is current limiting ability.

I have ohmed out fuses on a Reliance VFD drive before and they were closed, and not open.

but when turned on, there was some voltage but not all voltage on second half of fuse.

is this part of the current limiting aspect of a fuse, or is it simply a partially blown fuse, (maybe one of the dual elements gone)?

but I guess what I don't get is why the voltage there was voltage drop.

yeah, it must be the current limiting ability create more and more resistance, and slowly creates greater voltage drop, till it's gone.

( I guess I answered that myself)

but some guys I train don't believe me that you need to check voltage on both sides of fuse, sometimes they are bad, but ohm good.

which means you need to do it live.

against company policy, sometimes.

with the current NFPA 70E you have to pretty much be an astronaut to do what I mentioned above.

But I believe if you are troubleshooting 110 there is an exception that is similiar to the now non existent category zero.

but I dont' remember, since it's been 6 months.

which reminds me, if you see any long tail FR clothing, on sale, let me know.

I have been buying long tees from a tee shirt online, but if I can fine a FR rated one, it will add Calories to my existing over shirt/pants.

and if I have to remove the over coat for some reason, at least I will have still a FR shirt below.

instead of cotton right now.
 
godsquadgeek said:
but one thing I have seen and sort of have a question about is current limiting ability.

I have ohmed out fuses on a Reliance VFD drive before and they were closed, and not open.

but when turned on, there was some voltage but not all voltage on second half of fuse.

is this part of the current limiting aspect of a fuse, or is it simply a partially blown fuse, (maybe one of the dual elements gone)?

but I guess what I don't get is why the voltage there was voltage drop.

yeah, it must be the current limiting ability create more and more resistance, and slowly creates greater voltage drop, till it's gone.
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I think some styles of fuses can fail in the way you described. I think it is mostly an issue with semiconductor type fuses. I have not used a semiconductor fuse in at least a decade. Modern drives just do not need them.

I am not all that worried about current limiting. It just is not an issue for me. If I need a high SCCR, class J or CC fuses are often the most cost effective answer and they just happen to be current limiting. However, type F starters usually have a high SCCR and they are not current limiting.

many of our customers are big on getting rid of fuses to reduce the need for spares and to be able to get a unit back in service quicker. others only care about the lowest possible capital cost of the equipment.
 
Circuit breakers are mechanical - they will fail sometime. What if they fail to open when called upon?

Fuses have no moving parts - and when they fail they are done - no resetting.

Circuit breakers because they are mechanical cost more down the road if you want to do any testing to ensure they are still functioning properly, but miniature type and even next larger frames breakers cost more to test then to replace so they just get replaced if there is any concerns.

Fuses there is no test - if you perform any kind of test to cause it to open the circuit - it's life is over and it needs replaced. But the melting point of alloys used in the fuse link doesn't change AFAIK over time.

There are advantages and disadvantages to both types of protection. Both are used quite often for various reasons.

General purpose lighting and general purpose use types of circuits are almost all protected by circuit breakers however.

Industrial applications especially motor circuits - you generally are tripping the motor overload protection, if you are blowing fuses or breakers, you often have a serious problem and often need to replace/rewind a motor.
 
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