ECN Forum Forums General Topics of the Trade General Discussion Area Overcurrent Protection - Bussmann

Erwin,

In regards to the device that does not trip, I was not trying to single out one manufacturer. It can happen with any manufacturer, where the conditions of testing and maintenance are lacking. Although, I have heard similar comments in regards to your conclusion...however, I have no first hand knowledge of that, only second hand information about that and other various manufacturers.

Wirewiz,

I have searched the Bussmann SPD in regards to finding supporting information of replacing all three fuses, but have found nothing in print. However, I believe this to be a good maintenance practice. Perhaps, you can point out that the cost of an extra fuse is a minor cost in comparison to what could create a future maintenance cost.

Dan

Warren,

Sorry the links didn't work as expected. Perhaps if you can just go directly to our website, click on services, then on-line training you can get to our presentations which are downloadable. All of them are posted and available for download. If you cannot access this by doing the above, please email me with you address and I will send you a CD with all of the presentations. I can include any other information on this CD that would be of interest to you.

Dan

Bill,

Thanks again for letting me participate in your discussion and adding links to our information.

In regards to your question on the overcurrent protection knowledge needed by the average electrician, I would suggest the below three most important points, in order of importance.

1) Always make sure you know the available fault current and apply an overcurrent devices with adequate interrupting ratings per NEC 110.9. This is the most overlooked and important item of proper overcurrent protection. This is especially important for the service equipment and first level distribution panelboards. The application of current-limiting devices makes this less of an issue in these applications due to high interrupting rating capabilities.

2) Be aware of proper protection requirements of electrical systems components per NEC 110.10 and NEC 110.3(B). Many components may require a specific device, per NEC 110.3(B) in regards to the listing and labeling...such as HVAC equipment. This can also be extended to motor circuits, regardless of the single-phasing concerns. Fuse protection (with solid state overloads and single phase protection) are still the best solution for these applications.

3) Safety is the common thread in overcurrent protection. The first two points have addressed safety in regards to systems and electrical components, because this is the most common concern. However, when you add the human factor...this hits home even more and this is why this has been a major focus recently. Anyone who has seen an electrician with third degree burns understands what I am referring to with this discussion. I am not trying to imply that fuses solve all the problems in protecting the electrician, however they certainly help to offer a component of the total solution. The bottom line is that fuses can provide reliable overcurrent protection and can lessen the dangers to electricians in certain situations.

Dan,

Welcome Aboard!

I look forward to discussions regarding SCA calcs and such with you and the members in this forum.

I'll toss some scenarios out when time allows.

Scott SET

In an effort to suggest methods to provide human safety to the maintanace crews, current limmiting fuses and breakers help reduce arc flash significantly.

Dan,
Is it becoming more common for industrial facilities to use fuses instead of MCPs or MCCBs for short circuit protection in motor control centers. I was in locations several years ago that were doing this on the fuse manufacturers' recommendation due to the increased reliability and accuracy of fuses over breakers. These facilities had processes that could lose a lot of profit from nusiance tripping of breakers and time down replacing motors whose breakers did not trip.

Thanks Dan
wirewiz

Dan,

I just came across this Article at the CEE News Website and I figured I would share it with everyone.

Cooper Bussmann now offers online educational and training presentations on the NEC

Bill

gpowellpec,

In response to your question on fuses vs. circuit breakers in motor circuits:

I have not heard any issues with nuisance tripping of fuses or circuit breakers. However, I have heard issues with MCPs (and this is why the limits on sizing keep rising).

It seems like the trend lately has been to go to circuit breakers and MCPs. Why, because they think that the resettable feature of breakers is better than having to replace fuses and they do not have to have a qualified electrician to do this...just an operator.

However, the flaw in this logic starts with choosing convenience over protection and safety. Why?
1) The branch-circuit device in motor circuits (or as termed in 430.52, is the branch-circuit, short-circuit, and ground-fault protective device) is there to protect against short circuits. The overload relay is there to protect against overloads. OSHA requires that circuit breakers and fuses can not be reset unless the device opened due to a known overload. If you think about it, the fuse or circuit breaker is typically sized per 430.52 at 175% or 250% respectively because it is there only for short-cirucit protection. The overloads sized at 115-125%. Thus, if the fuse or circuit breaker opens, it is probably due to a short-circuit condition and the problem must be corrected before the device can be reset. Thus, resettability of breakers is really a mute point.
2) Given the above, if circuit breakers are used and since they are resettable would the possibility be a person to just try and reset the device before checking out the problem? This could be an issue unless OSHA rules are followed.
3) As discussed previously, the device is there for short-circuit protection. More specifically, short-circuit protection of the motor circuit. If you look in UL 508, damage is allowed to motor circuit components in the standard and high interrupting capacity tests. As long as the door does not blow open, contacts can be welded and overloads burned open which can require replacement and additional downtime concerns. However, if the device is tested to IEC 60947-4-1, Type 2 protection can be verified which assures no damage to the motor circuit components, other than light contact welding that is easily seperable. How do they achieve Type 2 protection? You need a very current-limiting device such as a Class RK1 or J fuse.
4) Continuing on this and the testing per UL 508. This testing is based upon the door closed, what if someone is troubleshooting the motor starter "hot" with the door open and creates a fault...how much protection will they have with this door open?? This too can be a safety issue that needs to be addressed if working equipment "hot".

The points I have mentioned above have been used to convert a number of large industrials from circuit breaker MCCs to fusible MCCs.

Hope this helps.

Thanks,
Dan