blown fuse detection, indication and remote notification

[shreesathe]

Can anyone shed some light on how one can acheive a blown fuse detection, indication and remote notification for a three phase NEMA motor starter which has a fused disconnect as its overcurrent protection device ? I am also interested in using the same wiring for an inhouse old automatically switched power factor capacitor bank we have that is protected through fuses.
Currently theere are small neon lamps beside the capacitors themselves that light up when the contactor are energized. The company that we bought this unit from is no longer in business. ANY HELP ??

 

[jraef]

Such is the main detractor from using fusible disconnects, that's why I prefer circuit breakers whenever possible.

Indication is no problem, lots of products available if you
Google "blown fuse indicator".

Remote annunciation takes a little more effort. You basically have 3 or 4 choices:
1) A 3 phase voltage monitor relay on the load side of the fuses, although that would not be able to discriminate from an overall line loss.
2) Power up 2 relays, with coil voltages the same as line voltage, from the load sides of the fuses, but has the same problem as above.
3) There are indicating fuses available that have a spring loaded pin in the fuse which pops out of the end when the fuse link blows. Then you can either buy or rig a device that trips a limit switch when one of the fuse pins pops up. Not available in all fuse types however. A relative is an "Indicator", the Bussman KAZ is an example. It goes in parallel to the fuse and pops up whenever the fuse link opens. Bussman also makes a special clip to hold it that has a micros switch that actuates when the KAZ pin pops up.

Google is your friend on this.

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376

 

[davidbeach]

If items 1) or 2) in jraef's list can be set to report only the loss of one or two phases but not all three, you can discriminate many blown fuses from an overall line loss since most fuses blow in response to SLG, LL, or LLG faults leaving at least one fuse. Overall line loss would cause all three phases to go dead. What this couldn't discriminate though is a blown fuse at the point of measurement vs. a blown fuse/open phase conductor somewhere upstream.

 

[jraef]

That's actually what I meant, thanks for pointing out my ambiguity David. I should have said overall phase loss, not line loss.

I should also have pointed out that the way the KAZ indicator works is that it is acutally a fuse as well, rated 10A (no time delay). You should only use it on a circuit with 50A fuses or higher. When the main fuse blows, the KAZ becomes the current path and since it is only rated 10A, it quickly blows as well. This means that you should NOT use this on critical systems such as semiconductor protection where that extra time of having a link in the circuit could mean a lot more damage. For a motor circuit though, they're fine.

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376

 

[waross]

There are some motor protection devices in use in the refrigeration industry that may be useful. They start as a phase loss/reverse phase protector. Then under/over voltage was added. Then voltage unbalance was added. Some units now have connections to both sides of the contactor and monitor contact integrity as well.
The contact checking feature may work as a blown fuse indicator.
Unfortunately, these units are for compressor protection and will open the control circuit for any and all conditions.
respectfully

 

[itsmoked]

These are just a few phase loss relays.
You should be able to find one that does exactly what you want for under $200. A phase monitor can also save your motors, something a blown fuse detector will not!

http://phaselossprotection.com/

http://www.macromatic.com/products/phase-monitor-relays.html

http://www.benderrelay.com/phase failure phase loss table.htm

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[shreesathe]

Thank you guys. All have provided excellent and insightful information. Now I am better equipped to provide the remote alarm that my motor starters need.

Now if I have to implement this for my capacitor banks where I only need fuse failure indication. Is there anyway to do this cheaper than the suggested solutions ? Since I have to put this on our 12 stage banks, 12 x 169$ is a lot of $ to justify. Any new ideas ?

 

[jraef]

What voltage?

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376

 

[shreesathe]

600V here in Canada

 

[jraef]

First off, are you sure the caps don't already have BFI included? Most do now.

If not, next you must decide on the nature of the installation. This simple method of BFI involve having a voltage potential present on the load side of the blown fuse, a safety issue if there is a chance that unauthorized personnel are going to be opening the enclosure. Keep in mind though that caps always have that risk, so unauthorized people should not be opening those boxes at all.

If that's OK, the simplest way is to just buy 3 x 600V pilot lights and wire them to the load side of each pair of fuses. #1 = ØA-B. #2 = ØB-C. #3 = ØC-A. If AØ fuse blows, lights 1 and 3 go out. If BØ fuse blows, lights 1 & 2 go out. If CØ fuse blows, lights 2 & 3 go out.

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376

 

[shreesathe]

Yes they do have the BFI. I am trying to see if I can get a circuit to work for its remote indication.

 

[jraef]

Sorry. I thought fopr the caps all you wanted was indicators, as in local pilot lights.

 

[shreesathe]

So any suggestions ?

 

[HCBFlash]

You say "neon lamps" at the cap's, telling us that there is a moderate A.C. voltage being used to energize them, and can reasonably surmise that the current used (or leaked) is minute.

You could probably simply parallel another set of indicator lights (neon or other) for a pretty cheap, simple solution. In a few different facilities I've worked on/in it's been simple to sell a remote (typically central shop located) monitoring/indication system to management, as cheaper and more usefull than lots of local monitor/indicators.

Please let us all know how this works out for you! and don't forget faq731-376

 

[shreesathe]

The problem I have with those neon lamps is they come on only when that (capacitor) stage is energized (the contactors pick up). There are instances when the electrician needs to know in advance if a fuse is blown rather than waiting for that stage to come on and then find out the fuse is blown.

 

[jraef]

Good point. Then you are back to the pin indicators.

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376