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Thread: Opinions on "Intelligent MCCs"

  1. #21
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    Quote Originally Posted by ELA View Post
    ... am curious about fail-safe operation...
    ELA...

    Fail-safe is an oxy-moron! Most process and equipment shutdowns, mostly unwarranted, few necessary, appear "safe" (ex-nukes)! But, studies show the subsequent restart most often results in catastrophe!

    If anyone is interested contact me for my paper, published in the Journal of System Safety Society, entitled: "Probabilistic Risk Analysis of Equipment Safety systems"! Or, I can present it on MHF as a new approach to a very, very old subject "false alarms"!

    Phil

  2. #22
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    I've seen pro's and con's with these SmartMCC's. One of the pro's is they help with troubleshooting. For example, we installed a small hp motor out of one of these, and one of the phase conductors wasn't stripped properly from the factory, causing a loss of phase. The electronic overload picked this up immediately, and actually told us that it was single-phasing. If this were out of an older MCC, we could have been single-phasing the motor until it finally gave out.

    On the downside, in my opinion eutectic alloy overloads are much more reliable and less expensive. I've had several electronic overloads just stop working all of a sudden (less than 3 years old), and those guys aren't cheap to replace (close to $1k). Also, this brings up the scenario if what happens if you lose network connectivity. I made the smart overloads we have continue to run, even if they lose communications, to prevent from taking the facility down, but during that time I am running unprotected. Also another downside is if someone has to replace an electronic overload overnight, they have to be computer savvy enough to program the relay. Also security issues arise when you can change motor protection with just a click of a button.

    Overall I still like the rugged eutectic alloys. It's unfortunate that Allen Bradley is slowly phasing them out, but I noticed they are selling electronic overloads that can be installed in normal MCC's. These don't rely on a connection to the network, so that's nice. They have an adjustable dial for the trip point, which I don't like because an electrician on the 2am backshift will almost always dial up the trip setpoint to get the motor running (at least in my facility), instead of figuring out why it actually tripped. But beggars can't be choosers.
    Last edited by adamscb; Yesterday at 08:53 AM.

  3. #23
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    Quote Originally Posted by Phil Corso View Post
    ELA... studies show the subsequent restart most often results in catastrophe...
    Coincidently, the 800M$ lawsuit was about failure during start-up!

    Phil

  4. #24
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    adamscb,
    Eutectic melting alloy OL relays are being phased out because they are now illegal in most of the world under the RoHS (Reduction of Hazardous Substances) rules. There are metal compounds in the alloys that can no longer be sold outside of the US and the market for them here is now too small to make it sustainable. We as an industry are starting to see a lot of changes now with a lot more to come as a result of this issue.
    __________________________________________________ ____________________________
    Many people are shocked when they discover I am not a good electrician...

  5. #25
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    Quote Originally Posted by Jraef View Post
    adamscb,
    Eutectic melting alloy OL relays are being phased out because they are now illegal in most of the world under the RoHS (Reduction of Hazardous Substances) rules. There are metal compounds in the alloys that can no longer be sold outside of the US and the market for them here is now too small to make it sustainable. We as an industry are starting to see a lot of changes now with a lot more to come as a result of this issue.
    Always wondered why they're phasing them out, that makes more sense. Unfortunate though, because those are cheap and dependable. As a wise man once told me, the cutting edge can still cut you.

  6. #26
    Join Date
    Jul 2006
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    2,246
    I'm kind of late to the party here, but-

    What's the average life of a generic starter vs a smart starter? Most computer-based equipment has a much shorter lifespan than relays, or even good quality PLCs.

    Unless you buy quality gear, the network components will also have a limited lifespan.

    Unless the network topology is really isolated, there's a possibility of external intrusion and control (that is, unfriendly access). Most IT people aren't paranoid enough in this regard.

    (I wish there were more controls-savvy network and IT engineers.)

  7. #27
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    Feb 2016
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    Quote Originally Posted by Phil Corso View Post
    ELA...

    Fail-safe is an oxy-moron! Most process and equipment shutdowns, mostly unwarranted, few necessary, appear "safe" (ex-nukes)! But, studies show the subsequent restart most often results in catastrophe!

    If anyone is interested contact me for my paper, published in the Journal of System Safety Society, entitled: "Probabilistic Risk Analysis of Equipment Safety systems"! Or, I can present it on MHF as a new approach to a very, very old subject "false alarms"!

    Phil
    Before electronics, fail-safe was simply 3 wire control with safety switches wired as normally open, held closed. That way, the common failure modes ( of for example a low oil pressure switch) would result in shutdown of all motor starters and the only way to restart was human intervention.

    This of course presumed that electrically shutting down the equipment at any time was a safe thing to do! As you say, simply stopping a machine may or may not in itself be a safe thing to do.

    As soon as electronics came into play (along with auto restart), the original intent and function of "fail-safe" changed.

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