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Thread: Estop of Several Motors

  1. #1
    Join Date
    Apr 2008
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    Logan, Ut
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    Estop of Several Motors

    Has anyone seen an estop circuit using a safety relay that kills power to several motors using two (K1 & K2) contactors. The only wiring diagrams I can find use two contactors for each motor. I don't know if this is a requirement or AB just likes selling more contactors. Any thoughts would be appreciated.

  2. #2
    Join Date
    Jul 2006
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    Ohio
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    Safety Relays

    I'm familiar with a "Safety Relay" as a specific item required for a product.

    A typical "Safety Relay" contains internal circuitry to sense safety circuit inputs and to set as required outputs that control the machine. Safety inputs are typically estops, light curtains, etc. Outputs are typically wired to relays/contactors are used to shut the machine down, such as the control contactor on a small ac motor.

    The Safety Relay can be simple, and can also be quite complex with advanced internal setups that are configurable. A number of manufacturers make them, not just AB. The cost is a direct reflection of the number of inputs, number of outputs, and custom configuration capabilities. For a system with a large number of I/O, a configurable Safety Relay often is the most cost effective.

    Wiring diagrams are readily available from the OEM. I happen to have used Safety Relays made by Phoenix Contact and Pilz for some applications. Their documentation was more than adequate for my needs.

    Modern machine design techniques calls for this kind of approach to handling inputs and outputs that affect safety, as one of the solutions to the results of a risk assessment of the machine.

    Is is required for your particular application? I don't know and cannot say, because IMHO it depends on the machine safety risk assessment for that particular piece of equipment.

  3. #3
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    To the best of my knowledge, Estop of motors requires meeting the Cat 0 or Cat 1 and does not specify the means. That diagram with one motor can be presumed to be a set of parallel motors if the circuit can handle the load.
    A rose by any other name is tax deductible [1978 Wayne Wilcox]
    People who read too many books get quirky. [2000 John Taylor Gatto]

  4. #4
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    There are specific IEC safety standards that require redundancy in the power circuit control devices. The two contactors are in series for that reason. One contactor does the normal on-off every day control and gets a permissive control from the safety relay, the second is only controlled by the safety relay as a stop device. The reason you will see it in the literature from A-B (and every other safety relay mfr) is because the only places where safety relays are mandated are IEC regulated countries, so all of the safety relays are targeting that marketplace.

    Here in the US you CAN adopt the IEC safety standards, but nobody is holding a regulatory gun at your head to do so... yet. But the gun is being loaded and as soon as everyone can agree on who is going to wear the holster, we will see it here as well.

  5. #5
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    Those applications with K1 and K2 controlling a motor are for applications two hand control, dual channel single fault and guardmaster lifeline.

    But, as was said earlier, a Risk Assessment is in order before deciding on the devices, because the devices and their set up are solutions to problems (safety risks) that can lead to enhanced safety.

    Also, be careful not to confuse the guardmaster series and others as replacement for LOTO, because control circuitry cannot be used as LOTO.
    Why is it, when it comes to the NEC, the obvious is never simple and the simple is never obvious?

  6. #6
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    Apr 2008
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    Logan, Ut
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    Pfalcon,
    I also assume that in the wiring diagrams, a single motor can be multiple motors. I wanted to get some feed back from others as to whether this is commonly done. The plant where I'm working usually has two separate safety contactors on the motor side of each VSD or starter. I'm questioning this practice and suggesting using a pair of contactors K1 & K2 to kill 480 VAC to all the motor starters. This would reduce the number of contactors and panel space, plus save cost. Just looking for some feedback from others on which method is being used by others.

  7. #7
    Join Date
    Apr 2008
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    116

    Risk Assesment

    3rd notice. "Risk Assesment".

    Are the three-phase motors exhaust fans? Or do these motors contol motion where personnel are exposed to hazzardous movement ,all-day, every day?

  8. #8
    Join Date
    Jan 2010
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    PHX, arizona
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    I have always seen and done the E-STOPS in the control circuits.
    Kill all power at its source except the safety circuit.

  9. #9
    Join Date
    Apr 2008
    Location
    Logan, Ut
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    OLD School

    Placing the Estop in the control circuit is old school. Assuming the risk assessment had determined that this is a category 4, all power must be removed. This question is not about the risk assessment, but the implementation of the safety contactors. I get the impression that not many here are familiar with the requirements. Many of companies have adopted this design to protect themselves against any liability.

  10. #10
    Join Date
    Jun 2010
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    Ontario, Canada
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    Quote Originally Posted by dnyman View Post
    Pfalcon,
    I also assume that in the wiring diagrams, a single motor can be multiple motors. I wanted to get some feed back from others as to whether this is commonly done. The plant where I'm working usually has two separate safety contactors on the motor side of each VSD or starter. I'm questioning this practice and suggesting using a pair of contactors K1 & K2 to kill 480 VAC to all the motor starters. This would reduce the number of contactors and panel space, plus save cost. Just looking for some feedback from others on which method is being used by others.
    If you have any motors running centrifugal fans/pumps or any load that would stop faster/safer during a controlled ramp down you can use something like this with the K1 and K2 ahead of the VSD(s).

    http://www.phoenixcontact.com/signal...1253_14953.htm

    Use the NO contacts to cut the enable signal to the drives so that it ramps down safely, then after the known time it takes them to stop have the timed contacts set to kill power to the drives. Just remember you have to size your K1 and K2 to the load of all the drives.

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