Estop of Several Motors

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dnyman

Member
Location
Logan, Ut
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.
 

kc8dxx

Senior Member
Location
Ohio
Safety Relays

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.
 

pfalcon

Senior Member
Location
Indiana
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.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
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.
 

billsnuff

Senior Member
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.
 

dnyman

Member
Location
Logan, Ut
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.
 

IMM_Doctor

Senior Member
Risk Assesment

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?
 

dnyman

Member
Location
Logan, Ut
OLD School

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.
 
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-level-matching/31253_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.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
It's a bit of a fad. I am not sure that anyone is doing any real thinking about whether it is a worthwhile thing to do or not.

The thing is that even if you hit the E-stop and the motor(s) fail to stop, it should not be a safety issue anyway as human beings should not be exposed to hazards that can only be deal with via an estop.

The reality of things is that for the most part, an estop is to protect the equipment or the product being made.
 

dnyman

Member
Location
Logan, Ut
K1 & K2 placement

K1 & K2 placement

Christoff84,
Why couldn't you place the K1 & K2 relay after the drive? In fact, the big argument for placing the relays after the drive is that the drive does not lose power and have to go thru a power up delay.
Have you designed multiple motor safety circuits where you use one set of K1 & K2 to kill power to several motors?
 
Christoff84,
Why couldn't you place the K1 & K2 relay after the drive? In fact, the big argument for placing the relays after the drive is that the drive does not lose power and have to go thru a power up delay.
Have you designed multiple motor safety circuits where you use one set of K1 & K2 to kill power to several motors?

You could place K1 and K2 after the drive, or before the drive. It's the designer's choice. I've done applications where we have the drive actively ramp down the motor and then kill power and I've done projects where we just cut the line side power to the drive. The advantage to the line side is you can cut power to several drives/motors using 1 set of contactors instead of individuals. That's just my preference, I'm not the engineer that has to stamp and approve it all, just the designer.

Mostly I've seen the dual contactor setup on hydraulic presses, to kill power to the hydraulic pump/valve control signals, as we are required to be CAT4/SIL3/Control Reliable based on the CSA Z142-10 for press safety which I believe is similar to ANSI B11.1
 
Last edited:
christoff84,
Have you designed multiple motor safety circuits where you use one set of K1 & K2 to kill power to several motors?

Yes I have. I've done systems where we use K1 and K2 to cut the 600V feed to a dozen motors (all small HP). As long as the fusing/wire size/contactor rating is good for the set of motors. Sometimes it just makes it easier then buying 6 or 8 extra contactors.
 

pfalcon

Senior Member
Location
Indiana
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.

Yes, Estop in the control circuit is old school. It's also current school in the US. Peeps are moving to it not for liability but because Europe did.

Where are you getting Cat 4 stop from? Current US definitions cover Cat 0, Cat 1, and Cat 2 [NFPA79:2007:9.2.2].

Before going further we need to understand what industrial standard you are using. My company uses NFPA79:2007.
 
Category B, 1, 2, 3, 4 come from the European standard EN 954-1. Category 4 is also known as Control Reliable (Dual Channel with Monitoring) according to the ANSI B11 (In the US) and CSA Z432 (in Canada) standards. I believe (but am not sure) that it is covered in OSHA 1910.217(b)(13).
 

pfalcon

Senior Member
Location
Indiana
It's a bit of a fad. I am not sure that anyone is doing any real thinking about whether it is a worthwhile thing to do or not.

The thing is that even if you hit the E-stop and the motor(s) fail to stop, it should not be a safety issue anyway as human beings should not be exposed to hazards that can only be deal with via an estop.

The reality of things is that for the most part, an estop is to protect the equipment or the product being made.

I do not disagree with that.

However, as a practical matter that is what the e-stop is mostly used for.

or just as a stop.

Bob,
At our site the Estop is almost exclusively for the safety of the operators. Most of our equipment is fast enough that by the time someone can initiate an Estop the machine is as wrecked as it will ever get.
I will grant you that Estop buttons typically don't help the operators. Its all the other safety devices that tie to the Estop that protect the operator. Estop ropes along conveyors and light curtains at load points are chief examples.
 
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