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Old October 17th, 2017, 06:08 AM   #1
phuz
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Upgrading an old SLC line to CLX / safety

I'm quoting a big line upgrade that currently has a L55 and 7 SLC 5/01 processors, all of which are islands. I plan to change to an L71S and my original intention was to use PointIO in the SLC cabinets (there are only 3-4 modules in each cabinet) and to use Guard IO so it can all be controlled from the GuardLogix. However, all the IO in the remote cabinets is 120vac and it doesn't look like there are any 120vac Guard IO modules, so I'm considering the 440C Guardmaster in conjunction with the regular PointIO modules. Replacing all of the existing motor starters with 24vdc coils is out of the budget for this job.
Does anyone have another suggestions that I'm not seeing?
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Old October 17th, 2017, 08:04 AM   #2
rdrast
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Use terminal mounted isolation relays. I do that almost all of the time for outputs (24 VDC Driver for 120 VAC output), and sometimes for inputs. No reason you can't.
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Old October 17th, 2017, 10:27 AM   #3
phuz
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Use terminal mounted isolation relays. I do that almost all of the time for outputs (24 VDC Driver for 120 VAC output), and sometimes for inputs. No reason you can't.
And that will meet safety requirements?
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Old October 17th, 2017, 11:07 AM   #4
Bit_Bucket_07
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Originally Posted by phuz View Post
And that will meet safety requirements?
Sure. If you use safety relays: http://ab.rockwellautomation.com/Rel...Control-Relays
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Old October 17th, 2017, 11:24 AM   #5
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Good enough for me! Thanks.
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Old October 17th, 2017, 01:07 PM   #6
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Keep in mind that in order for force-guided relays (aka "safety relays") to be effective, the normally closed auxiliary contact needs to be used as an EDM circuit back to the controlling safety device. There is nothing special about these relays except that the contacts are mechanically linked so you can detect a welded contact by monitoring the NC pole. If this is not done then the safety relay offers no advantage over a general purpose relay.
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Old October 17th, 2017, 01:14 PM   #7
phuz
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Keep in mind that in order for force-guided relays (aka "safety relays") to be effective, the normally closed auxiliary contact needs to be used as an EDM circuit back to the controlling safety device. There is nothing special about these relays except that the contacts are mechanically linked so you can detect a welded contact by monitoring the NC pole. If this is not done then the safety relay offers no advantage over a general purpose relay.
Makes perfect sense. Thanks.
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Old October 17th, 2017, 01:24 PM   #8
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And that will meet safety requirements?
It is hard to say.

We don't have any data on your safety requirements.

My initial thought is if you are replacing SLC5/01 I/O then your requirements aren't very high. Likewise if the motors starters do not include safety contactors, then safety relays to pull in the contactors are probably not needed either.

However, if you intend to raise the level of safety required in this upgrade, you will need to evaluate how you will meet those requirements.

You can't just throw "safety" hardware at everything and it will be ok.
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Old October 17th, 2017, 01:30 PM   #9
phuz
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It is hard to say.

We don't have any data on your safety requirements.

My initial thought is if you are replacing SLC5/01 I/O then your requirements aren't very high. Likewise if the motors starters do not include safety contactors, then safety relays to pull in the contactors are probably not needed either.

However, if you intend to raise the level of safety required in this upgrade, you will need to evaluate how you will meet those requirements.

You can't just throw "safety" hardware at everything and it will be ok.
I knew this reply would come . I was referring to safety levels along the lines of GuardLogix and Guard I/O control. The previous responses were just what I needed. Safety relay with monitoring feedback is perfect. The existing system, I believe, uses standard relays to drop out the starters. They currently have a keyed bypass switch to bypass numerous safety components, so this is a much needed upgrade.

On another note, is there a reason they have limited Guard I/O modules? I am still surprised that there are no 1756 modules.
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Old October 17th, 2017, 06:54 PM   #10
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Quote:
Originally Posted by phuz View Post
Safety relay with monitoring feedback is perfect. The existing system, I believe, uses standard relays to drop out the starters. They currently have a keyed bypass switch to bypass numerous safety components, so this is a much needed upgrade.
I might be misunderstanding but it sounds like you are planning on using force-guided relays to control the existing starters which act as your final disconnecting means. Assuming your using Guardlogix because you need to meet SIL 3 (ControlLogix can support up to SIL 2). Unless the existing starters have force-guided contacts I doubt that you will be able to meet your safety requirements as you must have feedback from your interposing relay as well as the final output contactor.
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