Smart MCCs

[Ingenieur]

AB has safety rated remote I/O that can be networked over ethernet that is attractive in many cases.

it seems like safety stuff gets more complicated as we try and integrate more and more safety features to protect fools from themselves. it is much easier to do this in software than hardwiring much of the time.

hardwired very simple
a string of supervised normally energized to close contacts from field devices (may have an interposing relay) holding a relay in that holds a uv in

the relay inputs contacts into the plc asva redundant parallel system
the plc performs all normal operating functions

very little difference
plc run the field devices into the plc and use outputs to hold the uv

for minimal wiring we have both

 

[petersonra]

hardwired very simple
a string of supervised normally energized to close contacts from field devices (may have an interposing relay) holding a relay in that holds a uv in

the relay inputs contacts into the plc asva redundant parallel system
the plc performs all normal operating functions

very little difference
plc run the field devices into the plc and use outputs to hold the uv

for minimal wiring we have both

once you get past a single in single out and have to wire a bunch a safety relays in series and/or parallel to get the desired result you will appreciate safety plcs more.

I agree it is "better" to use standard safety relays where there is just a single input and single output. but once you start mixing in estop pushbuttons, gates switches and locks, vfds, speed switches, various kinds of keyed system, and light curtains with muting systems, it can get complex quickly. It can get complex to the point where it is very hard for a field electrician to even troubleshoot it which makes it more likely he will fix it by jumpering something.

 

[Ingenieur]

once you get past a single in single out and have to wire a bunch a safety relays in series and/or parallel to get the desired result you will appreciate safety plcs more.

I agree it is "better" to use standard safety relays where there is just a single input and single output. but once you start mixing in estop pushbuttons, gates switches and locks, vfds, speed switches, various kinds of keyed system, and light curtains with muting systems, it can get complex quickly. It can get complex to the point where it is very hard for a field electrician to even troubleshoot it which makes it more likely he will fix it by jumpering something.

use them in different applications
not in a coal mine
there is no advantage only disadvantages
most of our safety strings have 10-15 devices

mine electricians prefer hardwired
even the younger guys
easier to troubleshoot
in fact if they could revert the machine controls back to relay logic from plc's they would

just as easy to jump a plc input or output
but both are a crime in my world

 

[ptonsparky]

use them in different applications
not in a coal mine
there is no advantage only disadvantages
most of our safety strings have 10-15 devices

mine electricians prefer hardwired
even the younger guys
easier to troubleshoot
in fact if they could revert the machine controls back to relay logic from plc's they would

just as easy to jump a plc input or output
but both are a crime in my world

Try using a different programmer if jumpering an input or output results in an unsafe operation, or operation at all. Then again, we still see sticks stuck into the starters to make things work. Something about better idiots.

 

[Ingenieur]

Try using a different programmer if jumpering an input or output results in an unsafe operation, or operation at all. Then again, we still see sticks stuck into the starters to make things work. Something about better idiots.

there is not way to prevent someone from intentionally circumventing a system
build a better mousetrap, along comes a smarter mouse :happyyes:

 

[zbang]

Ah, yes, the days of troubleshooting with a Bic pen (usually had one in the pocket) and a light bulb with 'gator clips on the leads. Oh, and jamming cardboard into relays that shouldn't operate. Happy to leave that all behind.

 

[petersonra]

there is not way to prevent someone from intentionally circumventing a system
build a better mousetrap, along comes a smarter mouse :happyyes:

the thing that offends me as much as anything is that it is often plant electricians and maint guys that do it. the very guys that ought to know better, if anyone does.

 

[Ingenieur]

the thing that offends me as much as anything is that it is often plant electricians and maint guys that do it. the very guys that ought to know better, if anyone does.

we frown upon it
loss of certification, ie, loss of job
fines
if an injury occurs or other egregious action, jail

I will say 99.9% do it right, very rarely do we find malfeasance
the consequences of improper work are amplified in some environments, mining being one (another being petrochemical, etc.)

 

[Jraef]

I don't need no smart MCCs... I got it covered.

 

[Ingenieur]

just one more wire and I can get this PLC running :lol:

it's only costing us $5,000/min

 

[Jraef]

Can you interface that into my SCADA system?


Sure, I'll get right on that...