Health and safety when using plc

bungouk

Member
Join Date
Jan 2013
Location
Huntingdon
Posts
2
Hi all,

I have this question below.

Describe the importance of health and safety when working with programmable controlled equipment

I have put a few things down for my assignment but doesnt seem to be alot that i have wrote. so thought i put the question to all you and ask kindly for all your thoughts

Thanks

Bungouk
 
I would suggest posting your thoughts you have already otherwise you may find very little help forthcoming. A lot of assignment questions get posted on the site.

Think about hazards and consequences to give risk. Think about existing equipment you have. Does it have a seperate safety system / guards etc? (I hope so)
Could somebody get killed if the plc went wrong? What about making online changes to the program?
 
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I have so:

It is very important to consider health and safety when working with programmable controlled equipment. Some things to consider are as follows below.

You should make sure the PLC has a single point of ground, this improves the electrical noise protection. The ground wires used should be kept short as possible and adequate wire size use, such as 2mm2 (14AWG).

You should supply a switch which can terminate the power from all PLC equipment used if need to.

A fuse of circuit breaker should be used to protect against over current on the supply wiring. Also each input/outputs could each have their own fuse for protection.

Some kind of anti surge protection should also be fitted to stop any lighting surges from damaging any of the PLC equipment.

Care must be taken to avoid placing low-voltage signal wires and communications cable next to AC cables as could lead to potential interference.

All wires should be adequate to carry the correct current for all DC/AC cables, If wrong cable used then this could end catching on fire. Also try to keep all wires as short as possible.


All connectors should be wired correctly and fitted securely, Avoid over tightening of screws in the connector to prevent damage to the connector.

Should make sure there are switches to isolate the PLC or individual modules so trained personnel can work on them item without electrocution.

Double check all connections before powering on as incorrect wiring, build could lead to physical injury to people, or damage to equipment.
 
Good guarding, wiring, and grounding practices should be followed regardless of whether or not a PLC controls a machine. Knowing what you know about how PLCs work, what are some hazards that may be present because the machine is automated using a PLC? Think about hazards to the operators or innocent bystanders, not just to the equipment.
 
Hi

Remember that a plc could be controlling a chemical plant or the air flow in a mine shaft, parts in a oil rig etc so the person writing the code needs to have a full understanding as to outcome if something goes wrong.


Donnchadh
 
Bungouk,

You should write at least a paragraph about using programming methods that do not make a machine MORE DANGEROUS because it is being controlled by a PLC than it would be with manual switches. For example, many beginners use PLC retentive latched outputs to control motors. If there is an error in the program, or a malfunciton of the PLC output module, or a power outage, the latched output could result in a dangerous situation (a dangerous machine restarting unexpectely). Yes, there should be other safety devices to prevent a PLC from being dangerous, but why should a PLC program be allowed to add to the possibility of danger? It is best to use PLC outputs that will drop out when power is lost and are not capable of going on again until another operator start commnad is given.

At least your instructor is thinking about this. This is the first that I have heard of any instructor being aware that the topic needs teaching.
 
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As already pointed out, think about operator safety.
Google machine safety, or Distrubuted safety and you should find some food for thought.
 
You should supply a switch which can terminate the power from all PLC equipment used if need to.

I would include that the code should be written so that if you lose power or remove power to the PLC it always should default to a safe condition.

First I've heard of an instructor to incluse this in a class, very good topic for discussion!
 
sorry Mae - I dont agree.
A SAFE Condition needs to be carefully understood.
the PLC is often needed to display what has happened.
for this reason taking the power off a PLC is no good.
However
Safety systems are wired specifically - search the site for these posts
 
@iant
A SAFE Condition needs to be carefully understood.
the PLC is often needed to display what has happened.
for this reason taking the power off a PLC is no good.
I agree with you completely in this.


This is from the OP's list of safety precautions:
You should supply a switch which can terminate the power from all PLC equipment used if need to.

I disagree with the OP's statement. All I am saying is that the OP needs to know what is going to happen if he looses power or includes a button (as posted in post #3) to remove the power to the PLC. I personally don't turn the power off of the PLC. Mine are all application specific. But when we lose power we have to know what the PLC is going to do when the power is removed and what is going to do when the power comes back on.
 
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@iant,
Does this clear up what I was trying to convey in my post? I don't want to confuse the OP. And I always try and learn from everybody on here including yourself. Thanks!
 
Nay...
PLC programmers are expendable, not unlike automobile tires.

Ya can't get anywhere without 'em, but they just get used up and thrown away when the next generation comes out. :sick:
 
This is from the OP's list of safety precautions:
You should supply a switch which can terminate the power from all PLC equipment used if need to.

I disagree with the OP's statement.
I could agree if the statement was changed to say somethig like this:
You should supply a switch (or master control relay) which can remove the power from all PLC Output-CONTROLLED equipment (but not from the PLC itself).
 
We use a system offshore, which is regulated by the government, called SAFE charts. Basically, it's a chart with predetermined permissives for any action that takes place on the platform. There are things a PLC or even a pneumatic control system can't do. Operators shouldn't, but we do see the results of mishandling of materials, or ignoring something that is in bypass.

If the SAFE logic is in place, and working properly, there's no need to shut down the PLC. I think this type of system should work anywhere else.

BTW, read my sig line:
 
The most important thing is to keep your finger nails cut short or you may break them or accidentally hit the wrong key.
 

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