Machine Safety wiring examples

milmat1

Member
Join Date
Aug 2005
Location
North Carolina
Posts
209
Anyone know a good source to see some wiring examples of machine safety systems ? Just for reference...


My lower rated systems with low access to danger will typically be something like this.
A couple of twist release e-stop buttons
Maybe a pull cord safety switch etc. All wired to a safety relay such as an MSR from AB,( single function safety relay).


Then the control voltage is fed through the contacts of the safety relay to feed any contactors, The PLC outputs, or actuators etc. So an E-stop function removes power from the controls and all PLC outputs etc.....



Also a set of contacts on the safety relay will feed the STO voltage to any VFD's. So in an Estop condition the VFDs are put into a CAT0 stop..


I would just like to see some examples of safety circuits in use. Especially any that are also using VFD's
 
Most safety vendors offer wiring examples for their products, although they are admittedly often ideal cases.


I know for sure the Siemens support site has safety application manuals, as well as wiring diagrams in the manuals for each safety device (safety relay, F-DI, F-DO, drive, etc).
 
Usually whichever safety switch you select will have several typical wiring examples. Keep in mind you have to know the safety category your machine is rated at.

Pilz and AB both have good manuals as well as just the paperwork that comes with each switch.
 
Also, Most of the manufacturers drawing examples are showing only a single VFD interfaced to a single safety relay. I often have several VFD's that must be stopped when an Estop is activated.
 
Give these a go. A lot of the literature for the hardware itself will include wiring/applications examples.


https://literature.rockwellautomation.com/idc/groups/literature/documents/rm/safebk-rm002_-en-p.pdf


http://downloads.pilz.nl/downloads/Docu-Machineveiligheid/safety_compendium_en_2014_01.pdf


Also, what do your Risk Assessments say the required Performance Level is? You current system may be suitable for lower PL levels, but it lacks DC for anything higher. The highest PL you can get with no DC is PLc and PLd with low DC. Depends on your specific application and the result ofyour RA.
 
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Safety standards an regulations on circuit design seem far, far less stringent in the USA compared with the UK and thus Europe.
 
Safety standards an regulations on circuit design seem far, far less stringent in the USA compared with the UK and thus Europe.

Yep, they give you more leeway before something happens but if something does happen... boy, do they come after you. There is no limit for torts awards in the US and each accident will cost you and your employer dearly.

So you go and make sure your machine is as safe as it can be. Without many standards and regulations dictating you to do so.
 
Safety standards an regulations on circuit design seem far, far less stringent in the USA compared with the UK and thus Europe.

Simultaneously less stringent and more set in the past. I think safety PLCs weren't even allowed



The government (OSHA) says that an employer shall provide a safe work environment. All the other standards and regulations (national electric code, UL, etc) are more recommendations than actual laws in most places. As the Pirates say, it's more of a guideline than a rule.


Also, there generally isn't really anyone checking compliance with anything right up until the moment someone gets hurt. Then the lawyers descend, and god help anyone involved. Following the rules in both letter and spirit doesn't protect your from blame, it just means you can probably get away with a smaller settlement.
 
Safety standards an regulations on circuit design seem far, far less stringent in the USA compared with the UK and thus Europe.


For the OEM yes, very flexible. But to the end user, OSHA is quite strict.



I strive to be able to honestly say I done everything possible to keep people safe. My worst nightmare is that someone would be hurt on something i designed that was not safe.
 
Safety standards an regulations on circuit design seem far, far less stringent in the USA compared with the UK and thus Europe.

On a few trips to the states, I've thought this, but there seems to be a big obsession with arc'ing for some reason.

Obviously both done wrong is quite bad, but not something I've ever understood.

I guess over here we fear the HSE knocking on your door, over there perhaps a lawyer, I don't know.
 

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