Machinery Safety 101

New contact block design for Emergency Stop devices from Siemens

One issue that fre­quently comes up when inspect­ing machinery is the con­tact blocks used on emer­gency stop devices. Until now, e‑stop devices were nor­mally fit­ted with the same con­tact blocks used on oth­er oper­at­or devices, and in cases where the e‑stop sys­tem is single chan­nel, you could lose the con­tact block off the back of the oper­at­or device and not be able to detect it. Since the latch­ing detent device on the but­ton is part of the but­ton and not part of the con­tact block, the but­ton would appear to latch down nor­mally, but the machine would keep running!

I got a news­let­ter in my email today from Siemens that included the fol­low­ing snip on their new 3SB34 emer­gency stop con­tact block and I though I’d share it with you!

Emer­gency stop con­tact block with mount­ing monitoring

Siemens E-Stop Contact Block 3SB34
Siemens 3SB34 E‑Stop Con­tact Block

It is com­mon prac­tice to equip actu­at­ors such as EMERGENCY STOP with stand­ard con­tact blocks. Now the new 3SB34 con­tact block with mount­ing mon­it­or­ing from the SIRIUS fam­ily offers increased safety – auto­mat­ic­ally mon­it­or­ing not just the con­nec­tion to the actu­at­or but also the cor­rect mount­ing on the EMERGENCY STOP. The mon­itored con­tact blocks are nor­mally closed con­tact blocks with pos­it­ive open­ing oper­a­tion. If the mount­ing is defect­ive or should it fall off the actu­at­or, the innov­at­ive con­tact block trig­gers an auto­mat­ic shut­down of the machine or plant (safe state). As long as the plant is oper­at­ing, you can be sure that all the neces­sary con­tacts are func­tion­ing perfectly.

The advant­ages are obvi­ous:
– Increased safety thanks to the test required for ini­tial com­mis­sion­ing
– High­er plant avail­ab­il­ity thanks to auto­mat­ic mon­it­or­ing of the mount­ing
status dur­ing oper­a­tion (accord­ing to the Machinery Dir­ect­ive)
– Space-sav­ing thanks to a com­pact design and small install­a­tion depth (max. 63 mm)
– Free slots for fur­ther con­tact blocks due to integ­rated mount­ing monitoring

The con­tact block is avail­able in two ver­sions – with screw con­nec­tion 3SB3400-0M or with spring-loaded con­nec­tion 3SB3403-0M.

For fur­ther inform­a­tion, click here.

Since I don’t sell any kind of con­trol products, you’ll have to talk to your loc­al Siemens rep­res­ent­at­ive to get pri­cing and availability.

If any­one has any exper­i­ences with these products that they would like to share, please leave a comment!

12 thoughts on “New contact block design for Emergency Stop devices from Siemens

  1. Debra Kolbow,

    We would be happy to include REES products in the study. We will be releas­ing the Research Pro­pos­al shortly so you can see what we plan to do. After that we can make arrange­ments to get samples from you. 

    Thanks for volun­teer­ing your products for our study!

  2. REES, Inc. also man­u­fac­tures a con­tact block attached to an adapter that opens the NC con­tact if removed from the switch oper­at­or. This fea­ture is avail­able on both our 22.5mm and 30.5mm oper­at­ors. Check out our web­site at

  3. Doug Nix,

    Allen-Brad­ley Rock­well has had self-mon­it­or­ing con­tact blocks since the 800E/800F lines have been avai­able in North America(2001, I believe). The 800T had these avail­able even longer. If you do a search for self-mon­it­or­ing con­tact blocks in Google there is a bunch of links to info on the AB con­tact blocks. Also, the 800F self-mon­it­or­ing blocks are not lim­ited to E‑stop but can be used on oth­er oper­at­ors as well. Part num­ber 800F- X01S.

    1. Thanks, Radek! I always appre­ci­ate get­ting feed­back from my read­ers. I have decided to con­duct a study of these products. I have reques­ted samples from Rockwell/A‑B, Tele­meca­nique, Schneider/Square‑D, Jokab, ABB and OMRON. I am draft­ing the study pro­pos­al now and will make it avail­able through the blog for any­one inter­ested. Once the study is com­plete I will be pub­lish­ing the white paper here as well.

      Thanks for the information!

  4. I have had a lot of feed­back on this post­ing from a lot of dif­fer­ent sources, some from my Linked­In net­works and from oth­er sources includ­ing this blog and Twitter.

    I have decided to con­duct a study of these com­pon­ents to see what each man­u­fac­turer is bring­ing to the mar­ket, and to pub­lish the res­ults through this blog and our com­pany web site. If you rep­res­ent a con­trols com­pon­ent man­u­fac­turer and would like your com­pany’s product included in the study, please con­tact me. The study will begin as soon as I receive samples from each manufacturer.

    I look for­ward to the oppor­tun­ity to get a close look at these import­ant components!

  5. That addresses some­thing that has bothered me about IEC style but­tons for some time. Of course, Allen Brad­ley has had the SMCB’s (self mon­it­or­ing con­tact blocks) for some time now, I believe more than 5 years.

    1. Anthony,

      Ok, it sounds like it’s time for some field research, since you and Frank say that at least Rock­well has an equi­val­ent product. If any­one else has a favour­ite product in this line, please com­ment or email me!

  6. Hi Doug, this approach is not unique to Siemens and has already been avail­able for years from oth­er man­u­fac­tur­ers. It is a very neces­sary adap­tion for pan­el moun­ted estops, where the block can fall off (regard­less if it is screwed on or bay­on­et moun­ted, this can hap­pen) and not be seen. With this approach, the cir­cuit opens imme­di­ately if the con­tact block comes off, a prop­erly designed cat­egory 3/4 con­trol sys­tem will detect the fault and not allow a restart until it is fixed

    1. Frank,

      This is the first time I have seen this in North Amer­ica, which is why I pub­lished the art­icle. I was aware of some oth­er man­u­fac­turer­’s ’emer­gency stop con­tacts’ but they did not provide this func­tion­al­ity. Can yu provide me some point­ers to the com­pon­ents from oth­er man­u­fac­tur­ers? Per­haps this would be a good oppor­tun­ity for a com­par­is­on article… 🙂

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