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. In cases where the e-stop system is a 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 thought 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 โ€” automatically monitoring the connection to the actuator and the correct mounting on the EMERGENCY STOP device. The monitored contact blocks are normally closed contact blocks with positive opening operations. 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 โ€” with screw connection 3SB3400-0M or with spring-loaded connection 3SB3403-0M. (Note: these products are now obsolete.)

Note that the 3SU1400-1AA10-1HA0 has replaced the 3SB34 discussed in this post.

Since I don’t sell control products, you’ll have to contact 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!

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10 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… ๐Ÿ™‚

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