Machinery Safety 101

New contact block design for Emergency Stop devices from Siemens

This entry is part 9 of 16 in the series Emer­gency Stop

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!

Series Nav­ig­a­tionUpdates to Pop­u­lar Art­iclesEmer­gency stop devices: the risks of installer liability

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!

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  6. 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!

  7. 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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