Skip to Content

Register Login

Industry Online Support

Technical Forum

Navigation

Why have to jump between M and PE in IMs for S7300

Created by: tan-nn at: 6/21/2010 10:21 AM (4 Replies)

Rating (3)

Thanks 6

5 Entries

6/21/2010 10:21 AM	Rate (0)
tan-nn Posts: 6 Rating: (0)	Dear my colleagues, Have one thing I am confusing in IMs for S7300 like this: I saw that have one jumper to short circuit between M (0VDC) and PE (earth) in power terminal of IMs. In fact, I don't know clearly what is the purpose of this. But I think it may damage to 24VDC power supply unit if accidentally, the L+ wire contact to PE during commissioning time. Because Power supply now is short circuit of output (L+ and M). Could anyone help me to explain this matter. Special thanks all, P/S: you can find attachment about drawing of IMs Tan.nguyennhat Attachment IM153.pdf (264 Downloads)
tan-nn Posts: 6 Rating: (0)
Suggestion To thank Quote Answer

6/21/2010 10:52 AM	Rate (1)
Ayman Elotaify Platinum Expert Joined: 5/28/2008 Last visit: 9/9/2024 Posts: 4515 Rating: (839)	tan-nn Dear my colleagues, Have one thing I am confusing in IMs for S7300 like this: I saw that have one jumper to short circuit between M (0VDC) and PE (earth) in power terminal of IMs. In fact, I don't know clearly what is the purpose of this. But I think it may damage to 24VDC power supply unit if accidentally, the L+ wire contact to PE during commissioning time. Because Power supply now is short circuit of output (L+ and M). Could anyone help me to explain this matter. Special thanks all, P/S: you can find attachment about drawing of IMs Tan.nguyennhat Yes you are right. But as you told "accidentlly". So if you connected M & PE., Please take care not to connect L+ to any of them. use Multimeter before power on the power supply. Please have a look on these pictures extracted from S7-300 Module data Hope this will help. Attachment PE.JPG (359 Downloads)
	Last edited by: Ayman Elotaify at: 6/21/2010 10:57 AM Last edited by: Ayman Elotaify at: 6/21/2010 10:54 AM Last edited by: Ayman Elotaify at: 6/21/2010 10:53 AM Ayman Elotaify
Suggestion To thank Quote Answer
This contribution was helpful to 1 thankful Users how come

6/21/2010 12:07 PM	Rate (0)
tan-nn Posts: 6 Rating: (0)	Thanks for your advises, Yeh, we have to be carefully if connected M and PE. But sometime, we can not prevent everything at site during operation time. It seems better and safety when we remove this jumper because nothing happen if L+ connected to PE. But I still do not why Siemens have jumper in theirs equipment. What is disadvantage when we remove the jumper. Please help me and tks alot. Tan.nguyennhat
tan-nn Posts: 6 Rating: (0)
Suggestion To thank Quote Answer

6/21/2010 6:52 PM	Rate (2)
H-H Platinum Member Joined: 7/2/2008 Last visit: 8/26/2024 Posts: 928 Rating: (308)	Hello tan-nn , The jumper should be either, Connected in case you have grounded reference installation which means that the M(0VDC) is not left free and connected to a zero reference which is the functional earth. OR Removed in case you have ungrounded reference installation which means that there's an RC combination (internally in the IM153)between the M (0VDC) and the functional earth. You can read more in SIMATIC Distributed I/O device ET200M manual. tan-nn What is disadvantage when we remove the jumper. It's not about advantages and disadvantages, it's about what kind of installation you have. SIMATIC Distributed I/O device ET200M(Page 54) 3.6.3 Configuration of an ET 200M with ungrounded reference potential In the configuration of the ET 200M with ungrounded reference potential, the occurring interference currents are deflected to the grounding wire via an RC network that is integrated in the IM 153-x. Application In extensive units it may be necessary, e.g. for the purposes of earth leakage monitoring, to configure the ET 200M with ungrounded reference potential. This is the case, for example, in the chemical industry or in power stations. ------------------------------------------------------------------------------------------ If you don´t want to ground the reference potential, then you must remove the bridge on the IM 153-x between the terminals M and the functional earth. If the bridge isn´t connected then the reference potential of the ET 200M is connected internally to the grounding wire via an RC combination and via the rail. This way, high-frequency interference currents are deflected and static charge avoided. tan-nn But I think it may damage to 24VDC power supply unit if accidentally, the L+ wire contact to PE during commissioning time. Because Power supply now is short circuit of output (L+ and M) 1-Working with live wires is not an easy mistake. 2-As Mr. Ayman said you have to use a multimeter and I personallyrecommend toALWAYS makesure L+ is not buzzering with M before you power up any part ofyour system after any kind of wiring modification*. 3- I don't know what is your CPU but did you know before that all 31X CPUs (not the 31X-C CPUs) have the same jumper (Look at attachment)and I've never seen it taken out. Did you take it out before?! 4- I recommend to protect your IM153 with 2.5A fuses. 5- tan-nn It seems better and safety when we remove this jumper because nothing happen if L+ connected to PE. You will be still connecting 24VDC directly to zero volt without any kind of impedance which means that your power supply may get damaged if it's not protected. Attachment has been extracted from SIMATIC S7-300 CPU 31xC and CPU 31x: Installation manual *In the last couple of weeks my colleague was about to lose bunch of fail safe modules (quite expensive) because he relied on a technician with more than 10 years of experience (but he was in a hurry)to connect 2 wires and he didn't check after him. No matter how experience you rely on and no matter how you trust yourself and others, always buzzer L+ with M before powering up because we all make mistakes and none of us is an angle. Best regards. H-H Attachment 31X CPUs - M and Earth.pdf (380 Downloads)
	Last edited by: H-H at: 6/22/2010 1:36 PM Small writing mistake
Suggestion To thank Quote Answer
This contribution was helpful to 4 thankful Users AMAZINGAHMED dchartier how come Ayman Elotaify

6/22/2010 7:26 AM	Rate (0)
Aret Posts: 2348 Rating: (264)	H-H, thanks, very good post. Connecting M with earth has one drawback - if somewhere in field there is low resistance between L and M (for example some water inside cable or something like) - you sensors would produce weird results, because grounded M from one side and bad resistance from the other produce current loop! So in our installations we always disconnect M and PE. PS.Connection may be in form of bridge (then you can simply unscrew it), in form of slider (you need to pull it to disconnect) and also it can be in form of plate - then it can't be disconnected. For example all 31xC CPUs have such plate - no chances to remove, even on deattaching plastic module cover.
Aret Posts: 2348 Rating: (264)
Suggestion To thank Quote Answer
This contribution was helpful to 1 thankful Users H-H

|

Share this page:

Share this page on...

Follow us on