Intrinsically Safe Earthing and Equipotental Bonding - Siemens 2

[DrDrreeeaaa]

Hi All

We have a Zone 1 IIA T3 (IEC) Hazardous area in which we are installing several intrinsically safe circuits

Were using Siemens ET200iSP which is an intrinsically safe IO rack system

Anyway, there's a line in the Siemens IO manual that says you're not allowed to connect the equipotential bonding system to the protective earthing conductor of the supply system.

It also says that the ET200isp rack and most of the Is equipment (including cable screens) needs to be connected to this equipotential earthing system.

I understand that they are trying to ensure potential equalisation between the IO circuit and the field to prevent potential differences, but if I can't connect the equip bonding system to the protective earth how do I ensure personal protection??

I think what they are trying to do is prevent potential rise on the PE system (in the event of ground fault, etc.) from appearing on the Is system (specifically cable screens) and the problems this would cause if a second fault occured (i.e between Is circuit and cable screen)

Help??

Thanks

 

[DrDrreeeaaa]

Has anyone used the ET200iSP? How did you do the Earthing?

 

[VEBill]

You shouldn't expect same-day response, especially on a weekend.

 

[Skogsgurra]

If you can find the corresponding German text, you may find that there's something lost in translation. I have experienced that quite often.

If you find the text, please give us the line(s) you ask about. I am quite good at translating Siemens manuals. So I could give it a try.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[DrDrreeeaaa]

Mate I wasn't getting impatient I was just trying to make the question more generic as it was a little specific and required someone to read the manual haha

Thanks for the offer; the manual is in English already, I am just a but perplexed with their recommendations and it's likely because of my lack of understanding so I was hoping someone could shed some light on why exactly they are telling me that the EB is not allowed to be connected to the PE, maybe if some one has seen this before or has a better understanding

 

[Skogsgurra]

Yes. I know that your manual is in English.

I also know that you cannot trust the translation. They are made by translators that know languages, but usually have no idea what they are translating. They therefore cannot imagine that there are different 'grounds' and sometimes chose the wrong word in the other language.

That is what I was saying. Offer still stands.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[itsmoked]

Yes, it rather sounds like you're being put in a spherical room and told to pee "only in the corner".

In reality I think they just want you to run a separate ground to the rack from the building ground. This way a fault to ground when the ground is accidentally open or carrying a fault current won't raise the the rack to an ignition voltage. Everything will still be safely grounded.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[DrDrreeeaaa]

Hi Skogsgurra,

Sorry, just realised that I didnt read all of your message (you prob. figured that out) my apologies sir

I think you're correct that another interpretation of the German would be very helpful

So, the German document is at the link below. The figure I am talking about is on page 105:

http://support.automation.siemens.c...tandard&viewreg=WW&objid=19138269&treeLang=en

I have also attached a snapshot of the page I am talking about so it's abit easier to get around to it.

Since we spoke last I have done some more research and the Siemens manuals refer to 'ground bus PA' as it is an industry standard (perhaps relating to Profibus PA) but they dont explain this anywhere

Additionally I have found a manual for the enclosure that Siemens recommends for this IO system (at the link below):

http://support.automation.siemens.c...tandard&viewreg=WW&objid=33271580&treeLang=en

On page 25 it shows the equipotential bar there and it looks like there is provision for it to be isolated from the enclosure. On page 14 it says 'Short lines connect the equipotential bonding rail to the enclosure. In this cases where the ground and equipotential bonding conductor are installed seperately, this connection can be disconnected'

The german version is at the link below:

http://support.automation.siemens.c...tandard&viewreg=WW&objid=33271580&treeLang=en

How does that sentence 'sound' in german?

So what I want to do is run a seperate earth cable from the MCC to the equipotential bonding conductor in the enclosure, so that potential rise due to earth fault will have a minimal potential rise on the cable screens (and the rest of the equipment)

 

[DrDrreeeaaa]

Hi Keith,

Yes that is exactly what I want to do, but the Siemens documentation is throwing me off track

Yes I have to be honest I am confused, in addition I am not an expert in this area so I am struggling to be sure I am designing things correctly when the manufacturer's recommendations are contradictory.

 

[DrDrreeeaaa]

OK so those links dont work too well. I have attached the german version of the enclosure manual

 

[ScottyUK]

Have a look at section 12 of EN 60079-14. That will likely clear up most of the queries w.r.t earthing for the IS system. The enclosure is designed to provide options to comply with the requirements of this standard.


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If we learn from our mistakes I'm getting a great education!

 

[Skogsgurra]

Sorry to be late. I see that Scotty has explained it already. But, I put some comments on the German papers and think they might be of some help.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[DrDrreeeaaa]

Thankyou all