3P + N + E with E and N the same

spaderkung

Member
Join Date
Aug 2007
Location
South Sweden
Posts
389
Hi, I'm at commissioning where not everything was discussed prior to my arrival. My unit has a 3P + N + Earth connector but at site they have 3P + Earth but they say the neutral and the earth are the same.

So can we then in the connecting cable to our unit simply bridge the earth and neutral core in the female contact at our end of the cable? My cabinet will then have its original connector w 5 terminals and the site will have the existing with 4 terminals.

Thanks in advance
 
I wouldn't do that personally, although they will be connected together on the authoritys' side somewhere.

If you don't need the N just swap your connector over, if you do, then someone will have to supply one!

You're not the first and certainly wont be the last!
 
As said above; No current through PE on purpose..

(Unless you're a Grid Operator using a PEN-system, which you're not)

Risks?
3W + PE cables are not designed to carry max current continuously through PE. And it's simply not allowed either.

Isn't there going to be a third party electrical inspector there after installation of new equipment? Pretty standard in the power and process industries in Sweden at least.
 
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It is more of an installation type question rather than PLC, an installations forum may give you better answers.

The system you describe is a recognised and valid system called TN-C, and as OkiePC says the combined Neutral/Earth can carry current. I don't know enough to say if it is good or bad, but it does exist and it is valid.

https://en.wikipedia.org/wiki/Earthing_system
 
The ground conductor between the service and your equipment will be carrying current. This is a no-no.

Exactly. If this conductor becomes broken or disconnected and your panel has no path then you have potentially energized every metal surface of the panel.

Also if the switchgear or PDP has ground fault monitoring then it will cause issues.
 
Thanks. Will verify if it is a PEN and have a local electrician to come.

If it's a real PEN (which it most probably isn't), you have to separate it to PE and N in your cabinet before using any of it for your consuming equipment and probably add a GFCI (JFB). Much like the same way you you would do in a service panel.

Typical in Sweden is that you get 3 phases + PEN from the grid then at first service panel PEN is separated into PE and N. PE can NEVER EVER be used again as PEN. That's why it's very very unlikely you have a PEN supplied for your equipment.
 
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The Neutral needs to come from the supply. The customer can pull a single core cable in for that. The neutral connection originates at the customer main and unless it is a separate installation it may not originate from anywhere else
 

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