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Old April 19th, 2018, 10:31 AM   #1
spaderkung
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3P + N + E with E and N the same

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
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Old April 19th, 2018, 10:59 AM   #2
janner_10
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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!
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Old April 19th, 2018, 11:47 AM   #3
spaderkung
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Thanks. We need the N because we run several internal devices on one phase each.

What are the the risks that you see?
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Old April 19th, 2018, 11:57 AM   #4
OkiePC
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Quote:
Originally Posted by spaderkung View Post
Thanks. We need the N because we run several internal devices on one phase each.

What are the the risks that you see?
The ground conductor between the service and your equipment will be carrying current. This is a no-no.
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Old April 19th, 2018, 12:05 PM   #5
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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.

Last edited by Dirt; April 19th, 2018 at 12:19 PM.
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Old April 19th, 2018, 12:11 PM   #6
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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
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Old April 19th, 2018, 12:23 PM   #7
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I'd feel safer adding a transformer (380 to 220 as I assume this is in Europe?) for single-phase devices.
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Old April 19th, 2018, 04:58 PM   #8
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+1 transformer, or replace components with 400V 1 phase versions.
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Old April 19th, 2018, 05:05 PM   #9
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Quote:
Originally Posted by OkiePC View Post
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.
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Old April 20th, 2018, 03:38 AM   #10
JesperMP
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Quote:
Originally Posted by spaderkung View Post
Thanks. We need the N because we run several internal devices on one phase each.
What are these devices ? How much power ?
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Old April 20th, 2018, 03:50 AM   #11
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NO DON'T DO IT !!! Deadly !
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Old April 20th, 2018, 05:19 AM   #12
spaderkung
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Thanks. Will verify if it is a PEN and have a local electrician to come.
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Old April 20th, 2018, 06:23 AM   #13
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Quote:
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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.

Last edited by Dirt; April 20th, 2018 at 06:41 AM.
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Old April 20th, 2018, 04:46 PM   #14
ktmtragic
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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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Old April 20th, 2018, 05:50 PM   #15
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I'd personally pull a new 5 core cable. Less confusion.
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