3phase power question

[engineer1000]

wiring 3 phase using a nueral line

Hi, Can someone give me some advice converning wiring up a 3 phase cabinet
I am wiring up a cabinet to house a 3 phase inverter. Have have MCBs for each phase that are fed into contactors controlled by a safety relay. I want to power up a single phase 230vav in 24vdc out smp. I can connect between neutral and one phase of the 3 phase system.
My question is do I need to put a contactor on the neutal line or a fuse or feed it straight to the psu?

 

[wade_hassler]

Re: wiring 3 phase using a nueral line

Your mention of 230V power tells me you're not in the US, but if you were, the neutral would nevernevernever be interrupted

 

[chuckey]

Re: wiring 3 phase using a nueral line

Likewise in the UK, leave the neutral alone. The French fuse the neutral. We once replaced all these French fuses with bits of copper tube!
Frank

 

[KlausST]

Re: wiring 3 phase using a nueral line

Hi,

in Germany... residual current protective devices definitevely do interrupt the neutral (N). But they don´t interrupt the protective Earth (PE) connection.
When neutral and protective earth is the same wire (PEN) then it is not interrupted.
I´ve never seen a fuse in N.
In PE or PEN a fuse is not allowed.

You should read through safety regulations of your country.

Klaus

 

[engineer1000]

Re: wiring 3 phase using a nueral line

Likewise in the UK, leave the neutral alone. The French fuse the neutral. We once replaced all these French fuses with bits of copper tube!
Frank

Hi Frank,
Looking at the 3 phase in factories in the uk none appear to have neutral. there appear to be 4 sockets 3 phase aqnd an earth. how could I power up say a single phase psu with this configuration, I've searched on google but have no answers, would really appriciate your experience

 

[engineer1000]

After looking at the 3 phase connections in a few factories the 3 phase connections appear to be 4 pins 3 phases and an earth line. With this configuration how can i connect up a single phase 240v ish psu???

 

[erikl]

Is this really a question from an engineer(1000)?

Use an arbitrary phase and the "earth" line, which hopefully isn't earth, but the neutral line.

 

[FvM]

Common neutral and protective earth line in power outlets has been abandonded about 50 years ago, PE is required by safety rules, so if you have a 4 pin connector, it must be expected to expose 3 phases and protective earth, but no neutral. You can't connect a single phase load to this outlet, or need to use a transformer.

Situation is different for fixed machine connections with sufficient cable cross section, in this case a common neutral and protective earth line may be used, but separate neutral and PE is strongly recommended.

Can you show a picture of the connector you are talking about?

 

[engineer1000]

Common neutral and protective earth line in power outlets has been abandonded about 50 years ago, PE is required by safety rules, so if you have a 4 pin connector, it must be expected to expose 3 phases and protective earth, but no neutral. You can't connect a single phase load to this outlet, or need to use a transformer.

Situation is different for fixed machine connections with sufficient cable cross section, in this case a common neutral and protective earth line may be used, but separate neutral and PE is strongly recommended.

Can you show a picture of the connector you are talking about?

I believe I can use a 400v transformer across two phases. It's only for a 1A power supply so I don't think this should be a problem.

 

[chuckey]

This is a typical solution. This is what I had to do when adding flow monitoring electronics to remote three phase pumps on 3l +E wiring.
Recently I added another single phase circuit to a three phase fuse board. Luckily it was all DIN, so one new ICBO (32A) picking up one phase, neutral (from ICBO) wired to the common neutral block at the bottom of board, earth wired to the earth bus bar. Its a bit different if the fuse board is in a different building and the wiring is underground!
Frank

 

[D.A.(Tony)Stewart]

Since you have a breaker (MCB) for the Line circuit capacity, no neutral protection is required other than Earth grounding, which is always done in every last distribution transformer to residential or industrial application.

If the power supply unit (PSU) has no short circuit protection, it could also have a smaller line fuse, based on it's rating, but that is only to protect the PSU.