Looking for an easy-to-understand explanation of 3 phase / 3 phase + N

[philectrical]

I have some questions about 3 phase.

1. Does the neutral come in with the supply as standard?
2. As most 3 phase equipment doesn't require an N, what are the circumstances where you need one?
3. When we do need one, why do we need one?
4. Am i right in presuming therefore that we'd mostly use 3c + E as our cable for 3p circuits or would we use a 5c?

Thanks

 

[ipf]

1. Yes

2. There will generally be single phase equipment required, also, if not, much 3 phase equipment these days, requires 230v controls, especially in commercial kitchens, for example.

3. As above.

4. Depends on what the actual circuit requires. Rarely use 5c, mostly 4c swa or singles in conduit, maybe.

Note. This is not an 'easy to understand explanation of 3 phase'.

 

[philectrical]

1. Yes

2. There will generally be single phase equipment required, also, if not, much 3 phase equipment these days, requires 230v controls, especially in commercial kitchens, for example.

3. As above, for example.

4. Depends on what the actual circuit requires. Rarely use 5c, mostly 4c swa or singles in conduit, maybe.

Note. This is not an 'easy to understand explanation of 3 phase'.

Thanks. So the 4c SWA will use 3x phase, 1x CPC plus we'll earth the steel wire, is that right?

 

[ipf]

Thanks. So the 4c SWA will use 3x phase, 1x CPC plus we'll earth the steel wire, is that right?

3 phases, Neutral and swa as CPC.

 

[nicebutdim]

Thanks. So the 4c SWA will use 3x phase, 1x CPC plus we'll earth the steel wire, is that right?

It seems as though you have a specific application in mind and it might be better to provide details.

I'm not long in this industry but, other than for certain loads, haven't yet seen 3 phase distribution without neutral. Generally 4c SWA for L1, L2, L3 & N, with earth provided separately.

 

[philectrical]

3 phases, Neutral and swa as CPC.

So what do we do with the neutral most of the time, just leave it floating in a connector?

 

[ipf]

So what do we do with the neutral most of the time, just leave it floating in a connector?

Where do you mean?
There should always be a N terminal available.

 

[philectrical]

Where do you mean?
There should always be a N terminal available.

Sorry that's what i meant, like put it in the connection but with no N coming out load side if the equipment doesn't need it?

 

[nicebutdim]

So what do we do with the neutral most of the time, just leave it floating in a connector?

Can you be specific about this, in terms of the application you're working on or have in mind?

3 phase DBs have a neutral bar. 3 phase isolators have a neutral terminal.

 

[pc1966]

So what do we do with the neutral most of the time, just leave it floating in a connector?

If you have a 3P & E connector for a load that definitely has no need of neutral, then you would not need to wire it with N to that point, but if it was wired then you would make sure the end was safely isolated. For smaller conductors some would just stick it in to a 2-way Wago terminal or similar so there is no exposed end that might come in contact with anything else.

However, in the more general case you would have 3P+N+E sockets and they must have the neutral connected. Even if your planned load is not needing it, someone in the future might repurpose it and without N and an imbalanced load they would probably damage the appliance.

Simple 3-phase motors do not need N, even if star-connected, but often motor machines using VFD and/or other controls, inspection lights, etc do need N as they are not always a perfectly balanced load and/or require 230V.