Neutals in control panels

[Veganic]

What are the pros and cons of having a neutral in a control panel? What extra problems does it bring or what problems does it solve? 3ph or 3ph+N?

[tragically1969]

What a really strange question !! What sort of answers are you hoping to get ?

[Veganic]

We used to just assume 3ph and put a small transformer in if 230V was required. Now with cheap single phase inverters a neutral is regularly required. Just wondering if there was any reason why we avoided neutrals for all those years.

[TimWilborne]

I wouldn't call it a really strange question... I think the only reason the neutral is normally avoided is the cost of the copper and the fact that it is unnecessary in a 3 phase setup, especially in the US where you have 480 3p but AC control voltages are normally 120 VAC so you have to use a transformer anyway. Just to add to the question since I don't have the definite answer either, how many of you cheat and use the ground in place of the neutral for that odd application of 1 leg of your primary voltage?

[tragically1969]

It is if you are in the UK, 99% of sites would have a neutral, if you choose not to take the neitral to the panel you need to select control gear with 415 input or put a transformer in. If you cheated like that in the UK you wouldnt be working for long !!

[Veganic]

I raised this to see what would come back. I was a suprised that it was seen as a really strange question. A neutral is not 'just another conductor' so was wondering what difference it really makes. It was prompted by wondering what the effects are of having a number of single phase inverters running together. Are harmonics going to be more of a problem than with 3-phase? A few years ago it was usual to have a 3 phase panel and transformer to 110AC to give a 'safe' control voltage (I know!). Neutrals in panels were not that common where I worked. The lack of responses probably thinking about a non-existant issue.

[tragically1969]

I thought it was strange as you are in the UK and neutrals are common place, thats all. May i ask if a neutral is not "just another conducter" then what is it ? I dont know what industry you have been in but i have been in various OEM machinery manufacturers for around 20 years now and we have never "avoided" neutrals, far from it in fact, if you can get a neutral into the panel then take it, it makes life easier.

[BobLfoot]

Something I jsut relearned the other day after 25+ years in the business. The presence of a neutral depends on the Transformer supplying your three phase. We have several Delta Transformers for 3ph power busses which means no neutral available. We also have "Y" Transformers which gives us a neutral to work with.

[TConnolly]

That would be a major code violation here as well. Besides, cheating like that doesn't work here because there is no way to derive a 120V (or even 230V) control voltage from 480V three phase and a neutral. A control transformer is required.

[TConnolly]

Bob, There are 240V delta systems in use in the US that have a neutral. The neutral is created by center tapping one winding of the transformer and grounding it at the transformer and then connecting a current carrying neutral at center tap. This creates a three phase + neutral system where 120 V + Neutral can exist between either of the legs adjacent to the center tap. The other leg is designated as the high leg and it must be explicitly identified as such by using orange insulation or an orange sleeve at the ends of the conductors. Loads may not be connected between the high leg and the neutral in this system. IMO, this arrangement should be deprecated, and while its use is decreasing there are lots of existing installations - 240V delta is the red headed step child of the Edison split phase distribution system used for most US residential power distribution that gives us both 240V and 120V in our homes. In industrial facilities I prefer seeing 480 wye and 208 wye. Edited October 11, 2008 by Alaric

[TimWilborne]

What I was talking about is I have seen 480V panels with an odd 277 device running off of 1 leg to ground. Another one is lighting running off of 277. Both can cause problems yet you rarely see a neutral leg as an alternative.

[leonuce]

Neutral is requiered to derivade a 120 volts from a Y connection ( neutral to hot line). If you have a Delta connection you can use the ground as a neutral to derivade a 120 volts, that's for 3PH, 220 volts system. If you have 480 volts system you can have 220 volts from neutral to a hot wire. You also can use a step down transformer; 480/120 or 220/120 volts. You have to be careful when conncting equipment otherwise you will violate the National Electrical code.

[TConnolly]

I wholeheartedly agree. Edited October 14, 2008 by Alaric

[Veganic]

the neutral is a grounded conductor would be a simple answer but not always a true one.

[TConnolly]

We call the neutral a grounded current carrying conductor over here. The ground is a grounded non-current-carrying conductor. (You know, being that we speak a more precise Englsih over here and all that. ) Edited October 14, 2008 by Alaric

[Veganic]

Your hyphenisationification has got me confused though.