# 415VAC Distribution in Controls Panel



## John (Jan 22, 2007)

Paulusgnome said:


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Is the MCCB in the control panel or somewhere else?


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## Big John (May 23, 2010)

Is it normal in NZ wiring to have three totally independent contactors controlling each phase of the same load? I would really like to see a mechanical interlock on those.


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## John (Jan 22, 2007)

Big John said:


> Is it normal in NZ wiring to have three totally independent contactors controlling each phase of the same load? I would really like to see a mechanical interlock on those.


They look to be just distribution terminal blocks


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## Big John (May 23, 2010)

John said:


> They look to be just distribution terminal blocks


 My mistake. I didn't even notice all the smaller conductors coming out of them. Thought that was some funky version of the safety contactors he mentioned.


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## Paulusgnome (Mar 28, 2009)

The items in the photos are distribution blocks.
There are two safety contactors, each is individually switched by the safety processor. You can just see part of the MCCB at the left of the photo.


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## John (Jan 22, 2007)

Paulusgnome said:


> The items in the photos are distribution blocks.
> There are two safety contactors, each is individually switched by the safety processor. You can just see part of one of them at the left of the photo.


A more inclusive picture would be helpful..


We love pictures:thumbup:


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## Paulusgnome (Mar 28, 2009)

I couldn't help but wonder at the wisdom of having all those smaller wires protected only by a 200A MCCB upstream. Admittedly, they are all run inside the panel, but if one of those wires were ever shorted to earth or another phase, they may well get a bit warm before the MCCB operates?


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## Wirenuting (Sep 12, 2010)

Paulusgnome said:


> I couldn't help but wonder at the wisdom of having all those smaller wires protected only by a 200A MCCB upstream. Admittedly, they are all run inside the panel, but if one of those wires were ever shorted to earth or another phase, they may well get a bit warm before the MCCB operates?


If it was designed and built under engineering supervision, then all is well and good in OZ.


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## Big John (May 23, 2010)

In the states that would still be legal under tap rules as long as all those conductors are protected before they leave the cabinet. It doesn't have to be engineered.


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## micromind (Aug 11, 2007)

In the USA, the 10' tap rule would apply. It's very common to see a big circuit terminated in a distribution block and tons of small wires going to smaller breakers/fuseholders. 

When you get right down to it, how else could it be done, other than a bunch of branch circuits in the panel that feeds it? And then, how would you arrange the disconnecting means?

I've built/ installed/ added onto lots of panels that had distribution blocks.


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## micromind (Aug 11, 2007)

Big John said:


> In the states that would still be legal under tap rules as long as all those conductors are protected before they leave the cabinet. It doesn't have to be engineered.


Rats! 

John beat me by 2 minutes......


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## John (Jan 22, 2007)

micromind said:


> In the USA, the 10' tap rule would apply. It's very common to see a big circuit terminated in a distribution block and tons of small wires going to smaller breakers/fuseholders.
> 
> When you get right down to it, how else could it be done, other than a bunch of branch circuits in the panel that feeds it? And then, how would you arrange the disconnecting means?
> 
> I've built/ installed/ added onto lots of panels that had distribution blocks.


The Ideal situation would to have the smaller breakers/fuse holders as close to the distribution blocks as possible.


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## John (Jan 22, 2007)

Paulusgnome said:


> The items in the photos are distribution blocks.
> There are two safety contactors, each is individually switched by the safety processor. You can just see part of the MCCB at the left of the photo.


A personal "I hate it when" the MCCB is in the middle of the panel. It's best when it's mounted top-right opposite the door cover hinge. That way everything Left and down is deenergized...including anything mounted on the door.


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## Aussielec (Apr 1, 2012)

Paulusgnome said:


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Where is this 200 amp MCCB located? Just be aware that if the supply is fed from a SB in a different building this control board needs a main switch installed. If it's fed from a detached SB but same building I would still say it still needs a main switch. If it's all part of the main SB that supplies the feed then no main switch is required but still preferred. 




Paulusgnome said:


> I couldn't help but wonder at the wisdom of having all those smaller wires protected only by a 200A MCCB upstream. Admittedly, they are all run inside the panel, but if one of those wires were ever shorted to earth or another phase, they may well get a bit warm before the MCCB operates?


As mentioned there's not really any other way to do it. Think about standard residential and commercial boards, the other side of the main switch is wired with cables much smaller then the incoming supply and the only form of protection is the upstream MCCB or fuse that protects the submains or consumer mains. No different to this.

Also if there is a short to earth then I would say the biggest problem is a touch voltage forming rather then the wires getting a little warm. That said the disconnection times for this instance can be up to 5 seconds because nothing in your control board is classified as hand held equipment.

Anyway just a few things to keep in mind.


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## Aussielec (Apr 1, 2012)

Paulusgnome said:


> The items in the photos are distribution blocks.
> There are two safety contactors, each is individually switched by the safety processor. You can just see part of the MCCB at the left of the photo.


Ah, missed that one. The 200 amp MCCB in the picture would be your main switch. I find it strange that the incoming cables at the top of the MCCB are about three times smaller than the cables coming out the bottom. Whats up with that?:001_huh:


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## Paulusgnome (Mar 28, 2009)

Aussielec said:


> Ah, missed that one. The 200 amp MCCB in the picture would be your main switch. I find it strange that the incoming cables at the top of the MCCB are about three times smaller than the cables coming out the bottom. Whats up with that?:001_huh:


They are just different cable types. The black cable is the flexi type iirc (its Sunday, I'm not at work today).

The concerns that I have about the distribution arrangement probably comes from my previous experience in switchboard design. I had been operating under the apparently-suspect assumption that all conductors should be appropriately-sized for the upstream overcurrent protection. While this may be valid for heavier-current switchboards, the rules are a little more relaxed in control panels.

In a domestic switchboard I would always use comb-type busbar to link up MCBs and/or RCDs, but I accept your point earlier that the wires running between main switch and MCB groups is seldom rated for the full supply current.

In the example of my photo, I would also prefe to see the branch CBs tied together with busbar, with single infeed terminals per group and fewer, larger-guage wires. This wouldn't make it much prettier, but would surely be a little more robust?


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## Frank Mc (Nov 7, 2010)

Paulusgnome said:


> I couldn't help but wonder at the wisdom of having all those smaller wires protected only by a 200A MCCB upstream. Admittedly, they are all run inside the panel, but if one of those wires were ever shorted to earth or another phase, they may well get a bit warm before the MCCB operates?


I believe the reg,s in Oz / NZ allow you to run up to 3m in a panel undersized...

HTH
Frank


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