2 Phase install

[the pict]

3 core SWA used to power a sub board N and 2 phases SWA as CPC, I said to the customers engineer that I have linked the two MCB,s so that in the event of a fault or for maintenace both phases will disconnect together, No dont want that he said dont need to be, ok I said you can alter it after I have signed it off, linked and sealed MCB,s and took a pic, Am I right comments guys and girls
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[shocking_eg]

im confused ?!?!
pictures please ?

 

[netblindpaul]

So, you have a half sized N conductor effectively also?
That is unless you have lots of 2ph loads?

 

[44ALLAN]

im confused ?!?!
pictures please ?

Ok I'll start the ball rolling lol.
Why would you want both phases to disconnect at the same time.............what are they feeding for starters?

 

[Knobhead]

Without knowing the nature of the load it’s hard to say anything about this setup. If there are DP loads then the incoming switch / MCB must break all phases and neutral with the proviso that the neutral must be late break.

With resistive loads then In = √((Ia²+Ib²+Ic²)-((Ia*Ib)+(Ia*Ic)+(Ib*Ic))) where Ic=0. For inductive loads where harmonics in the neutral cause a rise in current above the natural triplen you will have problems with the neutral conductor.

 

[Tiny Spark]

Ime assuming this is a 2 phase load such as a 110v DP (55v each phase) supply?

If so the breaker has to disconnect both phases at the same time same as you would for a 3phase supply.

 

[the pict]

OK L1 L2 are supplied from the main board to L1 L2 on the sub L1 supplies a washer and L2 a dryer B32 4 mm radial, a light circuit 4 florrys B6 lights are on the same phase as washer, I have linked the breakers in the main board so that both phases disconnect together, I mean would you de link a 3 phase breaker I think not, if your working on the sub wouldn't you want both isolated ? I would so they are linked in case some clown only reads one breaker and thinks, ok thats the laundry board isolated,
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[johnboy6083]

I agree. I'd want a common point of isolation, although technically it's not required. Think of the old Bill fuse boards for example, 3 fuses would need to be pulled for one TP circuit.

As the phases are 120 degrees apart, then neutral currents aren't an issue.
if the two lives were on the same phase, then I'd have an issue with that.

 

[Tiny Spark]

Ime a little confused, Why have you put a 2 phase sub board in?
I could understand it if you needed it for a double pole load but as you are feeding single phase loads I dont see the benefit?

 

[Silly Sausage]

Pict, maybe you should have just used a 3P breaker.
I'm assuming the 2 phases are 120[SUP]o[/SUP] apart, so Tony's post no 5 could well be of some importance.

 

[the pict]

All considerations mentioned have been taken into account, it is only the question of isolation, I am insisting on as johnboy put it a "common point of isolation"
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[netblindpaul]

I agree. I'd want a common point of isolation, although technically it's not required. Think of the old Bill fuse boards for example, 3 fuses would need to be pulled for one TP circuit.

As the phases are 120 degrees apart, then neutral currents aren't an issue.
if the two lives were on the same phase, then I'd have an issue with that.

Wrong, just so wrong.

 

[netblindpaul]

All considerations mentioned have been taken into account, it is only the question of isolation, I am insisting on as johnboy put it a "common point of isolation"
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I doubt very much whether ALL considerations have been taken into account.

List what you have considered then we can see if you have considered all you should have in your design.

 

[the pict]

Yawn
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