Help

Can you supply a machine with L1, L2 and L3, using a 3 phase supply to feed 3 seprate 230 volt cicuits. The total load is 38amp spread over the 3 phases. My concern is that they are all relying on the single nuteral core. It is 1.5mm, 4 core SWA over a distance of approx. 22 meters via a 3 pole type C MCB 16amp.

Regards

Alan J

What are the loads, how are they controlled ?

If the loads are balanced over the three phases there will be no current in the neutral..

john..

Without doing the cable calc the cable looks to be a bit on the light side.

Have you put a tong tester on the neutral to see what current it is carrying.

I won't even go into switch mode power supplies causing 3rd harmonic problems in the neutral because I have wiped it from my memory and replaced it with other stuff.

As above how balanced are the loads?

More info required

2 x 3kw elements 1 x2.2kw motor single phase 1 Toledo transformer for pcl supply 2 x .75kw heaters all fed via relays, contactors

How balanced are the loads, I don't want to presume they are split evenly across the phases but hopefully they are.

Do the heaters click on and off on a thermostat?

They are 3 seprate 230 volt single phase circuits circuits How is there no current in neutral ?

Yes controlled via Stats but both running most of time as water is drawn when machine in use most of day

athej said:

They are 3 seprate 230 volt single phase circuits circuits How is there no current in neutral ?

Yes controlled via Stats but both running most of time as water is drawn when machine in use most of day

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Because it is 3 phase magic

Not being cheeky here but I don't know your background, Have you done any 3 phase theory? Very basically:

The 3 phases are 120 degrees apart (which is due to the generator design) so take one moment in time, L1 would be at say 0 degrees then L2 would be at 120 degrees and L3 would be at 240 degrees. Now if the load on each one of them was equal then the resultant load that would travel down the neutral would be zero, this was proved in our college days was by drawing a vector diagram.

assume the 3kw elements are heaters ?

So whats on L1, L2 and L3 of the loads. i.e. 3kW element and PSU, 3KW element and 0.75KW heater etc etc

Neutral is not usually a problem unless the loads are harmonic generators (like lighting)

They are 3 seprate 230 volt single phase circuits circuits How is there no current in neutral ?

Thanks Roys

It Has all come Back Your a star

Thanks

Still concerned about load on a 1.5 mm sq cable.

Still concerned about loads switching off causing imbalance leading to high load on neutral.

Have you tong tested (clamp meter) neutral?

roys said:

Still concerned about load on a 1.5 mm sq cable.

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Doesn't really matter if the 16A MCB is staying. You could put whatever you want on the end of it.

roys said:

Still concerned about loads switching off causing imbalance leading to high load on neutral.

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They'd be on different phases.

Yes I am going to fully working machine Thusday I will take reading on neutral and post, The fault appeared after short time burning out the neutral cores on toledo Transformer.

Lurch said:

Doesn't really matter if the 16A MCB is staying. You could put whatever you want on the end of it.

They'd be on different phases.

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Forgot about the 16A MCB on the first post, time for bed me thinks, I've stopped thinking

Am I the only one old enough to remember when it was common so size the neutral smaller than the 3 phase conductors?
 

ProDave said:

Am I the only one old enough to remember when it was common so size the neutral smaller than the 3 phase conductors?
 

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Yes

Only kidding Dave

ProDave said:

Am I the only one old enough to remember when it was common so size the neutral smaller than the 3 phase conductors?
 

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I must have put miles of 3½c SWA in, it came as a surprise when a drum of 4c showed up.