How can N cable have 52A while another three phase is around 23A, 22A, 20A?

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I have met the problem in my work place! I have one DB with MCCB 60A 25KA with RCCB 63A 0.3mA Supplies to two line. line A have MCB 40A 25KA with RCCB 40A 30mA For Lighting circuit, and line B have MCB 40A 25KA with RCCB 40A 30mA For Power circuit. The Problem is the surface of the lighting MCB and RCCB temperature is higher around 55 drgree C and the Cable surface temperature is 60 degree C. First we thinking about the cable is small, so we change from 16mmsq to 25 mmsq already. the cable is over capacity already, but still cannot solve the problem. then we change the MCB and RCCB for this line. But this way still cannot be solve the problem. The temperature still high. This three phase when we measure are 23A, 22A, and 20A only, but the N cable is 52A. I wonder why this N cable have 52A, and why my MCB and RCCB temperature is high? So what Should I solve do to solve this problem? Please kine to help me. (^_^)
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
60?C is IMO not a huge issue. As far as the neutral current being twice as high as any ungrounded conductor, what type of loads does this serve? Even if all non-linear something doesn't seem right.
 

lefty

Member
Location
Oklahoma
3 phase or single phase?

3 phase or single phase?

I see that you mention 3 phase towards the end of your description, but in the beginning of the description it seems that you mention only two breakers. Is it possible that the neutral current is stacked, meaning that you have 3 circuits, and only have 2 phases/ ie single phase? Can you explain more, possibly a one line drawing would help.
 

Rick Christopherson

Senior Member
What are the voltage readings that you have from:

A-B
A-C
B-C
A-N
B-N
C-N
I got a PM from the original poster before I discovered this thread. I also asked him for these voltages. I also suggested that he try to take current readings with multiple conductors simultaneously through the clamp-on probe to see how the vector-sum of these wires compares with the sum of the magnitudes. (i.e. 2 wires in probe is vector sum, and reading the two wires separately would be the sum of the magnitudes.)

For example, If |N+G| ≠ |N| + |G|, then some of his neutral current is coming from another source via his ground. This is something we have seen in a few residential discussions on this forum.

If |A+B+C| ≠ N, then the system may not actually be a 3-phase system.
 
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