Hi there,
Just after some advice for a submain/DB I’m quoting. A client has asked for a 12way TP board to be installed in a warehouse and the length of run is 150 meters.
Section panel I’m coming from has a ZE of 0.05.
MCCB will be a Square D CDAE 63A so max zs 0.68 at 5 second.
Here’s my attempt at calculating it.
I’ve used the supply voltage of 230 even though it’s a 3 phase supply. I assume this is correct because I have single phase equipment fed off my new db. Just to confirm the max volt drop is from origin (meters) to final circuit and not just the submain?
I read somewhere to use 1.5% VD for sub mains, so 3.45V, which leaves some for the final circuits.
So firstly, do I calculate at 63amps as technically it can carry that or do I use amps calculated from the circuits I’m installing, which is about 20 amps per phase?
Calculated at 20Amps
TABLE 4E4B For 50 mm² : mV/A/m r = 0.99
Voltdrop = (mV/A/m x Length x Design current) / 1000
Voltdrop = ( 0.99 x 150 x 63 ) / 1000
Voltdrop = 2.97 Volts
Calculated at 63Amps
TABLE 4E4B For 150 mm² : mV/A/m r = 0.32
Voltdrop = (mV/A/m x Length x Design current) / 1000
Voltdrop = ( 0.32 x 150 x 63 ) / 1000
Voltdrop = 3.02 Volts
As you can see there’s an enormous difference. Which one do I use?
R1 for 50 mm² = 0.387 (milliohms/M)
R2 for 50 mm² = 0.387 (milliohms/M)
multiplier for 70 °C = 1.2
Zs = Ze + ((R1 + R2) / 1000 ) x length x multiplier
Zs = 0.04 + ((0.387 + 0.387 ) / 1000 ) x 150 x 1.2
Zs = 0.179
R1 for 150 mm² = 0.124 (milliohms/M)
R2 for 150 mm² = 0.124 (milliohms/M)
multiplier for 70 °C = 1.2
Zs = Ze + ((R1 + R2) / 1000 ) x length x multiplier
Zs = 0.04 + ((0.124 + 0.124 ) / 1000 ) x 150 x 1.2
Zs = 0.085 ohms
Both are well below 0.68 I need for the MCCB.
Firstly are these calculation correct? Another company has quoted 35mm for the same install but I can’t see how they’ve got to that.
Just after some advice for a submain/DB I’m quoting. A client has asked for a 12way TP board to be installed in a warehouse and the length of run is 150 meters.
Section panel I’m coming from has a ZE of 0.05.
MCCB will be a Square D CDAE 63A so max zs 0.68 at 5 second.
Here’s my attempt at calculating it.
I’ve used the supply voltage of 230 even though it’s a 3 phase supply. I assume this is correct because I have single phase equipment fed off my new db. Just to confirm the max volt drop is from origin (meters) to final circuit and not just the submain?
I read somewhere to use 1.5% VD for sub mains, so 3.45V, which leaves some for the final circuits.
So firstly, do I calculate at 63amps as technically it can carry that or do I use amps calculated from the circuits I’m installing, which is about 20 amps per phase?
Calculated at 20Amps
TABLE 4E4B For 50 mm² : mV/A/m r = 0.99
Voltdrop = (mV/A/m x Length x Design current) / 1000
Voltdrop = ( 0.99 x 150 x 63 ) / 1000
Voltdrop = 2.97 Volts
Calculated at 63Amps
TABLE 4E4B For 150 mm² : mV/A/m r = 0.32
Voltdrop = (mV/A/m x Length x Design current) / 1000
Voltdrop = ( 0.32 x 150 x 63 ) / 1000
Voltdrop = 3.02 Volts
As you can see there’s an enormous difference. Which one do I use?
R1 for 50 mm² = 0.387 (milliohms/M)
R2 for 50 mm² = 0.387 (milliohms/M)
multiplier for 70 °C = 1.2
Zs = Ze + ((R1 + R2) / 1000 ) x length x multiplier
Zs = 0.04 + ((0.387 + 0.387 ) / 1000 ) x 150 x 1.2
Zs = 0.179
R1 for 150 mm² = 0.124 (milliohms/M)
R2 for 150 mm² = 0.124 (milliohms/M)
multiplier for 70 °C = 1.2
Zs = Ze + ((R1 + R2) / 1000 ) x length x multiplier
Zs = 0.04 + ((0.124 + 0.124 ) / 1000 ) x 150 x 1.2
Zs = 0.085 ohms
Both are well below 0.68 I need for the MCCB.
Firstly are these calculation correct? Another company has quoted 35mm for the same install but I can’t see how they’ve got to that.