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I want to use the armour as my CPC but need to check it complies. The cable will be run from a SP Distribution panel to CU.
As per Selection and Erection Guidance Note 1 table D10a I can see a 10mm XLPE SWA requires a 31.1mm csa to comply, but only has 26mm on 2-core.
20171231_114229828_iOS.jpg - https://1drv.ms/u/s!ApQQCRGg1ka_gvxxrqQ0QslTR-xaHg
So the only way I might be able to use this is to calculate using adiabatic equation.

Is my calculation correct?

Voltage = 230v
Ze = 0.09 (to be verified, taken from old EIC)
I = 230/0.09 = 2,555A
I2 = 6,528,025
t = (Fig 3A1, 100A BS1361 Type 2a > 1,450A) = 0.1s
I2 x t (6,528,025 x 0.1) = 652,802
sq Root 652,802 = 807
k = 46 (TABLE 54.4 steel)
S = 807/46 = 17mm

So looking at table D10a above we can see 10mm XLPE SWA has csa of 26mm, but as I only need 17.5mm I will be fine ?

On a similar note, Table 4E4A advises 10mm 2-core SWA capacity in ducting is 71A
20171231_140220034_iOS.jpg - https://1drv.ms/i/s!ApQQCRGg1ka_gvxzxVXvCVCdScy83Q

But manufacturers notes say in duct I can run their cable up to 89A, I assume in this instance I could use manufacturers notes over Table 4E4A as Table 4E4A is only generic ?
SWA Capacity.pdf - https://1drv.ms/b/s!ApQQCRGg1ka_gvxyaNUN1GXpn1Ob8w

In reality I'll protect with either 50A or 63A MCB, but it's possible I might want to run at 80A in the future. Now I know the cable spec so I know it's safe; I can also leave cable spec with EIC, but is there anything else I should do to prevent another electrician in the future condemning the cable?

 
I want to use the armour as my CPC but need to check it complies. The cable will be run from a SP Distribution panel to CU.
As per Selection and Erection Guidance Note 1 table D10a I can see a 10mm XLPE SWA requires a 31.1mm csa to comply, but only has 26mm on 2-core.
20171231_114229828_iOS.jpg - https://1drv.ms/u/s!ApQQCRGg1ka_gvxxrqQ0QslTR-xaHg
So the only way I might be able to use this is to calculate using adiabatic equation.

Is my calculation correct?

Voltage = 230v
Ze = 0.09 (to be verified, taken from old EIC)
I = 230/0.09 = 2,555A
I2 = 6,528,025
t = (Fig 3A1, 100A BS1361 Type 2a > 1,450A) = 0.1s
I2 x t (6,528,025 x 0.1) = 652,802
sq Root 652,802 = 807
k = 46 (TABLE 54.4 steel)
S = 807/46 = 17mm

So looking at table D10a above we can see 10mm XLPE SWA has csa of 26mm, but as I only need 17.5mm I will be fine ?

On a similar note, Table 4E4A advises 10mm 2-core SWA capacity in ducting is 71A
20171231_140220034_iOS.jpg - https://1drv.ms/i/s!ApQQCRGg1ka_gvxzxVXvCVCdScy83Q

But manufacturers notes say in duct I can run their cable up to 89A, I assume in this instance I could use manufacturers notes over Table 4E4A as Table 4E4A is only generic ?
SWA Capacity.pdf - https://1drv.ms/b/s!ApQQCRGg1ka_gvxyaNUN1GXpn1Ob8w

In reality I'll protect with either 50A or 63A MCB, but it's possible I might want to run at 80A in the future. Now I know the cable spec so I know it's safe; I can also leave cable spec with EIC, but is there anything else I should do to prevent another electrician in the future condemning the cable?
I want to use the armour as my CPC but need to check it complies. The cable will be run from a SP Distribution panel to CU.
As per Selection and Erection Guidance Note 1 table D10a I can see a 10mm XLPE SWA requires a 31.1mm csa to comply, but only has 26mm on 2-core.
20171231_114229828_iOS.jpg - https://1drv.ms/u/s!ApQQCRGg1ka_gvxxrqQ0QslTR-xaHg
So the only way I might be able to use this is to calculate using adiabatic equation.

Is my calculation correct?

Voltage = 230v
Ze = 0.09 (to be verified, taken from old EIC)
I = 230/0.09 = 2,555A
I2 = 6,528,025
t = (Fig 3A1, 100A BS1361 Type 2a > 1,450A) = 0.1s
I2 x t (6,528,025 x 0.1) = 652,802
sq Root 652,802 = 807
k = 46 (TABLE 54.4 steel)
S = 807/46 = 17mm

So looking at table D10a above we can see 10mm XLPE SWA has csa of 26mm, but as I only need 17.5mm I will be fine ?

On a similar note, Table 4E4A advises 10mm 2-core SWA capacity in ducting is 71A
20171231_140220034_iOS.jpg - https://1drv.ms/i/s!ApQQCRGg1ka_gvxzxVXvCVCdScy83Q

But manufacturers notes say in duct I can run their cable up to 89A, I assume in this instance I could use manufacturers notes over Table 4E4A as Table 4E4A is only generic ?
SWA Capacity.pdf - https://1drv.ms/b/s!ApQQCRGg1ka_gvxyaNUN1GXpn1Ob8w

In reality I'll protect with either 50A or 63A MCB, but it's possible I might want to run at 80A in the future. Now I know the cable spec so I know it's safe; I can also leave cable spec with EIC, but is there anything else I should do to prevent another electrician in the future condemning the cable?
 

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  • pvc_xlpe.pdf
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Adiabatic looks ok but think you should be usink the value of 51 as K. Even though the cable maybe XLPE and rated for 90~C the connections/switch gear will probably be rated for 70~C.

10mm 2core installed reference method D has a CCC of 60A. The manufacturers data will again probably be for XLPE at 90-C....where your connections etc will be rated for 70~C. You are using the wrong table, you should be using 4D4A not 4E4A.
 
You are using the values for an XPLE cable run at 90°C, this is unlikely to be suitable for the connections into the CU as it is likely to be designed to run only up to 70°C.
If you look at table 10b that is for XPLE cable run at 70°C you will see that it complies.
However your calculation method is correct though taking into account that the time will be less than 0.1s and the I²t value for the fuse should be used in preference. Also if the cable is at 70°C then the K value would be 51.
So long as the cpc is not also a bonding conductor you will be OK.
But Lee got there first!:cry:
 
This is really helpful, guys thanks for detailed explanations.
that makes sense using 70°C.
So I now know XLPE @ 70°C complies, and I should use table 4D4A. But purely for the sake of improving my understanding where can I find the I²t value for the fuse?
 

It's been ages since I've seen that PDF on here hate. A was going to mention it...
 
Okay, found something similar for Bussmann, but I don't understand how to read chart. You get 100,000 (10 power 4) I follow bottom row until I get 100A, then up, but where to stop?
It looks more to me that it should be 10 power 5 as there is where thick black line is?
 
They are shown on a logarithmic scale.
Figures along the horizontal axis of the curve represent the continues current rating of the OCPD. The figures along the vertical axis represent time in seconds. find the current multiple of (In) at the bottom of the graph. Next, draw a vertical line to the point where it intersects the curve and then draw a horizontal line to the left side of the graph to find the trip time.
 
Okay, found something similar for Bussmann, but I don't understand how to read chart. You get 100,000 (10 power 4) I follow bottom row until I get 100A, then up, but where to stop?
It looks more to me that it should be 10 power 5 as there is where thick black line is?
For the I²t graph for fuses the line starts to become thick at the prearcing point i.e where the fuse starts to melt and ends at the point where the fuse separates (this is the point you want).
1x10⁵ is 100,000.
 

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