Can anyone give me the answer and source for this question on current carrying capacity

[Inverse]

Hello I just need to know the correct order and a source which shows me that it is that order please

When calculating the current carrying capacity

Is the correct order

Ib ≤ In ≤ It ≤ Iz

Or

Ib ≤ In ≤ Iz ≤ It

Niceone

 

[pc1966]

What do each of those terms refer to?

That might help you work out the order and why it is so.

 

[Inverse]

What do each of those terms refer to?

That might help you work out the order and why it is so.

Ib Design current
In current rating of protective device
It Tabulated current
Iz current carrying capacity of the cable in the situation where it is installed

 

[mainline]

Hello I just need to know the correct order and a source which shows me that it is that order please

When calculating the current carrying capacity

Is the correct order

Ib ≤ In ≤ It ≤ Iz

Or

Ib ≤ In ≤ Iz ≤ It

Niceone

Worth having a read

Cable Size and Protective Device Selection

05: Cable Size and Protective Device Selection The cable most commonly used in domestic electrical installations is the 70 °C thermoplastic PVC insulated and sheathed flat cable which is often refe…

the-regs.co.uk

 

[Inverse]

Worth having a read

Cable Size and Protective Device Selection

05: Cable Size and Protective Device Selection The cable most commonly used in domestic electrical installations is the 70 °C thermoplastic PVC insulated and sheathed flat cable which is often refe…

the-regs.co.uk

Thanks for your reply, I have read this before and it shows the formula without (It).

The reason that I’m asking is that I’ve been told by my tutor that the order that I think it is is incorrect but without giving me a source

The order I think it is

Ib ≤ In ≤ It ≤ Iz

The reason

First you calculate your design current

Then select a safety device that is equal or larger than that current

Then you find the tabulated current by applying factors such as grouping, insulation etc
Using this It ≥ In/CgCaCsCdCiCfCc

This is now the actual current that will pass through the cable

Iz value when larger or equal to (It) will correspond to a csa that will take this current

All these values come from bs7671 tables

This makes sense to me but I’m happy to find out I’m wrong and do it correctly, all I want is a source that shows me that I’m wrong

 

[Inverse]

Hello I just need to know the correct order and a source which shows me that it is that order please

When calculating the current carrying capacity

Is the correct order

Ib ≤ In ≤ It ≤ Iz

Or

Ib ≤ In ≤ Iz ≤ It

Niceone

Thanks for your reply, I have read this before and it shows the formula without (It).

The reason that I’m asking is that I’ve been told by my tutor that the order that I think it is is incorrect but without giving me a source

The order I think it is

Ib ≤ In ≤ It ≤ Iz

The reason

First you calculate your design current

Then select a safety device that is equal or larger than that current

Then you find the tabulated current by applying factors such as grouping, insulation etc
Using this It ≥ In/CgCaCsCdCiCfCc

This is now the actual current that will pass through the cable

Iz value when larger or equal to (It) will correspond to a csa that will take this current

All these values come from bs7671 tables

This makes sense to me but I’m happy to find out I’m wrong and do it correctly, all I want is a source that shows me that I’m wrong

This might make it clearer to what I mean and why I’m asking

Thanks

 

[mainline]

This might make it clearer to what I mean and why I’m asking

Thanks

View: https://www.youtube.com/watch?v=p4Bxog90TXA

 

[westward10]

You don't normally see It in the equation. What you would normally do is apply correction factors then select a cable/conductor for Iz from It they are just asking you to include It. Iz is not necessarily the same as It for example It could be 10A and Iz 15A. Remember It is not the current that will pass through the cable but the current carrying capacity of the cable required due to external influences, for example In is 16A so your cable (Iz) must be rated at 16A or above and without correction factors this is as read but correction factors can "squeeze" the rating of the cable down to say 13A hence a larger csa is required, Ib does not change.