Volt drop tables for LSF T&E

[atm84]

Which table do you use in BS7671 for volt drop for LSF Twin and Earth? There does not appear to be a table for LSF cable. 4D5 refers to the grey PVC cable and is not the right one to use for the white LSF. Any help would be appreciated.

 

[Engineer54]

Which table do you use in BS7671 for volt drop for LSF Twin and Earth? There does not appear to be a table for LSF cable. 4D5 refers to the grey PVC cable and is not the right one to use for the white LSF. Any help would be appreciated.

Why would it NOT be the right table for LSF cable?? Does the 70 C PVC insulation type have any bearing on the copper content of the cable??
As far as i'm aware both standard and general LSF cables are 70c, only cables rated at 90c will differ as far as mV values ...

 

[atm84]

Volt drop tables for LSF T&E

Because table 4D5 refers to thermoplastic insulated and sheathed. The LSF cable is ThermoSETTING insulated and thermoPLASTIC sheathed. There is a distinct difference between thermosetting and thermoplastic and operates at 90 degrees C.

 

[atm84]

Volt drop tables for LSF T&E

If you visit any cable manufacturer website it will say that the LSF cable is rated at 90c. Thermosetting insulated and thermoplastic sheathed.

 

[Meggerman]

Re: Volt drop tables for LSF T&E

If you visit any cable manufacturer website it will say that the LSF cable is rated at 90c. Thermosetting insulated and thermoplastic sheathed.

The insulation can affect the cables current carrying capacity due to different heat dissipation properties. The copper cores however are the same whether PVC or LSF, so volt drop will be the same for given CSA.

 

[atm84]

Volt drop tables for LSF T&E

Ok thanks mega man. Now which table would you use to calculate the current carrying capacity of LSF twin and earth which has thermosetting insulation and thermoplastic sheath with an operating temp of 90c?

 

[davesparks]

If it is being terminated into normal accessories which are rated at 70degrees then the table for 70degree cable.

You can only run a cable at 90degrees if the items it connects too are also rated to 90degrees.

 

[yellowvanman]

Re: Volt drop tables for LSF T&E

Ok thanks mega man. Now which table would you use to calculate the current carrying capacity of LSF twin and earth which has thermosetting insulation and thermoplastic sheath with an operating temp of 90c?

Why don't you try and get the details from the manufacturer!

 

[Richard Burns]

If you are using the cable (a multi-core thermo-setting insulated and thermo-plastic sheathed cable) in a situation where you can run it at 90 degrees then use table 4E2A, if it cannot be run at 90 degrees then 4D2A or 4D5.
However you are only talking about a couple of mV difference so if you are taking it so close that this makes a difference, you have no leeway for error.

 

[Risteard]

You can only run a cable at 90degrees if the items it connects too are also rated to 90degrees.

Exactly, and I would put money on them not being rated for 90 degrees.

 

[Engineer54]

Re: Volt drop tables for LSF T&E

If you visit any cable manufacturer website it will say that the LSF cable is rated at 90c. Thermosetting insulated and thermoplastic sheathed.

And there was me believing LSF insulation was just a 70C PVC derivitive, which i'm pretty sure it used to be when it first came on the market..

Anyway, as others have stated, it's very unlikely that these twin+eath cables will run as a 90C cable so you may as well use the 70C cable table for mV values anyway. The difference in mV values between PVC and XLPE is miniscule, especially when talking about the smaller size cables....

 

[atm84]

Volt drop tables for LSF T&E

I understand what you are saying but my calcs need to be spot on and need to use the correct table. Regarding your point on operating temp of equipment. I totally agree. Most distribution board manufacturers state that their equipment is rated at 70c. However a cable rated at 90c is still ok to use. Just because you use a 90c cable it does not mean that it will be 90c at the point of termination into accessories.

 

[Engineer54]

Re: Volt drop tables for LSF T&E

I understand what you are saying but my calcs need to be spot on and need to use the correct table. Regarding your point on operating temp of equipment. I totally agree. Most distribution board manufacturers state that their equipment is rated at 70c. However a cable rated at 90c is still ok to use. Just because you use a 90c cable it does not mean that it will be 90c at the point of termination into accessories.

Think i know that, I really can't see your point now, we are talking miniscule differences and seeing as your cables won't be operating at 90C, the 70C tables will be giving you the more realistic/accurate values of mV drop to be expected...

 

[shanky887614]

Re: Volt drop tables for LSF T&E

Think i know that, I really can't see your point now, we are talking miniscule differences and seeing as your cables won't be operating at 90C, the 70C tables will be giving you the more realistic/accurate values of mV drop to be expected...

Think i know that, I really can't see your point now, we are talking miniscule differences and seeing as your cables won't be operating at 90C, the 70C tables will be giving you the more realistic/accurate values of mV drop to be expected...

if we are talking about the resistance of the cable surely it wont change between normal and lsf if there both solid core.

 

[Engineer54]

It won't no, but the 90c table with XLPE insulation will allow a greater CCC and therefore will give a greater mV drop. All be it a pretty miniscule one....

 

[shanky887614]

It won't no, but the 90c table with XLPE insulation will allow a greater CCC and therefore will give a greater mV drop. All be it a pretty miniscule one....

2.5 is 18mv/a flat twin 70oC
2.5 is 16mv/a 90oC

I cant find a table for lsf twin though only multicore lsf

 

[Engineer54]

2.5 is 18mv/a flat twin 70oC
2.5 is 16mv/a 90oC

I cant find a table for lsf twin though only multicore lsf

I give up!! lol!!

 

[Meggerman]

OP unless this for some college assignment can you not just do your workings on 70oC and then you have overcompensated for it?

 

[shanky887614]

I give up!! lol!!

lol sorry was half asleep when I wrote that, sat on a deck chair listening to radio

meant to say thermosetting

 

[atm84]

Volt drop tables for LSF T&E

Skanksy I agree. There is not a table in BS. 7671 that provides details for specific twin and earth thermosetting.
4E2A is the closest

And before you start swearing the mv/A/m values are different in 4E2A than in 4D2A.