Discuss Adiabatic in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

Judd

-
Reaction score
59
Does anyone know if the adiabatic equation applies to aluminium conductors when calculating the csa of earthing conductors, or guide me to where I might be able to find an answer.
Cheers
 
what do you call a supply circuit? if it's a distribution circuit, 5 secs. max. applies, but the time/current graphs will give you the actual diss. time .
 
what do you call a supply circuit? if it's a distribution circuit, 5 secs. max. applies, but the time/current graphs will give you the actual diss. time .
Sorry it's a building with a block of flats the flats are fed from meters located in a communal hall with each flat fed from the bemco, I've never really understood why a shorter disconnection time requires a smaller earthing conductor, as It stands with a 5 second disconnection time min earth would be 18mm but with 0.4 disconnection time it drops to 5mm
 
yeah, but those figures are the max. allowable diss. time, not the actual time which you get from the time/current graphs.
 
Those graphs make my eyes goes fuzzy ?
so you need to look at them again and again... works with beer. eyes fuzzy after a few.
 
Sorry it's a building with a block of flats the flats are fed from meters located in a communal hall with each flat fed from the bemco, I've never really understood why a shorter disconnection time requires a smaller earthing conductor, as It stands with a 5 second disconnection time min earth would be 18mm but with 0.4 disconnection time it drops to 5mm
Because the fault clears quicker and the conductor will not get to a high enough temperature to melt, if it was 5 seconds there's plenty of cooking time.
 
Does anyone know if the adiabatic equation applies to aluminium conductors when calculating the csa of earthing conductors, or guide me to where I might be able to find an answer.
Cheers
I will have to check but the min size is 10mmsq
 
Table 52.3 has the minimum for aluminium wire as 16mm

Generally you don't want to use aluminium unless it is really necessary, say for cost reasons on big SWA style cables, as you have far more difficulties with terminating it and preventing galvanic corrosion.

The adiabatic limit is one you should be careful with, as the simple "rule of thumb" is half the phase conductor for conductors above 35mm, 16mm CPC down to 16mm phase conductors, and same CPC as phase below that (Table 54.7 but also scaled by adiabatic k-factors if CPC and phase are different materials).

So if your results are well below that you need to be very sure that the end-of-circuit Zs and OCPD really meet the disconnection times and fault currents you based the computation on. Then you get on to the regulations citing tables such as 54.1 for buried earth conductors, and 54.8 if it is TN-C-S supply, etc, that present further limits on how small your CPC/earth can be irrespective of the adiabatic result.
 

Reply to Adiabatic in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock