This official sponsor may provide discounts for members

Discuss Adiabatic calculation confirmation in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

D

#### DanBrown

Welcome to ElectriciansForums.net - The American Electrical Advice Forum

Could anyone just confirm my results for adiquate earthing size and calculation using the adiabatic equation...

My test was on a ring main circuit wired in 2.5/1.5 pvc..
My supply voltage is 247v
My Impedance is 0.38 ohms.
The circuit is supplied via a RCBO 32a C type

My results suggest that a min CSA earth is 1.78mm2 and my cable CPC is only 1.5mm2.

Is it a problem as such or not?? (still learning testing)

This official sponsor may provide discounts for members
J

#### Jono Pashley

assuming the rcbo is going to operate in 10ms then i get the minimum CPC size of 0.57mm2 dont have big red book with me to cross reference breaker trip times. Fault Current = 247/0.38=650A so Sa = the Square root of (650 squared X 0.01) then divided by 115 = 0.565 edit. just checked my design calcs books type C 32A minimum cpc size of 1.5 so it should be fine.

Last edited by a moderator:
K

#### kermit1202

as you have a ring you have 2 cpc's in parraral making your CSA of the CPC approx 3mm2.

S

#### super spark

Firstly I am unsure why an adiabatic calculation is required. Is the floor area covered above 100m2 ?

The voltage used must always be 230v , all the equations in BS7671 are based on this voltage. also voltages will fluctuate dependent on demand etc...

need a bit more details, I deal more with design and understand why I would need to use the adiabatic equation, but I do not see why you are using it here.

perhaps I am missing something???

This official sponsor may provide discounts for members