Sizing the earth cable

[xxlcdx]

Dear All,

I need help to size the correct earth cable to be used,
I have AC unit 20kva , I managed to size the power cable , according to the cable manufacturer datasheet : 4xCore 6mm2 can handle 53Amps (Maximum load current for the AC is 29 Amps)
but how to size the earth cable ?

Regards

 

[waross]

In most locations across the world, this is a matter for the local codes. Which country is your installation in and which code do you work under?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[7anoter4]

I agree with waross, of course.
However,it seems to me the rated voltage is 400 V[50 Hz].
See IEC 60364-4-41 Low-voltage electrical installations –Part 4-41rotection for safety –Protection against electric shock.
According to clause 413.1 of IEC 60364–4–41 the minimum cross section area of the earthing conductor has to be 6mm^2 copper[the same as main conductors].
In any case you have to check if it is capable to withstand the prospective fault current.
s[mm^2]=sqrt(I^2*time)/k is the cross-sectional area, in mm2
I =is the value (r.m.s) in A of prospective fault current for a fault negligible impedance, which can flow
through the protective device (see IEC 60909–0);
time=is the operating time of the prospective device for automatic disconnection in s;
k for copper conductor XLPE insulation =143 [See Annex A ]

 

[waross]

Under the Canadian code, the size of an equipment bonding conductor is determined by the size of the power conductors.
#6 AWG has an ampacity of 55A @ 60 deg. and an ampacity of 65A @ 75 deg.
The required size of an equipment bonding conductor under the CEC is #8 AWG.
#8 AWG has an ampacity of 40A @ 60 deg. and an ampacity of 50A @ 75 deg.
As a rule of thumb (but subject to some exceptions) an equipment bonding conductor will be two AWG sizes smaller than the power conductors.
The ratio between an AWG size and one size smaller is 1:3√2 = 1:1.26 (1/0.79)
The ratio between an AWG size and two sizes smaller is 13√2)² = 1:1.59 (1/0.629)
With power conductors of 6mm², a bonding conductor of a minimum 3.77mm² will meet the intent of the Canadian Code.
I suggest that with a cable of four equal cores, the fourth core will meet the minimum requirements of either the CEC or IEC
According to clause 413.1 of IEC 60364–4–41 the minimum cross section area of the earthing conductor has to be 6mm^2 copper[the same as main conductors].

Bill
--------------------
"Why not the best?"
Jimmy Carter