# Question about copper conductor size.

• posted

I have a large electric oven rated at 15KW resistive load, plus another 3KW for 3-phase induction motors.

Say 18KW total continuous running.

All this has to be connected to a 3-phase supply in delta.

How can I determine the conductor size for each of the 3-phase connections in Amps?

• posted

"Peter Jason" wrote in message news:e3mabg\$2f5p\$ snipped-for-privacy@otis.netspace.net.au...

PS the 3-phase is 415V

• posted

Many thanks; The electrician left out the SqRt3=1.732 in the denominator.

I get Amps = 18000/(1.732 x 415) = 25amps / conductor

Regards

• posted

I get 8ga copper. 31.3a (using the 1.73 factor to account for 3p, and 125% of computed load)

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Load is 34 amps a phase.Depending on length of cable run I would use anything from 6mm sq to 10mm sq.Assuming you are in the UK. regards Mark.

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If this is for use within Europe refer to EN 60204-1 or if it is for installation in the USA have a look at NFPA 79. This will give you the size of the cables to be used, you may need derate them dependent on the installation and the type of cable used. Unfortunately I do not have up todate copies of the standards at home so I cannot give you sizes today. I will try and post the info on cable sizes tomorrow. Also ensure that the fuses/circuit breakers are correctly sized to protect the cable.

BillB

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