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Anonymous Poster #1

Cable Size Reduction

12/04/2018 5:47 PM

Cable size reduction

I am looking for cable junction box which will facilitate me to reduce incoming cable Size to my equipment. Is it acceptable in Australia to use cable junction box? I couldn't find a suitable product

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#1

Re: Cable Size reduction

12/04/2018 5:55 PM

The proper way to do it is to use the oversize cable to pull in the cable that is the right size as the oversize one comes out. Then the junction box isn't needed.

Don't forget to down-rate the upstream end supply fuse(s) to allow for the correct size cable.

If in doubt, consult a qualified local Electrician, rather than an Anonymous Poster. One can find them in the local phone book, particularly Yellow Pages.

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#3
In reply to #1

Re: Cable Size reduction

12/04/2018 6:56 PM

The cable may have been "oversized" owing to voltage drop reasons, yet reduced near the supply and/or load to fit conditions at either end. There should be nothing wrong with a junction box for this.

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#5
In reply to #3

Re: Cable Size reduction

12/05/2018 9:37 AM

...provided the prospective short circuit current downstream of the junction box, on the smaller cross-section cable, is insufficient to melt the cable and cause a fire.

That's why pulling in the correct cable for the job is the correct thing to do, and generally why changing cable size in a circuit without some intervening circuit protection for the smaller cable is not permitted under BS7671.

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#6
In reply to #5

Re: Cable Size reduction

12/05/2018 10:05 AM

Don't be so tiresome. Of course the CB/fuse protection would be sized for the smallest cable.

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#7
In reply to #6

Re: Cable Size reduction

12/05/2018 11:12 AM

One hopes, for that is all the forum can do, that the original poster [OP] realises that criterion applies.

The jurisdiction in Australia is different, requiring trained individuals to carry out electrical work. One possibility is that, because the OP has had to ask the question, that poster falls outside the trained individuals requirement, thereby increasing the risk.

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#10
In reply to #6

Re: Cable Size reduction

12/06/2018 1:32 PM

The ampacity of a cable is not based just on the crossectional area of the conductors. The really critical factor is the temperature the insulation can withstand without deforming or igniting from the self-heating from carrying current. You would be amazed by how much current a bare 30 AWG wire immersed in circulated cooled oil can handle.

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#11
In reply to #10

Re: Cable Size reduction

12/06/2018 2:40 PM

Indeed, and the NEC reflects this in the multiple tables and correction factors for various ambient temperatures and conductor configurations.

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#2

Re: Cable Size reduction

12/04/2018 6:48 PM

Reducing from what size to what size? interior or exterior? length of run?

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#4

Re: Cable Size reduction

12/04/2018 7:02 PM

Consult BS 7671 - IET Electrical.

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#8

Re: Cable Size Reduction

12/05/2018 1:19 PM

Yes, if your just interested in cable reduction size due to voltage drop then this is quite commonly done.

Refer to your local standards for cable and associated protection sizing calculations.

Is this for hazardous area Zone 1, 2 or Zone 21,22 as per AS/NZS 60079.xx? If so these guys have what you need:

Stahl

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#9

Re: Cable Size Reduction

12/06/2018 5:45 AM

Short answer is "No". Any work requiring "junction boxes" is to be done by licenced electrician.

Facility wiring is determined by Australian Standards and building codes.

Direct connection of your equipment to the incoming supply also requires licenced individuals where the system wiring will not be modified, but your device wiring could be accommodated.

If your device is an "appliance", then it is to be connected using a correctly installed power point outlet.

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#12

Re: Cable Size Reduction

01/04/2019 9:50 AM

pl. specify what is the equipment.Is it an electric motor?

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