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Voltage Drop Calculation

05/19/2013 9:11 PM

In voltage drop calculation, when the phase conductor is 2 sets and earth conductor is 1 set utilized, should i consider the resistance and inductance are half of the value that the conductor have? how do i calculate?

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#1

Re: Voltage Drop Calculation

05/19/2013 9:21 PM

What constitutes a "set"?

Resistance has something to do with cross-section of conductors. All of them, providing the connections are able to carry the current.

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#2
In reply to #1

Re: Voltage Drop Calculation

05/19/2013 9:52 PM

2 sets [4x300sqmm XLPE/LSHF] + 1 x 150sqmm LSHF (E) total distance run of 250m.

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#3
In reply to #2

Re: Voltage Drop Calculation

05/19/2013 10:15 PM
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#4
In reply to #2

Re: Voltage Drop Calculation

05/19/2013 10:38 PM

Measure the current in one cable and calculate or measure with a meter. If current distribution is unequal,check why.

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#5

Re: Voltage Drop Calculation

05/20/2013 1:33 AM

The earth conductor is not part of voltage drop calculation. Using 4c cable means neutral cross section is same as that of phase. Ohms law applies with due consideration of 2 runs of phase and neutral conductor of equal cross section.

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#6
In reply to #5

Re: Voltage Drop Calculation

05/20/2013 2:14 AM

Using 2 sets of cables will help reduce the volt drop % instead of upsizing the cable?

In my point of view, it is not.

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#7

Re: Voltage Drop Calculation

05/20/2013 2:41 AM
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#8

Re: Voltage Drop Calculation

05/20/2013 3:40 AM

There shouldn't normally be any current in the earth conductor, as it is there only to carry the fault current until the moment the circuit protective device(s) disconnect the supply from the fault.

British Standard 7671 gives full cable sizing protocols.

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#9

Re: Voltage Drop Calculation

05/20/2013 5:26 PM

Some puzzlement here! If you have 2 sets 4 core, is that 3 phase and earth in each set - 2 cores for each phase, same colour/number core (whatever 3 phase colours/numbers you have)??

If that is so, you can happily halve the resistance and inductance compared to one cable.

However, if you mean single phase....

67model

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#10

Re: Voltage Drop Calculation

05/20/2013 11:48 PM

I think the OP is talking about a standard single phase (Line) (Neutral) (earth) or (Line 1) (Line 2) and (Earth).

Earth only carries the fault current, so it's not included.

You have to consider the length of the conductor to be twice the one way distance to the load.

The basic equation is R=pL/A, but for Electricians the equation has been simplified to use the info from the wire gage table and constants for Aluminum or Copper.

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#11

Re: Voltage Drop Calculation

05/21/2013 7:01 AM

Calculation is not easy. Measurement is better. Cable makers publish data - example below....

http://www.eland.co.uk/bs-standards/bs5467/cable61/swa-cable--bs5467-steel-wire-armoured-pvc.html

click on the tab marked "Download product spec" on the above web page.

Recent cables have the standard embossed on the sheath.

National standards usually include safe impedance values, but do not separate inductance, which does matter at 300 sq.mm.

Remember that if you run "go" and "return" in different cables you will increase losses (volt drop) seriously [causing cable failure] and values tabled for inductance will be wrong.

67model

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#12

Re: Voltage Drop Calculation

06/12/2013 9:46 PM

Please refer to the below Calculation format.

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