voltage drop

Frank35 · 27 Jan 2006

how do you calculate voltage drop?

plugwash · 27 Jan 2006

resistance of both current carrying cores multiplied by operating current.

Frank35 · 28 Jan 2006

Here in the USA we use this formula 2LAR/1000. L=length A=amps R=resistance we have a table in our code book that gives the resistance per 1000'. Do you have something similar?

Spark123 · 28 Jan 2006

In BS7671 (also referred to as the iee regulations) for the UK we have tables for volt drop for a given type of cable and csa of conductor. This is given in mV/A/m, millivolts per amp per meter.

(mV/A/m figure)*Ib*L / 1000 = volt drop where Ib is design current of circuit and L is length in meters.

plugwash · 29 Jan 2006

Frank35 said:
Here in the USA we use this formula 2LAR/1000. L=length A=amps R=resistance we have a table in our code book that gives the resistance per 1000'. Do you have something similar?

pretty much, we generally give the resistance of both phase cores in the table rather than doubling it afterwards but yeah otherwise pretty much the same.

DDoyle · 29 Jan 2006

We use the same in the UK.

We have tables in the back of our Regs Books (BS7671:2004) that gives the maximum load of a particular size and type of cable, giving several different ratings for installation method. Then below this table will be another which gives the volt drop for the given cable.

The calculation is mV*I*L/1000

or Volt drop per amp per meter * Current * Length and divided by 1000 to give the correct voltage. In the uk we are limited to 4% of the supply voltage or 9.2V@230V

voltage drop

Frank35

plugwash

Frank35

Spark123

plugwash

DDoyle

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