voltage drop

Frank35 · Posted: Fri Jan 27, 2006 3:37 am Post Subject: voltage drop

how do you calculate voltage drop?

plugwash · Posted: Fri Jan 27, 2006 11:10 am Post Subject:

resistance of both current carrying cores multiplied by operating current.

Frank35 · Posted: Sat Jan 28, 2006 3:01 pm Post Subject: voltage drop

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 · Posted: Sat Jan 28, 2006 5:39 pm Post Subject:

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 · Posted: Sun Jan 29, 2006 12:06 pm Post Subject: Re: voltage drop

Frank35 wrote:

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 · Posted: Sun Jan 29, 2006 2:57 pm Post Subject:

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