How to Calculate voltage drop ??

[Guest riddler]

Have always wondered even after a lengthy time in the industry how to work out voltage drop on standard 6,8, or 12 core alarm cable, as the stuff that we use does not have an awg rating.

Have I completely missed something or is it time for me to retire?

Do people out there still use it.

Our company only cares about it when systems dont work on commmision.

Thanks for any help and heelo to all.

riddler.

-=Made Batman famous maybe I can do the same for you=-

[Guest]

Have always wondered even after a lengthy time in the industry how to work out voltage drop on standard 6,8, or 12 core alarm cable, as the stuff that we use does not have an awg rating.

Have I completely missed something or is it time for me to retire?

Do people out there still use it.

Our company only cares about it when systems dont work on commmision.

Thanks for any help and heelo to all.

riddler.

-=Made Batman famous maybe I can do the same for you=-

41657[/snapback]

U=RxI where R is cable resistance and I is the current consumption.

R you will get from cable manufacturer and I u get by calculating currentdraws of detectors used..

[Guest IM_Alarms]

or R you can get from measurement of course!

and I you can get from measurement also,........... presuming the system is running already B)

[Service Engineer]

Your using that "U" again..? Ohms law ..?

V=IxR

Lets say the panel supplies 13.8Volts and we have a 100 meter cable run and the cable run resistance is 100 Ohms (I know it wont be that high but hey it makes the maths easy), then the current available at the end of the cable would be (13.8/100 = .138Amps) = 138mA. But that doesnt tell you the voltage dropped, just the current available at the end of the cable.

Have a look HERE for a more detailed description

[jb-eye]

Lets say the panel supplies 13.8Volts

41711[/snapback]

Lets make it realy simple Try this

Jef

[Brian c]

Lets make it realy simple Try this

Jef

41713[/snapback]

[added to favourites ]

[Service Engineer]

Have always wondered even after a lengthy time in the industry how to work out voltage drop on standard 6,8, or 12 core alarm cable

The easiest way is to measure the voltage at the panel/psu (say 13.8v), then walk to the device and measure that voltage (say 13.4v), subtract the lower reading from the higher reading and hey presto a 0.4v drop is calculated.

[jb-eye]

The easiest way is to measure the voltage at the panel/psu (say 13.8v), then walk to the device and measure that voltage (say 13.4v), subtract the lower reading from the higher reading and hey presto a 0.4v drop is calculated.

41719[/snapback]

Dave, not coming from the security industry (electrical contracting), it seems odd (to me) that someone would energise a circuit (any circuit) before testing it. So design and calculation is surely an important part, of the installation of security systems?

Jef

[Guest IM_Alarms]

I was talking about measuring the resistance of the cable and calculating (or knowing) the current of the device and working it out that way. or if it is up and running, you can measure the current at the panel and calculate the volt drop that way...... could save a long walk to the end of the circuit

[Guest]

You have to do calculations before u install in bigger premises since cable lenghts can reach easilly 300-500 metres, even longer and amount of detectors can be few ten or even hundred. Ore just one but power consuming detector.

If you don't count even estimations you can end up in situation that you add few extra PSU's that will cost you your nerves and the money..