Voltage drop in DC circuits.

[binky]

Does anyone know the appropiate formula for calculating this. The reason I ask is because I need to install a monitored mag door lock, but I need to connect up an indicator/buzzer a long way across a large carpark, and somehow I don't think bellwire will do the job !!

 

[bob]

1.5 or 2.5 SWA ??

bob

 

[binky]

Sounds about right, but not convinced I need armoured for this, just seems overkill for 12V

 

[binky]

Talking of SWA, has anyone ever found a way of joing SWA to brick lights - all the ones I've ever fitted seem designed for flex only, as in never enough room to terminate SWA glands to them.

 

[Andy™]

Talking of SWA, has anyone ever found a way of joing SWA to brick lights - all the ones I've ever fitted seem designed for flex only, as in never enough room to terminate SWA glands to them.

branch resin joint and flex to light. its not gonna be cheap!

 

[binky]

I doing a quote at the moment, and I don't really want to using flex to light because lights are to be mounted in a low wall, retaining a flower bed, plus wall is only 1 brick thick so can't contain cables within wall way to protect from digging. Though I could possibly channel a bit out and cement over?

 

[Andy™]

SY flex?

 

[binky]

I think it might turn into suck it and see on the day, priced for worst case of course

 

[Andy™]

steel conduit carefully bent to shape with box up against back of lights with waterproof coupler between...

 

[binky]

Was thinking potted joint, flex and plastic conduit to protect, oh and lots of silicone:^O

 

[davetheglitz]

Does anyone know the appropiate formula for calculating this. The reason I ask is because I need to install a monitored mag door lock, but I need to connect up an indicator/buzzer a long way across a large carpark, and somehow I don't think bellwire will do the job !!

Go back to your engineering days:-

Resistance (ohm) = Resistivity (ohm.m) x Length(m)/Area(m.m)

Automatically calculated by link below

http://http://www.allmeasures.com/formulae/static/formulae/electrical_resistivity/12.htm

If you know the current taken then ohms law to get volt drop (V = IxR)

Remember length is double the distance!!!!

 

[mercurystar999]

I've just used a t steel conduit box and a stuffing gland and filled it with that putty.

 

[binky]

Go back to your engineering days:-Resistance (ohm) = Resistivity (ohm.m) x Length(m)/Area(m.m)

Automatically calculated by link below

http://http://www.allmeasures.com/formulae/static/formulae/electrical_resistivity/12.htm

If you know the current taken then ohms law to get volt drop (V = IxR)

Remember length is double the distance!!!!

Thought DC was different due thermal effects - but can't remember hence question.

 

[davetheglitz]

Thought DC was different due thermal effects - but can't remember hence question.

Not as fas as I can see - heating effect will be due to power dissipation - and when you compare DC with AC RMS the dissipation will be the same. Obviously the AC goes up and down, so insulation could be affected by the high peak to peak voltage differential - but other than that there would be no difference.

 

[binky]

Not as fas as I can see - heating effect will be due to power dissipation - and when you compare DC with AC RMS the dissipation will be the same. Obviously the AC goes up and down, so insulation could be affected by the high peak to peak voltage differential - but other than that there would be no difference.

I always thought we used AC to reduce thermal effects as demonstrated by Edison and his rival in America a long time ago, along with proving AC was safer by electrocuting some poor ****** till he smoked, but wasn't actually dead. Mind you seeing as I'm only looking at a max 1Amp, I can't see this being much of an issue.

 

[Andy™]

AC is easier to transmit. fairly basic transformers for changing voltage etc, compared to what would be needed for DC

 

[binky]

http://www.discount-electrical.co.uk/section.php/101464/1/armoured-cable-joints/f1053a3f330ecf5c7100915d7babab1e

Anyone ever used these???

 

[Andy™]

used the resin joints

 

[green-hornet]

I have never really used the 3 way or tee joints but have used the stright joints a few times.

Torpedo resin joints are great for some repairs.

I did look at the above ground joints for doing some garden lighting but in the end never used them.