Someone explain a volt drop.

[Laine]

Hi,

Is a volt drop just the continual loss off electrical pressure along a wire due to its resistance? E.g. the longer the wire the more volts are dropped?

Can you do anything to overcome a volt drop?

Cheers,

Laine

 

[big-all]

if your talking domestic
as i understand it a greater rated cable than you need
say you need 5 amp use 13amp cable

could be wrong though

big all

 

[breezer]

cable is rated by its conductor size (its cross sectional area), not current carrying capacity. so ther for ther is no such thing as 13 Amp cable

Laine,you are right

basically:

Voltage drop is due to the resistance of the conductor itself, so the longer it is the higher the resistance gets.

To over come voltage drop you use a bigger cable. OR If you have a multi cored cable you use more cores. so if you had a 4 core wire armoured cable you could use 2 cores for live and 2 cores for neutral (earth being the wire armour) which is in effect using a bigger cable.

there are tables which tell the volt drop/foot of any specific cable size, using this and knowing the currrent draw you can work out what size cable is required.

This is true, no matter where the installation is, be it domestic, commercial etc.

it also applies to anything electrical, including speaker cables for sound systems, (thats another story) and burglar alarms, to name but two

 

[skwirrel]

Volt drop is proportional to resistance and current. viz-a-viz Ohms Law

V = IR where I is current & R is resistance

Resistance is proportional to length & inversely proportional to cross sectional area.


T

 

[murraysnudge]

You can put some values in here to see the effect.
I think the V drop is limited to 4% and then you increase cable size.

 

[Laine]

Cheers fully understood now

 

[ban-all-sheds]

To over come voltage drop you use a bigger cable. OR If you have a multi cored cable you use more cores. so if you had a 4 core wire armoured cable you could use 2 cores for live and 2 cores for neutral (earth being the wire armour) which is in effect using a bigger cable.

Be careful doing that that you don't exceed the csa of the armour. I won't steal Lectrician's thunder this time...

 

[AdamW]

cable is rated by its conductor size (its cross sectional area), not current carrying capacity.

[pedant] ACTUALLY, a cable is not "rated" by conductor size. In this instance, "rated" means "to specify the performance limits of". Size is not a performance attribute (at least that is what women tell me ) [/pedant]

I am not sure what the correct word would be, but "graded" or "scaled" would be a better choice than rated. You could say sized, I suppose.

I had an idiot at work who kept on "correcting me" every time I said "twin and earth" by calling it "13 amp cable". He insisted he was right and I was wrong. And he is a professor

Anyway, Laine, what you say is a decent enough explanation of what happens. Is this what you remember from physics class or just gleaned from articles and books?

When you have a power supply sitting there, unconnected, it is "potential energy". That is, there is all that energy there but you are not using it so it is just "potential". This is why "Volts" are more correctly referred to as potential difference. Now, when you hook it up to something, the wires offer resistance. This resistance causes a proportion of the energy flowing to be converted into heat before it gets to the motor/TV or whatever.

The thicker the cable, the more easily it will conduct. Now, the filament of a lightbulb is very thin. So, the resistance per metre is very high. Which is why a lightbulb can convert 100W of electrical power into light and heat with a relatively short piece of wire. If the filament was a piece of thick wire then you wouldn't get anything out of it.

As was said before, to overcome "voltdrop" you need to use a bigger cable. Theoretically you could use cables made of different materials but copper is so widely available and is a pretty good conductor.

 

[ban-all-sheds]

I had an idiot at work who kept on "correcting me" every time I said "twin and earth" by calling it "13 amp cable". He insisted he was right and I was wrong. And he is a professor

What a tw*t. What did he say when you pointed out the range of sizes available - did he have any theory as to why T&E was available in these sizes, and why it should all be called 13A cable, and not, for example, 6A cable, or 27A cable, or 50A cable?

 

[AdamW]

The stupid thing was, I was talking about 4.0mm2!!!

I had said "I wired my immersion heater in 4mm twin and earth, means it can carry 30A so I can upgrade to a twin element if I want later on". Then came the "Twin and earth? Don't you mean 13A cable?".

I wouldn't have minded but he was so adamant that I was wrong. Nope, it's not called T&E, it's called 13A cable.

 

[ban-all-sheds]

Were you torn between ignoring him completely and dumping half a ton of supplier catalogues on his desk open at the pages for T&E cable?

 

[TonyS]

The cable size doesn't matter in this case, but voltage rating does

See Capital Punishment

 

[Millennium_Boy]

I even used 10mm2 on ALL the Bonding in my property - the regulations state 4mm will do for Supplementary Bonding, but the larger the bonding conductor the better

 

[securespark]

I always appreciate a large bonding....

 

[Lectrician]

Thing is with 10mm supp bond, you cant be bonding to the latest regs for bathrooms - you would never get that into an accessory terminal!!