Electric gates. Long distance. Volt drop?

goodstuff!

I'm running a cable in for future electric gates. The run is 450m. I'm allowing for 1kw (too much? too little?). The smallest SWA i can come up with calculating volt drop is 10sq. Seems a bit excessive, am i right?

2011

Very roughly:

Assuming your motor is:
1000W
230VAC
90% efficient
Powerfactor of 0.85
Then motor FLC= 5.68 amps

10 sq.mm copper is 0.00183 ohms/m
Resistance for 450m = 0.8235
Volt drop = 0.8235 x 5.68 = 4.68 V

Max allowable volt drop from cut out to furthest point in a circuit = 5% of 230 which is 11.5 volts. Normally a 3% (6.9 V) volt drop from the main ditribution board is acceptable. So it would seem from the information provided that you should be OK.

I would suggest that you establish exactly what size the total load is.
Without this you are just guessing.

goodstuff!

Thanks 2011. It seems my calculations were correct after all. I suppose i should find out the general load for electric gates or can there be major differences?
Anybody know what they draw?

2011

goodstuff! wrote: »

Thanks 2011. It seems my calculations were correct after all. I suppose i should find out the general load for electric gates or can there be major differences?
Anybody know what they draw?

It has been a while since I have done them to be honest, so I can't remember.
Google is your friend! I am sure a data sheet will be easy enough to find.

M cebee

4.4mv*5.68*450 would give 11.2v drop by my reckoning

i googled the 4.4
dunno is it accurate

2011

M cebee wrote: »

4.4mv*5.68*450 would give 11.2v drop by my reckoning

i googled the 4.4
dunno is it accurate

I got the resistance per meter of 10 sq. cable from a table at work. It also agrees with this

M cebee

ya you dont use that resistance table

you use the mv/a/mt to calculate

Bruthal

Resistance of copper is 1.7 x 10^8 for a meter cube. For a 1 mm conductor a meter long that would be (1.7 x 10^8)/10^6 = 0.017 ohms.

For 10 square this is 0.017/10 = 0.0017 ohms or 1.7 milli-ohms.

Very close to the 1.8 milli-ohms used. This is the resistance of 1 meter of 10 square copper.

But a 1 meter run requires 2 meters of copper, so the milli-ohms per meter run would be 3.4 to 3.6 depending on which of the above you take.

Going by this, the volt drop is close to m cebee`s 11 volts for the 1kw motor load with its possible pf and efficiency included.

Bruthal

M cebee wrote: »

ya you dont use that resistance table

you use the mv/a/mt to calculate

Its the same thing, but the resistance table gives the resistance of copper per meter. The mv/a/mt is calculated to include 2 meters of copper for each actual meter run of cable.

Just double the resistance table reading to get the same answer.

2011

robbie7730 wrote: »

Its the same thing, but the resistance table gives the resistance of copper per meter. The mv/a/mt is calculated to include 2 meters of copper for each actual meter run of cable.

Just double the resistance table reading to get the same answer.

+1, you are correct. I was in work and I just looked at a cable resistance table on the wall, by bad.


I just looked it up 4.4mV/A/m is also correct, I just looked it up in ET101

Sorry Goodstuff, slight error but if your distribution board is close to the cut out you are probably OK.
As stated before, start by determining the load size.

Dony

My motors are 300watt each and these would be considered strong when geared etc.
You need to find the kit you'll be using and then their specs.

goodstuff!

Dony wrote: »

My motors are 300watt each and these would be considered strong when geared etc.
You need to find the kit you'll be using and then their specs.

Unfortunately it will be a couple of years down the line before the actual gates are fitted so i have no information on the units that will be installed.
So taking into account a pair of motors totalling 600w @ 450m, i'm coming up with 4sq SWA?

Bruthal

goodstuff! wrote: »

Unfortunately it will be a couple of years down the line before the actual gates are fitted so i have no information on the units that will be installed.
So taking into account a pair of motors totalling 600w @ 450m, i'm coming up with 4sq SWA?

You must of missed 2011`s calculation, at 1kw the 10 square will be borderline or worse.

600 watts would be just about ok on 10 square at that distance. Motors on too small a cable on a long run struggle to start efficiently. This problem would be reduced with a well geared down setup, but for a near half km run i would think 10 sq is a good idea. Will be an expensive cable though.