Voltage Drop

[securespark]

Assuming a selected cable's CSA can carry the load required of it, is the only consequence of excessive voltage drop a reduction in voltage at the destination of the circuit, or could there be other dangers?

 

[ricicle]

Failure of equipment to perform correctly in which certain dangerous situations could arise eg failure of discharge lighting

 

[securespark]

Yeah, I thought of that possibility. I should say that I was thinking of a domestic install sans discharge lighting.

 

[ban-all-sheds]

Motors not working properly?

LV halogen lamps going black?

Falsified EICs?

 

[LoveRocket]

As long as the supply voltage at the origins isn't just within tolerance, there will be no problem whatsoever. This issue is even further mitigated by the fact that we have a nominal supply voltage of 230 but it is in actual fact still 240v

 

[securespark]

So, if voltage drop were excessive, there wouldn't be any danger of overload on that cable?

Imagine the voltage at the cutout to be worstcase, ie 207V.

Then imagine a cable run such that voltage drop is excessive.

Imagine the long cable runs from a submain to a DB.

You would then have a voltage coming into that DB of less than 195V.

 

[LoveRocket]

How can a low voltage overload a cable? If it can carry the current, it can carry the current! Anyway, your cable should be protected with a suitable OPD

Have you ever seen a voltage at the cutout of 207v? (even under load?) I've never seen much below 230v...

 

[Lectrician]

I have seen two immersion heaters, a couple hand driers and a load of lighting all fed on a CIRC 100m run of 4mm MI.

It had been in for years.

Measured voltage was around 200-210 volt when loaded, the lights dipped and the hand driers laboured when you turned things on and off.

It helped that the site had it's own TX feeding two supplies either end of the site - as one was a long LV run, the TX had the voltage tapped quite high anyway.

 

[ban-all-sheds]

How can a low voltage overload a cable? If it can carry the current, it can carry the current!

I guess in theory if it was supplying a large SMPSU then that would draw more current to deliver its output, but that's an extraordinarily unlikely scenario, to the extent that it can be discounted for a domestic submain.

 

[Spark123]

It still shouldn't overload it too long to be an issue providing the mcb/fuse is selected properly.
Biggest problem is the current using equipment may not work correctly.
I suppose not enough voltage can cause excess heat in motors.
Any type of discharge light such as fluorescents may not function correctly - saw that on a food trailer once as the needle on the generators voltmeter wasn't set correctly.

 

[AdrianUK]

It still shouldn't overload it too long to be an issue providing the mcb/fuse is selected properly.
Biggest problem is the current using equipment may not work correctly.
I suppose not enough voltage can cause excess heat in motors.
Any type of discharge light such as fluorescents may not function correctly - saw that on a food trailer once as the needle on the generators voltmeter wasn't set correctly.

Thats a first! Are you sure they weren't trying to get 32A out of a little 2kVA Honda ..... which must be Ok "cos its got two of them 16A sockets mate"

Adrian

 

[securespark]

Have you ever seen a voltage at the cutout of 207v? (even under load?) I've never seen much below 230v...

Not quite. I found 212V on a ring final once.

 

[LoveRocket]

Have you ever seen a voltage at the cutout of 207v? (even under load?) I've never seen much below 230v...

Not quite. I found 212V on a ring final once.

But what was it at the cutout?

 

[securespark]

214V.

Still low.

My scenario's may seem far-fetched, but I'm trying to figure it out in my head.

So the general concensus of opinion is that even if there was excessive voltage drop, there would be no danger of overload to the cable unless that cable was not suitably protected (in which case it is in danger of overload anyway).

 

[LoveRocket]

I'm not following your thinking here SS, how on earth can a LOW voltage OVERLOAD a cable?

As Banal mentioned, certain active devices (such as SMPSs) may increase their current draw to compensate for low voltage, but these are very rare (and usually only small anyway).

Besides, even if the current did increase a lot, your cable should be protected by a suitable OPD - yes?

You're worrying about nothing mate!