Extra low voltage cable - is there a reason it's rated so low

Forums › Home Workshop DIY › Extra low voltage cable - is there a reason it's rated so low

hio77

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#236293 27-May-2018 16:03

So probably a stupidly simple answer to this...

but extra low voltage cable (eg garden stuff that's rated for 12v) Is there really a reason it's rated so low?

Seem to find the same wire used for the likes of gate openers, where it seems to be rated for a maximum 150V.

Potentially looking to use it as an alternative to cat5 for some low power situations requiring a bit more than what PoE will provide.

On paper, the wire gauge adds up to a far better option compared to using multiple pairs of cat5.

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#2023423 27-May-2018 16:17

voltage drop matters more at 12v than the higher voltages, so you get them rated for less current at 12v. Old halogen garden lights would really look bad with just a volt of drop, so thats what they target it around.

LED lamps usually have constant current regulation on them so are immune to that, so they now have way thinner cable for garden lights.

Not sure I would use that single insulated stuff for anything over 50v tho, since it looks like they have just copied US specs for it, and 50v is where it is no longer extra low voltage here.

for getting DC out to some outside stuff here, I have some old cisco IP phone powerbricks that put out 48v and then that into some old garden light cable, and at the other end a little board off aliex that drops it down to 12v for wifi IP camera and some LEDs etc.

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#2023424 27-May-2018 16:21

Right, so it's more of a rating to ensure it's used in a way that's expected... i did wonder.

i'd expect if i go with using it as an alternative (very much the same purpose as you have) then it would be 48v with a bit of a drop on it anyway

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#2023467 27-May-2018 17:22

This here on aliex looks like the kits I got to do it. Not using the 5v on it at the moment but the plan was that it could power some LED pixels off an ESP module when I get around to it.

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neb

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#2023534 27-May-2018 19:40

richms:
for getting DC out to some outside stuff here, I have some old cisco IP phone powerbricks that put out 48v and then that into some old garden light cable, and at the other end a little board off aliex that drops it down to 12v for wifi IP camera and some LEDs etc.

That's the best way to handle long runs of low-voltage DC, run a higher voltage over the long cable and then use a DC/DC converter at the destination to get the exact voltage you want, then you don't have to worry about voltage drops. For example I use outdoors-rated 12V power bricks to get 5V to embedded devices, and then a UBEC at the device to get an exact 5VDC no matter what the 12V has dropped to over the cable run. For something that needs 12V I'd run 24V and a converter.

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#2023572 27-May-2018 20:20

The voltage rating of the cable might also be rated based on how much mechanical protection the cable has. Rather than the insulation breakdown voltage. Or it could be as simple as the manufacturer wanting to say that that cable can be DIY installed, by marking a voltage lower than the point at which an electrician is needed.

Also water ingress can be a problem for single insulated cables outside. Which causes corrosion problems on DC cables. Which is why older garden lighting systems used low voltage AC instead.

Consider running say 24V AC over your cables. And rectify and regulate the voltage at the remote end.

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#2023588 27-May-2018 20:48

richms:
This here on aliex looks like the kits I got to do it. Not using the 5v on it at the moment but the plan was that it could power some LED pixels off an ESP module when I get around to it.

That looks a bit too DIY-ey, and not outdoors-capable without a lot of work. A golf-cart DC/DC converter is probably a better bet, those things'll run enough current for quite a bit of LED lighting, you just need to put heatshrink over the connection points.

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#2023593 27-May-2018 21:11

Consider running say 24V AC over your cables. And rectify and regulate the voltage at the remote end.

24v AC?

never thought of going that way..

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#2023599 27-May-2018 21:23

This is the tinned cable that I used to the low voltage(12V AC) pump in our goldfish pond.

https://www.jaycar.co.nz/7-5a-2-core-tinned-auto-marine-power-cable-30m-roll/p/WH3053

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#2023604 27-May-2018 21:30

k1w1k1d:

This is the tinned cable that I used to the low voltage(12V AC) pump in our goldfish pond.

https://www.jaycar.co.nz/7-5a-2-core-tinned-auto-marine-power-cable-30m-roll/p/WH3053

Double insulated, there we go now we are getting somewhere :)

AC is something i need to do more reading on... I know DC reasonably well..

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#2023618 27-May-2018 21:51

From an NZ Wiki.... sorry can't find the link again...

Extra low voltage < 50Vac, <120Vdc

Low voltage 50 to 1000Vac, 120 to 1500Vdc

High voltage >1000Vac, >1500Vdc

It is interesting that household 230Vac is a low voltage...

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#2023666 27-May-2018 22:19

neb:
richms:

This here on aliex looks like the kits I got to do it. Not using the 5v on it at the moment but the plan was that it could power some LED pixels off an ESP module when I get around to it.

That looks a bit too DIY-ey, and not outdoors-capable without a lot of work. A golf-cart DC/DC converter is probably a better bet, those things'll run enough current for quite a bit of LED lighting, you just need to put heatshrink over the connection points.

I think it was about half the price when I got mine. Didnt see any of those sealed converters that would stuff up the tube of the stainless outdoor light or I would have got one.

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#2023669 27-May-2018 22:28

I've found the sealed ones to be pretty solid.

unlike the equally sourced power supplies that went in the bin pretty fast..

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#2023685 28-May-2018 00:22

Gordy7:
From an NZ Wiki.... sorry can't find the link again...

Extra low voltage < 50Vac, <120Vdc

Low voltage 50 to 1000Vac, 120 to 1500Vdc

High voltage >1000Vac, >1500Vdc

It is interesting that household 230Vac is a low voltage...

Gotta love definitions. The above is simply for defining rules around working with different voltages.

There are a lot of switchboards, junction boxes etc with 240V wiring inside, and which have warnings that state - Danger High voltage. As saying, Danger low voltage doesn't make the hazard clear.

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#2023688 28-May-2018 00:59

k1w1k1d:
This is the tinned cable that I used to the low voltage(12V AC) pump in our goldfish pond.

https://www.jaycar.co.nz/7-5a-2-core-tinned-auto-marine-power-cable-30m-roll/p/WH3053

Just don't take the current ratings that Jaycar list for their cables as gospel. If you try and run 12V through the whole 30M of that cable at 7.5A You will only have 2.3V left for your load. And the reality will be even worse. As the volt drop calculator that I used, doesn't compensate for the cable heating up, which in turn causes the volt loss to increase even more.

Over long runs, there can be significant cost savings from using more voltage, with step down at the remote end. And another trick is to use a split rail system. Where you run 3 wires. with something like +12V, -12V, and 0V. At the remote end you can run both 12V and 24V loads without needing any voltage conversion circuits. You get 24V by connecting your load between the +12V and -12V wires. If you can keep the load on the +12V and -12V wires reasonably balanced, you can also make the 0V wire smaller. Although that system does require more thought to design, compared to single rail.

Split rail can also be used on long stereo speaker cable runs. Dependant on the type of amplifier used.

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#2023733 28-May-2018 09:32

hio77:

So probably a stupidly simple answer to this...

yes there is.

They have to be idiot proof, safety wise, as DIYers can be idiots .
115v for eg, is not something that many DIYers would know how to safely run outside .
12v may have been used for various things as thats a commonly used voltage , so common & cheap parts could be used in
the design.

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