In-ground power box

[JimsShed]

I'm planning to pour a 3m x 3m concrete slab in my yard on which to place my mount (AZ-EQ6). I'm not interested in building an observatory. The slab will be 7 metres from my shed which has power.
It occurred to me that it would be cool to have power at the slab. Maybe dig a trench to the slab and run the 12 volt power underground to some sort of powerbox in the middle of the slab, to save carrying out power packs every time I setup. In the box I could setup a panel with 12 volt outlets etc.

Has anyone seen a box on the market that could be placed in-ground and has a flush mounted waterproof lid?

[JA]

Hi Jim,

So do you really want it flush-mounted? I would have thought it be better mounted on some sort of stalk/post with a weatherproof outlet. Ok sorry I just re-read your post it was 12 Volt. I initially thought 240v, as per another thread.

12Volt should be OK, but still in conduit to protect your cable of course. Even if you can't find a dedicated waterproof box (although you should be able to use a 240v type plastic switch or GPO casing with screw off cover or or junction box with conduit entry), you could use also make the same with a short length of say 150mm PVC plumbing pipe/male threaded and a large PVC screw cap (inspection cover). Visit your favourite hardware store/bunnings to see the sort of thing I'm talking about. You want to be able to glue it with PVC cement to the conduit you are using so perhaps electrical fittings might be easier.

Best
JA

[glend]

Get it off the ground. Mount it on the side of your pier, or put in a power post.

[JimsShed]

JA I like your thinking. I noticed that Jaycar have weatherproof outlets which I could fit simply into a cover. If they get dirty, a quick blow out with the air hose would fix it. Yes, I'd run the cables through conduit.
Glen I was preferring to not put a post in because I have some constraints: occasional foot/dog/motorbike/mower traffic around the yard, I wasn't planning on installing a pier on the slab, and the slab will be smack in the centre of a walk through area.
However, If I go ahead with the in-ground approach I'll configure things so I can revert to a post if it doesn't work out. Ahhh the tinkering :)

[rrussell1962]

Hi Jim, if you are running 12v out of the shed to the slab (is it going to be where you set up at the moment?) it might be worth a quick check on the voltage drop if you are going to be both slewing and running dew heaters off the 12v supply.

[JA]

Hello Russell,

yes that's a very good point.

I couldn't find the manufacturer's spec, but I did see this video which shows a test where the AZEQ6 needs anywhere between 2 to 4 amps when running at 12-15 Volts. So it might be something to watch, given the cable distance required and cable gauge.

Best
JA

https://youtu.be/EYYwOn09tj8

[JimsShed]

Wont be long now. Just a few wires to connect and install a power supply in the shed. Even had plenty of room to include my active USB extension cable.

[GTB_an_Owl]

i do believe any electrical cable should be buried at a depth of 2 feet and be marked by a certain type of plastic tape above it - but if you are only doing 12v it may be ok
some of the leccies might want to chime in here

geoff

[JoelyE95]

AS3000 does not seem do differentiate Extra-Low Voltage from Higher Voltages (240v AC and the like). DC Cables are generally Insulated and Unsheathed. This means that they fall under a Category B System for determining the depth of cover.

Based on Table 3.6, it would require a minimum of 500mm cover from ground level to the top of pipe and marker tape 250mm below ground. Or 300mm if it was protected by a minimum 75mm of concrete poured over with market tape 150mm below ground and mechanical protection above the pipe.

If no one knew it was there, 12V from a battery can jump start your heart.

Food for thought.

Joel

[rrussell1962]

Out of interest, how does this apply to 12v garden lights supplied via a transformer? Is the difference that a typical garden light transformer can only supply 12v at, say, 220 VA which would be protected by the RCD at the power box whereas a car battery for example could have a much higher unprotected CCA? Or is it a case of interacting standards where any 12 volt garden supply needs to be supplied through an isolating transformer complying with a different standard?

[JoelyE95]

Reading through the standard again, it seems I missed something further in the back of the document.

Under Section 7.5.11.3, There are no depth-of-burial requirements for the safety of extra-low voltage cables. NOTE: Consideration should be given to the risk of mechanical damage.

However, throughout Section 7.5, there are various other protection requirements and notes such as;
- A Safety Isolating Transformer complying with AS/NZS 61558
- Basic protection is not necessary for voltages not exceeding 25 V a.c. or 60 V ripple-free d.c., in dry indoor conditions. Obviously this is outside now, to basic protection would be required, such as barriers or enclosures with a degree of protection of at least IPXXB or IP2X.
- Live parts shall be arranged so that short-circuit or arcing, either between live parts or between live parts and other conductive material, will not take place under the conditions that may reasonably be expected in service.
- Every extra-low voltage circuit shall be individually protected at its origin
against overload and short-circuit currents by a protective device.

I could probably go on here, but I reckon somewhere out there, a Google Search will yield the whole document.

As always, you should consult a registered cabler or electrician to ensure that it complies with the Wiring Rules.

Joel

[JimsShed]

First test has been a great success. Even did some live video from the shed via the active USB cable. So next task will be to put in an extension cable to enable in-shed use of an electric focuser.

[JA]

Hi Jim,

Good to hear that all's well. Did you mean a 240V AC extension cable ??

Best
JA

[JimsShed]

Hi JA, you can replace the short remote cord on the Skywatcher electric focuser motors with a very long one so long as the gauge is adequate. Only 9v. Other cables in the pipe are either 12v or 5v (USB).