Electrical layout for ROR observatory

[Astrokev]

If you've been following my ROR build thread you'll know that the main build is nearly complete. I'm now starting to think about a layout for the electrics and would be interested, and grateful, in your ideas and suggestions.

My observatory is a ROR design, with a small warm room attached - the attached pics give a rough overview of the design and layout of walls (lots more on my main build thread). I've installed two drainpipe conduits running from the warm room to the pier to help run cables to the scopes. I'm interested in imaging and will do this from a laptop either by the scope or, if I can fit a second monitor at the pier to help with focussing, from the warm room. My kit is an EQ6 mount, and for imaging I'll be using DSLR and CCD camera and guide camera.

I've got a basic understanding of electrics, but am certainly no expert, so I will probably get a local electrician to do the main installation, with me doing any trench digging and other grunt work as may be required.

My rough approach at present is to bring the mains supply into the warm room and keep mains voltage in this room only for safety, running a reduced supply to the pier to power the scope. Where possible, I'll put other cabling in the walls before putting up panelling. The warm room walls will be insulated. The other things I need to consider are -

• Consumer unit?
• Lighting circuits - LED's in the scope and warm rooms
• How many circuits do I need?
• Mains voltage requirements and number/positioning of sockets
• USB hub at the pier?
• Data cable needs?
• RCD protection?
• Other ???

If anyone can suggest options \ designs, or other things I should consider for the above I'd be really grateful.

Thanks

[JamesF]

I am not a qualified electrician either, but for my own build I have been pondering on the "power to the pier" issue.  It's not necessarily the case that low-voltage DC is safer than mains AC and it may also be simpler to run mains twin & earth to the pier with a transformer there rather than taking low-voltage high-current DC over fairly hefty cables from the warm room.  I'll be interested to read other opinions on this.

James

[alan4908]

Hello - a bit of input concerning electrics inside my own observatory - you can see what all this looks like by going to my album.........................

In the design for my observatory I also decided to keep all the mains in the warm room and low voltage dc to the main section. 

Mains AC: I asked a local electrician to run armoured cable from the house to the observatory, which is buried in a trench.  This terminates inside the observatory onto a master switch which supplies AC via numerous double sockets.  It's amazing how many sockets you need, don't skimp on these.  The incoming mains is protected by a simple 13 amp fuse and a surge protection circuit.

DC: The main 12v DC is supplied by a high quality power supply which powers about 90% of my astro equipment. This supplies power to a low voltage DC consumer box. The box contains fuses for the various pieces of astro kit.

Lighting: I went for low voltage LED lighting strip/tape (which is dimmable and colour changable). . 

RCD:  I don't have a separate RCD monitoring since the house consumer unit monitors all mains circuits. 

USB: I have two powered USB ports which have proved quite reliable, one inside the warm room and one at the pier. 

Data cables: the observatory is connected to the internet via mains over ethernet. I also have a separate LAN switch inside the room. 

UPS: I have an UPS for my mount, which supplies power for an adequate time to allow me to manually power it off in the event of power supply failure. 

Electric roof: since I'm into automated imaging, I have an electric roof which is based on a garage door opener. 

Roof sensors: I have sensors on the roll off roof - these inform the PC if the roof is open or closed. 

Mount sensors: since the roof can hit my scope - I have sensors on the mount which inform the PC is the scope is in the (safe) parked position. The roof can only close and open if scope is in the parked position.

Rain sensors:  I have three independent rain sensors. A main one from HitechAstro, which has never failed, but is reliant on my PC and mains power. An independent backup which is reliant on mains power and a backup to the backup which is battery powered. You may think is over engineered but the last thing I wanted is rain inside my observatory !

Alan 

[Dr_Ju_ju]

For my garden pier (out in the open air), I've run an armoured cable (buried & marked), from a switched double pole RCD, sat in the kitchen, with a dual 13A weatherproof, earth leakage protected outlet, bolted to the side of the concrete pier, then a short link to inside a weatherproof enclosure, which houses a PC & its power supply, a 5 port GB switch etc....

I have never had any problems with mains power in the garden, its just problems in the rest of the house, necessitating me to replace the main consumer unit (it was old, with wire fuses) with a twin RCD unit with appropriate trips etc.

[Guest]

Hi Kev. 

I have a full 240v ring main throughout my obsy. I have a double and single socket in the warm room both with usb power outlets, I have 3 double sockets in the obsy side, 2 of which also have usb points. One of these is directly attached to the pier for all scope and ancillary power needs. I also have a separate hub fixed on the outside of the pier that houses and runs 2 USB3 ports and a HDMI with room for one more USB3 or something at some point.

This is all supplied from an RCD fuse board in the garage via amoured cable.

I run a 1500w heater 24/7 (set at 12deg) and my dehumidifier along with a full gaming rig pc, all lighting runs off the main ring but fused down in the switches.

All runs beautifully. The pier hub works a treat also as I have my scope connected via a USB3 to hand controller cable for Meade Autostar Suite scope control while at the same time seeing what my ZWO ccd is doing via the other USB3 cable. The HDMI works brilliantly at the pier for another monitor for ccd focus at the scope. 

I see loads of other ideas here already so I'm sure you will get your set up spot on how you like it.

[michaelmorris]

• Consumer unit? - yes.
• Lighting circuits - LED's in the scope and warm rooms - your best option might be cheap dimmable multicoloured LED strips.  You can then chose whether they give off red or white light and control the actual light level as well.  Look on EBay.
• How many circuits do I need? - that would depend upon the amount of amps each circuit would be drawing
• Mains voltage requirements and number/positioning of sockets - carefully work out the maximum number of sockets you can possibly think you will need (Mounts, cameras, computers, monitors, lighting, 12v transformers, heaters, fans etc) - then double it!
• USB hub at the pier? - yes,  or you could make life even easier and have the hub mounted on the pier head or scope
• Data cable needs? - I would go for  a minimum of two active USB leads going from the warm room to the pier
• RCD protection? - yes
• Other ??? - plan it once, plan it twice, then add more!

If you want to view a monitor inside the observatory, another option is to put a window between the warm room and the obs.  Have your monitor on a swivel mount so that you can place it against the window or use it in the warm room.  This should reduce clutter and reduces the risk of dew getting into the monitor.  If you are using a laptop on the warm room, this then also gives you the option of having a double screen set up.

 

[Horwig]

I'll add my twopence worth.

My dome is built next to a stone outbuilding/shed, so no trad warmroom. The consumer unit for both is in the shed, and has an RCD, it's fed from the house via SWA, a fused spur from the shed then feeds the dome. The data cable from the dome to the house is SWA cat 5. I used to run on ethernet over mains, but the adaptors used to blow if they were switched off, became damp, then powered back up.

In the dome I have two Maplins linear 12V supplies, one 'dirty' supply does mount, dome and dew heaters, basically everything that would cause spikes, the other 'clean' supply is for USB hubs and cameras. Both supplies are in a warm cupboard in the dome, where the pc etc lives (and acts as a background heater). The mount/scope then has 2 heavy gauge 12v and an USB cables going to it. A Startech industrial 12volt powered USB hub lives on the scope.

Lighting is provided by a pair of LED 20watt floods, they work, but they are far too directional.

Mains sockets in the dome are external types to comply with safety regs, for some reason my mate who has done his sparking exams was happy that everything was ligit,  even if the equipment fed from the sockets could become soaked if it rained whilst the roof was open...

 

I'm not saying it's in any way a perfect solution, but it works.

 

Huw

[RayD]

19 hours ago, JamesF said:

It's not necessarily the case that low-voltage DC is safer than mains AC

Not sure I follow the logic of this.  230VAC can and will kill you pretty easily, 12VDC will have a hard time doing the same at the currents we are talking about.  230VAC is LV, 12VDC is ELV, with the latter being considered safe for use in Zone 1 applications (inside a shower cubicle).

Kev, if this is to be a permanent installation, then it legally needs to be notified under Part P.  You can do this yourself if you can demonstrate you are competent, and Building Control can check it, but I doubt that is going to be the case.  I qualified under 16th edition and I would struggle to demonstrate competence as I haven't taken any 17th or 18th edition refreshers.  If not, then you need a sparky to do the works, or at least test the installation and register it.  If you don't intend to do this then you should have the supply on a non permanent lead connected to a plug top.

Most important thing of all is that you need to consider the incoming earthing in to your house to decide which way you will need to earth the obsy.  It may be ok to run a 3 core SWA, but it may also need a totally separate earth rod at the obsy.  You can't take chances here as you may not trip breakers if it all goes wrong.

You don't necessarily need a consumer unit, but it does make it easier if you intend to have multiple circuits.  A standard shed feed just takes a 13A switch fuse from a final ring, and this is then separated out in adaptable boxes, but a 6mm (or 10mm depending on the length) SWA connected to a new 40A breaker in your indoor CU is a perfect job if easily accessible.

For sockets I would never use a final ring in an outbuilding unless you absolutely need to which, unless in a machinery workshop, is highly unlikely.  The UK is pretty well the only country still using final rings as most other countries have rightly decided that they are inherently higher risk than radials in the event of a ring cable disconnect fault.  They were only introduced post war due to the shortage of copper but have never been withdrawn and us reverted back to radials.  

In my obsy I have 2 radials, one for the warm room and one for the scope room.  These are 20A radials which still uses 2.5mm cable, but less of it.  I would be concerned if you think you would need more than 20A in any one of them.  The advantage of separate radials is a problem in one room won't take everything out (assuming you are using RCBO's). 

I wouldn't take a 230v supply up to the pier, but that's just my personal opinion.  You are bringing an extraneous item (your steel pier) in to an area of becoming a ground potential point, which it doesn't need to be and doesn't make sense.  However, there is no regulation stopping you doing it, so if this makes life easier then it is permissible.  However, you will have to earth bond it.

Lighting is simple enough.  Again mine is separated in to 2 circuits (6A each), with white and red light for each.  Inside the warm room I have a single 4-gang switch for all the lighting.

I know this topic rumbles on here time and time again, and as someone who spent 5 days in hospital and still bears the burn scars from an electric shock at work, I will again advise you to speak with a sparks, or at least ask the same question on the IET forums, we're a friendly bunch, honest.  I can assure you that if the guys on the IET forums started asking astronomy questions, I'd send them here.

[JamesF]

3 minutes ago, RayD said:

Not sure I follow the logic of this.  230VAC can and will kill you pretty easily, 12VDC will have a hard time doing the same at the currents we are talking about.  230VAC  is LV, 12VDC is ELV, with the latter being considered safe for use in Zone 1 applications (inside a shower cubicle).

I wasn't sure what currents we would be talking about, to be honest.  A mount might draw 5A when slewing?  A TEC on a camera might take the same again?  Dew heaters up to another 5A perhaps?  In that type of situation would it be unreasonable to be looking at a supply capable of delivering 20A to cover possible extras such as electronic focusers?  I'm guessing, but it's probably useful information to have in this thread.

James

[RayD]

1 minute ago, JamesF said:

I wasn't sure what currents we would be talking about, to be honest.  A mount might draw 5A when slewing?  A TEC on a camera might take the same again?  Dew heaters up to another 5A perhaps?  In that type of situation would it be unreasonable to be looking at a supply capable of delivering 20A to cover possible extras such as electronic focusers?  I'm guessing, but it's probably useful information to have in this thread.

James

I see.  No for 12VDC to be considered dangerous we are talking hundreds of amps, not a few.  12V in this application is absolutely safe (for you if not your kit if it shorts).

[RayD]

3 minutes ago, JamesF said:

In that type of situation would it be unreasonable to be looking at a supply capable of delivering 20A to cover possible extras such as electronic focusers?  I'm guessing, but it's probably useful information to have in this thread.

You're spot on here actually.  I run 2 x 13.8v bench power supplies, and the cable from them to my pier is 3.0mm thin wall, actually designed for nautical applications, which is rated at 20A.

[Gina]

I do much the same.

[Astrokev]

I'm going to take the simple approach here and just say a collective thanks to everyone who's posted so far. Really interesting and helpful. I think I need to go through the feedback more slowly and make some notes to help me with the next stage.

@RayD in answer to your recommendation - I will definitely be getting my local sparky round to advise and do the tricky bits (which is pretty much all of it with my level of electrical knowledge!).

I guess the first step is for me to plan out exactly what I think I need, in terms of number and location of sockets, outlets and switches etc (which will be difficult enough as it is, although I think I've gleaned that once I've worked out the number, I have to double it!) , and then get him round. One of the awkward bits, which I think I've mentioned in my build thread, is that I'd like to permanently wire the supply into the house, which ideally means running a trench. The problem there is I've got a sizeable pond and a 100 year old drain system blocking the obvious route, not to mention a patio area laid on top of an old tarmacadamed back yard originally built to withstand heavy lorry traffic! The alternative route, which is a little less problematic (in that it doesn't have the pond or drains) heads off at 90 deg in the wrong direction. Hopefully the electrician can offer some sage advice!

[michael8554]

Not mentioned so far:

What size conduit between warm room and scope room?

I used 50mm with Slow 90 Degree Bends, and even then found some cables reluctant to go round the bends.

Leave strong nylon cord in the conduit, twice as long as the run, then you can pull from either end without loosing the ends ?

Michael

[Astrokev]

36 minutes ago, michael8554 said:

Not mentioned so far:

What size conduit between warm room and scope room?

I used 50mm with Slow 90 Degree Bends, and even then found some cables reluctant to go round the bends.

Leave strong nylon cord in the conduit, twice as long as the run, then you can pull from either end without loosing the ends ?

Michael

Hi Michael

I've already installed the conduits. One is 40mm, the second full size drain pipe, which from memory is 76mm? Nylon cords are threaded through them, but these are only temporary - I need to put longer cords through once I've bought some!

[Gina]

Long cords plus something on each end that won't go into the pipe!   Yes, 50mm sink drain pipe with "slow" bends for me too.

[Astrokev]

7 hours ago, Gina said:

Long cords plus something on each end that won't go into the pipe!   Yes, 50mm sink drain pipe with "slow" bends for me too.

Yes, my cords are tied to temporary squares of wood - that won't fit down the pipes!

[Yawning Angel]

To get around your land hazards, you could run SWA above ground, so long as it is either UV stable or in suitable protection.

[Yawning Angel]

This is a handy calculator for the size of cable you'll need: https://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

[Gina]

My observatory is still running on an ordinary 13A extension lead.  I did put SWA in the ground years ago but never got round to connecting it in the house.  It's all ready for connecting to the consumer unit in the observatory.  That is one job I never finished!!

[michaelmorris]

The cables between my computer and desk and the pier don't run through a pipe conduit.  Instead I have square surface mounting trunking recessed into the floor so that the top of the conduit is flush with the floor.  That way it is easy to run new cables.  

https://www.screwfix.com/p/mini-trunking-38mm-x-16mm-x-2m/44320

[Rusted]

It's a shame they don't do a "slow" vertical elbow to avoid a sharp transition where a horizontal run meets a vertical transition.
I used this trunking to cross a door threshold and it was very difficult to do a neat job at either end when there was a solid mass of rather stiff cables.
It ended up with visible, curving cables at each end  and the top plate having to be cut well back at both ends.
I even added a second run beside the first to separate mains from signals as much as possible.
There was going to be adhesive skateboard "grip tape" on top but it became a "round to it" over the years.

[Gina]

Ah, this is where 3D printing comes in - so useful for so many things  ?

[GraemeC]

I would echo rayD's suggestions.  An electrician friend of mine came around to check on the wiring I had put in and he broadly approved of what I had done.  Im using protected cable from the house (buried in conduit) and a garage consumer unit (Screwfix do a good one: https://www.screwfix.com/p/wylex-4-module-2-way-populated-garage-consumer-unit/3401H)

My friend did say that I needed an earth rod for the installation.  Although the supply is protected in the house by an RCD the response time is slow for such a long cable.  The garden cable should also be earthed with an earthing rod - they are as cheap as chips and I bought the thicker version 5/8" which is banged all the way into the ground with a hefty hammer.  The earth cable attaches to a clip on the end of the rod.  A damp area of soil gives better performance.

I have 8 x 240V sockets inc USB, and a 12v power supply connected to 3 x cigarette lighter sockets and 3 x Hella type sockets.  These latter ones give a more positive engagement than the cigarette lighter sockets.  I also have 1 x main light and a strip of the LED coloured lights.

[Astrokev]

I've been playing with a very rough list of socket requirements for my warm room. Please don't laugh, but here is where I'm at (the consumer box is a stock photo and does not represent the number of switches I need!). If my understanding is correct, I'll run 1 or 2 powered USB cables from the double socket to a hub on the pier. This will then power other kit; dew-heater, guide camera etc. I'm looking to present a final version of this to me electrician friend to feed discussion. Comments, corrections and suggestions warmly invited and appreciated!