USB and other leads required for a pier

[Gina]

I have proper armoured cable buried more than a foot down and with stone slabs on top - that won't get dug through unless someone comes round with a full blown digger!!!  I don't do things by halves!! ?

?

[RayD]

1 minute ago, Gina said:

I have proper armoured cable buried more than a foot down and with stone slabs on top - that won't get dug through unless someone comes round with a full blown digger!!!  I don't do things by halves!! ?

?

I think they may be stopped by you shouting "OI!!!" before they cut through it ?

[Dr_Ju_ju]

Instead of Gina's slabs, 250mm soil pipe also works & has enough space for additional network cables etc.,

But you must ensure that both ends are capped to prohibit the ingress of rats, mice, hedgehogs etc....  & even though I live 100m from the M25, we still get grass snakes in the garden, and while not venomous, they emit a powerful odour if cornered...

[Terrierist]

Thanks for the very informative and interesting replies, lots to go at here.

@Dr_Ju_ju, I must be a grass snake as I emit powerful odours most of the time  

 

Kev

[mallorcasaint]

On 08/10/2018 at 21:16, RayD said:

Spot on.  Doing it properly is the key thing, which includes adequately mechanically protecting the cables to reduce the likelihood of damage (suitable location is a form of mechanical protection).

The point is, there is no need to have 240v at a pier, is there? I am talking about a pier outside, not inside an obsy. What equipment might need 240v? The mount, cameras, filter wheels etc all use DC. It is far safer to run 12v to the pier and it can supply every need.

[RayD]

30 minutes ago, mallorcasaint said:

The point is, there is no need to have 240v at a pier, is there? I am talking about a pier outside, not inside an obsy. What equipment might need 240v? The mount, cameras, filter wheels etc all use DC. It is far safer to run 12v to the pier and it can supply every need.

Yes I totally agree. I don't use 220v outside myself, I was just noting after it was mentioned that it needs to be done properly if used as it is potentially lethal. 13.8v is ideal if the supply is big enough and the cables adequately sized to prevent voltage drop. 

I'm certainly not advocating using 220v outside, far from it. 

[Astrokev]

Really interesting thread, which is now making me really nervous about doing the electrics in my observatory build!

Electrics are definitely not my strength, and will need to lean heavily on the experts on the forum when I start to work on this part of my build, or employ my local electrician. 

[adyj1]

If you are in any doubt about dealing with electrics, then employing a local electrician should be your first choice... 

[Gina]

Yes, I agree with that.  You really don't want to take any chances.  If you were nearer Kev I would have been happy to do your electrics for you.

[Dr_Ju_ju]

Mains electricity is nothing to be scared of, as long as you take some basic safety steps, e.g. don't make any circuit live, i.e. disconnected from the supply till you've run (using armoured cable) & properly terminated then tested using at least a multi-meter for short circuits and\or low resistances. Only then do you consider hooking up to the mains supply.

I'd also recommend, and personally use, in-line RCD devices e.g. https://www.ebay.co.uk/itm/Waterproof-Garage-Consumer-Unit-2-Way-63-Amp-RCD-6A-16A-MCB-Breaker-Fuse-Box-NEW/272953133762?hash=item3f8d464ac2:g:05UAAOSwiIRbllN1:rk:2:pf:1&frcectupt=true so if anything subsequently goes wrong, the power will automatically shut off.

 

 

 

[Gina]

That looks very much like the RCD I use for my observatory.

[Astrokev]

5 hours ago, Gina said:

Yes, I agree with that.  You really don't want to take any chances.  If you were nearer Kev I would have been happy to do your electrics for you.

That's a kind offer Gina - thank you. Sadly I'm pretty far away ?. I'll start by asking some stupid questions in SGL. 

I've done basic household stuff - rewiring light circuits and extending ring circuits etc when renovating my house 15 years ago, but some of the stuff people talk about re observatories are new to me. 

[Gina]

Sounds like you are already quite experienced Kev.

[Dr_Ju_ju]

Unless you want to double up on cabling, "outside" systems tend to be spurs, as opposed to ring-mains, so as long as you've spec'd the cable for minimum voltage drop at expected loadings over distance from supply (I usually add 100%, just to be on the safe side ?) then you should be ok...

 

[Gina]

To avoid the extra regulations and official checks that apply to outdoor spurs you need to have your observatory feed plugged into a 13A socket on the house ring main.  For your own protection this should then feed an RCD before going through an underground armoured cable to observatory.  The cable should be at least 30mm below ground level and marked with a suitable plastic tape to warn of mains cable below.

[Astrokev]

40 minutes ago, Gina said:

To avoid the extra regulations and official checks that apply to outdoor spurs you need to have your observatory feed plugged into a 13A socket on the house ring main.  For your own protection this should then feed an RCD before going through an underground armoured cable to observatory.  The cable should be at least 30mm below ground level and marked with a suitable plastic tape to warn of mains cable below.

The only problem there is that between house and observatory there is paving laid on top of a tarmac drive, and a 90 year old main drainage pipe that I don't want to go anywhere near, for obvious reasons! I may run the initial stretch over-ground until I hit the lawn. I don't think the regs state one must bury the cable, does it, so long as it's suitably marked etc?

Apologies to the OP as I seem to be taking over this thread.

[Gina]

No, if it's plugged in I think it just counts as an extension cable.  Beware of rats though and protect it.

[Terrierist]

19 minutes ago, Astrokev said:

The only problem there is that between house and observatory there is paving laid on top of a tarmac drive, and a 90 year old main drainage pipe that I don't want to go anywhere near, for obvious reasons! I may run the initial stretch over-ground until I hit the lawn. I don't think the regs state one must bury the cable, does it, so long as it's suitably marked etc?

Apologies to the OP as I seem to be taking over this thread.

Crack on old lad, the more ideas and information gained, the better for us all.

[Dr_Ju_ju]

If the run to the Obsy from the house, can be made along the boundary, with no interferences, to it, or any boundary fitments, I'd suggest fitting some 50\75mm down pipe, through which you can rub the mains cable(s) with enough space for additional network cables etc. The pipe can then be easily marked up with the appropriate safety stickers etc. e.g. https://www.ebay.co.uk/itm/10x-Danger-240-Volt-Safety-sticker-Mains-Voltage-Electrical-Warning-Labels-decal/152056161382?hash=item236740e466:g:D3cAAOSwubRXEYpm:rk:1:pf:1&frcectupt=true.

It is also easy to pug the ends to stop vermin entering, and to fit a draw cable loop for anything you've forgotten.

[Gina]

The only thing I found that stops rats ie wire wool.  Trouble is - it rusts.  Maybe paint it or a good dosing of oil...

[RayD]

You've done such a cracking job so far, Kev, it surely makes perfect sense just seek advice from an electrician as a poorly made electrical supply not only has the potential to hurt you, it has the potential to burn your obsy down.  

Depending on the type of incoming earthing system in your house you may be advised to have a separate earth rod at your obsy.  If you just export the earth conductor and add a RCD at the shed end on a TN-C-S system you can potentially cause problems, and it may be best to install it as a local TT system to separate the earth from the main house (a shed (or obsy) is extraneous i.e. it falls outside the main equipotential zone).  It is for this reason that the power supplied to pitches at caravan parks are generally TT as if your N conductor breaks or comes out of a plug in your extension lead, you could have an increased risk of electric shock.

See this video here which explains in basic terms why this is so important.

In the scheme of things having a sparky look at it is a small cost, and it means you then have a totally safe system and, as it would be notifiable works, it can then be notified by a Part P registered electrician.

I'm not saying you can't or shouldn't do whatever you want, of course you can, but at least a look over and a bit of advice by a properly qualified electrician will mean whatever route you go is safe.

[Gina]

In rural properties where the electricity supply is by overhead wires there is no Earth line supplied to the house - just Line and Neutral.  The Earth is provided by a copper rod several feet into the ground.  This is then connected to all metal objects around the house.  Where power is supplied to an outbuilding a distance away from the main dwelling it is best to provide a separate Earth rod for that outbuilding and use that for the local Earth (or Ground connection).  This means that any leakage to earth will unbalance the RCD which will then trip out.

Oh and as the video above says - NEVER connect Neutral to Earth!  Generally the Neutral wire won't have many volts on it but it depends on the balance of the load of the three phases.

[JamesF]

Following on from the video Ray posted, this one is also helpful:

 

I assume that the issue when you export the earth to an outbuilding with extraneous conductive parts is that the earth potentials of each end of the cable may well be different and by bonding the incoming earth you're actually extending the equipotential zone to include the outbuilding.

Our earthing here is, ummm, interesting.  We have an overhead HT supply feeding a transformer at the end of our drive.  Buried in the field are earthing cables that run to the transformer, and we get a TN-C-S style supply.  The earth also appears to be bonded to an earthing spike outside the house.  I'm guessing this is because the supply might once have been TT and was changed at some later point as a result of maintenance to the transformer.

James

[Gina]

I have the standard TT supply with Earth rod outside the back of the house.  Thus I use an earth rod outside the observatory which is connected to all the metalwork and the negative of the main 13.8v observatory power supply.

[JamesF]

I've thought about the arrangement of our supply numerous times in the past, but only just remembered that 30+ years ago the electricity supply to our house was overhead.  I bet that was just live and neutral, hence the earth rod.  I imagine it was switched to TN-C-S when the supply was put underground, though why I'm really not sure.

James