Terminating the earth cable from a local earth rod.

[Rusted]

Hi,

How should I properly terminate the observatory end of a 6mm^2 stranded earth cable from the local 2m earth rod?

Temporarily, I have just wrapped the cable around a handy screw head on the bare aluminium mounting with a large washer to contain the loose strands.

It looks horribly amateur and may even corrode over time. So I thought I'd use a suitably large, car type, crimping eye to be trapped under the same screw head.

Any better ideas?

Thanks.

 

[Ships and Stars]

I don't have an obsy but sounds like you have the right idea tidying things up with a ring terminal you can crimp on the end. 6mm2 is around 10-12awg wire I think.

Ring terminals are pretty cheap:

https://uk.rs-online.com/mobile/p/crimp-ring-terminals/6139413/

You might dab some wheel bearing or CV grease on it afterwards to protect the connection from the elements if it's somewhere you won't accidentally pick it up on hands/clothes and track into the house. In lieu of that, a few coats of outdoor paint like good old Hammerite or epoxy primer (like Bonda with zinc, great for rusty surfaces) should probably provide an adequate seal. Or just dab on silicone bath caulking! Don't know what kind of metallic reaction you would have over time between aluminium and steel fasteners, etc but others will perhaps weigh in that. An airtight seal should in theory prevent corrosion I'd think between dissimilar metals.

Edited February 12, 2020 by Ships and Stars

[Rusted]

Hi,

Thanks for the suggestions for sealing over the joint.
I would never have thought of that.

[Ships and Stars]

2 hours ago, Rusted said:

Hi,

Thanks for the suggestions for sealing over the joint.
I would never have thought of that.

I had a quick look and don't think you will have much of a reaction between steel and aluminium on this level, stainless steel apparently is a bit more reactive with aluminium, but still not a big deal if sealed over. If the obsy came with stainless fasteners into aluminium, then they most likely accounted for that. Enjoy the obsy, would love to have one someday.

[Rusted]

Thanks. It is only the mounting I am earthing.
Home made and mostly raw aluminium plate.
It isn't earthed by the timber pier.
The obs. floor is timber boarding.
The Obs. is mostly plywood and timber.

I was getting a strange "tickle" through my fingertips.
Mostly on the bare metal telescopes and accessories when I touched them.
Possibly leakage from the 12V drives PS?  2-core, no earth in and out.
I could also get a very dim glow from a neon "test" screwdriver.

So I bought a 2m earthing rod and sank it into the wet clay at the foot of the obs.
6mm^2 cable running straight down the timber pier from the mounting to the rod.
Which has its own massive cable clamp with rain cap.

The free end needed proper termination.
I thought there might be some rule about clamping.
Hence the thread.

[Gina]

The earth from the rod goes to my mount with a large earthing bolt and on to the distribution box in the warm room.  That is the main 13.8v power return.  Never had any tingles from anything.  Mine is 10m² earth bonding cable.

[Rusted]

Thanks Gina. 

I haven't noticed any tingles since the earth rod went in.
From fuzzy memory, I think there was 60V AC on the mounting.
This only occurred when the 12V drive PS was switched on.
I've bought a new multi-meter since then so I should check again.
With and without the earth connected.

[Guest]

This isn't specifically aimed at the amateur astronomer, but the radio amateur.  I think the basics could still apply...

http://rsgb.org/main/files/2019/12/UK-Earthing-Systems-And-RF-Earthing_Rev1.4.pdf

[DaveL59]

I'd terminate with a ring, solder it if you can, an anti-shake type washer between it and the surface you want to earth and then vasoline/silicone grease to protect it from moisture. Steel+aluminiun+copper will get you corrosion over time in damp environmetns, condensation may well induce it so worth protecting against.

Also if the Aluminium/metal parts you are earthing are not directly coupled to each other, add a short earth strap between each of them if you want it all earth bonded.

If you want to on-link to the PSU as well then you can get metal connector blocks for earthing so you can connect the earh rod line to that and then run links from the block to the relevant pieces of equipment. Worth protecting that in a box probably.

[Rusted]

Thank you both for your input. All good stuff.

Note that I now live in Denmark. Where earthing and three pin plugs are rare except in new installations.

I was having some new 2 pin sockets fitted by electricians and asked for an earth rod.
They seemed quite shocked but allowed me to drive an earth rod outside the house to kill the hum on my British Hifi.
I was then able to use 3-pin earthed plugs and sockets but only on a multi-socket strip for the Hifi. Everything else remained 2 pin.

When I built the observatory I had no plans for anything but a twin core extension lead and a flying lead multisocket.
But, the AWR drives were giving me a tingle so I ordered a 2m rod online and earthed the mounting.
At the same time I connected the earth leads on the AWR system for the first time.
All the metal plates of the mounting are all in intimate contact with each other.

I have plans to house the two [2 pin] 6 x multi-sockets in the observatory in a proper weatherproof box.
The mains wiring is protected by a device in the consumer unit and an old fashioned 10A cartridge fuse again in the CU.
All sockets and lights in the property are on the same 10A circuit!

[Danjc]

A flat earth bond used normally in lightening conductor systems with a load of oxide inhibiting compound on it could do the job. The clamp is normally used for 25x3mm lightening conductor tape but should clamp a 6mm braided cable ok.  
The compound is designed for electrical connections especially copper to aluminium and protects against moisture and oxygen but a type of grease as mentioned should suffice. 
 

https://www.edwardes.co.uk/products/kingsmill-bbcb-flat-earth-clamp-for-25mmx3mm-copper-tape?gclid=EAIaIQobChMI5L-XovrM5wIVBkTTCh1nFwU8EAkYASABEgIphfD_BwE

 

[wxsatuser]

6 hours ago, Rusted said:

Thank you both for your input. All good stuff.

Note that I now live in Denmark. Where earthing and three pin plugs are rare except in new installations.

I was having some new 2 pin sockets fitted by electricians and asked for an earth rod.
They seemed quite shocked but allowed me to drive an earth rod outside the house to kill the hum on my British Hifi.
I was then able to use 3-pin earthed plugs and sockets but only on a multi-socket strip for the Hifi. Everything else remained 2 pin.

When I built the observatory I had no plans for anything but a twin core extension lead and a flying lead multisocket.
But, the AWR drives were giving me a tingle so I ordered a 2m rod online and earthed the mounting.
At the same time I connected the earth leads on the AWR system for the first time.
All the metal plates of the mounting are all in intimate contact with each other.

I have plans to house the two [2 pin] 6 x multi-sockets in the observatory in a proper weatherproof box.
The mains wiring is protected by a device in the consumer unit and an old fashioned 10A cartridge fuse again in the CU.
All sockets and lights in the property are on the same 10A circuit!

I thought domestic supplies in Denmark were TT, where there would be an earth rod anyway.

If you have an out building that will need a rod as well as you found out.

Here in the UK the circuits in the house and out buildings should be protected by RCDs in a TT system.

Edited February 13, 2020 by wxsatuser

[Rusted]

3 hours ago, wxsatuser said:

I thought domestic supplies in Denmark were TT, where there would be an earth rod anyway.

If you have an out building that will need a rod as well as you found out.

Here in the UK the circuits in the house and out buildings should be protected by RCDs in a TT system.

Thanks. There is an RCD in the CU. Not sure of its abilities on the far end of a 30m long extension cable though.

Incorporating an earth into an all 2-pin socket, reversible plug system in an outhouse would seem to be voluntary.

British bought items used to "tingle" badly if a 2-pin plug was fitted, the earth wire discarded, and then plugged in "the wrong way." Metal sewing machines for example.
I used to mark the plugs with red and green tape to ensure they went in correctly until we quickly stopped using them altogether.
The Danish 10A standard CU fuse used to blow the whole house[!] system regularly on UK electric kettles. Max 2KW locally on a standard 2-pin plug!

Everything electrical, over here, is sold with moulded on, 2-pin, reversible plugs. Only washing machines use the Shuko plug. Even if you only have a standard 2 pin socket!
Just to add to the confusion they use 3-phase in domestic situations. Kitchen cookers use a unique, multi-pin plug.
Which is fitted by the dealer, at considerable extra charge, on purchase.  DHWs are strictly an electrician's job too. As is all "outside" work.

Because it is so expensive to hire an electrician nobody fits a night and day proximity sensor in their outside lighting.
It must cost Denmark heavily in the global CO2 stakes to have a 24x365, "Close Encounters landing strip" in every garden!

It seemed very odd when we first came over here to see a spaghetti of flex and multi-sockets running across the poshest of rooms for table lamps, TVs and audio equipment.
The number of wall sockets always seemed to be decades behind even 1950s UK standards everywhere we went. 

Hiring an electrician is to be robbed. £100 per hour minimum, even years ago, plus travelling time, meal breaks, maternity leave, school uniforms, etc, etc. Literally everything is plus 25% VAT.
Electrical wiring items, which can be bought for very small change at all DIY outlets, suddenly cost £50 each for a simple 2-pin socket and wall receptacle.
We paid more, for a few additional sockets in the kitchen, than a whole house rewire in Wales! I even chased a one meter drop of plaster myself to save literally £hundreds on the final bill!
Normal practice is plastic conduit down the wall! Or naked cable and clips!

 

[windjammer]

As I understand it, your symptoms may be due to multiple connections of ground to the neutral wire.  So making another ground connection may not help.  There should only be one connection of ground and neutral in the house, usually to a substantial metal item stuck in the earth etc.  Multiple connections give rise to ground loops where large currents can flow.

I have this problem as well, and I suspect some chinese made electronic gadgets (wall warts in particular) I use with ground/neutral connections are the cause.  The cure is to methodically remove stuff (gadgets, wired extension cables etc) until it stops.  I think there are also some fairly cheap test instruments you can get to sort this out.

Every once in a while I get the steam up to try and fix it, but so far not much success !

Simon

[Rusted]

Thanks Simon. I'll give that a try to see if I can isolate the culprit.
The AWR drives PS is not remotely a budget wallwart. It has a standard 2 pin plug and two protected output plugs.

The stepper motor leads have trailing earth leads now fitted with crimp on ring ends. Which I have connected to the mounting now I have an earth rod.
I've done a lot of 2-pin plug reversing over the years to minimize such problems. It often seems to work.

[wxsatuser]

22 hours ago, Rusted said:

Thanks. There is an RCD in the CU. Not sure of its abilities on the far end of a 30m long extension cable though.

 

Here in the UK for TT systems the out building will/should have an earth rod.
Depending on the ground more than one rod or ground mat might be needed.

If there is any extraneous metal in the out building, could be water pipe or other grounded metal, may be a pier, this is bonded to the rod.
RCDs should be fitted in the out building to make sure of tripping.

Anyway, as long as local regs are followed should be ok.

[Rusted]

2 hours ago, wxsatuser said:

Here in the UK for TT systems the out building will/should have an earth rod.
Depending on the ground more than one rod or ground mat might be needed.

If there is any extraneous metal in the out building, could be water pipe or other grounded metal, may be a pier, this is bonded to the rod.
RCDs should be fitted in the out building to make sure of tripping.

Anyway, as long as local regs are followed should be ok.

I'm afraid I haven't a clue about local regs because it isn't a hardwired set-up. There is no metalwork to speak of.
Just the big mounting on the first floor of my two storey observatory supported entirely on dry timber.

It always seemed to me that deliberately earthing metalwork gave faults a path to injure people.
Though the theory is probably that electrical faults will be directly earthed. Rather than be earthed by human bods.

[wxsatuser]

If they are not earthed or bonded and there is a fault on the equipment the current has to flow you if you touch it.

If there are no extraneous metal objects in the out building there is nothing to bond.

Extraneous means in contact with ground or buried in the ground.

[Rusted]

Thanks for the clarification. Understood.