Todays Earth Rod Efforts

[uksparks]

Hi,

As I mentioned last night, I was going to be putting the earth rods in for this summer house this morning.

I put 8 rods in, this was one stack of two, and two stacks of three rods.

The readings from the two that were 3 rods deep were around 10 Ohms per location, and the two rod stack was approx 17 Ohms.

I tested the first rod at approx 10 Ohms, then connected the second rod to the first which was 17 Ohms which them reduced the total down to approx 6 Ohms, then connected the third rod which was 3 deep and that bought it down to 3.2 Ohms.

So the Ra that I achieved today was a respectable 3.2 Ohms

All rods were connected together with 16mm earth.

I am going to go back next week and bang in another couple of piles of two rods so another four in total because I want to get that sub 1 Ohm reading.

Anyway, what do you think, 3.2 is not bad is it!!


Reading from first rod: 10.6 Ohms (3x 4ft 5/8" Rods)


Reading from second rod: 17.2 Ohms (2x 4ft 5/8" Rods)


Reading from third rod: 9.6 Ohms (3x 4ft 5/8" Rods)


Reading from first and second rod combined: 6.3 Ohms


Reading from all three rods connected together: 3.2 Ohms

 

[NDG Elecs]

Hi,

As I mentioned last night, I was going to be putting the earth rods in for this summer house this morning.

I put 8 rods in, this was one stack of two, and two stacks of three rods.

The readings from the two that were 3 rods deep were around 10 Ohms per location, and the two rod stack was approx 17 Ohms.

I tested the first rod at approx 10 Ohms, then connected the second rod to the first which was 17 Ohms which them reduced the total down to approx 6 Ohms, then connected the third rod which was 3 deep and that bought it down to 3.2 Ohms.

So the Ra that I achieved today was a respectable 3.2 Ohms

All rods were connected together with 16mm earth.

I am going to go back next week and bang in another couple of piles of two rods so another four in total because I want to get that sub 1 Ohm reading.

Anyway, what do you think, 3.2 is not bad is it!!


Reading from first rod: 10.6 Ohms (3x 4ft 5/8" Rods)
View attachment 29132

Reading from second rod: 17.2 Ohms (2x 4ft 5/8" Rods)
View attachment 29134

Reading from third rod: 9.6 Ohms (3x 4ft 5/8" Rods)
View attachment 29133

Reading from first and second rod combined: 6.3 Ohms
View attachment 29135

Reading from all three rods connected together: 3.2 Ohms
View attachment 29131

Good work. Bet you only get down to 1.5 ohms with the next rods driven in mate....sods law I think we call it! You could always put any RFCs on a 20A and tell them they can't use their electric shower and hob!! Tell them disconnection times are very very important!! Look forward to the update mate.

Neil

 

[mechelec]

3.2ohms is not bad it will be better when you get it finished ; )

 

[Richard Burns]

No a load of rubbish, pull them all out and start again!!:mad2::53:

I would say 3.2Ω is a pretty good reading, 71A fault current enough to trip a 10A MCB.
Pretty close to the resistors in parallel results actually which is interesting to know.
Thanks for putting in the effort to give us some feedback.

 

[uksparks]

I think I'll put two more locations in and end it there, I bet each will knock an ohm off the figure.

it about killed me off beating them in with a lump hammer!

By the time the group has settled the reading will have got better as its really only the bottom rods that are in are touching the earth as the others are flapping round due to the couplers.

 

[Richard Burns]

Manually driven gives you some definite points, I am just not sure if they are for stupendous effort or stubborness!

 

[NDG Elecs]

Manually driven gives you some definite points

I think the points are called callouses aren't they!

 

[uksparks]

The first one was easy, the second was a little touch, but the third rod was the killer, the deeper you go, it just gets sodding hard work.

I need to achieve a higher fault current really as 71A is pants, just looking at the time current tables in the BYB and max zs etc.

 

[Andy78]

I applaud your efforts with this one I really do. Looks like you will end up with something close to very good.

I have to say though, driving coupled rods with a lump hammer..... don't you like yourself very much ?

 

[Marvo]

I think I'll put two more locations in and end it there, I bet each will knock an ohm off the figure.

it about killed me off beating them in with a lump hammer!....

You must be mad, get an attachment for a jackhammer. Also if you want a better Ra go 1 rod deeper on all your existing locations rather than making new locations.

By the time the group has settled the reading will have got better as its really only the bottom rods that are in are touching the earth as the others are flapping round due to the couplers.[/QUOTE]

 

[uksparks]

Im not going to get a 0.2s disconnection with 71A, so need to improve that some what!

How many amps am i going to need to get 0.2s ? I know its RCD protected but thats not the point!

 

[uksparks]

You must be mad, get an attachment for a jackhammer. Also if you want a better Ra go 1 rod deeper on all your existing locations rather than making new locations.

By the time the group has settled the reading will have got better as its really only the bottom rods that are in are touching the earth as the others are flapping round due to the couplers.

[/QUOTE]

I could try putting another on the top of them, I could do with someone holding the rod so i can hold the hammer with two hands.

 

[Corbs]

I could try putting another on the top of them, I could do with someone holding the rod so i can hold the hammer with two hands.[/QUOTE]

or one of these much easier

[video=youtube;vvCZvNj8H30]https://www.youtube.com/watch?v=vvCZvNj8H30[/video]

 

[Marvo]

If you really want to be a diehard, instead of using a sledge hammer use a slide hammer. See this thread.

 

[uksparks]

I might need to get myself one of them! it took me two hours of hard graft getting those rods in!

 

[uksparks]

I'd need an SDS max bit wouldn't I? and I could rent a drill to do it, presumably an SDS max drill would do it or would I need something bigger?

 

[Corbs]

I could try putting another on the top of them, I could do with someone holding the rod so i can hold the hammer with two hands.[/QUOTE]


you tried something like this? might help

[video=youtube;0sLv4LLVPbA]https://www.youtube.com/watch?v=0sLv4LLVPbA[/video]

 

[Corbs]

I'd need an SDS max bit wouldn't I? and I could rent a drill to do it, presumably an SDS max drill would do it or would I need something bigger?

thats fine, prob normal sds would do but might take longer, but vid below is sds max demolition hammer

[video=youtube;VJYhHZYu_4g]https://www.youtube.com/watch?v=VJYhHZYu_4g[/video]

 

[uksparks]

Thats not a bad idea.

 

[telectrix]

i just get glennsparks to come round and snarl at the rod. the rod then drives itself in.:uhoh2:

 

[NDG Elecs]

I'd need an SDS max bit wouldn't I? and I could rent a drill to do it, presumably an SDS max drill would do it or would I need something bigger?

I got a cheap SDS Max from screwfix for a ton and bought a Bosch rod driver to go with it. The rod driver was bloody expensive but it has all paid for itself already. Only gripe is the last few TTs with crap Ra have all had PME upgrades available, so the kit is sat gathering dust!

I tried using an SDS plus to drive rods in; a lump hammer is better IMO. At least til your forearm starts to look like Popeye's that is.

 

[Deleted member 72666]

I could try putting another on the top of them, I could do with someone holding the rod so i can hold the hammer with two hands.

or one of these much easier

[video=youtube;vvCZvNj8H30]https://www.youtube.com/watch?v=vvCZvNj8H30[/video][/QUOTE]
That seemed to go in easy.......Is that house built on a swamp?

 

[Lucien Nunes]

And here's a Kango Model C doing the same thing in 1935. Of course in those days power tools were run direct from the mains without isolating transformers, and had metal cases and class 1 construction. So as the notice says on the side, it's important to earth the tool reliably (via the brown wire which was the proper colour then). But if the rod's not in yet...

I haven't driven any rods with my Model C but I have used it to dig up fence post footings and knock a wall down.

 

[PEG]

I've got a similar looking Wolf,bit later vintage,and for some unknown reason,we always ended up using it for boring holes through crossing timbers and telegraph poles...no clutch and lots of motor inertia,so when it went self-aware,it did so for ages...

There is nothing like getting continued service,from vintage gear,i think it is why i started collecting anvils...and it's catching...my protege has just recond a 1948 Atco mower,with a kick-start Villiers,and mowed his sisters' lawn with it. :yes:

 

[tomspark93]

Interesting read, I wonder how many people would have been happy with a reading between 100-200 ohms...

Just out out of interest, how come you decided to tt the summer house?

 

[IzzyS]

Who is paying for this experiment?

 

[uksparks]

Interesting read, I wonder how many people would have been happy with a reading between 100-200 ohms...

Just out out of interest, how come you decided to tt the summer house?

I TT'd it for two reasons, one is that its a TNCS supply and taking it 70m down the garden in my opinion is not going to fall within what I would call extending the zone within a sensible distance that I would be happy with, plus to TT it, the cost involved in that is not that much different to an extra core of 16mm x 70m.

Inside the main house, everything should be at equal potential, but down the garden its a bit unknown, and stuff will be plugged in and taken into the garden too.

Think about it this way, if you loose your neutral in the suppliers TNCS supply, your exported / exntended earth to the summerhouse has just been lost / removed, then you are left with an earth that is going to act as a return neutral for the supply, so if you were touching a piece of class I equipment and loose the neutral, then you will become part of the circuit and get a shock (more than likely).

The customer is also looking at connecting a hot tub off the summerhouse, and feel it would probably be best to use a TT at the remote end due to the slim chance of loosing a neutral in the DNO TNCS supply as any metal work would rise to 230v, and as they have a number of class I fittings going into the summerhouse, like lights around the outside, and appliaces within, then I feel a low Ra with a nest of rods would be better. It would't take much to come into contact with true earth when stepping out a hot tub.

Who is paying for this experiment?

its not an experiment, yet I do feel like I am wanting to better the reading down to a very good figure at less than 1 ohm. The time spent on the earthing im not charging for as will be making enough out of the install of the summerhouse.

 

[tomspark93]

Justified answer and good job! Keep us updated on any progress it'll be interesting to see how low you can get it.

 

[Spearmint]

It's nice to see someone putting all that effort in to make it a decent TT install.

 

[OtexElectrical]

Good work

 

[IzzyS]

It's an impressive result with so few rods. I'm guessing it's mostly clay?

I didn't mean to offend by calling it an experiment - it's just that you're exceeding the minimum requirements of BS7671, something that hardly anyone seems to do these days. I may have mistakenly got the impression you were just trying to see how low you could go on this particular job, rather than it being a contractual requirement.

In my experience, there's little chance of achieving reliable "TN" values, at a sensible cost, using driven rods (assuming correct spacing and buried interconnecting cable), so you must still rely on the RCD anyway.

Can you post up the measured Zs - it would be interesting to know how your Ra relates to the the overall loop impedance?

 

[Deleted member 9648]

Interesting read, I wonder how many people would have been happy with a reading between 100-200 ohms...

Just out out of interest, how come you decided to tt the summer house?

+1 :yes:

 

[Richt16]

Hi,

As I mentioned last night, I was going to be putting the earth rods in for this summer house this morning.

I put 8 rods in, this was one stack of two, and two stacks of three rods.

The readings from the two that were 3 rods deep were around 10 Ohms per location, and the two rod stack was approx 17 Ohms.

I tested the first rod at approx 10 Ohms, then connected the second rod to the first which was 17 Ohms which them reduced the total down to approx 6 Ohms, then connected the third rod which was 3 deep and that bought it down to 3.2 Ohms.

So the Ra that I achieved today was a respectable 3.2 Ohms

All rods were connected together with 16mm earth.

I am going to go back next week and bang in another couple of piles of two rods so another four in total because I want to get that sub 1 Ohm reading.

Anyway, what do you think, 3.2 is not bad is it!!


Reading from first rod: 10.6 Ohms (3x 4ft 5/8" Rods)
View attachment 29132

Reading from second rod: 17.2 Ohms (2x 4ft 5/8" Rods)
View attachment 29134

Reading from third rod: 9.6 Ohms (3x 4ft 5/8" Rods)
View attachment 29133

Reading from first and second rod combined: 6.3 Ohms
View attachment 29135

Reading from all three rods connected together: 3.2 Ohms
View attachment 29131

Can I ask were they placed in a straight line and what distance apart thanks for sharing

 

[Robson689]

Can I ask were they placed in a straight line and what distance apart thanks for sharing

They should be separated by the depth of the rod, so 3.6m deep, 3.6m apart for example with 3no rods coupled together

 

[Richt16]

This is where I get confused so if I drive two in to the ground 2.4m and then another two at 2.4 should the space between be 2.4 or 4.8 between them as seen different answers thanks for your support

 

[nicebutdim]

This is a question that attracts many different answers.

General consensus seems to be minimum separation of 1x - 1.1x driven depth. If you can go twice that distance, there's certainly no harm in doing so.

 

[pc1966]

Basically you only get "independent" Ra values to parallel if the rods are far apart, as they get closer together each rod is in its neighbours region of influence so the reduction in Ra from multiple rods gets less. This article has various formulae to allow estimation of those values:

Measurements and Calculations Of Earth Electrode Systems (BS 7430) | EEP

System earthing involves the provision of a connection to the general mass of earth. This connection should have a resistance not greater than that required to operate safety mechanisms to isolate the electricity supply from a fault situation.

electrical-engineering-portal.com

If you have 2 rods and the separation is around the rod's length then you are getting about 80-90% of the improvement you would see if they were very far apart, and that is usually good enough.

Generally if you can get down deeper, below 1m or so, it is better as what is critical to low Ra values is moisture in the soil. The top layer often dries out during summer droughts or can freeze in winter, greatly reducing the effectivity of the top 0.5m or so.