UK TT Earth Rod Submerged then Freezing

[gcwarr]

Hi All,

This is my first (as house holder, not electrical professional) experience of an earth rod.

We have just had a TT ‘island’ install of a hot tub supply. All is fine, but the recent large amount of rain has lead to the installed earth pit flooding with the entire top of the rod and earth connection being submerged.

I presume this is normal and perfectly acceptable? In fact a temporary benefit in terms of impedance to earth for the hot tub supply.

Given the recent freezing temperatures and snow on the ground, I would imagine it will have now also frozen before an opportunity to naturally drain away. I presume this is also expected and just a normal part of the seasonal conditions that an earth rod is designed to cope with?

Obviously it’s outside and below ground level so you would really expect these things to happen. Just want to make sure all is normal and not worry about something unnecessarily!

Thanks!

 

[Tom256]

Cold ground can certainly affect soil resistivity by > 10 times. It is one reason why a reading (Ra) for the rod of >200 ohms is considered unstable and thus not acceptable.

When I test I would change the periodic inspection from, if it was yearly, to every 11 months so as to hit different times of the year each rotation.
Such is the adopted method for rods on lightning protection systems.

Rods like all electrical systems require routine maintenance and that will take into account what is being inspected and the environmental factors that will be at play

 

[gcwarr]

Cold ground can certainly affect soil resistivity by > 10 times. It is one reason why a reading (Ra) for the rod of >200 ohms is considered unstable and thus not acceptable.

When I test I would change the periodic inspection from, if it was yearly, to every 11 months so as to hit different times of the year each rotation.
Such is the adopted method for rods on lightning protection systems.

Rods like all electrical systems require routine maintenance and that will take into account what is being inspected and the environmental factors that will be at play

I’m not too concerned about the reduction in effectiveness of the earthing as it was measured at install a few days ago around 23 Ohms. More any impact on the connection from it freezing and/or long term impact of potential corrosion.

I presume it’s normal for them to fill with water and also that this water may freeze occasionally?

Should I be considering wrapping the earth clamp connection with Denso tape for corrosion protection?

 

[Tom256]

I’m not too concerned about the reduction in effectiveness of the earthing as it was measured at install a few days ago around 23 Ohms. More any impact on the connection from it freezing and/or long term impact of potential corrosion.

I presume it’s normal for them to fill with water and also that this water may freeze occasionally?

Should I be considering wrapping the earth clamp connection with Denso tape for corrosion protection?

A lot depends on how it has been installed.
As with all Earthing systems they must be robust and sound against mechanical, chemical and oxidation damage. It is a further requirement that an Earthing connection be available for inspection.

BS 7430 is the go to for this, however, I suspect you never received a copy for Christmas to guide towards good practice. Maybe next year.
So, good practice would have Ideally the rod in an Inspection pit with lid, the termination of conductor to rod should ideally be 250 mm below ground.
Wrapping the termination in tape is not unheard of yet I find it will hide any issues that could go unseen and would need to be removed for inspection. However, suitable specialised compounds are available that can be used to protect against oxidisation. Do a search on Unial paste.

 

[timhoward]

More any impact on the connection from it freezing and/or long term impact of potential corrosion.

The main thing I'd be concerned about is the actual connection from the earth conductor to the clamp. I'd want to avoid that being underwater for long periods of time.
We can't do much about the rod itself; the bottom line is it's going to get wet and it's going last as long as it lasts and we are likely talking decades here. I don't think it's worth spending time worrying about that aspect. It's simple enough to bash in a new rod in 30 years time if required.

 

[Tom256]

The main thing I'd be concerned about is the actual connection from the earth conductor to the clamp. I'd want to avoid that being underwater for long periods of time.
We can't do much about the rod itself; the bottom line is it's going to get wet and it's going last as long as it lasts and we are likely talking decades here. I don't think it's worth spending time worrying about that aspect. It's simple enough to bash in a new rod in 30 years time if required.

Agreed.
All down to how installed and suitably robust.

As I said in my previous post good practice [as should always be the case in electrical installation yet sadly not] would have this covered.
Link to one such compound that can help prevent corrosion in joints within harsh environments. Link below:

Unial Jointing Paste

Uninal jointing pastes has a unique formula used to ensure a highly conductive connection is made and to prevent corrosion in joints.

www.jointingtech.co.uk

 

[Moley]

We use that paste a lot on HV joints (know usually as 'baby s41t' due to its colour). If you use it make sure you wear gloves. It is carcinogenic.

 

[Risteard]

Personally I always use Denso tape. Although watch your hands when applying it - it's pretty messy stuff.

 

[Mike Johnson]

To the OP, the majority of French rural properties are TT with the connection exposed to the elements, with the
below disconnection device bolted to an outside wall, does not seem to effect performance.