Is there any advantage to installing a ground rod instead of the combined earth to neutral in my CU

Tonyboy · Dec 16, 2023

Hello All
I was pondering an idea recently regarding the ground connection to my property. At present it has a combined Neutral to earth at the point it enters the building from overhead cables and immediately prior to the meter the earth from the CU joins what looks like a Henley type block installed by the power provider. The earth then goes into my CU.

In very bad weather there seems to be times when the inverter trips out my supply when it is on an overnight charge.In particular at the point it switches over to utility as a charging option. This so far seems only to happen in wet and windy weather, I have been keeping a track of the times it happens for a month or more.

My thoughts were that in the bad weather perhaps the earth and neultral from the supplier are somhow getting efftected by the conditions and then when my inverter takes power from the mains it trips out the house. It does not do it at any other time. I am unsure if this is mere speculation but it seems to be a real coincidence that it only happens in wet and windy weather and no other time. The other factor as yet to be explored is that overnight my electricity voltage rises to 149.5V or thereabouts from an average in the day of 130 V +or - 5 V.

This lead me to ponder if it would be better for the supply to be earthed by a ground rod which was seperate from the incoming supply and therefore eliminating any possibility it was due to the suppliers N-E connection having an issue at some point from the transformer to my home.

My neighbour has a ground rod arrangement that has been in place for well over 10 years and this was what prompted me to consider doing the same. Unfortunately the current neighbour was not the one that had this installed, it was there before they arrived.

I would welcome any advise or suggestions (helpful) if possible regarding this topic. I am not an electrician but am able to understand basic principles of the topic and I am not suggesting I do the work myself.

Thanks in advance
Tonyboy

mainline · Dec 16, 2023

Tonyboy said:
Hello All
I was pondering an idea recently regarding the ground connection to my property. At present it has a combined Neutral to earth at the point it enters the building from overhead cables and immediately prior to the meter the earth from the CU joins what looks like a Henley type block installed by the power provider. The earth then goes into my CU.

In very bad weather there seems to be times when the inverter trips out my supply when it is on an overnight charge.In particular at the point it switches over to utility as a charging option. This so far seems only to happen in wet and windy weather, I have been keeping a track of the times it happens for a month or more.

My thoughts were that in the bad weather perhaps the earth and neultral from the supplier are somhow getting efftected by the conditions and then when my inverter takes power from the mains it trips out the house. It does not do it at any other time. I am unsure if this is mere speculation but it seems to be a real coincidence that it only happens in wet and windy weather and no other time. The other factor as yet to be explored is that overnight my electricity voltage rises to 149.5V or thereabouts from an average in the day of 130 V +or - 5 V.

This lead me to ponder if it would be better for the supply to be earthed by a ground rod which was seperate from the incoming supply and therefore eliminating any possibility it was due to the suppliers N-E connection having an issue at some point from the transformer to my home.

My neighbour has a ground rod arrangement that has been in place for well over 10 years and this was what prompted me to consider doing the same. Unfortunately the current neighbour was not the one that had this installed, it was there before they arrived.

I would welcome any advise or suggestions (helpful) if possible regarding this topic. I am not an electrician but am able to understand basic principles of the topic and I am not suggesting I do the work myself.

Thanks in advance
Tonyboy

Your mains voltage is 130 volts ?

Tonyboy · Dec 17, 2023

mainline said:
Your mains voltage is 130 volts ?

Ooops no My mains voltage is 230V

davesparks · Dec 19, 2023

Tonyboy said:
My thoughts were that in the bad weather perhaps the earth and neultral from the supplier are somhow getting efftected by the conditions and then when my inverter takes power from the mains it trips out the house.

What exactly is tripping?

Whatever type of device is tripping it won't be due to the combined neutral and earth upstream of it. The device will be detecting something happening downstream of it which fits the profile of the type of fault it is designed to detect and disconnect.

Tonyboy · Dec 22, 2023

davesparks said:
What exactly is tripping?

Whatever type of device is tripping it won't be due to the combined neutral and earth upstream of it. The device will be detecting something happening downstream of it which fits the profile of the type of fault it is designed to detect and disconnect.

Hi davesparks.
The main switch in the cu trips it is an elcb circa 1980's possibly. What happens (and this is only when it is very wet and windy) is the elcb trips at the point the inverter switches over to utility at 02.00 to charge the batteries on cheap rate electricity. I have been monitoring it for a month or more and the only time it trips is wet and windy weather.
The cable to the inverter is SWA via an isolator in the cupboard the inverter is in, it is supplied from what was the 30 amp cooker circuit from the consumer unit and it enters the inverter cabinet via a soft start relay and then a circuit breaker before entering the inverters a/c input.
It is strange it only does this in wet and windy weather as there is no logical reason for it to be limited to these conditions. At all other times it works fine coming on at 02.00 until 6.00 and charges the batteries as well as supplying the solar outlets in line mode.

I had perhaps mistakenly thought that the fault was caused by something on the overhead lines/transformer before they entered the property and this then caused a situation where an earth leak back to the ELCB main switch was made worse or increased by an earth fault outside. The 30 amp MCB that serves the inverter does not trip only the main switch elcb.
I have been told that a lot of inverters do generate small high frequency currents to earth that can cause nuiance trips when they change over and this may be the issue and the old elcb may be a bit more sensitive to these spikes.
I am not an electrician but can understand ost of the principles.
As a second thought my ELCB is a MEM 80a 30mA and 240 V item and I have noticed that at night the voltage in my property peaks at about 249v + or _ 4 v. could this be something to do with the tripping? if so is this something the electricty suppier can limit to 240 v or less?

regards

Tonyboy

pc1966 · Dec 22, 2023

Tonyboy said:
The main switch in the cu trips it is an elcb circa 1980's possibly. What happens (and this is only when it is very wet and

The "true" ELCB would predate the 1980s and really should be replaced now, they are often properly referred to as VOELCB as they depended on a voltage between the installation's CPC system and a rod to true Earth. That is unreliable and fails to detect a number of hazardous situations.

The RCD (also called RCCB, and related RCBO) work be detecting an imbalance between L & N and so are better able to detect faults and shock situations. It is more likely you have one of those (from the 30mA specification you mention). A photo of your supply arrangement (cutout & meter, but any identifies redacted) and CU (consumer unit = fuse box) would help a lot with analysing things!

However, if your whole house is on a single 30mA then it is highly likely to trip due the the accumulation of leakage on all circuits. This can be made worse if the supply is subject to sudden voltage changes due to other storm issues (tress hitting cables, etc) as the current is given by I = C * dV/dt and so a high rate of change of voltage (dV/dt) can cause more current and hence a trip.

The best solution if you have all on a single RCD is to replace the CU with one using RCBO so each circuit has its own RCD protection, less leakage per circuit observed, and in the event of a trip less loss of other healthy circuits.

But in terms of having an earth rod connected to your main earth terminal it might be a good thing to do for various reasons, even if you keep the TN-C-S supply instead of TT, but it is unlikely to solve this problem.

mainline · Dec 22, 2023

Tonyboy said:
I have been told that a lot of inverters do generate small high frequency currents to earth that can cause nuiance trips when they change over and this may be the issue and the old elcb may be a bit more sensitive to these spikes.

Inverters can also stop certain types of rcds from working properly.
If several circuits share the same RCD as the inverter, you could create a dangerous situation.

An earth electrode in most cases does not provide a high fault current path it would be very unusual for the earth loop impedance from a simple earth electrode to be lower than about 20 ohms, and that is far too high to carry any sort of significant fault current without the entire earth system rising to a dangerously high voltage relative to the local earth ground.

Sometimes better to convert to a plain TT arrangement, then you can't import your neighbours' interference or fault currents.

Tonyboy · Dec 23, 2023

pc1966 said:
The "true" ELCB would predate the 1980s and really should be replaced now, they are often properly referred to as VOELCB as they depended on a voltage between the installation's CPC system and a rod to true Earth. That is unreliable and fails to detect a number of hazardous situations.

The RCD (also called RCCB, and related RCBO) work be detecting an imbalance between L & N and so are better able to detect faults and shock situations. It is more likely you have one of those (from the 30mA specification you mention). A photo of your supply arrangement (cutout & meter, but any identifies redacted) and CU (consumer unit = fuse box) would help a lot with analysing things!

However, if your whole house is on a single 30mA then it is highly likely to trip due the the accumulation of leakage on all circuits. This can be made worse if the supply is subject to sudden voltage changes due to other storm issues (tress hitting cables, etc) as the current is given by I = C * dV/dt and so a high rate of change of voltage (dV/dt) can cause more current and hence a trip.

The best solution if you have all on a single RCD is to replace the CU with one using RCBO so each circuit has its own RCD protection, less leakage per circuit observed, and in the event of a trip less loss of other healthy circuits.

But in terms of having an earth rod connected to your main earth terminal it might be a good thing to do for various reasons, even if you keep the TN-C-S supply instead of TT, but it is unlikely to solve this problem.

Hello pc1966
thanks for the reply. The fact that the voelcb can be tripped by external factors such as trees etc does lead me to think it is related to the weather prevailing at the time of the trips. When it is fine and dry the system works fine and it has done so for some time now.
I have been tracking the days it goes off and the voltage, at the time is does so and the weather aside, it is when there is a spike around the 249 +/- 5 v that the trip occurs.

I will try to get a couple of pics of the meter and inputs and add to this one of the elcb below.

I have heard that you can contact the electicity provider and request they limit the voltage to your property if you are having any issues with spikes. I think I read on this or another forum that the supplier fits a monitor for some period and then if they determine it to be above the 230 v +/- their own allowance they can restrict it from the transformer supplying the properties.
I live in a rural location and there are three houses fed from the same pole on this side of the road and 2 on the other side of the road.
As you say the device is old and would be better replaced but I don't have the money to do this just yet. so in the interim I am looking into a way to reduce the tripping if possible as a measure before getting all fo my CU changed and the upheaval that will entail.
Many thanks and regards
Tonyboy

[ElectriciansForums.net] Is there any advantage to installing a ground rod instead of the combined earth to neutral in my CU

Tonyboy · Dec 23, 2023

mainline said:
Inverters can also stop certain types of rcds from working properly.
If several circuits share the same RCD as the inverter, you could create a dangerous situation.

An earth electrode in most cases does not provide a high fault current path it would be very unusual for the earth loop impedance from a simple earth electrode to be lower than about 20 ohms, and that is far too high to carry any sort of significant fault current without the entire earth system rising to a dangerously high voltage relative to the local earth ground.

Sometimes better to convert to a plain TT arrangement, then you can't import your neighbours' interference or fault currents.

Hi Mainline and thanks for the reply.

My inverter is only fed from the mains supply over a 4 hour period at night and it does not have any tie into the grid for the output. The supply to the inverter is from the 32 amp MCB that was for the original cooker point in the property that is no longer used. This then provides power to the solar sockets during the charging time as the inverter is in effect in line mode when it charges the batteries overnight.

I have a seperate system in the house that is supplied by the inverter and I use the sockets to power my applainces via the inverter/batteries/solar panels. I do not have any way for the outpt of the inverter to be fed back into the grid so in essence it is an off grid system but with a backup input which is from the mains or can be via a generator as it also has a soft start relay in the cabinet. The whole system has its own protection system build into a purpose built cabinet and the output side of the cabinet is then fed to a separate CU to supply the solar sockets.

I am certainly learning a lot from the forum and thank you and others who have replied.

Regards

Tonyboy