PE and water pipes (yet another earthing thread)

[LostCause]

Hi all,

New to the forum after a bit of lurking. I'm totally lost with grounding & earthing strategies and I wonder if anyone can help? I've read a LOT of posts on here but can't quite find this stuff so sorry if this is a bit "page 1"!

In simple terms my question is: What do you do about water and gas pipes? What do you want their potential to be, and how do you do it?

To elaborate:

Ignoring the solar install, my house appears to be on TNC-S from the DNO, where PE is split off before the meter and goes past a couple of RCBOs and then ties to the earth block in a couple of DBs for the house. The earth block in one of the DBs is then tethered to the incoming gas and water pipes.

I'm trying to install a Voltacon 8kW off-grid inverter with grid backup which *I think* does a N-E bond on the output when running off-grid but breaks the bond and passes the earth terminal through when running on utility. My initial thought was that I would need an external relay to switch to a local earth rod when running on battery? (Or just, have a floating system and hope RCDs stop us being deaded) BUT... here's where my understanding runs out:

(1) Again, ignoring solar, if the water and gas is connected to PE, does this not create problems where the pipes go back to earth (as in, planet Earth)? I thought you shouldn't add a local earthing rod to the PE (or N) of a TNC-S because of import/export/ground loop/other possible issues? Maybe I misunderstood.

(2) ignoring (1) if you use local earth for off-grid but use the TNC-S PE for on-grid operation, do you switch which one is connected to your water? And if so, how?

Thanks!

 

[ArkCabinMan]

"TNC-S from the DNO, where PE is split off before the meter and goes past a couple of RCBOs and then ties to the earth block in a couple of DBs for the house. The earth block in one of the DBs......"

I honestly don't have a clue what any of these abbreviations and anachronisms might mean?

 

[LostCause]

Haha, my apologies! Yes, that was a lot of abbreviations....!

------------
TNC-S - An earthing strategy whereby properties are fed with just two conductors (for single phase), live & neutral. Neutral is bonded to a grounding rod at the transformer. Within the property, the neutral is then split out in to current carrying conductors and protective earths.*

DNO - Distribution Network Operator (i.e. "the grid" effectively)

DB - Distribution board

RCBO - Residual Current Breaker with Overcurrent protection (In the US maybe referred to as something like a GFCI ... maybe? i.e. a trip switch which trips if there's a current imbalance between the Neutral and Live)

PE - Protective Earth
------------

But to rephrase that part:

My house doesn't have a grounding rod. The transformer from the grid does; neutral and ground are bonded there. Live & Neutral come in to the property from the grid. N is then, within the property, split out in to become the current carrying conductor and the protective earth. The current carrying L & N conductors go through earth fault trip switches and then on to the distribution boards. Meanwhile, the N conductor is also (upstream of the trip switches) split to become the Protective Earth and is connected directly to the earth blocks in the distribution boards, which in turn connect to the water & gas.

Hence, in *on-grid* operation, within the property, all the neutrals, earths and pipework should all be at roughly the same potential. Should a Live-to-Earth or Neutral-to-Earth fault condition arise, the ''leak'' should hopefully return directly to the incoming neutral conductor, bypassing the RCBO/GFCI/Whatever and causing it to trip.

 

[MichaelK]

I honestly don't have a clue what any of these abbreviations and anachronisms might mean?

Darn, I wanted to say that!

As a general rule of thumb, NEVER ground anything to a gas pipe. Water pipes are OK. Follow the rule that all above-ground earthing connections, and all the below-ground earthing elements should be connected at one and only one location, so I would utilize the ground that is already there. Do NOT drive a second independent ground rod that is also connected anywhere to the above-ground earthing connections.

Any additional ground rod may be bonded to the below-ground elements that are already in place, such as your water pipes.

 

[Danke]

Darn, I wanted to say that!

As a general rule of thumb, NEVER ground anything to a gas pipe. Water pipes are OK. Follow the rule that all above-ground earthing connections, and all the below-ground earthing elements should be connected at one and only one location, so I would utilize the ground that is already there. Do NOT drive a second independent ground rod that is also connected anywhere to the above-ground earthing connections.

Any additional ground rod may be bonded to the below-ground elements that are already in place, such as your water pipes.

I just noticed I have a water pipe rubbing up a gas pipe, I guess I should put an insulating material between the two?

 

[Quattrohead]

I guessed you were in the UK. Every metal pipe has to be grounded.
In the USA there is no such requirement, we just have the messed up grounded center tap/split phase crap instead !!!

 

[ArkCabinMan]

Darn, I wanted to say that!

???

 

[LostCause]

Darn, I wanted to say that!

As a general rule of thumb, NEVER ground anything to a gas pipe. Water pipes are OK. Follow the rule that all above-ground earthing connections, and all the below-ground earthing elements should be connected at one and only one location, so I would utilize the ground that is already there. Do NOT drive a second independent ground rod that is also connected anywhere to the above-ground earthing connections.

Any additional ground rod may be bonded to the below-ground elements that are already in place, such as your water pipes.

Thanks for the reply. Interesting!

But, since my "ground that is already there" is also effectively the Neutral of the grid, I'm not sure I can connect the Earth of the inverter output to that? (Since it's bonded to Neutral in the inverter while running on solar/battery - and the inverter is an off-grid type which just has an AC input for backup, so it freewheels in terms of phase))

I just noticed I have a water pipe rubbing up a gas pipe, I guess I should put an insulating material between the two?

I would guess based on what Quattrohead says, if you're in the USA then, perhaps yes.

If you're in the UK like me, they're likely bonded elsewhere anyway so it probably doesn't matter (beyond physical wear and tear on them as they expand/contract maybe?)

 

[Charleswgibbs]

If there is a neutral-ground bond at the transformer, and then the neutral (acting as ground) is connected to the pipes, doesn't that create a ground loop?

 

[Mattb4]

Here in the US grounding to iron/copper water pipes is considered an obsolete method although allowed there are restrictions. Some countries I have read it is not allowed.

https://electrical-engineering-portal.com/water-pipes-grounding-purposes

My home does not have metal pipes therefore there would be no good grounding point.

 

[timselectric]

Treat everything as it is.
Inverter input L-N-G as provided by the DNO.
Inverter output L-N-G to loads.
Do not add any additional grounding or bonding. (Assuming that you are sure that the inverter does it internally)
There is no loop, you are just extending what is there.

 

[400bird]

Here in the US grounding to iron/copper water pipes is considered an obsolete method although allowed there are restrictions. Some countries I have read it is not allowed.

https://electrical-engineering-portal.com/water-pipes-grounding-purposes

My home does not have metal pipes therefore there would be no good grounding point.

I was required to bond/ground my iron/copper main water entrance in 2018 under 2016 code. I had the required grounding elsewhere, but the inspector required I run a ground over the water main.

 

[Mike 134]

I guessed you were in the UK. Every metal pipe has to be grounded.
In the USA there is no such requirement, we just have the messed up grounded center tap/split phase crap instead !!!

Here in Chicago we use the water pipe as our grounding point. Gas pipes end up grounded both from being buried in the earth before entering the house and through the various gas appliances that also have electricity brought to them with the ground wire connected to the metal frame of the appliance.

 

[LostCause]

My home does not have metal pipes therefore there would be no good grounding point.

My understanding in the UK code is that pipework is not earthed to provide grounding for the property (although - my thinking is - surely it does exactly that!?) but to keep it at the same potential as "the electrics". For example, if you put your hand on your electric oven and your kitchen tap simultaneously, they're both the same potential, even if something in your neighbour's property is exporting to Earth somehow.

I assume that's the logic in the UK's IET code anyway. But it changes all the time, much like the US one I guess..!?

If there is a neutral-ground bond at the transformer, and then the neutral (acting as ground) is connected to the pipes, doesn't that create a ground loop?

I would have thought so, yes. Right??

Treat everything as it is.
Inverter input L-N-G as provided by the DNO.
Inverter output L-N-G to loads.
Do not add any additional grounding or bonding. (Assuming that you are sure that the inverter does it internally)
There is no loop, you are just extending what is there.

Great, thanks very much for the reply!

If you'll forgive my terrible MS Paint drawing (it's all I've got with me today ) are you saying I go from this:




To this:


Again, please forgive the drawing and poor layout; I'm not actually a 3 year old Obviously the diagram is also missing a breaker and fault protection between the inverter and the distribution board.

It would be great if this is what you mean, as it's pretty straight forward this way. Certainly I like it more than the idea of having responsibility for active switching of the earthing through an external relay.

I've not tested the inverter yet, but my understanding is [in terms of Earth at least] it's a straight pass through when in Line mode, but on PV/Battery it bonds N-E on the output terminal. Once I get some juice to it I can check that.

I really appreciate everyone's help so far!

 

[timselectric]

My understanding in the UK code is that pipework is not earthed to provide grounding for the property (although - my thinking is - surely it does exactly that!?) but to keep it at the same potential as "the electrics". For example, if you put your hand on your electric oven and your kitchen tap simultaneously, they're both the same potential, even if something in your neighbour's property is exporting to Earth somehow.

I assume that's the logic in the UK's IET code anyway. But it changes all the time, much like the US one I guess..!?

I would have thought so, yes. Right??


Great, thanks very much for the reply!

If you'll forgive my terrible MS Paint drawing (it's all I've got with me today ) are you saying I go from this:

View attachment 114047


To this:
View attachment 114048

Again, please forgive the drawing and poor layout; I'm not actually a 3 year old Obviously the diagram is also missing a breaker and fault protection between the inverter and the distribution board.

It would be great if this is what you mean, as it's pretty straight forward this way. Certainly I like it more than the idea of having responsibility for active switching of the earthing through an external relay.

I've not tested the inverter yet, but my understanding is [in terms of Earth at least] it's a straight pass through when in Line mode, but on PV/Battery it bonds N-E on the output terminal. Once I get some juice to it I can check that.

I really appreciate everyone's help so far!

Yup, that's it.

 

[LostCause]

Yup, that's it.

Perfect, thanks @timselectric ! Much appreciated.

 

[bruce_loco]

is your inverter an offgrid/hybrid inverter?

 

[12VoltInstalls]

As a general rule of thumb, NEVER ground anything to a gas pipe. Water pipes are OK.

Having received some jaw-opening jolts removing a kitchen sink drain I’d not agree

 

[timselectric]

You won't pass an inspection in my area. Unless you ground the water and gas service per the NEC.

 

[LostCause]

Unless you ground the water and gas service per the NEC

Sorry for long delay, just revisiting this.... Out of interest, do you know what NEC has to say about this? I.e. what would grounding the water and gas per NEC actually involve?

In IET / BS regulations (which is the NEC equivalent that applies to me in the UK) my understanding is all metal pipework MUST be earthed to the same as the AC, which in most cases means bonding directly to the property's Main Earthing Terminal (MET), which is in turn connected directly to the PE or N of the supply cable from the DNO, depending on whether it's TNC or TNC-S. But I could be wrong, again, I'm no electrician!