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It is stated in multiple places (diy.stackexchange, web searches), that "Ground and Neutral should be bonded at the main service panel".

My residence in Germany is supplied with 3-phase power, and has "modern" wiring. Recently renovated, new wiring with ground conductor, and a subpanel. The main panel and subpanel are joined by a 5 conductor 10 mm^2 line, i.e. there is an independent ground conductor joining. The only ground electrode is a metal bar going into the earth next to the service entrance, i.e. at the main panel. No idea what is buried there, but it looks roughly 20-30 years old. Galvanization still good above ground.

This is all one structure. Main panel first floor, subplanel second floor, 20 m joining line.

For my residence,

A) Should Ground be bound to Neutral at the main panel, and only at the main panel?

B) Should the subpanel have a Ground electrode?

Related question, for US residence.

Best explanation I've found, but is not explicit about German Code

Second residence requires a ground electrode, but does my subpanel?

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4 Answers 4

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It depends on the supply to that property and its earthing arrangements. It could potentially be TNC, TNC-S, TN-S or TT

If it has an earth spike like you suggested it is probably a TT system. It is important you understand the distinction and I suggest you look up those earthing arrangements mentioned above they are well documented with diagrams.

In TT systems the earth neutral must not be bonded together at any point in the installation. The Live and Neutral alone make their way back to the transformer while the earthing will make its way outside the building separately and onto an earthing spike.

NOTE: The following paragraph I have block quoted and this paragraph is a disclaimer against it as it would appear subjective and only anecdotal in the experience of this region. As another user pointed out they have experienced the opposite in regard to the TT systems being historic. It does not alter the overall answer for the user who asked the question. However, I feel it adds context to the region so have left it as is.

"It should be pointed out that TT systems are a historic system and the trend is to phase them out as much as possible as the impedance path to earth can sometimes be so poor that it affects the ability of the system to earth the system correctly."

So no the Neutral and Earth should not be bonded to each other and secondly no your sub panel should not have its own spike it should be connected to the main earthing bar within the property that will then in turn connect to the earthing spike. This is important because you don't want multiple and different impedance paths to ground. With a TNS/TNC system the supplier provides you with the earthing arrangement for you and will guarantee a (ZE) value.

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  • Absolutely not, TT is, in many places, taking over TN-x because now we have effective and cheap RCD and TN-x setup is more expensive. I don't know in US, but in Europe TT is most common and lenghty replacing other systems. In Germany they have a 'unusual' custom, in TN-C installation to ground the neutral even at user's location, don't know why, but electricians says so. (Germany uses both TT/TN-C, so it depends on location)
    – DDS
    Commented Mar 12, 2018 at 17:00
  • TNS and TNC-S is only prohbitive if the base infrastructure is not in place to support it. In some localities the provision of the earth be it separate or combined has always been there therefore the only additional cost is the supply cable having an earthing conductor. Perhaps in the localities you mention it is indeed the case that TT is more pronounced for that reason but historical differences aside regardless it doesnt change the answer to the users question.
    – Ryan Walkowski
    Commented Mar 12, 2018 at 17:24
  • Thank you for the answer that is most targeted towards my situation :) I will do the research on the different earthing systems.
    – Tyson Hilmer
    Commented Mar 13, 2018 at 8:28
  • @RyanWalkowski [OT]not only, if an failure occurs on 'provider's' protection conduit, users won't be protected (and provider can be sued), on TT system, protection is almost totally customer side, so provider can't be involved for 'safty' issues. Also copper isn't actually cheap and runing a fifth conductor, on a national basis, increases not little the whole cost (that the customer have to bear). [/OT]
    – DDS
    Commented Mar 13, 2018 at 8:42
  • @DDS In fairness to your point of view I have updated my answer to reflect the subjective nature of our experiences of TT being less and more pronounced within our respective areas.
    – Ryan Walkowski
    Commented Mar 13, 2018 at 21:17
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Ryan Walkowski's answer is in so far correct as there are the differents systems TT, TN-C, TN-C-S or, sometimes, TN-S.

Acoording to my knowledge, in Germany, TT is mostly used in installations in very rural areas, e. g. on farms where there is a transformer for only a handful of houses. In these cases, the N provided by the provider isn't reliably enough close to the earth potential, so you have to create your own earth potential. I am not sure, but it might be that in these cases breakers which cut both live and neutral are required as neutral can have a substantial potential compared to earth.

In more urban areas, usually a variant of TN is used. That means that the neutral of the installation is considered to be earthed. In this case, there is a connection between N and PE.

In this case,

  • TN-C means that N and PE share the same wire, aka PEN. This is only used in very old installations and not allowed any longer (or, at least, only allowed for wires of more than 10 mm²).
  • TN-C-S means that the wires which enter the house have a PEN as before, but somewhere in the installation, either in the main panel or in the sub panels, PE and N are split up, and, from this point onwards, may not be combined again. (This is essential for RCDs, but also for other reasons.)
  • TN-S means that N and PE enter the house already split up and, as well, may not be combined again.

Your ground electrode probably goes into the foundation (where it makes a huge ring) or to a very long grounder (earth rod, ground rod, Staberder) which can be several meters long. Its presence is not a hint towards the existence of a TT or TN system, as Ryan indicates. Instead, it should be conntected to the ground bar (Potentialausgleichsschiene) of the building where all ground lines run together:

  • ground of the electrical installation
  • ground of some telephone installation etc.
  • connection of antenna lines etc.
  • water and gas pipes etc.

In a TN system, all participients of the neighbourhood form a huge ground connection which is improved by every member. It can carry much higher currents towards the earth than in a TT system and your breakers trip when you have a short circuit between L and PE. In a TT system, however, this current is very limited, thus an RCD is absolutely needed here.

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Neutral SHOULD'NT be connected to ground (at least here in Italy where distribution system is TT).

Ground electrode, if the regulation is like italian, it requires a SINGLE ground system per building [all the ground contacts in a building and related areas must be at same potential], this is to avoid that someone touching two different grounds at a time, gets a shocked because on a system there is a phase-to-ground failure and not on the other (in this case get a full 240V phase to ground) touching two green-yellows. An old metal bar buried is a good ground (you can just test it's resistance, if it's low, it's OK). In the end: if you have a ground on the 'main' panel, connect to it the green-yellows coming from the secondary panel.

I don't know if in Germany is mandatory, but it's highly suggested that the system is protected by GFCIs (differential switches), it can be a single protecting all or one per circuit.

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  • What is the resistance level that is acceptable? In the U.S. a ground rod (or spike) needs to be below 25 ohms or a second rod/spike is required to be driven at least 6' away from the first then no measurement is required. Do you use Ufer grounds or concrete encased electrodes? (Connecting at least 20' of 1/2" rebar or #4 copper wire in the foundation as the grounding electrode). Just trying to understand why the neutral and ground are not connected at the service this is required for most installs in the U.S.
    – Ed Beal
    Commented Mar 13, 2018 at 22:26
  • For Germany I don't know, for Italy we have 'traditionaly' 20 ohms (from time when we didn't had RCDs), now the regulator prescribes 'enough to guarantee safety'. And this can be translated into 1,5KOhm for home use, it's 30mA at 50V that is our 'minimum' low voltage, below is very low voltage, as our RCD must break over 30mA, but around 20Ohms is a more common value as following the prescription on how to design and build the system, 20 ohms is almost guaranteed.
    – DDS
    Commented Mar 14, 2018 at 10:33
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Dirt is a terrible conductor. That's why we don't make wires out of it.

Why it's called neutral: Neutral is supposed to be near earth potential - if you are standing barefoot in the rain and touch the neutral wire, not much should happen. The secondary purpose is to minimize the voltage between other conductors and earth - that's why neutral is "in the middle" rather than at a corner.

The jobs of earthing

Current travels in loops. Earth wiring has an important job: returning natural electricity to the soil: lightning and ESD. That's why the earthing spike (ground rod) is tied to the earth wiring.

Remember how we aim to hold the neutral wire at earth potential? That doesn't happen by wishing. There needs to be a bond between neutral and the earthing spike to establish that reference. It could hypothetically be any kind of bias, but 0V is easy to do with a piece of copper. This bonding could be any of several places, but obviously, it must be somewhere both neutral and earth wires are present.

And we need to return human-made electricity to source. If artificial electricity has a ground fault, where leakage occurs to the earthing system, we want that leakage to efficiently return back to source. Source is the supply (hot and neutral) - we're not so worried about neutral-earth faults, so we're mostly worried about hot-earth faults and we'll want to return that current to neutral. If it is a bolted fault (dead short), we will want it to trip the overcurrent device (breaker) so it must carry current. This requires very low-resistance -- dirt will not suffice. So it's back to a copper neutral-earth bond.

The grand union

These requirements, together, call for a grand union of the neutral wire, the earthing system, and the earthing spike. Long experience in North America has shown you want that neutral-earth bond in exactly one place -- and that should also be the place the earthing spike/electrode ties in.

If you don't have that grand union, you will be omitting some of the above-mentioned protections.

SOP in North America is for that grand union to be in the main service point (main panel), and neutral and earth to be rigidly separated in each subpanel.

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  • This is for US, here in EU that's rarely the case (for home's systems), more common in industrial where the factory has medium-voltage connections. Here usually the 'protection' is bonded only at transformers side and neutral is fully separated from protective conductor.
    – DDS
    Commented Mar 13, 2018 at 8:49
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    @DDS That means your earthing system is unable to return human-made electricity to source in large quantities. If tripping your overcurrent breaker depends on returning 100A to source, it can't. Instead it will float up your protective earthing up toward 230V, electrifying your earthing system. OTOH if your site is RCD protected, you will probably get 30ma to trickle through dirt, so at least an RCD will trip. You're really, really, really gonna want that RCD.
    – Harper - Reinstate Monica
    Commented Mar 13, 2018 at 15:09
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    For this very reason we have RCD compulsorily installed in all houses since about 1970s.
    – DDS
    Commented Mar 13, 2018 at 15:28
  • @DDS Interesting. Notably, there was a copper shortage in the 1970s.
    – Harper - Reinstate Monica
    Commented Mar 13, 2018 at 15:33
  • I don't think it's due to it, about that age we moved from 127V two (out of three) phases to 230V (phase-neutral) because heavy home appliances started coming heavily around. [My grandpa has in his hardware store some bulbs from that age rated 127V and also some old appliances have a switch to select 127/220V]
    – DDS
    Commented Mar 13, 2018 at 15:40

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