Connecting ground to neutral in main panel | on ElectriciansForums
Guest viewing is limited

Discuss Connecting ground to neutral in main panel in the Electrical Engineering Chat area at ElectriciansForums.net

Joined
Jun 15, 2020
Messages
39
Reaction score
1
Location
Zagreb
Hello everyone ?
It's totally confusing for me. It is my understanding that the neutral and the ground busbars should be connected at the main distribution board (schematic attached), but not at the auxiliary or sub panel. But why?
I know that if I connect them in sub panel the current from neutral will flow through ground wires and metalic in the house, and it's dangerous. But, what is difference? The other sides of this wires are already connected together, their origin is neutral and ground busbar in main panel that are already connected!!?? ?
 

Attachments

  • [ElectriciansForums.net] Connecting ground to neutral in main panel
    Ground to neutral.jpg
    190.6 KB · Views: 13
The rules on the N-E link vary a lot by country. In the UK, for example, the link is only done by the electricity provider (DNO = distribution network operator) and not within an installation. However, if using a generator then the generator has the link (as if it were the electricity supplier) but transfer switches here in the UK have to switch neutral as well for this reason (so only one external N-E link is present at any point in time).

In other countries it is done at the main DB (as you show) and goes by various different names.

The key points behind having only one N-E link are basically down to safety:
  • Shock - an open fault on a cable carrying current does not lead to "earthed" metalwork becoming live.
  • Fire - a high neutral current does not circulate through earth metalwork and bonding conductors that is not rated for such a sustained level of I^2R heating.
  • Testing - so you can easily separate N and E at one place close to the power source to perform an insulation test on the N conductor to make sure the above are true.
 
The rules on the N-E link vary a lot by country. In the UK, for example, the link is only done by the electricity provider (DNO = distribution network operator) and not within an installation. However, if using a generator then the generator has the link (as if it were the electricity supplier) but transfer switches here in the UK have to switch neutral as well for this reason (so only one external N-E link is present at any point in time).

In other countries it is done at the main DB (as you show) and goes by various different names.

The key points behind having only one N-E link are basically down to safety:
  • Shock - an open fault on a cable carrying current does not lead to "earthed" metalwork becoming live.
  • Fire - a high neutral current does not circulate through earth metalwork and bonding conductors that is not rated for such a sustained level of I^2R heating.
  • Testing - so you can easily separate N and E at one place close to the power source to perform an insulation test on the N conductor to make sure the above are true.
This answer is great. I could be wrong on this, but my take is everything connected to the neutral will add to the neutrals resistance to ground. Adding the ground to the MDP only, will ensures that the resistance to ground is retained.
 
I think you are a bit confused when talking about resistances.
Put simply :
The neutral wiring (which should always be treated as "live") carries the load current. If it gets broken, then something doesn't work but nothing exposed is pulled high by the load current.
The earth wiring is there to keep exposed conductive parts at a safe voltage relative to ground.

There are electrical systems where there is no connection between "neutral" and earth known as IT. They are pretty well unheard of in domestic environments as a single fault will "do nothing" - everything still works, but internally it could be that "live" is now earthed and "neutral" is "hot"), and nothing will trip until there's a second fault. it's also difficult to get a reliable floating supply other than from a standalone generator or isolating transformer. In my day job I deal with IT power systems (it's fully floating with no intended connection to earth), and we have a) monitoring equipment to detect faults, and b) full time monitoring/control of the installation by qualified people.

But back to regular domestic supplies. As PC1966 says, over here our DNO usually provides the earth - though that does have some issues. Over in the US it seems it's normal for the householder to provide an earth rod and to earth the neutral - which would seem to make it a customer provided multiple earth system (effectively you and your neighbours are sharing your earth rods).
The basic principle is that if you have a fault in your installation or an appliance, then current will flow from line (hot) to ground via the earth (ground) wires, and that current will be sufficient to blow a fuse or trip a breaker. At the same time, during the time between the fault occurring and the fuse/breaker disconnecting the supply, the touch voltage (i.e. what someone would feel if stood on ground and touching some "earthed" metalwork) needs to stay low enough that it isn't dangerous (under our rules, that's 50V for AC circuits).
It would actually work for the electricity supplier to earth the neutral at the substation (transformer), for you to provide just your local earth, and not to link neutral and earth anywhere else. But that makes the above fault handling (automatic disconnection of the supply to faults by a fuse/circuit breaker) heavily reliant on the quality of those two earths - and the ground in between.
My assumption is that those who write your wiring codes decided that having every property provide an earth rod AND earth the neutral to it would significantly reduce the fault impedances - and avoid problems where a poor earth rod means that a fault persists, the fuse doesn't blow, and in the mean time there are dangerous voltages present on "earthed" bits of metalwork. Over here that's done by the DNO (the people who pipe the lecky to our houses) putting lots of earth electrodes in the local network - called protective multiple earthing - and so providing a low impedance earth to most premises.
 
I think you are a bit confused when talking about resistances.
Put simply :
The neutral wiring (which should always be treated as "live") carries the load current. If it gets broken, then something doesn't work but nothing exposed is pulled high by the load current.
The earth wiring is there to keep exposed conductive parts at a safe voltage relative to ground.

There are electrical systems where there is no connection between "neutral" and earth known as IT. They are pretty well unheard of in domestic environments as a single fault will "do nothing" - everything still works, but internally it could be that "live" is now earthed and "neutral" is "hot"), and nothing will trip until there's a second fault. it's also difficult to get a reliable floating supply other than from a standalone generator or isolating transformer. In my day job I deal with IT power systems (it's fully floating with no intended connection to earth), and we have a) monitoring equipment to detect faults, and b) full time monitoring/control of the installation by qualified people.

But back to regular domestic supplies. As PC1966 says, over here our DNO usually provides the earth - though that does have some issues. Over in the US it seems it's normal for the householder to provide an earth rod and to earth the neutral - which would seem to make it a customer provided multiple earth system (effectively you and your neighbours are sharing your earth rods).
The basic principle is that if you have a fault in your installation or an appliance, then current will flow from line (hot) to ground via the earth (ground) wires, and that current will be sufficient to blow a fuse or trip a breaker. At the same time, during the time between the fault occurring and the fuse/breaker disconnecting the supply, the touch voltage (i.e. what someone would feel if stood on ground and touching some "earthed" metalwork) needs to stay low enough that it isn't dangerous (under our rules, that's 50V for AC circuits).
It would actually work for the electricity supplier to earth the neutral at the substation (transformer), for you to provide just your local earth, and not to link neutral and earth anywhere else. But that makes the above fault handling (automatic disconnection of the supply to faults by a fuse/circuit breaker) heavily reliant on the quality of those two earths - and the ground in between.
My assumption is that those who write your wiring codes decided that having every property provide an earth rod AND earth the neutral to it would significantly reduce the fault impedances - and avoid problems where a poor earth rod means that a fault persists, the fuse doesn't blow, and in the mean time there are dangerous voltages present on "earthed" bits of metalwork. Over here that's done by the DNO (the people who pipe the lecky to our houses) putting lots of earth electrodes in the local network - called protective multiple earthing - and so providing a low impedance earth to most premises.
Oh sorry for the confusion, I was not explaining how ground works. I was attempting with my best knowledge to explain why in the US you would only ground the neutral at the MDP and not every sub panel.
"I could be wrong on this, but my take is everything connected to the neutral will add to the neutrals resistance to ground. Adding the ground to the MDP only, will ensures that the resistance to ground is retained."
 
"I could be wrong on this, but my take is everything connected to the neutral will add to the neutrals resistance to ground. Adding the ground to the MDP only, will ensures that the resistance to ground is retained."
I'm not sure my parsing of that makes sense!

The short answer is safety. If you deliberately link N-E at locations other than the origin of the system you run the risk of open faults making metalwork live and so presenting an electric shock risk (failure of combined N+E path) and/or small bonding conductors overheating and starting fires (open N diverting normal current via ground wires that are sized only for adiabatic limit of fault clearing).

Even the 'origin' location link has its issues as @Simon47 says. In the UK it is only the DNO (supplier) that is allowed to do it as they generally have higher standards of planning and joint-making than is the norm for domestic electrics. (No offens intended for the great domestic sparks on this forum, but you are not the ones I am thinking of here!)
 
I'm not sure my parsing of that makes sense!

The short answer is safety. If you deliberately link N-E at locations other than the origin of the system you run the risk of open faults making metalwork live and so presenting an electric shock risk (failure of combined N+E path) and/or small bonding conductors overheating and starting fires (open N diverting normal current via ground wires that are sized only for adiabatic limit of fault clearing).

Even the 'origin' location link has its issues as @Simon47 says. In the UK it is only the DNO (supplier) that is allowed to do it as they generally have higher standards of planning and joint-making than is the norm for domestic electrics. (No offens intended for the great domestic sparks on this forum, but you are not the ones I am thinking of here!)
Right, thanks for your explanations.
 

Reply to Connecting ground to neutral in main panel in the Electrical Engineering Chat area at ElectriciansForums.net

Similar threads

The power company only brings in 3 wires which is 2 live and 1 neutral wire. It’s our responsibility to add the ground rod to bond the neutral...
Replies
3
Views
584
It might be ok
Replies
6
Views
528

Recommended Sponsor News

Exclusive Forum Offer! Free euro 2024 wall chart for first 10 responses!

Hi everyone,

We have 10 exclusive Uheat EURO 2024 Wallcharts to giveaway for Electricians Forum Members! The first 10 people to reply YES to this thread - I will message and get them sent out to you just in time for this years tournament! GO GO GO

Quickwire Now Sponsor ElectriciansForums.net

I am sure you will join me in welcoming our newest sponsors of ElectriciansForums.net - Quickwire! They have decided to join us after seeing you guys discussing their products here. Now we have an expert on board that you can chat to @Quickwire-Sam who will be happy to answer your queries!

[ElectriciansForums.net] Quickwire Now Sponsor ElectriciansForums.net


@Quickwire-Sam said "At Quickwire, we're all about speed, safety, and reliability. We're a family-run business, and every Quickwire connector is proudly made right here in the UK, ensuring noticeable quality. In short, Quickwire is the fastest connection method on the market. Whether you're an experienced electrician or a DIY enthusiast, Quickwire makes electrical connections ridiculously quick and easy. We're passionate about blending British craftsmanship with innovation. If you have any questions or if there's any way we can help, please just ask me!"

PCBWay Now Sponsor ElectriciansForums.net!!

I hope you will all join me in welcoming our newest sponsor to the forum PCBWay! You can contact their friendly people by sending a message to @PCBWay who will be happy to answer your queries.

Welcome to the community and thanks for your sponsorship!

[ElectriciansForums.net] PCBWay Now Sponsor ElectriciansForums.net!!

PCBWay provides services including PCB Prototype and batch Production, PCB Assembly (SMT), 3D Printing, CNC Machining, PCB Design, Electronics Modules Selling, etc. We are committed to meeting the needs of global makers from different industries in terms of quality, delivery, cost-effectiveness, and any other demanding requests in electronics.

[ElectriciansForums.net] PCBWay Now Sponsor ElectriciansForums.net!!

Search Electricans Forums by Tags

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

YOUR Unread Posts

This website was designed, optimised and is hosted by untold.media Operating under the name Untold Media since 2001.
Back
Top