Why do we need separate neutral and earth wires when the neutral is
earthed a the two are joined together at the point of entry anyway?
Why not have two terminals - live and earth - and use the earth as the
return path?

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On 19/03/2025 21:36, Scott wrote:

Why do we need separate neutral and earth wires

Because they serve two completely different purposes. Neutral is a
current carrying wire in normal use. Earth should not be current
carrying, and is there as a path for current to pass under fault
conditions. Neutral can be switched, earth should be a permanent
connection. Neutral is classed as a "live" wire, earth is not etc.

when the neutral is
earthed a the two are joined together at the point of entry anyway?

That depends on the earthing system in use; with TN-C-S (PME) then yes
they are combined at the main cutout where the service enters the building.

With TN-S, they are combined at a substation, not at the building.

With TT, there is no earth provided at all by the suppler, you will need
your own arrangement, and it is not necessarily connected to neutral at
all.

Why not have two terminals - live and earth - and use the earth as the
return path?

There is an earthing system TN-C (Where T = "Terre" aka Earth, N =
Neutral, C = Combined), that does work as you describe - no separate
earth, and neutral used as earth directly. However I don't think I have
ever seen an installation like that in the UK, it is very uncommon.

For more detail, see:

https://wiki.diyfaq.org.uk/index.php/Earthing_Types#Earthing_Types


--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk | \=================================================================/

--- SoupGate-Win32 v1.05
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On Thu, 20 Mar 2025 11:50:12 +0000, John Rumm wrote:

On 19/03/2025 21:36, Scott wrote:

Why do we need separate neutral and earth wires

Because they serve two completely different purposes. Neutral is a
current carrying wire in normal use. Earth should not be current
carrying, and is there as a path for current to pass under fault
conditions. Neutral can be switched, earth should be a permanent
connection. Neutral is classed as a "live" wire, earth is not etc.

when the neutral is earthed a the two are joined together at the point
of entry anyway?

That depends on the earthing system in use; with TN-C-S (PME) then yes
they are combined at the main cutout where the service enters the
building.

With TN-S, they are combined at a substation, not at the building.

With TT, there is no earth provided at all by the suppler, you will need
your own arrangement, and it is not necessarily connected to neutral at
all.

Why not have two terminals - live and earth - and use the earth as the
return path?

There is an earthing system TN-C (Where T = "Terre" aka Earth, N =
Neutral, C = Combined), that does work as you describe - no separate
earth, and neutral used as earth directly. However I don't think I have
ever seen an installation like that in the UK, it is very uncommon.

For more detail, see:

https://wiki.diyfaq.org.uk/index.php/Earthing_Types#Earthing_Types

You could switch off the isolator so all systems are dead and measure the resistance between the black and earth with a bonding meter.

--- SoupGate-Win32 v1.05
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On 20/03/2025 16:31, jon wrote:

On Thu, 20 Mar 2025 11:50:12 +0000, John Rumm wrote:

On 19/03/2025 21:36, Scott wrote:

Why do we need separate neutral and earth wires

Because they serve two completely different purposes. Neutral is a
current carrying wire in normal use. Earth should not be current
carrying, and is there as a path for current to pass under fault
conditions. Neutral can be switched, earth should be a permanent
connection. Neutral is classed as a "live" wire, earth is not etc.

when the neutral is earthed a the two are joined together at the point
of entry anyway?

That depends on the earthing system in use; with TN-C-S (PME) then yes
they are combined at the main cutout where the service enters the
building.

With TN-S, they are combined at a substation, not at the building.

With TT, there is no earth provided at all by the suppler, you will need
your own arrangement, and it is not necessarily connected to neutral at
all.

Why not have two terminals - live and earth - and use the earth as the
return path?

There is an earthing system TN-C (Where T = "Terre" aka Earth, N =
Neutral, C = Combined), that does work as you describe - no separate
earth, and neutral used as earth directly. However I don't think I have
ever seen an installation like that in the UK, it is very uncommon.

For more detail, see:

https://wiki.diyfaq.org.uk/index.php/Earthing_Types#Earthing_Types

You could switch off the isolator so all systems are dead and measure the resistance between the black and earth with a bonding meter.

You would need to disconnect the main EQ bonding to get a reliable
reading. Otherwise you could find yourself measuring the loop impedance
through someone else's TN-C-S earth indirectly.

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk | \=================================================================/

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Thu, 20 Mar 2025 17:30:43 +0000, John Rumm wrote:

On 20/03/2025 16:31, jon wrote:

On Thu, 20 Mar 2025 11:50:12 +0000, John Rumm wrote:

On 19/03/2025 21:36, Scott wrote:

Why do we need separate neutral and earth wires

Because they serve two completely different purposes. Neutral is a
current carrying wire in normal use. Earth should not be current
carrying, and is there as a path for current to pass under fault
conditions. Neutral can be switched, earth should be a permanent
connection. Neutral is classed as a "live" wire, earth is not etc.

when the neutral is earthed a the two are joined together at the
point of entry anyway?

That depends on the earthing system in use; with TN-C-S (PME) then yes
they are combined at the main cutout where the service enters the
building.

With TN-S, they are combined at a substation, not at the building.

With TT, there is no earth provided at all by the suppler, you will
need your own arrangement, and it is not necessarily connected to
neutral at all.

Why not have two terminals - live and earth - and use the earth as
the return path?

There is an earthing system TN-C (Where T = "Terre" aka Earth, N =
Neutral, C = Combined), that does work as you describe - no separate
earth, and neutral used as earth directly. However I don't think I
have ever seen an installation like that in the UK, it is very
uncommon.

For more detail, see:

https://wiki.diyfaq.org.uk/index.php/Earthing_Types#Earthing_Types

You could switch off the isolator so all systems are dead and measure
the resistance between the black and earth with a bonding meter.

You would need to disconnect the main EQ bonding to get a reliable
reading. Otherwise you could find yourself measuring the loop impedance through someone else's TN-C-S earth indirectly.

One would need to measure it first to determine if resistance is in the
correct range.

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