Grounding systems

Thread Starter

hrabarian

Joined Aug 28, 2016
3
Hello—I’m a long time lurker and first time poster!

My question is about detailing the differences between an ungrounded system, a grounded system, and an insulated neutral system.

Here’s my understanding, and feel free to jump in where you deem appropriate:


An ungrounded system is found in many systems and was code until sometime in the 1950s. It is simple two wire. If an ungrounded system were to fail then it would create hot appliances that sent voltage to whatever they touched. Effectively the literal ground is the return path.


A grounded system is code for houses in the USA post 1950s. This system has several variants, but in general it has 3 wires. Hot, Neutral, and Ground. The ground is not considered a current conductor except for emergent situations. An emergent situation would be where the insulation breaks down, and the machine’s frame becomes hot.

The during an emergent situation the ground will create a low resistance (and higher amperage) path for voltage to ground and away from the environment. This improves safety by preventing fires, and electrocution. However because the grounding wire and the neutral wire is bonded behind the breaker, the system will shut down the piece of equipment.

A neutrally insulated system is one where the grounding is not bonded to the neutral behind the breaker. This system provides less safety than a typical grounded system, but it allows for the machinery to continue to operate. This system is favored on ships, and other systems where continued operation is a greater concern than human life. The major issue here is that if two phases go to ground then we get a high current short and breakers will open.
 

MaxHeadRoom

Joined Jul 18, 2013
19,066
An ungrounded system has no reference to earth ground, so this would not necessarily provide a return path.
In No3, if the grounding is not bonded to the neutral, then it would essentially be the same as No 1 Ungrounded system?
Obtain a copy of Soares Book on Grounding by Eustace Soares.
Max..
 

Thread Starter

hrabarian

Joined Aug 28, 2016
3
An ungrounded system has no reference to earth ground, so this would not necessarily provide a return path.
In No3, if the grounding is not bonded to the neutral, then it would essentially be the same as No 1 Ungrounded system?
Obtain a copy of Soares Book on Grounding by Eustace Soares.
Max..


The difference between an ungrounded system and a neutrally insulated system being that a neutrally insulated system still has a wired low impedance path to ground.

An ungrounded system has no wired low impedance connection to ground. Think about the 2 wire systems from pre 1960s.
 

MaxHeadRoom

Joined Jul 18, 2013
19,066
The difference between an ungrounded system and a neutrally insulated system being that a neutrally insulated system still has a wired low impedance path to ground.

An ungrounded system has no wired low impedance connection to ground. Think about the 2 wire systems from pre 1960s.
??
I understand No2, but where is the 'neutrally insulated system' referenced to earth ground?
If it has a low impedance to ground then how is it defined as 'neutrally insulated'?
Max.
 

Thread Starter

hrabarian

Joined Aug 28, 2016
3
??
I understand No2, but where is the 'neutrally insulated system' referenced to earth ground?
If it has a low impedance to ground then how is it defined as 'neutrally insulated'?
Max.

Neutrally insulated has a neutral from the transformer.

Low impedance path to ground is literally just that. A low impedance path to ground (or water in the case of a ship).
 

MaxHeadRoom

Joined Jul 18, 2013
19,066
This, to me anyway is starting to make absolutely no sense!
If
a neutrally insulated system still has a wired low impedance path to ground.
how can it be neutrally insulated?
You maybe need to explain in a diagrammatic form!
Max.
 

yellowfish

Joined Feb 9, 2009
21
1# OK
#2 OK
#3 is illegal and non existent unless you physically remove the ground connection in the electrical panel. The utility provides three wires, hot+hot+neutral. You MUST provide ground connection to the electrical panel, otherwise it won't pass inspection.
 
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