ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Recent Posts
Al Hildenbrand - Minneapolis - obituary
by bcpappas - 02/02/23 08:01 PM
by renosteinke - 01/27/23 09:52 PM
Does NEC 551.71 (F) apply to dwellings?
by BigB - 01/20/23 10:46 AM
Power submeter connections
by HotLine1 - 01/19/23 09:09 AM
New in the Gallery:
Burger King crown sillyness
Burger King crown sillyness
by wa2ise, December 11
240/208 to a house
240/208 to a house
by wa2ise, October 9
Who's Online Now
1 members (mbhydro), 21 guests, and 11 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Joined: Aug 2004
Posts: 15
I know that in an ungrounded system, the neutral conductor is not connected to the equpment grounding conductor. But, does the neutral conductor of an ungrounded system need to be connected to earth (to an electrode)? I am looking for the answer in the code book, but any answer'd be appreciated.

Joined: Mar 2003
Posts: 849
No Neutral on a ungrounded system

Joined: Aug 2004
Posts: 15
Can an ungrounded system in a health care facility serve 120v load therefore requiring to have a neutral conductor?

Joined: Oct 2000
Posts: 2,722
Broom Pusher and
On an Ungrounded system, there is no Intentional Connection of the system to Earth Ground (or to enclosures Intentionally Bonded to Earth Ground), through either a Solid Connection or an Impedance / Resistance.

This means there is no physical Bonding of the Power System
(such as the Secondary Side of the Transformer delivering AC Power from the Utility Company)
to the Earth Ground / Metallic Raceways and/or Enclosures.

The Metallic Raceways and Enclosures WILL be Bonded together, and connected to a Locally Established Grounding Electrode System, but the Power System will not be connected to these items - hence the System is "Ungrounded".

The Power System may, or may not, incorporate the use of a "Neutral Conductor" - depending on the configuration; but still no Conductor is Intentionally Grounded, and the System has no "Grounded Conductor".

The most common configuration used for Ungrounded Systems (at least in my area - So. Calif.) is the Ungrounded 3 Wire Delta. Voltages of 480 VAC and 600 VAC, but may be some 240 VAC systems out there too.

Although Grounding a System does not achieve any merit in normal performance, it does effect the stresses imposed on Insulation and such.
An Ungrounded system may have an extremely high Potential to Ground at different points along the system's connected Equipment - at times exceeding the nominal rated Voltage by maybe 3 times as high!
This is due to Capacitive Coupling effect between the Power System's Conductors and the Grounded surfaces / Equipment / etc.
A Grounded System (solidly or through an Impedance / Resistance), will stabilize the Potential to Ground, thus reduce the Insulation Stresses.

Much more to cover on this stuff, and other Members can explain much better than I, so feel free to reply for additional info.
Also check the Technical Reference Section for Schematics, additional information.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Aug 2004
Posts: 15
thanks scott for clearing that up. One questoin I had it then ungrounded system have two disadvantages?
1. cannot obtain steady voltage because there is no voltage reference.
2. cannot dissiplate high surges inflicted on to the electrical system (say a lightning surge)

Joined: Apr 2002
Posts: 2,527
Carefully differentiate between bonding, grounding and grounding electrode.

Please, please, please get a new, old, tattered or borrowed edition of Soares' Book on Grounding and Read It Cover To Cover—Over And Over until you begin to follow it. Plan to take thirty years or so thinking it over.    ;-)

Bonding (As expertly explained by resqcapt19) is minimization of potential difference through limiting touch·and·step voltage.

Nowadays, utilities typically provide three-phase service only as soldily grounded four-wire-wye, but continue to maintain existing three-wire ungrounded systems.

Below 1kV, sole ‘earth return’ [between made electrodes] can not be relied on for effectively low impedance for rapid clearing of overcurrent devices.

Grounding-electrode conductors, though, are needed for bulletproof continuity to the grounding electrode—as a critically important pair being a ‘dissipation sink’ for capacitively, inductively and resistively coupled transient overvoltage/overcurrent.

[This message has been edited by Bjarney (edited 03-23-2005).]

Link Copied to Clipboard

Tools for Electricians
Tools for Electricians

* * * * * * *
2023 National Electrical Code (NEC)
2023 NEC Now Available!
* * * * * * *

2020 Master Electrician Exam Preparation Combos
2020 NEC Electrician
Exam Prep Combos:
Master / Journeyman


Member Spotlight
Los Angeles
Posts: 349
Joined: April 2004
Top Posters(30 Days)
BigB 4
triple 3
Popular Topics(Views)
303,012 Are you busy
232,123 Re: Forum
216,775 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.5