ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat Box
Recent Posts
New tool
by gfretwell - 10/22/20 12:08 PM
Where is Everyone?
by Bill Addiss - 10/17/20 07:04 PM
Beyond Belief
by gfretwell - 09/27/20 12:03 AM
New in the Gallery:
Facebook follies, bad wiring
FPE in Germany pt.2
Who's Online Now
0 registered members (), 16 guests, and 16 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Ground Detectors #152046 10/30/03 01:05 PM
Joined: Oct 2000
Posts: 3,631
Admin Offline OP
[Linked Image]

[Linked Image]

[Linked Image]
This is an old ground detector. The 230 volt bulbs are paired in series, 2 per phase, for used on the 480 volt system.


Tools for Electricians:
Re: Ground Detectors #152047 10/30/03 10:06 PM
Joined: Aug 2002
Posts: 1,081
ThinkGood Offline
Please explain what this is for--I don't quite follow. If a circuit came in contact with a ground, would it not trip the OCPD?

Re: Ground Detectors #152048 11/01/03 08:55 AM
Joined: Aug 2001
Posts: 7,520
pauluk Offline
It would be used on an UNGROUNDED system, in this case 480V delta.

In such a system a single ground on one phase would not trip out an OCPD (but a second, simultaneous ground on another phase might).

As the first unintentional ground might otherwise go unnoticed, the ground detector is fitted to provide an indication of a ground fault.

Re: Ground Detectors #152049 11/01/03 05:19 PM
Joined: Apr 2002
Posts: 2,527
Bjarney Offline
Ungrounded-delta {or even ungrounded-wye} plant distribution has a successful history for process-interruption minimization, but if you don’t act quickly after first fault, it gets messy—potentially with two or more overcurrent devices operating simultaneously. If you want to research this further, there is a {rare} online paper about it — for applying such a system one has to be well aware of the first-fault limitation and the need for action when it occurs. It is very problematic if one transformer set feeds two different areas of a plant, or worse yet, two different facilities under different ownership. The tradeoffs have to be carefully understood by all when adopting this system-grounding method.

There is understandable reluctance for many utilities to provide this type of service for their customers because its limitations have to be well understood by all to be effective. It is more likely found in cases where a facility buys power from the utility at medium voltage, or “primary” service, and the plant has complete control over all distribution and loads connected to the {typically 480V or 600V ungrounded-∆} system. If the utility owns the [480-600 or up to 4160V] secondary windings—essentially the grounding “source”, then it may be a poor choice from a reliability and service-continuity standpoint. There will be regional practices and local customs, but in many cases utilities flat out refuse to serve anything except for [480Y/277V or 600Y/347V] 4-wire grounded-wye service to limit repeated ‘rat-race’ complaints and finger-pointing from their customers.

If in the case where [phase-to-neutral loads are served, like 277- or 347-volt lighting loads] the distribution system must be solidly grounded. An absolutely insane stopgap mutation in system grounding is a corner-grounded-delta arrangement, except possibly for an isolated single-transformer/single-motor configuration, for all too often that seems to cause its own set of headaches.

Re: Ground Detectors #152050 11/01/03 05:47 PM
Joined: Apr 2002
Posts: 2,527
Bjarney Offline
electure — The book page with the nippled lamps and horseshoe filaments really points out the antiquity of the system, and matches well with the apparent age of the switchboard. [Never mind the broken lamp with its handy 480V exposed-live parts.]

[Linked Image from]

There is a lot of this type of stuff still in service out there—however ancient, misunderstood and neglected. It’s not hard to imagine a painter tipping a ladder up to the switchboard and planting a kneecap into the broken lamp.

Re: Ground Detectors #152051 11/01/03 09:02 PM
Joined: Aug 2002
Posts: 1,081
ThinkGood Offline
Thanks for the great explanations, gentlemen!

kneecap into the broken lamp

Re: Ground Detectors #152052 05/07/04 10:35 PM
Joined: Jan 2003
Posts: 18
Inspector Grump Offline
Us old guys worked with that fine equipment daily, we had digital wooden box meters!



2020 National Electrical Code
2020 National Electrical
Code (NEC)

* * * * * * *

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


Member Spotlight
Posts: 27
Joined: December 2004
Show All Member Profiles 
Top Posters(30 Days)
BigB 3
Popular Topics(Views)
270,742 Are you busy
204,967 Re: Forum
193,085 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.3