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#37153 - 04/22/04 02:17 PM Ground Detection Lights.
Sandro Offline
Member

Registered: 12/30/01
Posts: 449
Loc: Stoney Creek, ON, Canada
Got a call from the furniture store today. He said the hydro inspector was by and asked that he get ground detection lights installed for his 100A 600V service. Very rarely do I get asked to install this. I am aware that Delta 3ph systems require this and many of this type of system is still used in the older part of the city. Why do I need these lights on the Delta systems and never on the Wye? Any websites or insight on ground detection lights and how they work would be appreciated.

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#37154 - 04/22/04 02:34 PM Re: Ground Detection Lights.
Anonymous
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#37155 - 04/22/04 02:39 PM Re: Ground Detection Lights.
CDN_ELECTRICIAN Offline
Member

Registered: 01/22/03
Posts: 75
Loc: Concord,Ontario,Canada
Basically it's to indicate that there is a ground fault on one phase of the Delta System.
This is so that if somebody is aware of would could potentially happen if more than one phase went to ground there is a great potential to damage to equipment and somebody could get hurt.

Wye systems already have a potential to ground there for if there is a fault the overcurrent device (breakers or fuses) would trip.

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#37156 - 04/22/04 02:54 PM Re: Ground Detection Lights.
Anonymous
Unregistered


keep in mind, As I see it if you have a center tapped grounded delta with a high leg the lights would be kinda worthless.
Me thinks this only has any value on a three wire ungrounded delta which to me is scarry as hell in a retail situation.(As in code requirements to bring neuts to panel boards and so on.) I have only seen this in an industrial application for motor loads only. Please, someone let me know if I am wrong here.

[This message has been edited by kentvw (edited 04-22-2004).]

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#37157 - 04/22/04 03:20 PM Re: Ground Detection Lights.
Sandro Offline
Member

Registered: 12/30/01
Posts: 449
Loc: Stoney Creek, ON, Canada
Thanks for all replies.

Kent....you may be correct. The system in question here runs only the motor loads in the store (furnace load and separate AC unit), the store also has a separate 120/208V service for power and lighting.

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#37158 - 04/22/04 03:34 PM Re: Ground Detection Lights.
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
There are varying degrees of sophistication for ground detection on LV ungrounded systems. Note that there can be ungrounded-delta as well as ungrounded-wye systems. It may be that the retail store is in an area with an older low-voltage network {converted industrial property?}

With this configuration, there is no solidly-grounded neutral conductor—hence no “phase-to-(nonexistent)-neutral” loads can be served. It is important to realize that one ground fault on such a system will theoretically run forever, but a second fault will cause multiple overcurrent-device operations, shutting down undesired circuits with likely safety implications. With this, it is crucial that the first fault be located and cleared or it can get messy and time-consuming to resolve.

A detailed paper on ungrounded-LV [and high-resistance-grounded] distribution systems is www.neiengineering.com/papers/paper1JN.pdf

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#37159 - 04/23/04 04:54 AM Re: Ground Detection Lights.
CDN_ELECTRICIAN Offline
Member

Registered: 01/22/03
Posts: 75
Loc: Concord,Ontario,Canada
Kent

The area from which (province of Ontario, Canada) used to supply (PUC's)[actually in some area's still do] based on a Delta system to all services that were based on 575 Volt services.
These usually were buildings of Industrial and larger commercial.

In my younger days, we had to install Delta/Wye auto transformers to drop down to the 120/240 or 120/208 voltages for the general loads.

Most of the PUC's today are converting their supply system to Wye.

I'm not a 100% sure but I believe that the reason is: If a building (on Delta)has a fault it could cause problems back up the supply line and affect other customers?

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#37160 - 04/23/04 06:18 AM Re: Ground Detection Lights.
Anonymous
Unregistered


Thanks CDN_Electrician
We have delta systems here in the states as well and there are many 480v systems with a center tapped neutral and a high leg on B phase. I have only run into an ungrounded delta once. The system fed a motor control center in a meat packing plant. So I understand why you would want to know if there was a ground fault on any given phase, since, as stated the system could run forever with one leg grounded. in trying to answer Sandro's question I do not understand the purpose of having an ungrounded delta system feeding a building. Also, as I see it if Sandro's customer does have a grounded delta system the light system would be of no value. ( Must admit I have never given this any thought until Sandro posted on this topic.) Can anyone provide an education on this?

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#37161 - 04/23/04 12:40 PM Re: Ground Detection Lights.
Tony Moscioni Offline
Moderator

Registered: 05/15/01
Posts: 144
Loc: CANADA
Rule 10-106 Alternating-Current Systems

(1) Except as otherwise provided for in this Code, alternating-current systems shall be grounded if:

(a) By so doing, their maximum voltage-to-ground does not exceed 150 V; or

(b) The system incorporates a neutral conductor.

(2) Wiring systems supplied by an ungrounded supply shall be equipped with a suitable ground detection device to indicate the presence of a ground fault.

Rationale for Rule 10-106.

Many components of ac systems are suitable only for voltages up to 150 V, and we need assurance that such systems will not be stressed beyond that point. When a system having no neutral and operating at a voltage above 150 V (eg, a 220 V delta 3-wire system) experiences a ground fault, no current flows to operate the overcurrent protection and the circuit can continue to function. However, should a subsequent fault to ground occur on a different phase, current will now flow between the two grounded fault points. There can be considerable damage at both fault locations and, on occasion, fire or other damage may occur along the random path that the fault current has followed.

Intent for Rule 10-106

In Subrule (1), whenever the voltage on an ac circuit can be limited to not more than 150 volts-to-ground or wherever a neutral exists, we connect the system to ground to provide that voltage limitation, thereby protecting the insulation and the devices connected to the circuit. This also provides a fault current path, to allow the operation of the overcurrent devices.

In Subrule (2), we recognize that some industries use delta systems which operate at voltages greater than 150 V between phases, allowing the plant to continue operating without a shutdown, even when there is a ground fault. Ground detection is essential for such systems, to inform maintenance personnel that a ground fault has occurred. Normally, this fault will be repaired during a scheduled maintenance shutdown. If the fault is not found and corrected before a second ground fault occurs, the plant will experience an unscheduled shutdown, and the damage will usually be considerably more extensive than it would have been had it been a grounded system. A note in Appendix B intends that the ground detection device be labeled as to its purpose and be visible to the people responsible for the system.


Tony Moscioni
Electrical Inspector
Electrical Safety Authority

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#37162 - 04/23/04 03:54 PM Re: Ground Detection Lights.
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
Practically, there is a problem where two or more customers/meters/buildings are fed from an ungrounded-secondary transfomer bank {delta, wye or 1ø.} If for instance, one place has ground-detector lights and a fault [insulation failure] develops anywhere in the system, the lights will show it. In the simplest sense, for multiple locations, it can get frustrating tracing the problem. Now, if that same 600V {or 480V} system is solidly-grounded wye, then a fault will typically operate an overcurrent device, and isolate itself.

[Warning: Rambling ”war story” follows.] I used to work in a plant that was 95% “hosedown” {very wet} having 14 [750-2500kVA] secondary-unit substations, all with [12kV primaries and] 480Y secondaries. Thirteen of those unit subs were operated ungrounded {XO bushings ‘flying in the breeze’} and one solidly grounded, so it was the only true 480Y/277V system at the plant. The only reason it was grounded was that its single load was an electrode boiler. The grounding was enforced by the boiler insurer—Factory Mutual in this case.

The other 13 had “ground lights”, which were nothing but a gasketed hinged-cover can with three external 6O-watt lamps in vaportight fixtures, and three internal 480-120V 100VA control-power transformers. When a fault showed up in any of the 13 systems, supervisors were trained like Pavlov’s dogs to run around furiously shutting down various 480V gear until local ground lights returned to their normal equally-dim state. {On a solid phase-to-ground fault, one of the three ground lamps extinguish, and the other two glow at full brightness.} The funniest incident was finding one of the ground-light sets flickering madly, only to later locate a loose 100-amp 480V pin-and-sleeve extension-cord end spitting steam from being flooded by hosedown.

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