Indicator lamps 1

[kitha]

I have seen indicator lights installed on distribution panels between the phases and neutral in most of panelboards manufactured to Japanese standards and some Asian countries. What happens to an indicator light installed between a phase and the neutral in case of an earth fault of that particular phase?

 

[DanDel]

If the neutral is grounded and there is a fault to ground, the phase-to-ground voltage would become zero(or close to it). This would cause the phase-to-neutral lamp to go out. This would also cause a large amount of fault current and(hopefully) a trip of a protective device.
Are you sure the lights were used for a grounded system? Usually this type of indicating system is used for an ungrounded system to show when one phase goes to ground. There will be no fault current on this system(for one phase to ground), and the ground connection can be traced and repaired without a power interruption.

 

[kitha]

The system is a grounded system 400V3ph,230V1Ph. What do you mean by the lamp " to go out"? You mean it burns? I know, there's a logic and sense if this is done for ungorunded systems.

 

[DanDel]

What I mean by 'go out' is that it changes from its normally illuminated state to an un-illuminated(or nearly un-illuminated) state, because there is no voltage across the filament due to the phase-to-ground short circuit.

Normally, in a grounded system, there is a certain voltage between phase and neutral. If you connect an indicator lamp between phase and neutral, it will illuminate, correct? Typically, in a grounded system, the neutral is grounded.

What do you mean by 'a grounded system 400V3ph,230V1Ph'?

Is it wye(star) connected, 3-phase, 4-wire, 400V phase-to-phase, 230V phase-to-neutral, neutral grounded?

Or is it a 3-phase, 3-wire corner-grounded delta?

Or 3-phase, 4-wire center tapped delta?

 

[kitha]

yes it is Y connected neutral grounded system. Really will the lamp will go out or burn as the voltage reduces and if the protective device does not trip, still the system can supply the required watts to the bulb, that means, when the voltage reduces the current increases and the bulb burns i guess. Please comment.

 

[DanDel]

No, that is not correct. This is basic Ohm's Law; please do some basic research.

 

[peebee]

Any chance the system was originally ungrounded, then later converted to grounded?

Are you sure you are really looking at a neutral conductor, rather than the center point of the wye-connected lamps, which is then connected to ground?

DanDel is dead on, the 3-lamp ground fault indicator would make no sense on a grounded system. You get a ground fault on a grounded system, and you trip a breaker, then all the lights go out, not just the little pilot light, all you building lights.

On an ungrounded system, the light goes out due to undervoltage, just like if you'd turned a switch off.

The lights don't burn out except every few years or so due to normal wear and tear, same as any incandescent light bulb.

Stop arguing with Danny Boy, he knows what he's talking about.

 

[DanDel]

Danny Boy?

 

[potty]

I think the question we should ask is the purpose of those indication light. Those lamp are definitely NOT for ground fault indication.

The lamps are usually used to indicate if there is incoming supply from the source. Sometimes they have two sets of indication lamp. One for the incoming source and another set of lamps for outgoing (even though they can see from the breaker close/open status). It is also to indicate if any of the three phases are not energised.

In the case of an earth fault, the lamp just doesn't light up. Most of the time the lamps are still intact (in working condition) after the fault has been rectified or cleared.

I hope this helps.

 

[peebee]

Maybe you're right, potty. Usually round here we just use the lights on the ceiling to tell if the power's working. But maybe you're on to something.

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O Danny Boy, St. Patrick's Day is coming soon. . . .

 

[jbartos]

Suggestion: Normally, the indicating lights signal that the circuit is energized. However, "indicator lights" could also be annunciating lights that work with an inverted logic. If the situation is normal, there is no light and if there is a failure the annunciator light is lit indicating nature of the failure. The way the original posting is posed, the annunciating feature cannot be ruled out. Each concept has its advantages and disadvantages. E.g. in a normal indication, if a lamp is burned, it is not immediately known that there is a failure. The light may need a push to test feature. The annunciator having a light off most of the time, has a weakness in the logic inversion rather than in the burned lamp.