Dear Friends, We have an installation in Kuwait where we are planning to hold an exhibhition.Now the event management company has stated that he will be using Special Efects Lighting (MARTIN MOVING HEADS) comprising of PAR and METAL HALIDE lamps controlled by computer ,again of MARTIN make .
Further here in Kuwait the local wiring regulations state that one has to comply the following with regards to earth fault protection(GFCI):
1.For lighting circuit we have to go for 300 milliamps earth leakage relay(GFCI).
2.For power circuit we have to go for 30 milliamps earth leakage relay.
4.For motor loads adjustable type earth leakage relay maxm of 500 milliamps.(generally 1 milliamps per KW)
Kindly let us know the setting of earth leakage relay(GFCI) we should go for the ELECTRICAL FEEDER feeding power to the MOVING HEAD of Martin make. Further I had a very heated discussion with the event management company's Electrical Engineer who vehemently stated that no GFCI be connected to the feeder supplying to his MOVING HEAD (Special Effect Lighting)panel because the MOVING HEADS have an inherent unbalanced neutral current problem which will be picked up by the GFCI and give trip spoiling the event.He says in MOVING HEADS thro computer control large block loads of light(PAR and Metal Halide) is turned ON and OFF rapidly. But I am not convinced.
The Electric scheme of the installation is as follows.
1.CUT OUT - 300 amps,415 volts three phase capacity which takes the supply company power and is additionally protected by a three phase MCCB.
2.MSB(Main Switch Board) - 6 ways with three phase and single phase MCCB.MSB feeds power to motor loads and FDBs.
3.FDBs(Final Distribution Board) - 6/8 ways feeding final light and small power.They are basically double busbar type with seperate section for light and small power each protected by dedicated earth leakage( 30 milliamps for small power and 300 milliamps for light circuit).
That is too long a QUERY, in short the event management co. engineer has requested to forgo the GFCI clause.Please advice if I should take his request.
I've had experience with theater lighting in the past, but not PAR/Metal Halide types controlled in this way. It sounds as though the event's enginner is saying that the set-up in use has a considerable current flowing to ground due to the switching.
So your local code in Kuwait specifies 300mA protection for lighting and 30mA for "power." Which level of GFI protection would be needed here must depend upon the exact way the requirements are interpreted. Does the 300mA provision apply only to circuits feeding fixed lighting outlets? In other words, would your code allow 300mA on the feeder because it's for lighting, or would it be classed as a "power" outlet (into which you just happen to plug a lighting console) and thus need 30mA protection?
Re: EVENT lighting GFCI doubt??#137960 08/04/0305:54 AM08/04/0305:54 AM
Thank god!! I got a moderator with Theater lighting.The event lighting engineer says due to rapid switching there is always current in the neutral.This current he says will cause nuisance tripping - now should I take his word and forgo the accepted practice of providing GFCI for this installation. Further your clarification on whether to go for 30 or 300 milliamps is a but secondary to the main problem of providing a GFCI or not,hope you got it.Please reply.
Re: EVENT lighting GFCI doubt??#137961 08/04/0306:34 AM08/04/0306:34 AM
Electrical Engineer who vehemently stated that no GFCI be connected to the feeder supplying to his MOVING HEAD (Special Effect Lighting)panel because the MOVING HEADS have an inherent unbalanced neutral current problem which will be picked up by the GFCI and give trip spoiling the event.He says in MOVING HEADS thro computer control large block loads of light(PAR and Metal Halide) is turned ON and OFF rapidly.
In effect, you are saying you have a high harmonics content. The same phenomenon exist in modern offices since computers and other electronics have switching mode power supplies. Yes, the average current in the neutral can be greater than that of any one phase. But, I'm afraid I don't know why this would trip the RCD. (It could be the RCD is too slow to see the instantaneous current)
Even if it would, there are solutions. The simplest that I can think of would be to convert the lights to single phase. Other solutions include filtering the power to reduce the harmonics content.
[This message has been edited by C-H (edited 08-04-2003).]
Re: EVENT lighting GFCI doubt??#137962 08/04/0306:48 AM08/04/0306:48 AM
Here is a link to a document from Schneider about ground fault protection. On page 21 there is some information about harmonics. What is interesting is that it doesn't mention any potential problems with the ground fault protection from this.
This can’t be the first time they’ve used this equipment. You would think that the lighting manufacturer and stage-production crew has to have dealt with the matter previously. It sounds like it is an electromagnetic-compatibility issue that should have been long since addressed.
What is being proposed as providing equivalent safety in place of protective devices normally provided for power circuits? That the installation is temporary should not be an acceptable excuse for defeating recognized, minimal safety devices.
Do your rules in Kuwait specify GFI protection for feeders, or only for final circuits? If feeders are not required to be GFI protected, and you run power to a panel for the lighting equipment, then would your wiring be considered a sub-feeder rather than a final branch circuit?
Just an idea: If the earth fault protection is needed because this is a TT system, you could use an voltage operated earth fault breaker. You could also use an earth fault breaker with separate current transformer. Instead of putting the current transformer around the phase and neutral, put one around the earth conductor. When there is a current in the earth conductor the earth fault breaker will trip.
Re: EVENT lighting GFCI doubt??#137966 08/06/0304:19 AM08/06/0304:19 AM
Hello Pauluk, I will answer to your query regarding regulation on GFI protection to Feeders Here we can either provide GFI protection at feeder end or at the final end circuit distribution board.It is a matter of convenience .Normally for small installations like the one in question we have Over current and short circuit protection of high breaking capacity at main feeder.
Over current and short circuit protection of lower breaking capacity + GFI protection at Distribution board end.
Whereas for larger installations we do have at main feeder end earth fault relay operated CIRCUIT BREAKER (ACB or others) with thermal magnetic trip.
Re: EVENT lighting GFCI doubt??#137967 08/06/0306:17 AM08/06/0306:17 AM
OK, I was just looking at it from the point of view of whether you would provide a feeder (not GFI protected) to a large 3-phase outlet (e.g. IEC309 100A or similar) to which the lighting people would connect their distribution panel.
Have you checked with the lighting engineer as to whether it is harmonic neutral current or actually leakage to ground which is the problem?