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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Jean-Pierre Coetzee on September 24, 2016, 04:45:38 AM
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Hello all,
In one of our halls the fluorescent lights cause noticeable bars on our projectors that are run on VGA cable, the bars go away when the lights are turned off. I haven't climbed into the roof to see if the VGA lines are running anywhere near power but this has only began happening about 2 weeks ago and we had no issues before that and wanted to know if anyone had any other idea about what can be causing the issue.
Thanking you
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Has anything else changed? New equipment in other places?
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In one of our halls the fluorescent lights cause noticeable bars on our projectors that are run on VGA cable, the bars go away when the lights are turned off. I haven't climbed into the roof to see if the VGA lines are running anywhere near power but this has only began happening about 2 weeks ago and we had no issues before that and wanted to know if anyone had any other idea about what can be causing the issue.
I suspect a failing ballast in a light fixture. Replacement is pretty easy, but if you're replacing a magnetic ballast with an electronic one, the wiring may be different. The wiring diagram is on the label of every replacement ballast I've ever seen.
If your light fixtures use the 1+1/2" (T-12) tubes, you should replace them. T-12 are very inefficient these days, and they tend to have a more annoying flicker than T-8 (1") or T-5 (5/8") lamps. The sockets are the same for T-12 and T-8 tubes, so you can keep the fixture and replace the ballast and tubes.
If your fixtures have magnetic ballasts (magnetic ballasts weigh several pounds each whereas electronic ballasts are less than a pound each), replace them. They are also inefficient by today's standards.
Fluorescent lamps are on the verge of being a dying technology in favor of LED lighting. You've got a few options for retrofitting to LED:
- Replace all of the fixtures with LED fixtures
- Replace just the lamps with LED retrofit tubes (the kind designed to work with the existing ballast)
- Remove the ballasts and lamps and insert LED retrofit tubes (the kind designed to work without the existing ballast)
I don't really like the second option, as it's slightly less efficient due to energy consumed by the ballast. If the ballast is failing, you wouldn't be able to use such a retrofit anyway.
There is a caveat: some LED fixtures/retrofits may introduce radio frequency or electromagnetic interference. I don't have any experience with that, so maybe some of the other folks here can shed some light on that issue. (Pardon the pun.)
Fluorescent lamps (the tubes) are considered hazardous waste because they contain mercury. Contact your waste collection company for disposal options in your area.
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In one of our halls the fluorescent lights cause noticeable bars on our projectors that are run on VGA cable, the bars go away when the lights are turned off.
Sometimes it's not the fluorescent lights themselves causing the hum. It can just be the amperage load on the subpanel causing the ground to move around. I've seen a few installs where the AC power for the projector was tapped onto the lighting circuit subpanel, just out of convenience. If that subpanel also has a green Ground-Neutral bonding screw in place, then as the amperage loads change, the voltage on the EGC ground will also change. If your projector has a shielded connection back to the computer at your mixing console, then all sorts of ground loop hum bars can be created. I know this because I saw it myself once. Crazy to figure out at first, but pretty simple to find once you know what to look for. I now run a lot of Baluns for projectors over Cat5 and hum bars are a non issue.
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Sometimes it's not the fluorescent lights themselves causing the hum. I can just be the amperage load on the subpanel causing the ground to move around. I've seen a few installs where the AC power for the projector was tapped onto the lighting circuit subpanel, just out of convenience. If that subpanel also has a green Ground-Neutral bonding screw in place, then as the amperage loads change, the voltage on the EGC ground will also change. If your projector has a shielded connection back to the computer at your mixing console, then all sorts of ground loop hum bars can be created. I know this because I saw it myself one. Crazy to figure out at first, but pretty simple to find once you know what to look for. I now run a lot of Baluns for projectors over Cat5 and hum bars are a non issue.
Sorry for the late reply was a long weekend. In South Africa neutral and ground is separate all the way to the service inlet so there is no jumper between the two anywhere in the building, or at least shouldn't be...
Nothing has changed recently, I also noticed that it was causing a buzz on the monitors which went away when the florescent lights are turned off and those two circuits aren't even on the same phase so the only possible link between them is the grounding system, seems like I am going to have to get an electrician in to check every single fluorescent light as this might be related to a sporadic GFIC trip we've been getting at the distribution panel. Added to the confusion the last time I spoke to the electrician he said that the fluorescent lights are not connected to ground at all since they are double insulated and therefore do not need to be grounded according to the code.
So further faultfinding:
1. Monitor amp also buzzes and goes away when fluorescent lights are turned off and are not even on the same phase
2. Nothing has changed recently
3. Lights are not grounded so issue must be on the neutral?
4. There are sporadic GFIC trips that seems to have no cause and have no repeatable pattern
Other notes:
Live 1, Live 2, Live 3, Neutral, Ground are all separate conductors through to the inlet from the electrical company.
I am not sure if the metal frame of the fluorescent lamp is bonded to ground anywhere since this only came into code in South Africa after the lights were installed.
The electrician replaced the GFIC about a week ago to try and sort out the sporadic trips and we though it was solved but evidently it was not, this also did not change anything regarding the hum issues.
I'm thinking along the same line as Jonathan in that a ballast might be failing but there are 40 fluorescent lights in the venue so which one will probably be a matter of time to find out since none of flashing or struggling to start up.
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I'm thinking along the same line as Jonathan in that a ballast might be failing but there are 40 fluorescent lights in the venue so which one will probably be a matter of time to find out since none of flashing or struggling to start up.
It will mean a little work for your electrician, but rather than disconnecting each ballast until you find the faulty one, you may be able to get into a junction box and disconnect half the lights. If the hum bars stay, it's on the lights that weren't disconnected. If they go away, it's on the lights that were.
By isolating half (20 of 40), then half again (10 of 20), then half again (5 of 10), then almost half (3 of 5), you may be able to identify the culprit (out of 40 lights) in 5 or 6 tries -- depending on how the lights are wired. I use this method for all sorts of troubleshooting.
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It will mean a little work for your electrician, but rather than disconnecting each ballast until you find the faulty one, you may be able to get into a junction box and disconnect half the lights. If the hum bars stay, it's on the lights that weren't disconnected. If they go away, it's on the lights that were.
By isolating half (20 of 40), then half again (10 of 20), then half again (5 of 10), then almost half (3 of 5), you may be able to identify the culprit (out of 40 lights) in 5 or 6 tries -- depending on how the lights are wired. I use this method for all sorts of troubleshooting.
Seems reasonable to me, another suggestion I got was to check the voltage between the live and neutral on each branch and one should be quite a bit above 0, your way seem to be a little less work.
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I realize changing the lights to LED is a bit drastic but just FYI I noticed our maintenance guy at church changing a whole suspended ceiling light fixture from florescent to LED so I asked why he didn't just disconnect the ballast and change the bulbs. He explained that the defuser on the old ones were cracked, and hard to change and the whole fixture was low quality and the new fixture cost $46 with "bulbs" The LEDs are mounted to the reflector and permanently wired in, no bulbs.
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Another consideration is modifying the fixture to put 120 VAC on the pins of the lamps. Personally, I have no problem with it-but I have heard that some AHJ take issue-and you have the whole "listing" question mark. Just make sure where you stand on that before you choose a course of action.
Just because they make it and sell it doesn't make it ok or a good idea. Big box stores still market non-weather resistant outlets for outdoors and non-code compliant outdoor covers.
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Another consideration is modifying the fixture to put 120 VAC on the pins of the lamps. Personally, I have no problem with it-but I have heard that some AHJ take issue-and you have the whole "listing" question mark. Just make sure where you stand on that before you choose a course of action.
Just because they make it and sell it doesn't make it ok or a good idea. Big box stores still market non-weather resistant outlets for outdoors and non-code compliant outdoor covers.
Good point. I did that at home, but In a public place like a church I guess the new fixture is a better way to go. It's listed, and BTW it has no pins, sockets, or lamps.
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Another consideration is modifying the fixture to put 120 VAC on the pins of the lamps. Personally, I have no problem with it-but I have heard that some AHJ take issue-and you have the whole "listing" question mark. Just make sure where you stand on that before you choose a course of action.
Just because they make it and sell it doesn't make it ok or a good idea. Big box stores still market non-weather resistant outlets for outdoors and non-code compliant outdoor covers.
The ballast output can be much higher than 120 VAC -- up to 600V to start the lamps. So the fact that you're putting 120 VAC on the wiring and sockets shouldn't be an issue.
This page (http://www.electrical101.com/fluorescent-ballasts.html) shows a typical T-8 ballast, the label of which lists an open circuit voltage of 580Vrms maximum.
Just because something makes sense and is safe doesn't mean the AHJ will understand it. And what an AHJ doesn't understand won't be approved. ::)
The OP is from South Africa, so American codes won't mean much to him. That's why it's important to understand how your local AHJ (Authority Having Jurisdiction -- also known as "the inspector") interprets your local codes. We can agree here that something is safe, but that doesn't mean that it complies with legal requirements.
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The OP is from South Africa, so American codes won't mean much to him. That's why it's important to understand how your local AHJ (Authority Having Jurisdiction -- also known as "the inspector") interprets your local codes. We can agree here that something is safe, but that doesn't mean that it complies with legal requirements.
I just did a corporate gig last weekend for a 3,000 employee picnic, and the only thing the company safety officer was worried about was making sure the generator fuel containers were at least 10 feet away from our small generators (a few 7KW, 3KW and 2KW to power to porta potties, duck race and such) and he supplied fire extinguishers that were placed at each genny. He never looked at nor cared about any of the actual AC power distro.
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The ballast output can be much higher than 120 VAC -- up to 600V to start the lamps. So the fact that you're putting 120 VAC on the wiring and sockets shouldn't be an issue.
This page (http://www.electrical101.com/fluorescent-ballasts.html) shows a typical T-8 ballast, the label of which lists an open circuit voltage of 580Vrms maximum.
I know you know better, so I am going to be picky. I have customers that answer the question "How much power do you need in this shop/outbuilding?" with "I need 220 volts." That is meaningless as to the amount of energy available. When you connect 120 VAC mains to the tombstones on a flourescent fixture with the existing wiring (22 or 24 AWG?) voltage is not the issue-available fault current is. You can dead short a ballast and you'll never see anywhere near 20 amps of current flow-dead short a 20 amp circuit to the tinfoil fixture with a tiny wire and you might have plenty of fireworks to start a fire before you ever get enough current to trip that breaker. I could be wrong-but I strongly suspect that that is the concern.
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I just did a corporate gig last weekend for a 3,000 employee picnic, and the only thing the company safety officer was worried about was making sure the generator fuel containers were at least 10 feet away from our small generators (a few 7KW, 3KW and 2KW to power to porta potties, duck race and such) and he supplied fire extinguishers that were placed at each genny. He never looked at nor cared about any of the actual AC power distro.
So using logic, he wanted a 10 ft long fuel line from the container to the generator and the generator could not have a built in fuel tank.
I know what he really meant was it was OK for the generator to have a built in fuel tank and be located next to a pickup truck full of fuel with a extra tank and pump mounted in the bed but extra fuel for the generator had to be 10 ft away. That makes sense.
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I know you know better, so I am going to be picky. I have customers that answer the question "How much power do you need in this shop/outbuilding?" with "I need 220 volts." That is meaningless as to the amount of energy available. When you connect 120 VAC mains to the tombstones on a flourescent fixture with the existing wiring (22 or 24 AWG?) voltage is not the issue-available fault current is. You can dead short a ballast and you'll never see anywhere near 20 amps of current flow-dead short a 20 amp circuit to the tinfoil fixture with a tiny wire and you might have plenty of fireworks to start a fire before you ever get enough current to trip that breaker. I could be wrong-but I strongly suspect that that is the concern.
Actually, I think it's 18 AWG. 22-24 AWG is like phone wire, and that's certainly not what's in a fluorescent fixture.
I hadn't really thought of fault current issues like that. But that table lamp next to your easy chair is wired with an 18 AWG cord plugged into a 20A circuit. Oh, yes, the incoming leads on the ballast are also 18 AWG.
I don't think they're really too concerned about fault current inside of the metal housing of a fluorescent light fixture. The likelihood of a short fault is very low (the wires are protected from damage), and if there is arcing, it's contained in the metal housing.
The biggest problem I see is that someone pulls out an LED retrofit tube from a fixture that's had the ballast bypassed and tries to put a fluorescent tube in. The worst that'll happen is it won't work.
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The biggest problem I see is that someone pulls out an LED retrofit tube from a fixture that's had the ballast bypassed and tries to put a fluorescent tube in. The worst that'll happen is it won't work.
The ones Installed at home have 120 AC to one end and neutral to the other, so your right, there would be no voltage on the heaters and not enough voltage to light a standard bulb.
They are also available with 120 volts to one end and nothing on the other. That would quickly burn out the heater but otherwise not work.
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Actually, I think it's 18 AWG. 22-24 AWG is like phone wire, and that's certainly not what's in a fluorescent fixture.
I hadn't really thought of fault current issues like that. But that table lamp next to your easy chair is wired with an 18 AWG cord plugged into a 20A circuit. Oh, yes, the incoming leads on the ballast are also 18 AWG.
I don't think they're really too concerned about fault current inside of the metal housing of a fluorescent light fixture. The likelihood of a short fault is very low (the wires are protected from damage), and if there is arcing, it's contained in the metal housing.
The biggest problem I see is that someone pulls out an LED retrofit tube from a fixture that's had the ballast bypassed and tries to put a fluorescent tube in. The worst that'll happen is it won't work.
It is 18ga,
Never seen smaller after working on thousands of them over the years.
Really old ones actually may have thicker wires.
And that 18ga is perfectly adequate to trip a 20A breaker -even in 277V ones
-witnessed this often when called to bail-out facility maintenance guys who can't seem to figure out a magnetic t-12 to electronic t-8 conversion (the wiring is always different -but always shown on the new ballast label)
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-witnessed this often when called to bail-out facility maintenance guys who can't seem to figure out a magnetic t-12 to electronic t-8 conversion (the wiring is always different -but always shown on the new ballast label)
Amazingly, many people are simply terrible at following a schematic. This is especially troublesome if they happen to be in the maintenance department. I'm teaching a basic audio electronics class to College juniors this semester, and even getting them to understand how to wire the most simple circuit imaginable is tricky. Yes, a battery, momentary contact switch and a light bulb. And they can get that wrong on a desktop electronic playground.
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Amazingly, many people are simply terrible at following a schematic. This is especially troublesome if they happen to be in the maintenance department. I'm teaching a basic audio electronics class to College juniors this semester, and even getting them to understand how to wire the most simple circuit imaginable is tricky. Yes, a battery, momentary contact switch and a light bulb. And they can get that wrong on a desktop electronic playground.
No wonder people have trouble figuring out 3-way switches. That's probably the most confusing electrical thing most people will ever come across.
Reference the drawing below: "It must be right. I flip the switch and the light comes on. I flip it again and it turns off. But why does the switch get hot when it's off? And why does the battery die?"
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No wonder people have trouble figuring out 3-way switches. That's probably the most confusing electrical thing most people will ever come across.
Reference the drawing below: "It must be right. I flip the switch and the light comes on. I flip it again and it turns off. But why does the switch get hot when it's off? And why does the battery die?"
You need a longer circuit 8) :o ::)
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Amazingly, many people are simply terrible at following a schematic. This is especially troublesome if they happen to be in the maintenance department. I'm teaching a basic audio electronics class to College juniors this semester, and even getting them to understand how to wire the most simple circuit imaginable is tricky. Yes, a battery, momentary contact switch and a light bulb. And they can get that wrong on a desktop electronic playground.
Keep in mind that you had a very unfair advantage over the generation you are teaching. You used to be able to tear electronics apart and figure out how they worked-and you didn't have media sufficient to occupy 48 hours of each day. Maybe an hour of TV a couple nights a week-in bad weather? Otherwise find something to satisfy your curiosity.
My dad was an educator-recently he commented that a lot of students have trouble translating the classroom to real life. I suspect the same is try of a schematic to real live wires-or a desktop playground to real live wires. I have a couple of young maintenance techs that are eager to learn-my training this week consisted of explaining a schematic to one of them, then sending him out to a machine and having him marry an old control panel to a new machine. Give me a year or two and I'll put him up against your college degreed engineers any day of the week ;).
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No wonder people have trouble figuring out 3-way switches. That's probably the most confusing electrical thing most people will ever come across.
Even more confusing on an international forum; a "three way switch" in the USA is what the rest of the world calls a "two way switch"...
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Even more confusing on an international forum; a "three way switch" in the USA is what the rest of the world calls a "two way switch"...
Really, it's a single pole, double-throw switch (SPDT). But what is the universal term for a 4-way switch?
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But what is the universal term for a 4-way switch?
Rotary?
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Literally dug up from a year ago but thanks for the reply. I simply worked around the problem by changing the projectors refresh rate to 50Hz(same as the mains cycle) and it's minimized to the point where nobody complains.
Management has issues believing techs when a qualified electrician says its fine, won't say anything about other code violations that apparently also gets signed off on...
Country is South Africa BTW...
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Really, it's a single pole, double-throw switch (SPDT). But what is the universal term for a 4-way switch?
"Intermediate"
An intermediate switch is, of course, no more than a DPDT switch cross-wired.
One of these in a box with a couple of speakons is a real easy way to track down phase errors in speakers or the wiring thereof.