emergency lighting ballast operation

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Twoskinsoneman

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
Sorry about the crudeness of this drawing I made it with Paint.
Had a fixture that is dual fed 277vac and 48vdc. The 48vdc was not functioning. (Power off 277 circuit and light goes out). Changed the 48vdc ballast (inverter) and it was fixed. But I now have a couple of questions.

#1 How exactly does the set up below work? Mainly does the 48vdc ballast feed the lamps by itself or does it work with the AC ballast to power the lamps. If your AC ballast failed would the 48vdc ballast still power the lamps? the reason I ask is because there is a similar fixture with an issue but it does not power on at all. I was told it was relamped and no-fix. Does this indicate both ballast are bad or can a failed AC ballast cause the problem?

#2 What is the unit connector for? The installation instructions state "Do not mate connector until installation is complete and AC power is supplied." In the cautionary section the instructions state "To prevent electrical shock do not mate connector until installation is complete and AC power is supplied to the unit." When I replaced the 48vdc ballast to fix the first fixture I noticed that the original installer never connected the unit connector at all...

acdcballast1.jpg


Thanks as always.
 
Twoskinsoneman said:
Sorry about the crudeness of this drawing I made it with Paint.
Had a fixture that is dual fed 277vac and 48vdc. The 48vdc was not functioning. (Power off 277 circuit and light goes out). Changed the 48vdc ballast (inverter) and it was fixed. But I now have a couple of questions.

#1 How exactly does the set up below work? Mainly does the 48vdc ballast feed the lamps by itself or does it work with the AC ballast to power the lamps. If your AC ballast failed would the 48vdc ballast still power the lamps? the reason I ask is because there is a similar fixture with an issue but it does not power on at all. I was told it was relamped and no-fix. Does this indicate both ballast are bad or can a failed AC ballast cause the problem?

#2 What is the unit connector for? The installation instructions state "Do not mate connector until installation is complete and AC power is supplied." In the cautionary section the instructions state "To prevent electrical shock do not mate connector until installation is complete and AC power is supplied to the unit." When I replaced the 48vdc ballast to fix the first fixture I noticed that the original installer never connected the unit connector at all...

acdcballast1.jpg


Thanks as always.
Click to expand...
With 48v dc all the lamps light up or only the bottom most one?
 
Never worked on a 277VAC / 48VDC fixture.

But my WAG, based on experience with self contained battery back up ballasts the unit connector is the 'turn on switch' without it connected there will be no output.
 
iwire said:
Never worked on a 277VAC / 48VDC fixture.

But my WAG, based on experience with self contained battery back up ballasts the unit connector is the 'turn on switch' without it connected there will be no output.
Click to expand...

They are used quite often in the telecom industry, the 48 Vdc is drawn from the power plant for the teleco equipment. Usually in large switching stations.
 
Twoskinsoneman said:
Sorry about the crudeness of this drawing I made it with Paint.
Had a fixture that is dual fed 277vac and 48vdc. The 48vdc was not functioning. (Power off 277 circuit and light goes out). Changed the 48vdc ballast (inverter) and it was fixed. But I now have a couple of questions.

#1 How exactly does the set up below work? Mainly does the 48vdc ballast feed the lamps by itself or does it work with the AC ballast to power the lamps. If your AC ballast failed would the 48vdc ballast still power the lamps? the reason I ask is because there is a similar fixture with an issue but it does not power on at all. I was told it was relamped and no-fix. Does this indicate both ballast are bad or can a failed AC ballast cause the problem?

#2 What is the unit connector for? The installation instructions state "Do not mate connector until installation is complete and AC power is supplied." In the cautionary section the instructions state "To prevent electrical shock do not mate connector until installation is complete and AC power is supplied to the unit." When I replaced the 48vdc ballast to fix the first fixture I noticed that the original installer never connected the unit connector at all...

acdcballast1.jpg


Thanks as always.
Click to expand...

I think you almost answered your own questions in your post itself.

1)The 48v 'dc ballast' is actually an inverter and it makes use of AC ballast for controlling current flow through lamps.If it had to control the lamps current by D.C,then it should have a resistor with a wattage rating equal to the total rating of lamps,which is a wasteful control.So its output is A.C and it should control the current through AC ballast available and so if the AC ballast is disconnected,the lamps will not glow.

2)If the unit connector is made before the installation is complete,rated voltage would be present in the lamp holders posing a hazard.

Finally,one question regarding' I noticed that the original installer never connected the unit connector at all...'Before replacing 48vdc ballast (inverter),did you make the unit connector to fix the problem?
 
T.M.Haja Sahib said:
I think you almost answered your own questions in your post itself.

1)The 48v 'dc ballast' is actually an inverter and it makes use of AC ballast for controlling current flow through lamps.If it had to control the lamps current by D.C,then it should have a resistor with a wattage rating equal to the total rating of lamps,which is a wasteful control.So its output is A.C and it should control the current through AC ballast available and so if the AC ballast is disconnected,the lamps will not glow.

2)If the unit connector is made before the installation is complete,rated voltage would be present in the lamp holders posing a hazard.

Finally,one question regarding' I noticed that the original installer never connected the unit connector at all...'Before replacing 48vdc ballast (inverter),did you make the unit connector to fix the problem?
Click to expand...

The unit connector was never connected on the first unit. The lights did not work on 48vdc. I replaced the DC ballast, did NOT connect unit connector on the replacement ballast. Lights now work on 48vdc.
 
As drawn the DC inverter operates 1 lamp when 277 fails. It has an internal NC relay that is held open by the line voltage. The blue wire is a lamp lead across NO contacts that act as a pass through to the lamp. When power fails the lamp lead is disconnected and the inverter is powered on to feed the lamp.
 
ron said:
After looking at the block type diagram on the Instruction Sheet at http://www.bodine.com/products/central.html#for the Bodine CB90-48 ballast, it seems that it switches the regaular ballast off. The regular ballast is essentially downstream of the DC ballast so it doesn't attempt to parallell. DC is the standby power.
Click to expand...

The cited reference states when AC power is lost. The diagram clearly shows 277 going to the ballast and the inverter at the same time.
 
iwire said:
I figured that, but I still have not worked with the device shown. :)
Click to expand...

Yeah, the only place I have every seen them used was in switching stations, kinda redundancy they like to use, the 277 volt circuit is usually on generator, and with the massive amount of battery backup they have at 48 volts, it makes sense to use what they already have. Until I wired a switching station, I didn't know they made such a beast! :)
 
Twoskinsoneman said:
#1 How exactly does the set up below work? Mainly does the 48vdc ballast feed the lamps by itself or does it work with the AC ballast to power the lamps. If your AC ballast failed would the 48vdc ballast still power the lamps? the reason I ask is because there is a similar fixture with an issue but it does not power on at all. I was told it was relamped and no-fix. Does this indicate both ballast are bad or can a failed AC ballast cause the problem?
Click to expand...
That diagram looks to be from a typical battery backup ballast. When AC is present, light works normally. When the power goes out, the backup ballast powers one lamp (usually at a diminished capacity).
If the light doesn't work when normal power is applied, it is most likely the AC ballast is bad. A bad battery backup ballast usually will not interfere with the normal operation of the light fixture.
Twoskinsoneman said:
#2 What is the unit connector for? The installation instructions state "Do not mate connector until installation is complete and AC power is supplied." In the cautionary section the instructions state "To prevent electrical shock do not mate connector until installation is complete and AC power is supplied to the unit." When I replaced the 48vdc ballast to fix the first fixture I noticed that the original installer never connected the unit connector at all..
.
Click to expand...
As posted above, the unit connector puts the battery backup ballast "in service" (you'll see the same thing in exit lights).
The only consequece of not connecting those wires is no lamps will light when the power goes out.

EDIT: Oops, I glanced over the 48v leads going to the backup ballast. Is it made to operate with either voltage or does the 48v leads need to be connected to a power supply?
I would think you could use either/or, but not both.
 
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Stevareno said:
That diagram looks to be from a typical battery backup ballast. When AC is present, light works normally. When the power goes out, the backup ballast powers one lamp (usually at a diminished capacity).
If the light doesn't work when normal power is applied, it is most likely the AC ballast is bad. A bad battery backup ballast usually will not interfere with the normal operation of the light fixture.

As posted above, the unit connector puts the battery backup ballast "in service" (you'll see the same thing in exit lights).
The only consequece of not connecting those wires is no lamps will light when the power goes out.

EDIT: Oops, I glanced over the 48v leads going to the backup ballast. Is it made to operate with either voltage or does the 48v leads need to be connected to a power supply?
I would think you could use either/or, but not both.
Click to expand...

Here is how it looks to me:

The ballast is given a 48 VDC input from a central battery (maybe its for a telecomm building). The 277 V input is both applied to the AC ballast and the DC ballast. It runs the AC ballast under normal operation, and it also tells the DC ballast when to turn on and start running off the battery.


Under normal operation, the 277V input is applied to the normal AC ballast. It is also applied to the DC ballast and causes the DC ballast to route normal power to the bottom lamp (power comes from the AC ballast on the blue wire, runs through a contactor in the DC ballast, and to the lamp via the red wire.)

When power is lost, the contactor opens the blue-red contact in the DC ballast, and the DC ballast applies power to the lamp.
 
No, the AC ballast is not required to run the emergency lamp.

Any good emergency backup is going to work during either a power failure, or a normal ballast failure.
 
Thank you all for great input (even iwire's WAG was appreciated when I wasn't getting any responses :p)

You all seem to be correct. With some playing around (technical term for OJT) and emails to manufacturers I have learned that you're correct, the DC ballast will function to turn on one bulb if the AC power fails. The only thing I'm still unclear on is if the AC ballast fails and the AC sense input to the DC ballast is still there will the DC ballast activate?The AC ballast failure does not directly affect the DC ballast operation, however with the DC ballast still sensing the 277v does this mean you won't get back up lighting?
 
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The only other thing was the manufacturer insist that without the unit connector plugged in the DC ballast will not operate. But I can assure you that the DC ballast I recently put in does NOT have it's connector connected (going to remedy it though) and when I remove AC power it does work off the DC. I checked it pretty thoroughly. AC and DC sources on, three bulbs lighted, open AC OCPD, all but one bulb goes out, turn off DC OCPD the single light left goes out... Can't wrap my head around why except some kind of internal failure of the unit connector circuit.
 
Twoskinsoneman said:
Thank you all for great input (even iwire's WAG was appreciated when I wasn't getting any responses :p)

You all seem to be correct. With some playing around (technical term for OJT) and emails to manufacturers I have learned that you're correct, the DC ballast will function to turn on one bulb if the AC power fails. The only thing I'm still unclear on is if the AC ballast fails and the AC sense input to the DC ballast is still there will the DC ballast activate?The AC ballast failure does not directly affect the DC ballast operation, however with the DC ballast still sensing the 277v does this mean you won't get back up lighting?
Click to expand...

If the "service" ballast fails the light fixture will remain dark unless AC power is lost to the battery back-up ballast (or the test button is pushed).

Referrring back to your OP question #2, I learned the hard way to unplug the unit connector leads. The socket leads of the battery back-up ballast can give you a good jolt if the unit connector is plugged together.

It is fairly typical in new installs to find these unit connectors unplugged (for reasons known only to the installer). I will plug these in as I install them even if I am unsure of the time frame of commissioning the new circuit. IMO, there is the chance that no one will return to pull the belly pan and connect the inverter once the lights are turned on. Maybe the fire marshall will catch it or a maintenance tech 5 years down the road.

I try to keep several manufactures cut sheets for these battery ballasts as they are somewhat standardized but the diagrams can save you a headache. GE tech support has told me they do not recommend using their T8 instant-start ballasts in conjunction with a battery ballast. Whatever.
 
Twoskinsoneman said:
The only other thing was the manufacturer insist that without the unit connector plugged in the DC ballast will not operate. But I can assure you that the DC ballast I recently put in does NOT have it's connector connected (going to remedy it though) and when I remove AC power it does work off the DC. I checked it pretty thoroughly. AC and DC sources on, three bulbs lighted, open AC OCPD, all but one bulb goes out, turn off DC OCPD the single light left goes out... Can't wrap my head around why except some kind of internal failure of the unit connector circuit.
Click to expand...

If you look at the instructions for the ballast Ron posted, the unit connector should be left open for some combinations of the number and type of lamps.
 
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