Mountain Sparky
Member
- Location
- Colorado USA
Why would losing a neutral on a 277 volt lighting circuit burn up a magnetic metal halide ballast?
Burned up metal halide ballast
- Thread starter Mountain Sparky
- Start date
- Status
- Location
- Massachusetts
Or was the lost neutral on a feeder or service?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
See if this helps. Just use 480/277V instead
Last edited:
Mountain Sparky
Member
- Location
- Colorado USA
yes it is
Mountain Sparky
Member
- Location
- Colorado USA
See if this helps. Just use 480/277V instead
that would do it....
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
My understanding, and I might be wrong, is that over voltage drives the ballast core onto saturation. When saturated there is not enough counter EMF to limit current on the windings and thus the windings will begin to have more current flow. The current flow heats the coils until they overheat.
Am I correct? I am curious about this as well.
Am I correct? I am curious about this as well.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Yes. The normal current flow is limited by the circuit which consists of a relatively fixed voltage drop across the lamp and the remaining voltage being dropped by the inductive impedance of the ballast coil. Once the ballast is driven into saturation, the current required for a given voltage drop (more than double the normal voltage drop) will be far higher than just twice the normal current.
Note that unless the ballast also contains an autotransformer or isolation transformer circuit, the entire excess load current will also pass through the bulb, and may damage it too. It is a question of which fails first.
- Status