A short to ground...?

[Saferguy]

Will somebody agree or desagree with this...theory..?
Contractors at my place of work,... by mistake..., hooked up a neutral wire to the -hot wire- of a different 120 v. branch circuit.
One of the loads in this branch was a fluorescent light fixture ballast.
The ballast blew up and the branch power protective breaker tripped....
Some electricians there, are of the opinion that the breaker tripped because of an over current condition...and not necessarily because of a short to ground... Clamming that the hot wire in that circuit had been disconnected previously.
However, in my opinion, some of the other circuit loads, such as computers and other... had their neutral grounded...and I believe a short to ground took place via this other branch circuit neutral wire....!
Am I correct in this assumption....?

Thank you, for any input on this.

Saferguy.
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[hurk27]

Re: A short to ground...?

First with the circuit having one hot on one phase and the neutral connected to a hot on another phase you will have 240 or 208 volts on this circuit and this would explain the ballest being distroyed. Now if there was any neutrals connected to ground at the load end of this circuit, This would be a NEC violation. But it would also triped the circuit breaker feeding the neutral without any over voltage going to the ballest. So no ballest damage would have occured. Now if the circuit did see 240/208 volts then it is possable that when the ballest let go it caused an overload in the circuit or the winding went to ground causing the breaker to trip. Now if there was any computer's on this circuit and they had TVSS protection the TVSS can load the higher voltage down enough to trip a breaker. But if the ballest is at any distance from the TVSS then it would not have protected the ballest, and the ballest would have still been distroyed.
Not knowing what all had been damaged it's hard to tell what took place but it does sound like an over load from 240/208 volts running through the ballest. One thing you could do is if there is any TVSS like a plug strip on those computers check to see if the green protection LED is still lit. If it is not then they took a hit also.
They are lucky you didn't loose any computers.

 

[charlie b]

Re: A short to ground...?

First of all, let us not allow ?language? to get in the way of ?communication.? By definition, a ?short circuit? is an ?overload.? It is the extreme case of an overload. The more common usage of the two terms distinguishes them by saying a ?short circuit? is essentially a zero resistance connection from hot to ground, whereas an overload is a high resistance connection that allows more current than the device would normally carry.

I can?t draw pictures and post them, so I?ll describe a picture, and ask you to draw what I am describing. Start with three horizontal lines to represent a 120/240 volt panel. Add labels for Hot, Neutral, and Other Hot. Like this:

Hot ____________________

Neutral ___________________

Other Hot _________________

Now draw a breaker symbol leaving the top line upwards, going to the right, draw a symbol for a light bulb, then draw a line that connects back to the neutral bar in the panel.

Next draw a breaker symbol leaving the bottom line downwards, going to the right, draw a symbol for a heater (resistor), then draw a line that connects back to the neutral bar in the panel (make it a separate neutral all the way back to the panel.

Finally, draw a curved line that starts at the neutral side of the light, and goes to the hot side of the heater/resistor. At the same time, erase (or just cross out) the original neutral line that ran from the light back to the panel. This represents the wiring error your described.

Now you can see what Wayne has already described. The light will now have a power supply of 240 volts. This would create an overload in the breaker, and it may (or may not) trip on the overload current. In any case, the light (ballast) would be destroyed. In that act, the internal parts of the ballast could create a short circuit, which certainly would have tripped the breaker.