Electrician Talk banner

21 - 35 of 35 Posts

·
Registered
Joined
·
31,151 Posts
What would happen if you did not corner grd. the transformer ? What is a grd. alarm ?
If you did not ground the transformer, you would have an ungrounded system and everything would work fine.

When you have the first ground fault, you would then have a corner grounded system, but the ground would be remote from the transformer.

Ground alarms can be as simple as lights tied to each phase, with an inline resistor to prohibit the lamp from lighting under normal conditions (due to capacitance coupling*). When you have a fault the lamp lights on the grounded phase.

*I THINK or as I understand it.

Or this
http://www.bender.org/ground_fault_for_ungrounded_large_systems.aspx
 

·
Registered
Joined
·
372 Posts
If you did not ground the transformer, you would have an ungrounded system and everything would work fine.

When you have the first ground fault, you would then have a corner grounded system, but the ground would be remote from the transformer.

Ground alarms can be as simple as lights tied to each phase, with an inline resistor to prohibit the lamp from lighting under normal conditions (due to capacitance coupling*). When you have a fault the lamp lights on the grounded phase.

*I THINK or as I understand it.

Or this
http://www.bender.org/ground_fault_for_ungrounded_large_systems.aspx

A simple ground detector consists of three lamps connected in a wye configuration with the center point grounded,under normal conditions the lamps burn dimly, when a phase wire becomes grounded the lamp on that phase goes out and the other two lamps burn brightly.
 

·
Salty Member
Joined
·
31,081 Posts
A simple ground detector consists of three lamps connected in a wye configuration with the center point grounded,under normal conditions the lamps burn dimly, when a phase wire becomes grounded the lamp on that phase goes out and the other two lamps burn brightly.
That is certainly a great old school method, I brought it up on a forum before and the EEs were horrified, called it unsafe, unprofessional and insisted you must buy a listed ground detector. :rolleyes:
 

·
Registered
Joined
·
372 Posts
A simple ground detector consists of three lamps connected in a wye configuration with the center point grounded,under normal conditions the lamps burn dimly, when a phase wire becomes grounded the lamp on that phase goes out and the other two lamps burn brightly.
The Ground Detection Lights are designed for operation on a 3 Phase, Ungrounded System or Hi Resistance Grounded System. It will not work on any type of Solid Grounded System.

The 3 lights are wired in a “WYE” Configuration with the center of the “WYE” grounded.

The Lights are rated at the Full Voltage of the system, thus a 480V System requires 480V Pilot Lights.

In normal operation all 3 lights will be at approx 57% Brightness.

When one phase of the power system shorts to ground, the Light the Ground is on will go out, the other 2 lights will be at Full Brightness.
 

·
Registered
Joined
·
31,151 Posts
The Ground Detection Lights are designed for operation on a 3 Phase, Ungrounded System or Hi Resistance Grounded System. It will not work on any type of Solid Grounded System.

The 3 lights are wired in a “WYE” Configuration with the center of the “WYE” grounded.

The Lights are rated at the Full Voltage of the system, thus a 480V System requires 480V Pilot Lights.

In normal operation all 3 lights will be at approx 57% Brightness.

When one phase of the power system shorts to ground, the Light the Ground is on will go out, the other 2 lights will be at Full Brightness.
While I agree, Bob's poin t was and is

That is certainly a great old school method, I brought it up on a forum before and the EEs were horrified, called it unsafe, unprofessional and insisted you must buy a listed ground detector
I would bet your system was utilized for years and then some one came up with a ground detector that listed and, thats the way it is.

On the system I noted I an almost positive I saw a ground detector system installed like this, but I have made at least one mistake in my life, this could be number 2?
 

·
Salty Member
Joined
·
31,081 Posts
While I agree, Bob's poin t was and is



I would bet your system was utilized for years and then some one came up with a ground detector that listed and, thats the way it is.

On the system I noted I an almost positive I saw a ground detector system installed like this, but I have made at least one mistake in my life, this could be number 2?
The thing is, there is nothing in the NEC that requires the ground fault indicators to be listed.


The lamp method works fine if someone is keeping an eye on it. The few times I have seen them they were in prominent spots that mantainace personal would see many times a day.
 

·
Registered
Joined
·
4,665 Posts
That is certainly a great old school method, I brought it up on a forum before and the EEs were horrified, called it unsafe, unprofessional and insisted you must buy a listed ground detector. :rolleyes:
I'd tell them to look up the theory and go pound sand. Ain't nothing wrong with the light bulb method.

While I agree, Bob's poin t was and is



I would bet your system was utilized for years and then some one came up with a ground detector that listed and, thats the way it is.

On the system I noted I an almost positive I saw a ground detector system installed like this, but I have made at least one mistake in my life, this could be number 2?
Bob beat me to it:

The thing is, there is nothing in the NEC that requires the ground fault indicators to be listed.


The lamp method works fine if someone is keeping an eye on it. The few times I have seen them they were in prominent spots that mantainace personal would see many times a day.

And consider the possible failure modes: If a bulb burns out it would be obvious as it would be the only one NOT glowing at reduced intensity.

And if...well that's it. If any bulbs burn out they would be dark without any other bulbs being bright, so it pretty much tells you the fault is you need a new bulb.

Now do those new fancy "ground fault indicators" have such a foolproof method of telling you if they suffer an internal breakdown? Doubt it. :no:

I would not hesitate at all to use the lamp method on a new installation. Simple, cheap, foolproof.
 

·
Registered
Joined
·
1 Posts
Dont forget to corner ground, bond H2, B phase, to case ground on the transformer. Without this imporatant part, the conduit and all the equipment could become energized without a ground path. Just found this problem at local machine shop. Very dangerous. As someone mentioned earlier it will drive the start up guys crazy as you will have H1, 480 volt to ground, H2, 0 volt to ground, and H3, 480 volt to ground. Across each phase will be 480 volt.
 

·
Registered
Joined
·
28 Posts
does anyone have a picture of a back fed trans corner bonded? I'm doing my first one like this and would like to see one all wired up!
 

·
NJ-IEC
Joined
·
14,387 Posts
I have120/208 at my Jobsite. I need 277/480 to supply a temp material hoist. My shop has a step down 480 primary to 208 secondary transformer. They want me to use this transformer and wire it reversed. My primary being my load for my hoist and my secondary being my line from my mdp. Voltages will still match the transformers rating. Just the line and load will be reversed. Any one installed a transformer this way? Any thoughts?
If it's not rated to do that you're in violation of the NEC. :whistling2:
 
21 - 35 of 35 Posts
Top