230.95 and resistance grounding
- Thread starter lizzie14
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bphgravity
Senior Member
- Location
- Florida
Re: 230.95 and resistance grounding
See section 250.36 for a description and the rules when installing this type of system. Basically, the use of a high-impedance system is to limit the fault current to ensure continuity of power so that an orderly shut-down and/or repair can be made.
See section 250.36 for a description and the rules when installing this type of system. Basically, the use of a high-impedance system is to limit the fault current to ensure continuity of power so that an orderly shut-down and/or repair can be made.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: 230.95 and resistance grounding
The same as it would be for a "zero resistance" grounded system. Presuming you have a 480/277 WYE secondary, the measurement phase to neutral is 277. However, the voltage from phase to ground (i.e., planet Earth), or more to the point from neutral to planet Earth, is a different matter. A fault will create a path for current in the GEC, which will establish a voltage from neutral to ground.
The same as it would be for a "zero resistance" grounded system. Presuming you have a 480/277 WYE secondary, the measurement phase to neutral is 277. However, the voltage from phase to ground (i.e., planet Earth), or more to the point from neutral to planet Earth, is a different matter. A fault will create a path for current in the GEC, which will establish a voltage from neutral to ground.
Re: 230.95 and resistance grounding
Our resistively grounded system is sized to limit the neutral current to 5 amps (approx 69 ohms for 600V and 55 ohms for 480V). There is literally a resistor in series with the neutral. If you tried to supply a line-to-neutral load you would create a voltage divider. Simply put, stuff wouldn't work.
Re: 230.95 and resistance grounding
I am not sure why. The code panels seem to have a severe distrust of anything other than solidly grounded systems - at least for the ones us mere humans use.
I like impedance grounded systems. I think they are safer and more reliable. I'm not sure I've ever seen a connection between ground and an electrical system that made the system any safer.
JAO
carl
All impedance grounded systems I have seen have the resistor between the neutral and the ground. So any load connected between neutral and line would get 277V and would work fine. But, the code clearly says, "No line to neutral loads".
I am not sure why. The code panels seem to have a severe distrust of anything other than solidly grounded systems - at least for the ones us mere humans use.
I like impedance grounded systems. I think they are safer and more reliable. I'm not sure I've ever seen a connection between ground and an electrical system that made the system any safer.
JAO
carl
Re: 230.95 and resistance grounding
lizzie14,
250.36 -- HIGNS -- are permitted on ac systems of 480 volts to 1000 volts 3phase. That's not the same as 480/277. Also, the resistor connects between the derived neutral and the GEC,which in turn forms the equipment bonding jumper. The EBJ is connected to your equipment grounding terminal.
The reason line to neutral loads are not served is that there is no neutral in your panel,the neutral stopped back at the resistor.If there is a neutral in your panels then something is installed improperly.
I hope that some of this may help you out.
lizzie14,
250.36 -- HIGNS -- are permitted on ac systems of 480 volts to 1000 volts 3phase. That's not the same as 480/277. Also, the resistor connects between the derived neutral and the GEC,which in turn forms the equipment bonding jumper. The EBJ is connected to your equipment grounding terminal.
The reason line to neutral loads are not served is that there is no neutral in your panel,the neutral stopped back at the resistor.If there is a neutral in your panels then something is installed improperly.
I hope that some of this may help you out.
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