kwired
Electron manager
- Location
- NE Nebraska
Never mind, I don't know what I may have been seeing when I replied before, I certainly am not seeing it that way now. I think I possibly got the 120 and 150 somehow mixed up.
250.20 SYSTEM GROUNDING (B)
- Thread starter bobby ocampo
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bobby ocampo
Senior Member
What if it is 480 volts delta NO midpoint conductor, 3phase, 3 wire only. Will the code allow it to be UNGROUNDED?
bobby ocampo
Senior Member
250.20 (B)(1)Where the system is 1-phase and can be grounded so that the MAXIMUM voltage to ground on the ungrounded conductor does not exceed 150 volts
Does it mean that if it is single phase and the maximum voltage to ground exceeds 150volts the code allows it to be UNGROUNDED?
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Yes, if your statement means that the line to line voltage is >150V and there is no center tap neutral. But all conditions for ungrounded systems will then apply.
bobby ocampo
Senior Member
Why would the code allow UNGROUNDED for voltage to ground higher than 150volts? While not allow UNGROUNDED for lower than 150 volts to ground?
K8MHZ
Senior Member
- Occupation
- Electrician
How would you ground a 240 volt single phase separately derived system? This section (1) refers to connecting a hot conductor to the earth. (2) is for wye systems and (3) is for hig leg deltas.
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kwired
Electron manager
- Location
- NE Nebraska
There are no "hot" conductors until a grounded conductor is established. This is part of the reason for confusion with many people when they see a corner grounded system. Or a situation I ran into recently with European equipment that I connected. The Equipment was designed for 240 volts single phase - but in most European installs that is 240 volts to ground. They send out a transformer with that equipment and it is two wire output 240 volts one side grounded. The equipment guy seemed surprised when I told him I had no problem understanding how to connect that he said most electricians tell him you cant ground a 240 volt lead, I told him you can ground any lead - you just can't ground two different leads of the system.
bobby ocampo
Senior Member
250.20 (B)(1)Where the system is 1-phase and can be grounded so that the MAXIMUM voltage to ground on the ungrounded conductor does not exceed 150 volts
Why will the code allow a system greater than 150 volts to ground be UNGROUNDED and not allow it for system with lower than 150 volts to ground?
Why will the code allow a system greater than 150 volts to ground be UNGROUNDED and not allow it for system with lower than 150 volts to ground?
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Ask the CMP?
K8MHZ
Senior Member
- Occupation
- Electrician
I totally disagree with that.
K8MHZ
Senior Member
- Occupation
- Electrician
My thinking is that (B)(1) applies to systems normally used in dwellings and that the NEC is indirectly making dwelling grounding requirements through the requirement that (B)(1) details.
bobby ocampo
Senior Member
How does the Code define premises wiring? Does premises wiring only applies to dwelling units?
It's in Article 100 Definitions...
kwired
Electron manager
- Location
- NE Nebraska
Define "hot conductor".
I am assuming most would call it a conductor that has potential to ground. Until you establish a ground reference in any voltage system, you don't have significant potential to ground - you can have capacitively coupled voltages but they typically don't have much power behind them for under 600 volt systems.
A few posts back you asked "How would you ground a 240 volt single phase separately derived system?"
You can ground either leg, but not both at same time. There is no "hot" until the opposing leg is grounded.
- Occupation
- Licensed Electrician
Good thing for grounded and ungrounded huh?
bobby ocampo
Senior Member
Does premises wiring applies only to dwelling units based on the definition of premises wiring in the Code?
K8MHZ
Senior Member
- Occupation
- Electrician
I understand you line of thinking, but what if I have a generator with no grounded conductor. Does that mean there is no 'hot' conductor?
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
You have two (or more) warm conductors instead.
They are all ungrounded conductors, which is why the code tends to use that rather than "hot" as a descriptive term.
kwired
Electron manager
- Location
- NE Nebraska
Absolutely, none of them are "hot" until one of them becomes grounded - whether intentionally grounded or not. It will be safe to touch any conductor of the system, just don't touch more then one conductor at a time. Once one of them is grounded you have a ground reference and you need to be more careful about ensuring you are insulated from ground before it would be safe to touch any other ungrounded conductor.
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- Location
- Illinois
- Occupation
- retired electrician
Did you read the definition?
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