Grounding Rod For Portable Generators Necessary?

[ThomasH]

Theoretically, if there was no resistance in the wire and all connections were perfect, neutral would be at zero across it's entire length from the pole to the end of all branch circuits. But it's not. There is resistance in wires that can be hundreds of feet long, and there are connections that aren't perfect. So voltage measured at different points in a neutral circuit will be different. Do you understand that?

How neutrals can have voltage, as opposed to being at the same electrical potential as the earth, is that there are various 120 volt loads on each portion of the 240 volt center tapped supply. So if one is highly loaded, and the other lightly loaded, there will be some voltage measurable on the neutral. It's basic ohms law.

And derived neutrals can certainly float, it depends on how they are derived. It was commonly done by putting two electrolytic capacitors across the 120v to the chassis in earlier transistor amplifier design, and commonly done with vacuum tube amps.

I'm done, this is not the discussion that the poster asked for.

 

[grsthegreat]

you know, im an electrician and even im sick of this thread

 

[Hivoltage98]

you know, im an electrician and even im sick of this thread

Ok. I agree. But the original question was " do I need a ground rod?". The answer is no. You don't need a ground rod. NFPA 70 article 250.34


A generator is a "separately derived system". BUT - 250.20 (D) FPN says - an alternate ac power source such as an on site generator is NOT a separately derived system if the neutral is solidly interconnected to a service supplied system neutral.

Do we drive a ground rod if we install a generator outside? **** yes. A 400 kw generator in a steel soundproof enclosure has a good chance of getting hit by lightning. We BOND the rod to the metal frame of the genset. 99% of the time that's what the engineer wants.

Here are a few definitions for reference..
Ground- 1. the earth.
2. A conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth or to some conducting body that serves in place of the earth.

Grounded conductor - a system or circuit conductor that is intentionally grounded. ( typically called the neutral).

Grounding conductor- a conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes.

Grounding electrode conductor - the conductor used to connect the grounding electrode(s) to the equipment grounding conductor, to the grounded conductor, or to both, at the service, or at the source of a separately derived system.

A ground rod, ground ring, 2' square plate, metal underground water pipe, is a grounding electrode. Typically you need 2 grounding electrodes at a service ie: ground rod and cold water pipe, 2 ground rods 6' apart.
Resistance of a ground should be 25 ohms or less.

The grounded conductor and grounding electrode are bonded Together at the service.

The bonding of the two makes a system.
The grounding electrode system does 2 things,
1. Provides a path for lightning discharge ( not that it won't destroy stuff in its path)
2. Provides a reference to ground for the service in a fault situation.
scenario1. John lives on a block with 10 other houses. John lives closest to the transformer. The scrapper that roams johns street decides he wants the ground wire that runs from the transformer to the ground rod at the bottom of the pole. The grid ground isn't such a great connection, so John's transformer outside his front window is not happy. The transformer now finds the next path to ground, which is johns service. It sees johns ground rod and cold water pipe ground and is happy. If not for johns grounding electrode system, the transformer would have looked for the next available ground. Maybe ms. Jones house down the street. If it didn't have a ground to love, the scenario of a "floating neutral can happen".

Scenario 2. Johns house loses his grounded conductor. His house is ok hopefully because his grounding electrode system is keeping a floating neutral in check.

In electronics static discharge and isolated grounds come into play, but that's a whole different thread. Lol

My god I had to whip out the code book for this. It was a good brush up.

 

[grsthegreat]

Ok. I agree. But the original question was " do I need a ground rod?". The answer is no. You don't need a ground rod. NFPA 70 article 250.34


A generator is a "separately derived system". BUT - 250.20 (D) FPN says - an alternate ac power source such as an on site generator is NOT a separately derived system if the neutral is solidly interconnected to a service supplied system neutral.

Do we drive a ground rod if we install a generator outside? **** yes. A 400 kw generator in a steel soundproof enclosure has a good chance of getting hit by lightning. We BOND the rod to the metal frame of the genset. 99% of the time that's what the engineer wants.

Here are a few definitions for reference..
Ground- 1. the earth.
2. A conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth or to some conducting body that serves in place of the earth.

Grounded conductor - a system or circuit conductor that is intentionally grounded. ( typically called the neutral).

Grounding conductor- a conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes.

Grounding electrode conductor - the conductor used to connect the grounding electrode(s) to the equipment grounding conductor, to the grounded conductor, or to both, at the service, or at the source of a separately derived system.

A ground rod, ground ring, 2' square plate, metal underground water pipe, is a grounding electrode. Typically you need 2 grounding electrodes at a service ie: ground rod and cold water pipe, 2 ground rods 6' apart.
Resistance of a ground should be 25 ohms or less.

The grounded conductor and grounding electrode are bonded Together at the service.

The bonding of the two makes a system.
The grounding electrode system does 2 things,
1. Provides a path for lightning discharge ( not that it won't destroy stuff in its path)
2. Provides a reference to ground for the service in a fault situation.
scenario1. John lives on a block with 10 other houses. John lives closest to the transformer. The scrapper that roams johns street decides he wants the ground wire that runs from the transformer to the ground rod at the bottom of the pole. The grid ground isn't such a great connection, so John's transformer outside his front window is not happy. The transformer now finds the next path to ground, which is johns service. It sees johns ground rod and cold water pipe ground and is happy. If not for johns grounding electrode system, the transformer would have looked for the next available ground. Maybe ms. Jones house down the street. If it didn't have a ground to love, the scenario of a "floating neutral can happen".

Scenario 2. Johns house loses his grounded conductor. His house is ok hopefully because his grounding electrode system is keeping a floating neutral in check.

In electronics static discharge and isolated grounds come into play, but that's a whole different thread. Lol

My god I had to whip out the code book for this. It was a good brush up.

i told him no 8 pages ago with the code requirements.

 

[grsthegreat]

Ok. I agree. But the original question was " do I need a ground rod?". The answer is no. You don't need a ground rod. NFPA 70 article 250.34


A generator is a "separately derived system". BUT - 250.20 (D) FPN says - an alternate ac power source such as an on site generator is NOT a separately derived system if the neutral is solidly interconnected to a service supplied system neutral.

Do we drive a ground rod if we install a generator outside? **** yes. A 400 kw generator in a steel soundproof enclosure has a good chance of getting hit by lightning. We BOND the rod to the metal frame of the genset. 99% of the time that's what the engineer wants.

Here are a few definitions for reference..
Ground- 1. the earth.
2. A conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth or to some conducting body that serves in place of the earth.

Grounded conductor - a system or circuit conductor that is intentionally grounded. ( typically called the neutral).

Grounding conductor- a conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes.

Grounding electrode conductor - the conductor used to connect the grounding electrode(s) to the equipment grounding conductor, to the grounded conductor, or to both, at the service, or at the source of a separately derived system.

A ground rod, ground ring, 2' square plate, metal underground water pipe, is a grounding electrode. Typically you need 2 grounding electrodes at a service ie: ground rod and cold water pipe, 2 ground rods 6' apart.
Resistance of a ground should be 25 ohms or less.

The grounded conductor and grounding electrode are bonded Together at the service.

The bonding of the two makes a system.
The grounding electrode system does 2 things,
1. Provides a path for lightning discharge ( not that it won't destroy stuff in its path)
2. Provides a reference to ground for the service in a fault situation.
scenario1. John lives on a block with 10 other houses. John lives closest to the transformer. The scrapper that roams johns street decides he wants the ground wire that runs from the transformer to the ground rod at the bottom of the pole. The grid ground isn't such a great connection, so John's transformer outside his front window is not happy. The transformer now finds the next path to ground, which is johns service. It sees johns ground rod and cold water pipe ground and is happy. If not for johns grounding electrode system, the transformer would have looked for the next available ground. Maybe ms. Jones house down the street. If it didn't have a ground to love, the scenario of a "floating neutral can happen".

Scenario 2. Johns house loses his grounded conductor. His house is ok hopefully because his grounding electrode system is keeping a floating neutral in check.

In electronics static discharge and isolated grounds come into play, but that's a whole different thread. Lol

My god I had to whip out the code book for this. It was a good brush up.

i told him no 8 pages ago (post 27) back in 2011 i believe. code hasnt changed.

 

[CobyRupert]

I'm done, this is not the discussion that the poster asked for.

Regarding carrying on a conversation about something related after the poster has been given an answer, repeat after me: "It's Ok. It's Ok. It's Ok".

Hivoltage98: Any idea why a 400 amp service requires a bigger grounding electrode conductor to the ground rod then say a 100amp service, when as per code, you shouldn't rely on the earth as a ground path conductor? (And the purpose of the EGC (equipment ground conductor) that you run with circuits is to get fault current back to it's source (transformer or gen) so the breaker will trip, not to get fault current into the ground.)

 

[grsthegreat]

ok..im gone from this post...later all

 

[Hivoltage98]

Regarding carrying on a conversation about something related after the poster has been given an answer, repeat after me: "It's Ok. It's Ok. It's Ok".

Hivoltage98: Any idea why a 400 amp service requires a bigger grounding electrode conductor to the ground rod then say a 100amp service, when as per code, you shouldn't rely on the earth as a ground path conductor? (And the purpose of the EGC (equipment ground conductor) that you run with circuits is to get fault current back to it's source (transformer or gen) so the breaker will trip, not to get fault current into the ground.)

1.The conductor is larger because the wire is sized according to the size of the service. If a fault would occur, the conductor needs to be sized for the maximum fault current.
2. The code never says not to trust the earth as a ground path conductor. If you drive a ground rod, you should always check that it has a reference to ground. Ou also need a second ground, ie.. Cold water pipe.
3. The fault current needs to go back to the grounded conductor. Remember it's a system. The grounded conductor is the return path for current. The grounding electrode is strictly for fault current. It's a safety wire.

 

[Kaavin]

Grounding a portable generator that *NOT* connected to a house is not necessary. OSHA states that the unmodified frame of the generator serves as the ground! Here is a link to the official OSHA document on that topic:
https://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.pdf

Safety first now!

 

[Hivoltage98]

Grounding a portable generator that *NOT* connected to a house is not necessary. OSHA states that the unmodified frame of the generator serves as the ground! Here is a link to the official OSHA document on that topic:
https://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.pdf

Safety first now!

Yep. That's the reference to nfpa 70