Mep-802a. Any reason not to drive ground rod?

ribs1

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Hello,
I have my generator connected through a transfer switch with neutral bonded at main panel.
The cable from the generator to the house is about 150 feet. Is there any reason not to also drive a ground rod at the generator?
Thanks
 

Scoobyshep

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If you have it connected to the house you are grounded.

Depending on local codes you may not want another rod. For example : if you drive a rod at the generator that rod becomes part of the grounding network, I have had municipalities get bitey over this because now it needs to be able to carry the load that it might see in its life time. Since it is part of the overall ground it needs to be sized for the service main (typically 6 or 4 awg).

If you dont drive a rod, the grounding conductor can be sized to match the generators maximum output.
 

Coug

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Only one ground rod in the system.

The ground wires can also carry current, and there can be issues if there is an imbalance in the system due to multiple ground rods.

It used to be code to ground standby generators at the generator, but current code is that the grounding goes through the house system, and grounds at the gen are not allowed.
 

ribs1

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Only one ground rod in the system.

The ground wires can also carry current, and there can be issues if there is an imbalance in the system due to multiple ground rods.

It used to be code to ground standby generators at the generator, but current code is that the grounding goes through the house system, and grounds at the gen are not allowed.
Thanks
 

m32825

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Only one ground rod in the system.

The ground wires can also carry current, and there can be issues if there is an imbalance in the system due to multiple ground rods.

It used to be code to ground standby generators at the generator, but current code is that the grounding goes through the house system, and grounds at the gen are not allowed.
Code in my area calls for additional grounds at detached buildings (which are tied into the panel and structure), but one and only one point of bonding (service entrance, before first use).

I sorted through this topic a while back in this post:

 

Abrant23

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Code in my area calls for additional grounds at detached buildings (which are tied into the panel and structure), but one and only one point of bonding (service entrance, before first use).

I sorted through this topic a while back in this post:

This is accurate per the NEC. You can drive as many ground rods as you'd like, but it can only be bonded to the neutral at the first means of disconnect. Our code requires ground rods at any outbuildings as well. Its also smart to have one for the gen set too.
 

Guyfang

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One of the reasons there are so many different versions to this song is because lots of folks live in another state, the people asking the questions.
 

Chainbreaker

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This is accurate per the NEC. You can drive as many ground rods as you'd like, but it can only be bonded to the neutral at the first means of disconnect. Our code requires ground rods at any outbuildings as well. Its also smart to have one for the gen set too.
This doesn't apply to the OP's situation, however for anyone coming along and using this thread's info to gnd their generator there is a caution though. I am of the understanding there is a distance restriction on how close a gnd rod can be to the main house panel's gnd rod. I recall reading somewhere you do not want to drive an additional gnd rod at generator closer than ~25' of the main panel's gnd rod when generator uses a 4 conductor hookup utilizing electrical panel gnd. The issue is potential for developing ground loop currents if gnd rods are too close to one another.

Reference: MEP-003a Hook Up Sticky. Post # 152 per SS member "Coug" in the first paragraph.

"You shouldn't need/have a ground rod on the generator because there can be a voltage differential on the ground path between the two ground rods that can mess things up. The older NEC code said to ground generators, but the newer ones say not to if it's tied into the house's ground system."

So my take was that if you are running a 4 conductor feed (2 hots, neutral & gnd) and are within ~25' to breaker panel's "electrical panel gnd" no driven gnd rod is necessary at generator.

This is pertinent to 2 of my generators parked next to my garage adjacent to wall that has my breaker panel with gnd rod driven below it. So, anyone coming along & reading this with "similar circumstances" should make sure they consider that advice or when in doubt use the services of a "Licensed Electrician" to insure your hook-up is in compliance with your local electrical codes.

If any of this is in error or has changed, please chime in & cite a source.
 
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Abrant23

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use the services of a "Licensed Electrician" to insure your hook-up is in compliance with your local electrical codes.

This is the most important part of this response. There are so many different factors that come into play when installing a backup generator, depending on transfer switching method, location, mounting, and enclosure type the generator is located. If in doubt, ask someone who does it for a living!
 

Chainbreaker

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Yes, Abrant23 is 100% right, there are a lot of scenarios to consider...

For example: If one is periodically using a standalone load bank not connected to house wiring for generator testing/troubleshooting purposes and you disconnect your genset's 4 conductor house feed cable with gnd going to house in order to hook up to a cable adapter going to a load bank, you are then breaking your house ground connection & then your genset becomes a Self-Derived System (SDS).

In that scenario, you need to hook genset's gnd lug to a driven gnd rod & reconnect the neutral bond grounding strap/lug on genset. I have that situation when load testing and connect up to a driven gnd rod about 30+ feet away from house.

In my case with, MEP-002a's neutral to gnd cable lug on frame, I installed an onboard heavy-duty switch for reconnect/disconnect of genset's neutral wire to genset gnd lug that I use when running a load test in SDS mode. With the MEP -802/03 series you don't need to add a switch since there is an onboard neutral bond tab you can utilize. Don't forget to reconfigure genset neutral bond appropriately when reconnecting to house hookup.

Edit: In post #1 in this thread, you can see a picture (last picture, hard to see the screw due to flash reflection, its just left of handle) of the switch I used and my DIY lockout screw to insure switch remains in correct mode. I must manually remove screw & turn switch to put into SDS mode & reverse when in House configuration.
 
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Mullaney

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Thinking about our neighbor at the print shop...

They have a dispatch center here in the mechanical building. Every other week, promptly at 0800, their propane powered generator kicks off and runs at speed for a half hour. Unattended. Nobody walks out there and looks at it or opens the fence or anything else. It just fires up and runs. Same time on the alternating week, one of the mechanics (same one every time) comes out and checks the engine oil and radiator fluid level.

The switch gear is automated and there is a battery bank between the equipment and power.

It seems like a heck of a nice way to have power and know that they have a functional backup power source.
 

Coug

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Thinking about our neighbor at the print shop...

They have a dispatch center here in the mechanical building. Every other week, promptly at 0800, their propane powered generator kicks off and runs at speed for a half hour. Unattended. Nobody walks out there and looks at it or opens the fence or anything else. It just fires up and runs. Same time on the alternating week, one of the mechanics (same one every time) comes out and checks the engine oil and radiator fluid level.

The switch gear is automated and there is a battery bank between the equipment and power.

It seems like a heck of a nice way to have power and know that they have a functional backup power source.
Having it checked every other week seems excessive, but it really depends on what the standby generator is classified as.
Generators in medical backup systems have a lot of specific requirements on how often they get checked, tested under load, etc. The ones I do for an Alzheimer's center and a rehab center do a standard weekly run of about 15 minutes, and every year they have to have someone with some type of certification do a 1.5 hour load test and sign off.

For non-medical generators, there really aren't any requirements, unless the fire marshall in that jurisdiction came up with them.
Most standby units I work on fire up every week for 12 minutes. Some are every other week, some once a month, depends on how the customer wanted them set up, but standard is once a week.
Once a year they are supposed to be checked out. Some customers are religious about this, and schedule it months in advance.
Others don't bother.
I've had generators that were installed (not by me, I just do repairs) and never touched until they failed. Current high score is 14 years old on the original battery, oil, filters, and no valve adjustment.
Many customers have no clue for anything to do with their equipment, and the fact that it's all automated is the only reason it actually works. Taking the human out of the equation is often a good thing, especially when the power goes out.

(I do Generac standby generators for a living in case you were wondering)
 
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