Transfer Switch Grounding

[garyde]

I have Generac Homelink Upgradeable Manual Transfer Switch (Model: G0068521 Serial: 3009887938).

The neutral is switch and I believe when this happens it is a separately derived system.

The manual recommended the generator attached to the transfer switch needs to have its neutral bond to the generator frame and the generator needs to be attached to a grounding rod.

My question is why does a grounding rod need to be attached to the generator when the house the transfer switch is on is already grounded, i.e., what risk is exposed?

Thank you

 

[James]

I have Generac Homelink Upgradeable Manual Transfer Switch (Model: G0068521 Serial: 3009887938).

The neutral is switch and I believe when this happens it is a separately derived system.

The manual recommended the generator attached to the transfer switch needs to have its neutral bond to the generator frame and the generator needs to be attached to a grounding rod.

My question is why does a grounding rod need to be attached to the generator when the house the transfer switch is on is already grounded, i.e., what risk is exposed?

Thank you

If the house has its own ground rod permanently connected then by connecting the generator to it, you are doing as the manual recommends, as in attaching a ground rod to the generator.

you will still need the N to ground link at the generator.

however if the ground is provided by your electricity supplier, this can't be relied on in the event of a power outage as it may be disconnected either by the fault (think fallen tree or digger slices cable) or it could become disconnected whilst repairs are made to the dead section of the network.

If this is the case, it is imperative to have a good ground reference to prevent any fault currents being passed down the disconnected cable and injuring people working on the network.

 

[garyde]

If the house has its own ground rod permanently connected then by connecting the generator to it, you are doing as the manual recommends, as in attaching a ground rod to the generator.

you will still need the N to ground link at the generator.

however if the ground is provided by your electricity supplier, this can't be relied on in the event of a power outage as it may be disconnected either by the fault (think fallen tree or digger slices cable) or it could become disconnected whilst repairs are made to the dead section of the network.

If this is the case, it is imperative to have a good ground reference to prevent any fault currents being passed down the disconnected cable and injuring people working on the network.

James thank you

A separate ground is required on the portable generator, my question is why?

In what situation would electrocution, fire, etc. become likely if you did not separately attach a grounding rod to the generator?

 

[James]

It would help to provide protection against shock if the generator became disconnected from the house.

Also remember that if the postman gets injured from a damaged cable and you have NOT followed the manufacturers instructions, it leaves you in a much worse position when it comes to court.

I realise the above is not a technical reply but the general idea with electrics like this is to ensure you have a reliable connection to earth and that a fault anywhere in the system will result in disconnection from the electrical source.

disconnection due to fault is done in one of 2 ways normally.

1. by ensuring the current flowing across a fault from live to ground is high enough to trip the breaker (the N to ground link helps with this)

2. by using a current monitoring device that constantly compares current in the live and N wires. RCD in uk speak or GFI in American lingo. this device is likely to work much better if the generator has a good ground reference.

 

[garyde]

It would help to provide protection against shock if the generator became disconnected from the house.

Also remember that if the postman gets injured from a damaged cable and you have NOT followed the manufacturers instructions, it leaves you in a much worse position when it comes to court.

I realise the above is not a technical reply but the general idea with electrics like this is to ensure you have a reliable connection to earth and that a fault anywhere in the system will result in disconnection from the electrical source.

disconnection due to fault is done in one of 2 ways normally.

1. by ensuring the current flowing across a fault from live to ground is high enough to trip the breaker (the N to ground link helps with this)
get
2. by using a current monitoring device that constantly compares current in the live and N wires. RCD in uk speak or GFI in American lingo. this device is likely to work much better if the generator has a good ground reference.

Thanks James - this makes sense
If the generator had a ground fault but the connection to the house was still intact and you were standing on wet ground and touch the generator chassis, could you still get electrocuted if it was not attached to a grounding rod?

 

[James]

Kind of,
basically you are trying to make sure that any things you can touch simultaneously are at the same potential (voltage) so as not to cause a current to pass through the body.