Residential rewire grounding

[southbaysumo]

I am rewiring a 2 unit residence with a subpanel in each unit. The service is 100 feet away on a seperate garage. I plan to bond the hot/cold water and gas to one subpanel along with bonding the water service within 5 ft. of entering the building. I"m also thinking it would be a good idea to bond the 2 subpanels together. Part of me also thinks that to be to code The water service grounding should just be taken all the way back to the service entrance which is much more inconvenient. Also I'm thinking I need a ground rod since the ervice is on a seperate building. Do I have to run a ground wire to each sub panel or just one if the panels are bonded todether. Both units share common water and gas piping. Thanks, Bob

 

[kwired]

Do a little reading through art 225 part II.

Does the 2 family unit have a common area where the panels for both can be placed together? If so that is where they should be located.

In general a separate building can only be fed with one supply. The one supply can have 1 to 6 disconnecting means grouped together. The branch circuit panels would not need to be located in same location as the main disconnects.

 

[stew]

If you are rewiring then are you also installing new feeders? If so you use a 4 wire feeder to each panel and bond one to the common piping. In most cases you will need 2 ground rods at the service. I would not locate both panels in the same place if this is a duplex. If you are replaceing the panels I would use a panel with a main breaker. Although its not a requirement it is nice that each unit has a way to shut its entire panel off. I assume there is a main disconnect at the garage service? The panels do not need to be bonded together.

 

[PDK]

I don't believe that not having a main breaker is an option. NEC 225.36 states that the disconnecting means shall be service rated. According to the listing and labeling provided by the panel manufacturers, the only way that the panel is service rated is by installing a backfed breaker in a MLO panel or by installing a panel with a main in it.

 

[kwired]

If you are rewiring then are you also installing new feeders? If so you use a 4 wire feeder to each panel and bond one to the common piping. In most cases you will need 2 ground rods at the service. I would not locate both panels in the same place if this is a duplex. If you are replaceing the panels I would use a panel with a main breaker. Although its not a requirement it is nice that each unit has a way to shut its entire panel off. I assume there is a main disconnect at the garage service? The panels do not need to be bonded together.

This is a separate building supplied by a feeder(s). It must have a main disconnect(s) at the separate building. 225.30 in general does not allow multiple feeders to supply a separate building.

225.30(B)(1) may allow for more than one feeder to the building. It says "Multiple-occupancy buildings where there is no space available for supply equipment accessible to all occupants." However there is pretty much always space available outside so I really don't see where this could be used in very many cases.

I would run one feeder to a common point accessable to all occupants inside nearest point of entrance or outside. Put two disconnects there do your grounding electrode system there and subfeed to a panel in each occupancy.

 

[stew]

so the garage is not attached? I just assumed it was. guess if I had read the post properly I would have responded differently of course. my bad. I wires solution makes sense. Now you still have a service drop at the garage with a service disconnect. It would seem that the ground rods would go there to form the ges. You also need one at the duplex structure as well.