2X100 AMP service questions

[deltix]

Hi. My first post here. I have C-10 here in California (LADWP area), however I don't do much of, if any, high voltage stuff. I do low voltage. Now I'm working on own property, some improvements, one of them being updating electrical.

What I have is one service feeding two meters with main disconnects outside and two panels (sub panels), one inside each unit. Units are really small, 300 and 500 square feet. I need to redo everything. I have few questions just to make sure I don't screw up anything.

1. Two grounding rods 8 feet apart, #6 GEC (THHN stranded copper as I will be pulling it trough EMT and flex, continuous from end to end), not bonded to the water line as everything is redone with PEX. I assume that I can use the same rods for both units.

2. Thinking of going with 2AWG feeder to inside panel. 1AWG if really necessary. On smaller unit that is little bit further I could downsize main breaker to 80A-90A just to keep smaller AWG wire.

Does above sound right?

 

[david]

Hi. My first post here. I have C-10 here in California (LADWP area), however I don't do much of, if any, high voltage stuff. I do low voltage. Now I'm working on own property, some improvements, one of them being updating electrical.

What I have is one service feeding two meters with main disconnects outside and two panels (sub panels), one inside each unit. Units are really small, 300 and 500 square feet. I need to redo everything. I have few questions just to make sure I don't screw up anything.

1. Two grounding rods 8 feet apart, #6 GEC (THHN stranded copper as I will be pulling it trough EMT and flex, continuous from end to end), not bonded to the water line as everything is redone with PEX. I assume that I can use the same rods for both units.

2. Thinking of going with 2AWG feeder to inside panel. 1AWG if really necessary. On smaller unit that is little bit further I could downsize main breaker to 80A-90A just to keep smaller AWG wire.

Does above sound right?

I think it is good that you recognize the need to do electrical maintenance on your property.

Can't really give you any answers here.


Perhaps you could ask another electrician about the metal conduit you described using to protect your grounding electrode conductor.

You said there is pex through out. You could ask another electrician to verify that the main water line entering the building is also pex

 

[Dennis Alwon]

Hi. My first post here. I have C-10 here in California (LADWP area), however I don't do much of, if any, high voltage stuff. I do low voltage. Now I'm working on own property, some improvements, one of them being updating electrical.

What I have is one service feeding two meters with main disconnects outside and two panels (sub panels), one inside each unit. Units are really small, 300 and 500 square feet. I need to redo everything. I have few questions just to make sure I don't screw up anything.

1. Two grounding rods 8 feet apart, #6 GEC (THHN stranded copper as I will be pulling it trough EMT and flex, continuous from end to end), not bonded to the water line as everything is redone with PEX. I assume that I can use the same rods for both units.

2. Thinking of going with 2AWG feeder to inside panel. 1AWG if really necessary. On smaller unit that is little bit further I could downsize main breaker to 80A-90A just to keep smaller AWG wire.

Does above sound right?

1. Yes 2 rods at least 6' apart but further is better and a #6 grounding electrode conductor will be fine. Be careful about running a grounding electrode conductor thru conduit as you will have to bond the pipe to the rod. Can't you just sleeve it with PVC and then just run it in the ground?

2. The minimum service allowed by the NEC for a dwelling is 100 amps. When you say #2 do you mean aluminum? If so that is good to the inside panel if the panel supplies the entire load of the unit. Is there not an exterior breaker? What code cycle are you guys using

 

[david]

1. Yes 2 rods at least 6' apart but further is

2. The minimum service allowed by the NEC for a dwelling is 100 amps.

230.79 (D) rating of the service disconnecting means 2020 NEC
60 amps

310.12 (A) for services rated 100 amps through 400 amps
To the original poster I'm sorry I didn't know we could answer your questions

As Dennis pointed out a GEC installed in metal conduit has to be bonded to the conduit

You mentioned pex through out but if the building water supply is a metal water pipe you must bond to the street side within the first five ft where it enters the dwelling

I'm not sure if there is a basement common to both dwellings or hallways common to both you may need a third panel for those common areas if any.

There may be additional utility regulations regarding a common area meter

Here dwelling unit meters have to have horn by pass.

But if the owner of the duplex does not reside in one of the dwelling units the utility requires a lever by pass meter socket for the common areas.

Even if you're doing the work yourself you may want to consult locally with a residential electrical contractor or inspector in your local area

 

[augie47]

I may have overlooked it but clarify are these dwelling units ?

 

[Dennis Alwon]

I may have overlooked it but clarify are these dwelling units ?

I assumed they are those small dwellings and I mentioned dwelling units in my post

@david if they are dwellings as I suspected

230.79(C) One-Family Dwellings. For a one-family dwelling, the service
disconnecting means shall have a rating of not less than
100 amperes, 3-wire.

 

[david]

I assumed they are those small dwellings and I mentioned dwelling units in my post

@david if they are dwellings as I suspected

I assumed they are those small dwellings and I mentioned dwelling units in my post

@david if they are dwellings as I suspected

Yes I made the same assumption sorry that does need clarification.

Yes (C) says for a one family dwelling but the OP said two meters and two units. (C) does not say dwelling unit or units
It says dwelling

My assumption would have then been a two family dwelling (duplex) and that would fall under (D)

Only (C) states 3 wire do we want to open that can of worms for an OP that states he has low voltage experience and he is working on his own property?

 

[Dennis Alwon]

My assumption would have then been a two family dwelling (duplex) and that would fall under (D)

I would never have read that to mean (D). I see each unit as a single family dwelling and thus need 100 amps, but perhaps I am incorrect. Strange that a single family unit would need 100 amps but a duplex doesn't ????

Anyway we don't know what the units are and whether they are attached or not.

 

[augie47]

Hi. My first post here. I have C-10 here in California (LADWP area), however I don't do much of, if any, high voltage stuff. I do low voltage. Now I'm working on own property, some improvements, one of them being updating electrical.

What I have is one service feeding two meters with main disconnects outside and two panels (sub panels), one inside each unit. Units are really small, 300 and 500 square feet. I need to redo everything. I have few questions just to make sure I don't screw up anything.

1. Two grounding rods 8 feet apart, #6 GEC (THHN stranded copper as I will be pulling it trough EMT and flex, continuous from end to end), not bonded to the water line as everything is redone with PEX. I assume that I can use the same rods for both units.

2. Thinking of going with 2AWG feeder to inside panel. 1AWG if really necessary. On smaller unit that is little bit further I could downsize main breaker to 80A-90A just to keep smaller AWG wire.

Does above sound right?

The #6 GEC should be sufficient and as others have stated, IF you wish to enclose it in a raceway PVC would be preferable.
If your POCO allows you can run one GEC from your meter (assuming two gang meter socket) or a #6 from each disconnect.


If we are addressing dwelling units 310.15(B)(7) will allow you to use a #4 Cu or #2 AL for each dwelling feeder.

 

[david]

I would never have read that to mean (D). I see each unit as a single family dwelling and thus need 100 amps, but perhaps I am incorrect. Strange that a single family unit would need 100 amps but a duplex doesn't ????

Anyway we don't know what the units are and whether they are attached or not.

Yes I know. It becomes more relevant with buildings with a large amount of dwelling units

Dwelling single family a building that consist solely of one dwelling unit. So if the op is in fact talking about a building such as a duplex then (C) does not apply

 

[david]

The #6 GEC should be sufficient and as others have stated, IF you wish to enclose it in a raceway PVC would be preferable.
If your POCO allows you can run one GEC from your meter (assuming two gang meter socket)

True, For the OP'S benefit 250.64 (D) (3) common location 2020 NEC

 

[david]

IF you wish to enclose it in a raceway PVC would be preferable.
I or a #6 from each disconnect.

If projected from physical damage a #8 would be allowed from each disconnect
250.64 (D) (2) 2020 NEC individual grounding electrode conductors

 

[david]

If we are addressing dwelling units 310.15(B)(7) will allow you to use a #4 Cu or #2 AL for each dwelling feeder.

If the calculated load supports it. The feeder could be 90 or 80 amps as the OP ask. I f the calculated load supports it the feeder could be 60 amps but the 83 % would be off the table since it only applies to 100 through 400 amp rated services
Table 310.16 2020 NEC
75 deg C #4 alum or # 6 copper.

 

[david]

If the calculated load supports it. The feeder could be 90 or 80 amps as the OP ask. I f the calculated load supports it the feeder could be 60 amps but the 83 % would be off the table since it only applies to 100 through 400 amp rated services
Table 310.16 2020 NEC
75 deg C #4 alum or # 6 copper.

Or dwelling unit feeders

 

[tortuga]

Also keep in mind you can't use the optional calc if the feeders do not have an ampacity of 100A.
What are the loads?
24kw Electric on demand water heaters and all electric tiny house with full laundry and EV chargers?

 

[deltix]

Thanks everyone. I already did some work. GEC going to grounding rods (8ft apart) is protected. That I knew i need to do. It is bonded to the conduit using grounding bushing at the main disconnect and subpanel. Units are detached. There are actually three units total, but third, front one has it's own service. Main water supply is on the other side of the property from two mentioned units, yes, copper, but converts into pex that runs throughout the whole property. It is impossible to have two back units connected to the main water supply copper line. All wiring is copper, no aluminum. One unit is studio, no washer, no dryer, no dishwasher. 300 sqaure feet. Second one is small one bedroom with washer and dryer, not sure about anyting else at this point. Both units have gas stove and oven. FYI, both units had 50A single pole service until now! Yes, it is 100 years old property.

 

[david]

Thanks everyone. I already did some work. GEC going to grounding rods (8ft apart) is protected. That I knew i need to do. It is bonded to the conduit using grounding bushing at the main disconnect and subpanel. Units are detached. There are actually three units total, but third, front one has it's own service. Main water supply is on the other side of the property from two mentioned units, yes, copper, but converts into pex that runs throughout the whole property. It is impossible to have two back units connected to the main water supply copper line. All wiring is copper, no aluminum. One unit is studio, no washer, no dryer, no dishwasher. 300 sqaure feet. Second one is small one bedroom with washer and dryer, not sure about anyting else at this point. Both units have gas stove and oven. FYI, both units had 50A single pole service until now! Yes, it is 100 years old property.

You haven't said what code cycle you are under.
You now mentioned that the units are detached not sure from what but if you mean single family dwellings, than Dennis was right and you can ignore every thing that I posted.

At least we got it right your upgrading dwellings