Service grounding question

[delaware74b]

I am the process of installing new service equipment on 2 apartment buildings. Each building will have a 1000-amp main breaker feeding approximately 15 meters on a sq-d ez stack. Incoming feed is 120/240 single phase with 3 sets of parallel 500 AL xhhw. #6 bare to 2 ground rods 6 feet apart. I am also running a bond wire to the 2" copper water line where I comes into the building. My question is the #2 copper (or 1/0 AL) the proper size, based on NEC 250.66? I will also have to bond the gas line in one building. That boiler provides all domestic hot water and baseboard heat in both buildings. Do I use the same #2 size for the gas line or is it 2/0 cu based on 250.122? The boiler room has its own 100 amp subpanel coming off a 225 amp panel next to the meter stack.

These apartments are from the 1950's with original panels and wiring that has been not touched. Panels are being replaced after the new main gear is turned on.

 

[Smart $]

... My question is the #2 copper (or 1/0 AL) the proper size, based on NEC 250.66? I will also have to bond the gas line in one building. That boiler provides all domestic hot water and baseboard heat in both buildings. Do I use the same #2 size for the gas line or is it 2/0 cu based on 250.122? The boiler room has its own 100 amp subpanel coming off a 225 amp panel next to the meter stack...

Water pipe GEC needs to be 2/0 Cu or 4/0 Al.

The gas piping will typically be bonded with the EGC in the electric circuits supplying the gas boiler equipment. If not, you can jumper from the EGC to the piping. The circuit rating determines EGC or jumper size.

 

[delaware74b]

Thanks. I see it's based on the sum of the parallel feeds (or 1500mcm). I thought it was based on the single 500, not the sum.

My boss, inspector, and I missed that one!

 

[DrSparks]

I am the process of installing new service equipment on 2 apartment buildings. Each building will have a 1000-amp main breaker feeding approximately 15 meters on a sq-d ez stack. Incoming feed is 120/240 single phase with 3 sets of parallel 500 AL xhhw. #6 bare to 2 ground rods 6 feet apart. I am also running a bond wire to the 2" copper water line where I comes into the building. My question is the #2 copper (or 1/0 AL) the proper size, based on NEC 250.66? I will also have to bond the gas line in one building. That boiler provides all domestic hot water and baseboard heat in both buildings. Do I use the same #2 size for the gas line or is it 2/0 cu based on 250.122? The boiler room has its own 100 amp subpanel coming off a 225 amp panel next to the meter stack.

These apartments are from the 1950's with original panels and wiring that has been not touched. Panels are being replaced after the new main gear is turned on.

Wow! A 1000amp main for 15 apartments?! Seems a bit excessive to me. Sizing the GEC is always done by the sum of the cross section of parallel feeders. The biggest it is required to be no matter what, however, is #3/0 cu.

 

[kwired]

Wow! A 1000amp main for 15 apartments?! Seems a bit excessive to me. Sizing the GEC is always done by the sum of the cross section of parallel feeders. The biggest it is required to be no matter what, however, is #3/0 cu.

He did say it was single phase 120/240. May not be so excessive if there is all electric heating/water heating.

You get roughly similar available VA out of a 600 amp 208/120 system

 

[DrSparks]

He did say it was single phase 120/240. May not be so excessive if there is all electric heating/water heating.

You get roughly similar available VA out of a 600 amp 208/120 system

Electric heat would definitely do it.

 

[mwm1752]

Smart is correct but---------Your gas pipe bonding may have a different answer if the use of CSST is installed as part of the gas branch piping.

 

[delaware74b]

The first building has 2 separate house services we're combining into one (for billing purposes) 225-amp main house panel. Out of that panel, a 100-amp subpanel feeding the boiler room, which supplies all domestic hot water and baseboard heat in both buildings. Also, feeding another 100-amp panel for the tenant coin-op laundry (2 washers and 2 dryers).

Each original tenant panel has a 50-amp main, 40-amp range, 2 20a 240 a/c window units in a slide-through frame, 2 15a recep/lighting circuits, 2 2 20-amp kitchen circuits. These panels are the original 16-space GE panels from the late 50's. All cloth-covered romex with the undersized bonding (ground) wire.

The replacement panels will be 24-space Homeline MLO's fed with a 60-amp breaker in the meter stack. We oversized the new service and meter stack with a spare service available. One building will have a 225-amp capable spare, while the other building will has a 125-amp rated spare.

The existing services are in groups of 2 in a 2-gang meter pan, panels in garages on opposite side of block wall. The walls need to be rebuilt as they're puling away from the building. Also not all tenants have access to these garages where their panels are located. New panels are being located in areas where all tenants have access. Also, POCO has their secondaries running horizontally on insulators between the first and second floor windows. The fire company would have no access to second floor windows due to this service setup.

 

[DrSparks]

The first building has 2 separate house services we're combining into one (for billing purposes) 225-amp main house panel. Out of that panel, a 100-amp subpanel feeding the boiler room, which supplies all domestic hot water and baseboard heat in both buildings. Also, feeding another 100-amp panel for the tenant coin-op laundry (2 washers and 2 dryers).

Each original tenant panel has a 50-amp main, 40-amp range, 2 20a 240 a/c window units in a slide-through frame, 2 15a recep/lighting circuits, 2 2 20-amp kitchen circuits. These panels are the original 16-space GE panels from the late 50's. All cloth-covered romex with the undersized bonding (ground) wire.

The replacement panels will be 24-space Homeline MLO's fed with a 60-amp breaker in the meter stack. We oversized the new service and meter stack with a spare service available. One building will have a 225-amp capable spare, while the other building will has a 125-amp rated spare.

The existing services are in groups of 2 in a 2-gang meter pan, panels in garages on opposite side of block wall. The walls need to be rebuilt as they're puling away from the building. Also not all tenants have access to these garages where their panels are located. New panels are being located in areas where all tenants have access. Also, POCO has their secondaries running horizontally on insulators between the first and second floor windows. The fire company would have no access to second floor windows due to this service setup.

Couple of things. Firstly, I'm familiar with the old NM with an overall fabric jacket, but I've never seen any with a "bonding wire" before. I've seen old BX with an aluminum ground reinforcing wire. Secondly, 60 amps is fine as long as it doesn't exceed your total connected load per unit.

 

[delaware74b]

DrSparks - I call the undersized bare wire a bonding wire due to its size and the fact it's tied to all the metal device boxes with no connections to the devices except for their mounting screws.

Generally, the tenants don't trip their current 50 amp main breakers, so the 10 amp increase in the new panels should be nothing more than a little reserve capacity.

 

[DrSparks]

DrSparks - I call the undersized bare wire a bonding wire due to its size and the fact it's tied to all the metal device boxes with no connections to the devices except for their mounting screws.

Generally, the tenants don't trip their current 50 amp main breakers, so the 10 amp increase in the new panels should be nothing more than a little reserve capacity.

Yeah, but I've never seen one in the old cloth romex before.

 

[kwired]

Yeah, but I've never seen one in the old cloth romex before.

Pretty sure I have. Definitely in 12-2, but was not required to be same size as it is today if used for equipment grounding. But seem to recall seeing it in a 6-3 one time, and it was only a 16 or 14 AWG bare conductor. But most of the time a cable with conductors that large was always a type SE cable so it is pretty rare to find a 6-3 NM cable that old in the first place.