Grounding 2 family dwelling

[Turbo1002]

I need help grounding a 2 family dwelling in NYC. This is a 100 amp service with one service drop (one set of service entrance conductors). It goes to a duplex meter pan box. Then from each meter there is a service panel each having its own service disconnect switch. Do I need two separate #8 wires going to the
water main for egc and two separate ground rods for each service panel? If, I only need one water main and rod how would you run the grounding wires?

 

[Buck Parrish]

Treat it as one service. However if you have two different water main services. I would think one main water line grd. electrode would be an adequate electrode. (with in 5 feet of entrance) The water heater equipment ground will bond the water pipe. I've had an inspector want me to run a grounding electrode to each water line. But I didn't agree.
Ground rods will be as one service. Bring them out of the meter pan.

 

[Turbo1002]

Treat it as one service. Should both panels have the bond screw installed from the neutral bar to ground? If I bring the egc (water main and rod) to one panel what happens in the other? It is the first point of disconnect from the service. Only one water main service.

 

[darekelec]

Hey, man. I am also in NYC. Recently inspectors got more strict on grounding services here. Although there is a couple of ways to ground service recently everybody here installs a grounding bar like this

http://stormcopper.com/design/Electrical-Ground-Bars.htm

next to service and terminates wires there with copper lugs. Anybody, please, respond if regular lugs are code compliant.
This works for all sizes of services. See 250.54(F)(3).
Run Your GEC to water pipe within 5 feet - size depending on service conductors (table 250.66) - green #8 for hots #2 and smaller.

http://www.safecoelectric.com/images/resources_pdf/NEC2008 Table 250.66.pdf

If you sleeve it with emt you have to bond conduit on both sides with fittings and same size green wire.

http://forums.mikeholt.com/showthread.php?t=144690

I would run 2 GEC taps from bar to each panelboard (2 in your case) with service switch and terminate them in neutral bars.

Of course keep the green screws at neutral bars tied to enclosure

Bond service raceways and enclosures with same size green conductor. Avoid paralleling Neutral conductor.

Run #6 to ground rod - supplementary GEC required here in NYC. Nobody asks here to check for 25 ohm or less resistance. Can anybody answer if it should be 25 ohm or less or second rod driven?

Some inspectors would ask to provide Intersystem Bonding Terminal but for most the copper grounding bar is enough for other utilities (telephone, catv, dish) to tie their grounds. Just attach to bar 3 extra spare lugs.

Ask more questions if needed. I am happy to answer as I was answered professionaly many times on this forum. :thumbsup:

 

[Turbo1002]

Awesome, thank you. It is hard to get a solid answer from the AHJ around here. What are you referring to when you say " avoid paralleling neutral conductor"?
So, I am treating it like two separate services that share the EGC's?

 

[Turbo1002]

One more question please. Should I come off of the ground bar and go straight to the meter pan to bond that as well. Or come off the neutral bar to bond the meter when using migb's because I have concentric knockouts.

 

[darekelec]

Turbo wrote
If I bring the egc (water main and rod) to one panel what happens in the other? It is the first point of disconnect from the service. Only one water main service.
Answer;
That was allowed practice around here for decades - ground the 'biggest' service switch. It was not code compliant, though.

Turbo wrote
What are you referring to when you say " avoid paralleling neutral conductor"?
Answer;
When bonding metal raceways (conduit, offset nipples) to Neutral bar do not run green wire and attach it from neutral bar to meter can or neutral in meter. Not only its redundant but violation. You would get 2 same wires in raceway. Just install 1 bonding bushing (migb) on emt or nipple and go with #8 to closest neutral bar.

Turbo wrote
One more question please. Should I come off of the ground bar and go straight to the meter pan to bond that as well?
Answer;
No.
Keep that neutral to case connection in meter pans and do not worry about it. It bothered me for many years as it causes 'objectionable current' to flow on metal parts but thats an enclosure that electricians do not have control over. That's a PoCo area.

Here is a similar thread that recently was on forum
http://forums.mikeholt.com/showthread.php?t=153275

I liked one response in that thread from PowerSupportElec;

You need to see what your power company wants. I can't imagine that they would want an isolated neutral, but NYC makes stupid decisions all the time.

:lol:That's so funny but true.

Before everybody here grounded the 'biggest service switch' and now everybody installs grounding bars.

As I stated at beginning of this thread there are a couple of ways to ground services. Around here electrical contractors' choice now is the bar cause it works every time although it adds extra 70$ and more time in labour.

Let me use your thread and ask more code inclined electricians if a cheaper solution would work;
Can Turbo in his case connect GEC to neutral in service end box and go to water pipe and unbroken to rod and save couple of hundred of bucks? The connection in end box would have to be listed for grounding and bonding thus a c-tap irreversible (compression) connector.
But then PoCo here has a rule of not more than 2 used openings in their end box or they have to install a detail bar. Would that penetration increase the number by 1 and potentially to 3. or does that rule apply only to power conductors? Does anybody here have access to Con Edison's rules so I could learn more.

If I am asking too many questions on somebody else's forum just let me know.

 

[darekelec]

Don't forget about 'service bonding'. Even the rigid pipe from street should have migb on and be bonded to end box and that to migb on conduits or nipple going to meter cans. If you have a through that also has to be bonded using green wire from T 250.66. It's better to install those migb bushings before inserting wires. The code and interpretation did not change there. Just do it as in the past if you know basic rule for that.
If you want a detailed and precise answer how to do it you would have to describe your equipment layout.
Basically you want a good connection of metal parts to neutral (without paralleling) so if there is a ground fault of hot service conductor to equipment there is a good return path for current on neutral back to utility transformer and big kaboom in your service.