Bonding to sub panel

[buck33k]

I have a 200 amp meter/main on the exterior of a dwelling which feeds a MLO panel 30 feet inside. The feeder to the MLO panel is 4/0 4/0 2/0 Al with a #4 Al grounding conductor. GEC is #6cu to two ground rods.

Can the metal water piping be bonded to the MLO panel grounding conductor? If so, how should it be sized? Would you need to increase the size of the grounding conductor back to the service disconnect per 250.66?

After reading 250.104(A)(1) and 250.104(B) I need some clarification .

Buck

[ February 08, 2005, 01:00 AM: Message edited by: buck33k ]

 

[physis]

Re: Bonding to sub panel

"shall be bonded to"

"service equipment enclosrue"
"the grounded conductor at the service" (I emphisized "at")
"the grounding electrode conductor where of sufficient size"
"one or more grounding electrodes used"

See "Service Equipment" and "Grounding Electrode Conductor" in Article 100.

Can the metal water piping be bonded to the MLO panel grounding conductor?

No.

Basicly it can be bonded anywhere from the grounding electrode system up to the main bonding jumper at the service and including the service enclosure. But it can't be connected by an EGC.

Is 250.52(A)(1) satisfied? It looks a lot like 250.104(A) but requires bonding within 5 feet of entrance of the building and the water pipe is included in the grounding electrode system.

 

[bphgravity]

Re: Bonding to sub panel

This example makes no sense to me.

Per the requirement, a #2 AL or a #4 CU bonding jumper is required for the water pipe. The grounding electrode system is only requiring #6 CU electrode conductor.

The #4 AL EGC is of sufficent size to be considered the effective fault path for a 200A feeder, yet I cannot connect my water bond to it. Why not? I don't see why the bond to the water pipe needs to be any larger than the largest equipment grounding conductor as required per 250.122.

What could possibly energize the interior water pipe that would necessitate a bonding jumper larger than largest EGC and GEC?

 

[buck33k]

Re: Bonding to sub panel

I may be wrong, but It would seem to me that the water piping could be bonded to any sub panel, providing the equiptment grounding conductor for that panel was #4 cu. and the water pipes were not part of the grounding system. It would then be bonded AT the service by means of a #4 cu.
There is no requirement for the water pipe bond to not be spliced.

 

[physis]

Re: Bonding to sub panel

It would be nice to have a guy here, (like Charlie E.) from CMP 5. We'd probably keep him pretty busy.

 

[physis]

Re: Bonding to sub panel

It would seem to me that the water piping could be bonded to any sub panel,

It would then be bonded AT the service

The location of a bond is where it's mechanically connected. Not where it goes electrically.

 

[suemarkp]

Re: Bonding to sub panel

If it was any other pipe, then you could. But water pipe bonding seem to be handled differently, perhaps because they could turn into a grounding electrode if a plumber changes things.

Most pipes are bonded with wires per 250.122, but water pipes are 250.66. Most bonding can be done to any panel if the feeder has a sufficiently large EGC. But water pipe bonds must go to the Service Equipment.

 

[hurk27]

Re: Bonding to sub panel

It does not matter which electrode is used or all electrodes that can be use to form a grounding electrode system. It is required to make this connection at the service! A sub panel is not service equipment.

250.24 Grounding Service-Supplied Alternating-Current Systems.
(A) System Grounding Connections. A premises wiring system supplied by a grounded ac service shall have a grounding electrode conductor connected to the grounded service conductor, at each service , in accordance with 250.24(A)(1) through (A)(5).
(1) General. The connection shall be made at any accessible point from the load end of the service drop or service lateral to and including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means .

It has to be connected at the service not the sub panel.

Edit to add that the grounding electrode system is only good for two things. Protection from voltages from a higher source, and from a lightning strike. Nether of which I would want to enter my house to get to the grounding system. The main service is as far as I would ever want lightning to enter my house.

[ February 09, 2005, 06:19 PM: Message edited by: hurk27 ]

 

[buck33k]

Re: Bonding to sub panel

The water piping system in the building I was refering to is isolated from the earth by means of plastic piping entering the building from the water source (as most new construction is).

The metal water piping could be subject to lighting strike and I'm assuming that is why it is to be taken directly to the service, GEC, electrodes, etc. I did not consider lightning, and thought only in terms of the piping becoming energized by the electrical system in the building.

Buck

[ February 09, 2005, 11:41 PM: Message edited by: buck33k ]

 

[gndrod]

Re: Bonding to sub panel

Hi buck33k,

GEC is #6cu to two ground rods.

The GEC for a 200A main disconnect lists #4 AWG Copper in Table 250.66. Is there an exception or is the #6cu really a GEC or do you mean supplementary ground for subpanel? Have I missed something in the interpretation?

rbj, Seattle

 

[wirenut1980]

Re: Bonding to sub panel

rbj,

The GEC for a 200A main disconnect lists #4 AWG Copper in Table 250.66. Is there an exception or is the #6cu really a GEC or do you mean supplementary ground for subpanel? Have I missed something in the interpretation?

I think it is #6 Cu bonding jumper because of 250.53(E) in 2002 NEC, but I could be wrong.

 

[cpal]

Re: Bonding to sub panel

In a dwelling the interior water piping is required to bonded as directed in the following paragraph. It may be a good idea to check out Definitions in article 100 regarding the folloing term "Service Equipment"

250.104 Bonding of Piping Systems and Exposed Structural Steel.
(A) Metal Water Piping. The metal water piping system shall be bonded as required in (1), (2), (3), or (4) of this section. The bonding jumper(s) shall be installed in accordance with 250.64(A), (B), and (E). The points of attachment of the bonding jumper(s) shall be accessible.
(1) General. Metal water piping system(s) installed in or attached to a building or structure shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or to the one or more grounding electrodes used. The bonding jumper(s) shall be sized in accordance with Table 250.66 except as permitted in 250.104(A)(2) and (A)(3).


When connecting to ground rods check 250.66(A) Connections to Rod, Pipe, or Plate Electrodes. Where the grounding electrode conductor is connected to rod, pipe, or plate electrodes as permitted in 250.52(A)(5) or 250.52(A)(6), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.

250.50 Requires all of the electrodes listed in 250.52 that are present at premises MUST be tied together.
The point of tie is at the service equipment or more commonly called the main disconnect.

In the case of a 200A service No. 4 Cu to the water pipe from the main, and a No 6 Cu to the rod or rods from the main. Neither of these GEC or Bonding Conductors should come from the MLO Panel.

Charlie

 

[buck33k]

Re: Bonding to sub panel

gndrod
Yes, the #6 was a GEC and the sole connection to the ground rods.
You probably saw the reference allowing it in cpal's post - 250.66(A).

thanks
Buck

 

[necbuff]

Re: Bonding to sub panel

There is an exception in 250.104 . If you have a multiple occupancy building and each water piping system is metallically isolated from each other, the water pipe BOND may be taken to the remote panel and attached to the EGC and sized to 250.122.... This comes in handy where a building is sharing a water system but there is PVC between each unit. Note this is only for bonding the piping not used as grounding electrodes.

[ February 12, 2005, 04:01 PM: Message edited by: necbuff ]