On Thu, 13 Jun 2019 07:55:03 -0600, bud-- wrote:

On 6/10/2019 11:53 AM, wrote:
On Mon, 10 Jun 2019 09:09:50 -0700 (PDT), trader_4
wrote:

On Sunday, June 9, 2019 at 10:40:23 PM UTC-4, wrote:
On Sun, 9 Jun 2019 20:01:54 -0500, Terry Coombs
wrote:


Â* When is it necessary ? I've just replaced the panel out in the shop
(aluminum buss bars on the old one were giving problems) and I have a 3
wire service run out there . At this time the only place the neutral is
bonded to ground is in the meter box . It has been suggested to me to
bond them in the main panel too ... but that seems redundant to me ,
they're only the thickness of a piece of plywood apart . I have
considered installing a ground rod at the new panel but am concerned
about the potential for ground loop currents .

If you only have 3 wires in the feeder going to the shop you need to
bond the neutral and ground out there too or there is no path for
fault current. You also need a ground electrode out there. Current
code requires a 4 wire feeder and isolating neutral and ground in sub
panels but if the wire was already there when the 1996 code was
adopted the 3 wire feeder is grandfathered in.
Ground loops are not an issue but carrying circuit current in the
grounding conductor is, That is why you do need another ground
electrode. Essentially you are creating another service in the second
building and creating a new ground reference there.
In the electrical biz, you can't have too many ground electrodes but
they all need to be bonded together.

His main question appeared to be whether the neutral and ground need
to be bonded in the MAIN panel if they are already bonded at the meter
which is right next to it?


That is open to debate. A strict reading of the NEC says the PoCo
should not have bonded the neutral in their can but since they do not
have to follow the NEC, the language was tweaked a little (again 96 as
I recall) so it is all "service equipment" and you still rebond the
neutral in the service disconnect enclosure where the code says the
"Main Bonding Jumper" is supposed to be. That is usually just a green
screw on the neutral bus or a strap.
The hitch is that the MBJ "shall remain accessible" and inside the
meter can isn't. Sanity prevailed. Meter cans are usually made so the
can is bonded to the neutral anyway. There is no way to avoid it.

Some inspectors require that there be no metallic paths between the
meter can (a PVC sleeve) and that you only bring 3 wires in. Then we
did not care what they did in the can, the MBJ was clearly in the
service disconnect enclosure.

The grounding electrode conductor can land anywhere from the service
point (usually the mast head on an overhead drop) to the service
disconnect enclosure. That is how they can land it in the meter can.
If you have an underground service lateral, the service point is
usually the transformer connection at the street. Yes you usually own
that wire in the yard. You typically do not own an overhead drop.


A slightly broader view - the requirements for grounding-bonding on a
service entrance are much tougher than past the service. Assume an
overhead drop and EMT service entrance. The EMT from the meter can to
the service panel is likely to be connected through concentric/ecentric
knockouts at each end. That is not allowed for bonding and the meter can
and EMT section are then not "grounded". Around here the practice was
for the GEC exiting the panel to go through a ground clamp on the EMT
then to the electrodes. That bonded the EMT but left the meter can. The
bond between neutral and meter can is then critical. The EMT riser above
the meter is connected through a hub, which is good for bonding.

I am too lazy to look it up, but I think if the EMT between the meter
can and service panel does not have concentric/ecentric knockouts, an
EMT connector through the right sized hole is also not an approved bond
and a "grounding locknut" (not an ordinary locknut) or other means has
to be used.

The EMT between the meter can and service panel is in parallel with the
neutral wire but that was not considered a problem here.

If PVC conduit is used, more likely now, the bonding problems go away,
but bonding the neutral to the meter can is then also critical.

The way I read Terry's post there is a utility meter separated from the
panel by 1/4" of plywood. Sounds like a service panel, not a
feeder-subpanel. Or that discussion may be in addition to a "new panel"
at a separate shop building run off of a 3-wire feeder. Neutral-ground
bond and earthing electrode(s) apply to both. More stringent bonding
(above) only applies to a service.

I would want a Main Bonding Jumper in a service panel (is required in a
separate building 3-wire feed subpanel). For a service with no MBJ in
the service panel the bonding (as above) on the ?metal pipe? from the
meter can is a particular question.

Raceways for service conductors get extra protection because there is
no real overcurrent protection on a service conductor.
Feeders are protected at their ampacity but service conductors are
not. . A bolted fault on a service conductor is as likely to burn out
the drop as it is to blow the primary fuse on the transformer. It will
certainly get hot enough to roast that squirrel running along it.
That is why your typical branch circuit breaker has a 10,000a AIC but
the service disconnect/main breaker will be 65ka AIC or more.