Thread: Condo Subpanel Wiring Question

This panel is located in a unit of a condominium. It's not the best picture (since you can't see the ground bar) but here's the situation. I've got a 3 wire feed (the ground that appears to be a grounding electrode is actually the grounds twisted together from the branch circuits). The ground bar does not physically have a bonding strap to the panel but is attached to the enclosure. My understanding is this should be a 4 wire feed with the grounding electrode attaching to the ground bar. I realize that there is the possibility that they are using the metal conduit as the grounding electrode, but how do I know that?? This was in a 1969 condominum. Apparently, there was a Zinsco in it's place several years ago that they updated to a Square D. Don't know what year that happened. Any advice on how to write this up would be greatly appreciated!

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There should be an IGB (insulated grounding bushing) at both ends of the conduit if they are using it for the ground back to the service panel. It's normally pretty easy to install if there isn't one, unless there are other problems, or if the conduit isn't intact all of the way back to the panel.

They look like this guy here:
Find Insulated Ground Bushing, 2" and other Electrical Fittings at Aubuchon Hardware

The bonding strap is not necessary if the ground terminal bar is fastened directly to the panel, without the plastic insulating blocks.

Originally Posted by Reis Pearson

I realize that there is the possibility that they are using the metal conduit as the grounding electrode, but how do I know that??

By looking at the conduit, you should be able to tell metal from PVC, if not, take your screw driver and 'scrap' the conduit part you can see, if it is metal, your screw driver will just slide, if PVC, it will dig into the PVC (if the screw driver edges are not all rounded off.

A better and safer way is to take a multimeter (or any voltage tester device, even those neon lights, except their leads are usually too short) and test for voltage from the hot main lugs to neutral (you should get around 120-125 volts each leg), then from the hot main lugs to the enclosure (you should get the same thing), then from the hot main lugs to the inside the conduit (you should get the same thing - if you don't, either the conduit is not metal, or it is metal and just not grounded).

Huh? A couple of problems ... some with the pic, some with the post.

If it's not the main panel - neutral buss should not be bonded to the panel. The ground wires need a separate buss - and are always bonded to the panel.

Feeders get a separate ground wire ... an insulated one ... period. (Well, not quite .... the ground wire need not be insulated if a cable, like SER, is used as the wiring method). Whether you need a bushing is determined by the wire size alone - not what it's used for. You don't get to use the pipe as your ground wire for feeders - only branch circuits.

So, how do you know something is a feeder? Simple; it has a breaker or fuse at the end of it. A branch circuit has no breaker or fuse after it leaves it's source. (That's the short version).

Originally Posted by John Steinke

Feeders get a separate ground wire ... an insulated one ... period. (Well, not quite .... the ground wire need not be insulated if a cable, like SER, is used as the wiring method). Whether you need a bushing is determined by the wire size alone - not what it's used for. You don't get to use the pipe as your ground wire for feeders - only branch circuits.

John,

You need to go read: (from the 2008 NEC - underlining and bold are mine)

215.6 Feeder Equipment Grounding Conductor.
Where a feeder supplies branch circuits in which equipment grounding conductors are required, the feeder shall include or provide an equipment grounding conductor in accordance with the provisions of 250.134, to which the equipment grounding conductors of the branch circuits shall be connected. Where the feeder supplies a separate building or structure, the requirements of 250.32(B) shall apply.

Now you need to go to:

250.134 Equipment Fastened in Place or Connected by Permanent Wiring Methods (Fixed) — Grounding.
Unless grounded by connection to the grounded circuit conductor as permitted by 250.32, 250.140, and 250.142, non–current-carrying metal parts of equipment, raceways, and other enclosures, if grounded, shall be connected to an equipment grounding conductor by one of the methods specified in 250.134(A) or (B).
(A) Equipment Grounding Conductor Types. By connecting to any of the equipment grounding conductors permitted by 250.118.
(B) With Circuit Conductors. By connecting to an equipment grounding conductor contained within the same raceway, cable, or otherwise run with the circuit conductors.
Exception No. 1: As provided in 250.130(C), the equipment grounding conductor shall be permitted to be run separately from the circuit conductors.
Exception No. 2: For dc circuits, the equipment grounding conductor shall be permitted to be run separately from the circuit conductors.
FPN No. 1: See 250.102 and 250.168 for equipment bonding jumper requirements.
FPN No. 2: See 400.7 for use of cords for fixed equipment.

Now you need to go to:

250.118 Types of Equipment Grounding Conductors.
The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:
FPN: For effective ground-fault current path, see 250.2 Definition.
(1) A copper, aluminum, or copper-clad aluminum conductor. This conductor shall be solid or stranded; insulated, covered, or bare; and in the form of a wire or a busbar of any shape.
(2) Rigid metal conduit.
(3) Intermediate metal conduit.
(4) Electrical metallic tubing.
(5) Listed flexible metal conduit meeting all the following conditions:
a. The conduit is terminated in listed fittings.
b. The circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.
c. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground return path does not exceed 1.8 m (6 ft).
d. Where used to connect equipment where flexibility is necessary after installation, an equipment grounding conductor shall be installed.
(6) Listed liquidtight flexible metal conduit meeting all the following conditions:
a. The conduit is terminated in listed fittings.
b. For metric designators 12 through 16 (trade sizes through ½), the circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.
c. For metric designators 21 through 35 (trade sizes ¾ through 1¼), the circuit conductors contained in the conduit are protected by overcurrent devices rated not more than 60 amperes and there is no flexible metal conduit, flexible metallic tubing, or liquidtight flexible metal conduit in trade sizes metric designators 12 through 16 (trade sizes through ½) in the grounding path.
d. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground return path does not exceed 1.8 m (6 ft).
e. Where used to connect equipment where flexibility is necessary after installation, an equipment grounding conductor shall be installed.
(7) Flexible metallic tubing where the tubing is terminated in listed fittings and meeting the following conditions:
a. The circuit conductors contained in the tubing are protected by overcurrent devices rated at 20 amperes or less.
b. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground return path does not exceed 1.8 m (6 ft).
(8) Armor of Type AC cable as provided in 320.108.
(9) The copper sheath of mineral-insulated, metal-sheathed cable.
(10) Type MC cable where listed and identified for grounding in accordance with the following:
a. The combined metallic sheath and grounding conductor of interlocked metal tape–type MC cable
b. The metallic sheath or the combined metallic sheath and grounding conductors of the smooth or corrugated tube-type MC cable
(11) Cable trays as permitted in 392.3 and 392.7.
(12) Cablebus framework as permitted in 370.3.
(13) Other listed electrically continuous metal raceways and listed auxiliary gutters.
(14) Surface metal raceways listed for grounding.

There are *A LOT* of choices *OTHER THAN* ...

Feeders get a separate ground wire ... an insulated one ... period.