• We will be performing upgrades on the forums and server over the weekend. The forums may be unavailable multiple times for up to an hour each. Thank you for your patience and understanding as we work to make the forums even better.

3 phase power in old apartment building, no ground.

Merry Christmas
A

ABR

Member
Location
Puerto Rico
Occupation
GC
Hello,

To start, I would like to state that I am a GC, not an electrician. We are working on an apartment remodel and found a situation where the there is no ground. It is an old style, two wire building where all the plugs had been changed to three holes (without any grounding). The panel is 3 phase because the old HVAC air handler ran on 3 phase power. There is no way to provide a mechanical ground.

The existing solid copper wiring is in bad shape (we found some outlets jumped with speaker wire laid under tile). Some of the existing EMT is usable but a lot is not; some wires are just stuck in the conduits and there is no way to get them to move. The easiest option is to run new conduit along the ceiling (all concrete construction) and cover it with a gypsum false ceiling. I was reading through the NEC and cannot decide what the proper conduit would be (we even considered NMC without conduits).

It seems that ungrounded and unbonded EMT is just a bead idea, which leaves PVC for the new runs. That seems fine since the ceiling space shouldn't be subject to physical damage (though not sure 1/2" gypsum is really much protection). I also suggested to the electrician that we change the panel and add GFCI/AFCI combo breakers.

Any feedback on this solution would be appreciated. Does the PVC conduit (back to the main panel, where they're being replaced) with GFCI/AFCI breakers and stranded copper wire seem like the best solution in this scenario? Normally I would just let the electrician do his thing, but I thought I would ask since I don't see an ideal solution here.

Thank you.
 
Fred B

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
First off EMT is allowed to act as the EGC (equipment grounding conductor) without any additional "ground" wire. Requirements for additional bonding of the EMT vary depending on size of EMT and use of concentric KO of an enclosure, among other limitations. So the system may not be as "ungrounded" as you think.

Just because you find the building is 3 phase doesn't mean its ungrounded with no ability to have "mechanical ground". It is unlikely for an apartment building to have an ungrounded delta system but more likely to be a 3 phase wye system or less likely a grounded high leg delta (notably evident from a panel having every 3rd breaker slot open (unused) when using of single pole breakers for 1 phase loads.) So the panel would have mechanical grounds available at the panel, even if it appears to not be used (note above).

Issue of not being able to pull out of wire from a particular conduit might be a paring of conductors going to a different location and a j box not found or a broken or sheered off section of conduit. Sometimes individual conductors will twist around each other during the installation process making removal of individual conductors difficult or seemingly impossible.

Use of PVC has restrictions from a building code side that are unique to an area and not necessarily a NEC issue so consideration of local codes may impact the use of PVC conduit. That said if your option is for PVC it would have to have an EGC added whereas stated above EMT can be the EGC when properly installed.

Your mention of NMB as an option, it can be a viable option if local codes don't restrict use within a multi-family dwelling. some areas will mandate the use of MC when using cable wiring, so local codes would indicate such as well as any limitation related to NEC and use of NM cable under specific conditions.

You reference the idea of the PVC (and any conduit of that matter) and use of stranded conductor rather than solid. If properly sized for the circuit served either will work. Stranded will pull easier through multiple bend points of a conduit than would solid, but some devices have termination points that are harder to terminate stranded onto. Personally I prefer stranded anytime I have to "pull" but short sections that you can push though solid is ok.

AFA your suggesting a panel change out, it can be advisable depending on age and condition of the equipment, also availability of breakers that are compatible would be a consideration. If panel is still in good condition and not outdated that would accept the AFCI/GFCI breakers that would be required on a remodel of the dwelling on specific circuits, depending on code cycle of NEC your area is using, the use of such breakers "may" work in the existing panel. Your electrician would be best to advise on that.

Use of "speaker wire" as a circuit conductor is just a big NO from the start so it is wise you are correcting those issues.
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
This is typical an old building, the metal raceways are the EGC so yes there is a "ground".
 
Doc13067

Doc13067

Senior Member
Location
Bucks County/Philadelphia, PA USA
Sounds like that solves everything. The conduit is the ground. I’ve worked in buildings like this. Depending on the size and construction of the building you might not be allowed to use NM cable (334.10) and you may be restricted to EMT and MC. And one other thing I would add is check with the inspector before adding PVC even if the NEC doesn’t prohibit it. I once used it for a generator install and the ATS which was on the exterior wall became a sunroom and the inspector flirted with the idea of failing me over the PVC. He said something about the fumes when it burns. He made a call and then passed me but I just want to warn you to make sure.
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Just a code reference if you're interested.

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:
(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 size of the conduit does not exceed metric designator 35 (trade size 11∕ 4).
d. The combined length of flexible metal conduit, flexible metallic tubing, and liquidtight flexible metal conduit in the same effective ground-fault current path does not exceed 1.8 m (6 ft).
e.
If used to connect equipment where flexibility is necessary to minimize the transmission of vibration from equipment or to provide flexibility for equipment that requires movement after installation, a wire-
type 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 3∕ 8 through 1∕ 2), 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 3∕ 4 through 11∕ 4), 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 metric designators 12 through 16 (trade sizes 3∕ 8 through 1∕ 2) in the effective ground-fault current path.
d. The combined length of flexible metal conduit, flexible metallic tubing, and liquidtight flexible metal conduit in the same effective ground-fault current path does not exceed 1.8 m (6 ft).
e.
If used to connect equipment where flexibility is necessary to minimize the transmission of vibration from equipment or to provide flexibility for equipment that requires movement after installation, a wire-
type 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, flexible metallic tubing, and liquidtight flexible metal conduit in the same effective ground-fault current 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 Type MI.
(10)Type MC cable that provides an effective ground-fault current path in accordance with one or more of the following:
a. It contains an insulated or uninsulated equipment grounding conductor in compliance with 250.118(1).
b. The combined metallic sheath and uninsulated equipment grounding/bonding conductor of interlocked metal tape–type MC cable that is listed and identified as an equipment grounding conductor
c. The metallic sheath or the combined metallic sheath and equipment grounding conductors of the smooth or corrugated tube-type MC cable that is listed and identified as an equipment grounding conductor
(11)Cable trays as permitted in 392.10 and 392.60.
(12)Cablebus framework as permitted in 370.60(1).
(13)
Other listed electrically continuous metal raceways and listed auxiliary gutters.
(14)
Surface metal raceways listed for grounding.
Informational Note: For a definition of effective ground-fault current path, see Article 100.
Click to expand...
 
You must log in or register to reply here.
Top