2 prong electrical outlets

[David Maas]

I was in a home that had both 3 prong and 2 prong electrical outlets. The house was built in 1964. The wiring was run in conduit. The 3 prong outlets tested correctly showing a ground. How do you test if the 2 prong outlets are grounded?

Thanks

[Darren Miller]

They are not grounded. here's what I tell my clients about 2 slot receptacles.

Ungrounded 2 slot receptacles are present in several areas of this house. These receptacles are typical of a house this age. When used with 2 prong cords such as lamps, these receptacles are acceptable. However, they should never be used in areas where I recommend GFCI's. In those areas, they are particularly dangerous and should be replaced with grounded GFCI's. In all cases, you should never improperly 'adapt' a grounded appliance (one with three prongs) to one of these ungrounded receptacles. Safety would be improved by upgrading the receptacles to modern standards. One way to do this is to install GFCI’s in place of the two-slot receptacles. There are other ways to upgrade the receptacles, and any good electrician should know how to do the job.

[neal lewis]

Use a simple two lead tester to find out of the circuit is grounded.

[Galen L. Beasley]

They are not grounded. here's what I tell my clients about 2 slot receptacles.

Ungrounded 2 slot receptacles are present in several areas of this house. These receptacles are typical of a house this age. When used with 2 prong cords such as lamps, these receptacles are acceptable. However, they should never be used in areas where I recommend GFCI's. In those areas, they are particularly dangerous and should be replaced with grounded GFCI's. In all cases, you should never improperly 'adapt' a grounded appliance (one with three prongs) to one of these ungrounded receptacles. Safety would be improved by upgrading the receptacles to modern standards. One way to do this is to install GFCI’s in place of the two-slot receptacles. There are other ways to upgrade the receptacles, and any good electrician should know how to do the job.

I’m pretty sure that the codes allow for ungrounded GFCI’s as an acceptable 3 prong replacement in an ungrounded system as long as they are marked as having no equipment ground. Although the latter statement indicates that upgrading to modern standards using a GFCI is acceptable, the previous statement seems to indicate that GFCI’s must be grounded. This seems like it could be confusing, however it could just be me as I’m easily confused.

[David Maas]

Thanks for the information. Appreciate it.

[James Kollhopp]

Some homes have ungrounded outlets and that’s not a problem in itself. For older homes, I believe the NEC prohibits the use of 3-slot outlets when there is no grounding system. Ungrounded 3-slot outlets should have the ground slot filled with an epoxy or a pin designed for this use so no 3-prong plug can be used in it, or replaced with a 2-slot outlet. GFCI’s are often added to ungrounded circuits to provide protection, and some local codes allow this as an alternative to grounding. Three prong receptacles having no ground should be listed as such “no equipment ground”.

[Rick Cantrell]

Some homes have ungrounded outlets and that’s not a problem in itself. For older homes, I believe the NEC prohibits the use of 3-slot outlets when there is no grounding system. Ungrounded 3-slot outlets should have the ground slot filled with an epoxy or a pin designed for this use so no 3-prong plug can be used in it, or replaced with a 2-slot outlet. GFCI’s are often added to ungrounded circuits to provide protection, and some local codes allow this as an alternative to grounding. Three prong receptacles having no ground should be listed as such “no equipment ground”.

Well.... Maybe, kinda sorta, but, not exactly.

[Alton Darty]

I was in a home that had both 3 prong and 2 prong electrical outlets. The house was built in 1964. The wiring was run in conduit. The 3 prong outlets tested correctly showing a ground. How do you test if the 2 prong outlets are grounded?

Thanks

The two prong outlets are ungrounded. If the existing grounding type outlets are indicating that they are grounded properly the conduit is being used as the equipment ground. The conduit can serve as the equipment ground. Adding grounding outlets should take care of any issues. Or was the conduit EMT?


From NEC 2005
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 with an additional
equipment grounding conductor

[Raymond Wand]

There are several different approaches to solving this:

1) If the wiring is done through conduit or BX, and the conduit is continuous back to the panel, you can connect the third prong of a new receptacle to the receptacle box. NEC mainly - CEC frowns on this practice.

2) If there is a metallic cold water pipe going nearby, and it's electrically continuous to the main house ground point, you can run a conductor to it from the third prong. You MUST NOT assume that the pipe is continuous, unless you can visually check the entire length and/or test it. Testing grounds is tricky.

3) Run a ground conductor back to the main panel.

4) Easiest: install a GFCI receptacle. The ground lug should not be connected to anything, but the GFCI protection itself will serve instead. The GFCI will also protect downstream (possibly also two prong outlets). If you do this to protect downstream outlets, the grounds must not be connected together. Since it wouldn't be connected to a real ground, a wiring fault could energize the cases of 3 prong devices connected to other outlets. Be sure, though, that there aren't indirect ground plug connections, such as via the sheath on BX cable.The CEC permits you to replace a two prong receptacle with a threeprong if you fill the U ground with a non-conducting goop.Like caulking compound. This is not permitted in the NEC.

The NEC requires that three prong receptacles without ground that are protected by GFCI must be labelled as such.

[Jerry Peck]

I was in a home that had both 3 prong and 2 prong electrical outlets. The house was built in 1964. The wiring was run in conduit. The 3 prong outlets tested correctly showing a ground. How do you test if the 2 prong outlets are grounded?

Thanks

As I recall, the NEC required grounding of all grounding-type receptacles prior to 1959 (2-prong receptacles are not grounding-type) and required grounding-type receptacles for all receptacles in 1959 or 1962 - the catch is that your area may not have adopted those codes until later ... which does not affect the fact of what was considered safe by the national standard NEC (which is a good reference, regardless of whether it was adopted locally or not).

The metal conduits have been required to be grounded since, oh, about ... 1897 in the code which became known as the 'First NEC' even though that was not the name of it. That means that the metal conduits are required to be grounded, which means grounding proper grounding-type receptacles easy to do.

[Michael Thomas]

Also:

1) I point out to Home Inspection clients that many manufacturers of modern electronic equipment often present in "home offices", "home theaters" and similar areas require that it be attached to a receptacle outlet providing an effective ground - if not, the manufacturer's warranty is voided.

2) In at least one community where I inspect (Evanston IL), the AHJ requires upgrades to ungrounded circuits in such locations when any other "significant" electrical work is performed anywhere in the structure.

3) So, ungrounded outlet circuits may produce unexpected expenses.

[Gunnar Alquist]

... the catch is that your area may not have adopted those codes until later ... which does not affect the fact of what was considered safe by the national standard NEC (which is a good reference, regardless of whether it was adopted locally or not).

Historically, California has been 3 years behind the code cycle. This may be true of other states as well. So, the 1962 NEC would not have been adopted until 1965. As a result, many homes built in the 1960s did not have grounded receptacle outlets. I owned a home that was constructed in 1963 and all of the grounding conductors in the NM cable were really teeny. Looked like #16.