You've raised a good point about the complexities and potential hazards of using older BX cable (also known as armored cable or AC) without a dedicated grounding conductor. Let's break down the issue

Understanding the Problem:
Old BX Cable

Older BX cable (AC) relied on the metal armor itself to provide a grounding path. However, the armor's effectiveness as a grounding conductor can degrade over time due to loose connections, corrosion, and physical damage. It's not considered a reliable grounding path by modern standards.

Modern BX (AC with Ground)

Modern AC cable contains a dedicated, insulated grounding conductor (usually a green or bare wire) in addition to the circuit conductors. This provides a reliable and low-impedance ground fault path.

12/2 BX without Steel Grounding Conductor

If you have 12/2 BX without the insulated grounding conductor, you're dealing with the older style that is

not considered to have a reliable grounding path.Your Questions and Concerns


GFCI and Grounded Receptacles

You're correct in observing that wiring a GFCI outlet and then installing standard grounded receptacles creates a situation where the grounding screw of the receptacle makes contact with the metal box. This can create a false sense of security, and introduces potential problems. This is not an approved method and is considered unsafe.2.

Indirectly Using the Ground

By connecting the receptacle's ground screw to the box, which is then in contact with the BX cable's armor, you are indirectly using the armor as a potential grounding path. However, as stated before, the metal armor is not a reliable grounding path.3.

Creating a Hazard



Yes, this is a hazardous situation! Here's why: Fault Current Path

In the event of a ground fault (e.g., a live wire touching the metal enclosure of an appliance), the fault current should flow back to the source through a low-impedance grounding path, tripping the circuit breaker or GFCI quickly. With the reliance on the BX armor, the impedance (resistance) of the path may be too high. This can result in:

Insufficient current to trip the breaker

A smaller fault current might flow, but not enough to trip the breaker. This can energize the metal parts of appliances and create a shock hazard.

Slow tripping

Even if the breaker eventually trips, the delay could be long enough to cause a dangerous shock.

Heating of the armor

The high resistance can cause the armor to heat up, potentially leading to a fire.

False Sense of Security

People see a three-prong outlet and assume there's a proper ground. They might plug in sensitive electronic equipment that relies on a good ground for safety and performance.

Code Violations

What you're describing violates electrical codes in virtually all jurisdictions. The code specifically prohibits using the armor of old-style BX cable as the primary grounding conductor.

GFCI Protection and Ungrounded Receptacles GFCI Protection is Allowed

Electrical code typically permits the replacement of a two-prong receptacle with a three-prong receptacle if the circuit is protected by a GFCI.

The Key Requirement

If the GFCI protection is installed, you MUST label the three-prong receptacles with: "No Equipment Ground." This is to make it clear that equipment plugged into the receptacle will not be grounded.

How GFCI Works

A GFCI outlet monitors the current flow in the hot (ungrounded) and neutral (grounded) wires. If there is an imbalance of 5 milliamps or more (indicating that some current is leaking through an unintended path, such as a person), the GFCI trips very quickly, cutting off the power and preventing a dangerous shock.

In Summary



Never rely on the armor of old BX cable as the primary grounding conductor. Wiring standard grounded receptacles on an old BX circuit without an insulated grounding conductor is dangerous and violates code. GFCI protection is a mitigation strategy in some situations, but it's not a substitute for a proper ground. When using GFCI protection on ungrounded receptacles, follow the code requirements for labeling. The best solution is to replace the old BX cable with modern cable that includes a dedicated grounding conductor whenever possible. Consult with a qualified electrician to assess your specific situation and ensure compliance with local codes. They can provide the safest and most appropriate solution for your wiring needs. Flag for review