Joe_z
New User
- Location
- Chicago, IL
- Occupation
- Electronics Engineer
The short version:
Is there anything in the electric code that disallows the following scenario:
A 480VAC single phase load is connected to 2 of the phase wires of a 480V 3 phase circuit.
The 3rd phase wire is insulated and left in place. It is not connected to the load, but it remains connected to the circuit breaker.
No neutral wire is required for the load and is not present.
The circuit breaker is a 3 pole device as would be used in any normal 3 phase circuit.
The long version:
I work as an electronics engineer for a major manufacturer of electronic appliances sold around the world. Our products use a variety of small AC and DC motors (<1/2HP up to 5HP) in commercial and residential applications.
My focus is on the commercial side in North and South America (primarily the US and Canada) and the products I deal with are often used with all the common voltages (120V, 208V, 240V, 480V, and 600V) in both single and three phase applications.
Historically, the products I work on were offered in models that used single phase and 3 phase motors. More recently, we've released a new product that only comes in a single phase model but we still support 480V as a single phase device.
Our recommendation for retrofitting 3 phase installations with the new single-phase-only product is to use 2 phase wires to supply the device and insulate the third unused phase wire.
I have heard from 3 different electricians and electrical engineers that doing this is not compliant with the NEC.
I have also been told once or twice that doing things this way will prevent the breaker from working correctly.
Nobody so far has given me references to the sections of the NEC which disallow this, hence my question: is this really disallowed by the NEC, and if so, which sections cover it?
I am not an expert on the NEC, but I do work on the electrical design for products that electricians and electrical engineers have to deal with every day, so I would like to understand if our recommendations are problematic in some way so that we can improve them.
Is there anything in the electric code that disallows the following scenario:
A 480VAC single phase load is connected to 2 of the phase wires of a 480V 3 phase circuit.
The 3rd phase wire is insulated and left in place. It is not connected to the load, but it remains connected to the circuit breaker.
No neutral wire is required for the load and is not present.
The circuit breaker is a 3 pole device as would be used in any normal 3 phase circuit.
The long version:
I work as an electronics engineer for a major manufacturer of electronic appliances sold around the world. Our products use a variety of small AC and DC motors (<1/2HP up to 5HP) in commercial and residential applications.
My focus is on the commercial side in North and South America (primarily the US and Canada) and the products I deal with are often used with all the common voltages (120V, 208V, 240V, 480V, and 600V) in both single and three phase applications.
Historically, the products I work on were offered in models that used single phase and 3 phase motors. More recently, we've released a new product that only comes in a single phase model but we still support 480V as a single phase device.
Our recommendation for retrofitting 3 phase installations with the new single-phase-only product is to use 2 phase wires to supply the device and insulate the third unused phase wire.
I have heard from 3 different electricians and electrical engineers that doing this is not compliant with the NEC.
I have also been told once or twice that doing things this way will prevent the breaker from working correctly.
Nobody so far has given me references to the sections of the NEC which disallow this, hence my question: is this really disallowed by the NEC, and if so, which sections cover it?
I am not an expert on the NEC, but I do work on the electrical design for products that electricians and electrical engineers have to deal with every day, so I would like to understand if our recommendations are problematic in some way so that we can improve them.
