You don't have to call the heating company, any licensed electrician can install a grounding conductor or new wiring from the service panel to the furnace.
If a heating company installed your new furnace, they are responsible for making the correction connections to electric power. I get the impression you installed it yourself.
The National Electrical Code requires new wiring installations to have grounding conductors, and new permanently installed equipment to have connections for a grounded conductor if the equipment is connected to the electric service panel.
Most cities in the United States have adopted the NEC as a basis for their own electrical codes, and often add rules and stronger restrictions of their own. They also allow buildings with electrical wiring that predates that requirement to not have grounded conductors, as long as no substantial changes are made to the wiring. They might require that equipment that is designed for connection to grounded conductors have to be properly grounded.
Using the cold-water metal pipe for the ground connection is no longer adequate, in some areas it is not acceptable because the metal piping might be connected to plastic piping and hence you will not have a ground connection at all, or the metal piping in one section is galvanized steel and in the other section it is copper - I have this situation - and in this case the steel is separated from the copper with a dielectric union, which is an insulator, which interrupts any grounding.
Many cities require the natural gas pipe to be grounded on the customer side of the meter where the pipe enters the house, with a separate grounding conductor back to the service panel.
The Carrier furnace is designed to meet those equipment requirements.
The grounding conductor is usually called the ground wire and is bare or has green insulation. It is for electrical safety, in case there is a wiring fault inside the furnace, the stray or excessive current flow will go through the grounding conductor and the furnace metal parts will not be electrically energized - what people colloquially call "hot". This is a personal hazard as anyone who touches any exposed metal parts could be shocked. The grounding conductor also ensures that the stray current flow from an electrical fault will not go through the metal piping for the gas lines.
You mention an igniter, so I assume you have natural gas or propane service, and the only need for electric power is for the igniter and the blower motor(s). Usually that is 120 VAC. The black wire is the energized wire and is called the hot wire and goes to the circuit breaker or fuse in the service panel. The white wire is the grounded conductor and is called the neutral and goes to the neutral bonding block in the service panel. The white wire carries the same current as the black wire.
Unfortunately, sometimes the wiring is not done correctly and the black and white wires are swapped You should use a voltmeter or multimeter to verify the white wire is indeed correctly wired.
So, you cannot use the white wire for grounding purposes.
I do not know why the igniter did not work when you wired the ground connection to the white wire, unless there was some kind of GFCI (Ground Fault Circuit Interrupter) within the control for the furnace. These circuits are not difficult to include in the controls.
A GFCI works by measuring the current flow in the hot wire and the neutral wire (both inside the unit). These two currents should be the same, current in the black wire equals the current in the white wire. If there is an imbalance, often as small as 5 milliamperes ( 0.005 amperes or the current required to light a tiny half-watt light bulb or neon lamp), the GFCI will trip its relay and remove power from the circuit.
My theory here is that since you had connected the green screw to ground some small current flowed out it rather than through the neutral connection. But it is not a good theory.
You did not say anything about having to "reset" the control, but a self-resetting GFCI (due to power cycling) is possible. That would explain why it worked when you removed the jumper between the green ground screw and the white wire. But I have not read anything about such circuits as it has been quite a few years since I have kept up with changes to the NEC and equipment safety design.
So the quick answer to your question is : the furnace will work properly without a ground connection back to the service panel. There are probably millions of furnaces installed in this country - one in my father's house, for example - that do not have a grounding conductor connected to the furnace.
But it will not be considered electrically safe by your insurance company. If there is any problem caused by the furnace that results in an insurance claim, they could refuse to provide coverage because the furnace was not properly grounded.
Saturday, November 28, 2009 4:30 am CST