Main service mast has four wires entering…two larger gauge insulated wires, one smaller gauge insulated wire and one neutral (see photo 086).
When I inspected the main service panel, the two larger gauge insulated wires connect to the left and right main lugs of the service panel and the smaller gauge insulated wire connects in the middle (see photo 083). The neutral (difficult to see) runs to the right behind the existing wiring and connects to the common neutral/ground buss bar at the bottom.
When I take voltage measurements (from the respective lug to neutral buss bar) I got the following readings:
– Large left main feeder wire to neutral ~124 VAC
– Large right main feeder wire to neutral ~124 VAC
– Smaller center feeder wire to neutral ~199 VAC
I also checked each circuit voltage at the conductor connection point of each circuit breaker. Received nominal voltage of ~124 VAC from each…except the red wire on the three pole circuit breaker, second down on left side (according to writing on the dead front panel this three pole breaker serves the “Air Cond”). When I checked this breaker, I received nominal ~124 VAC from the black and brown wires to neutral and ~199 VAC from the red wire to neutral.
In addition to the typical two hot and one neutral lines, it seems like there is an additional 200 VAC service line that serves this home/service panel, however, I’ve never seen 200 VAC like this before and I’m perplexed.
I’m trying to understand if there is something wrong or if this was something normal when the home was originally constructed. Any help/advice would be great.
Although the voltages are a little off it appears that this is a 3 phase, 4 wire Delta system. The nominal voltages to neutral/ground for that system should be around 120-208-120 and 240-240-240 phase to phase, did you check those phase to phase voltages?
The panel appears to be a split bus panel with the lower portion fed from the single phase 2 pole CB in the upper left.
I did check the phase to phase and although it to was a little off the 240-240-240, it was close. And yes, I agree it appears to be a split buss panel.
I’ve also done a little more research and found the term “wild leg” or “high leg” that refers to the 200 volt leg of the service.
Since you had 124 vac to neutral on two legs you should have 248 volts phase to phase on those two legs. Although there are many slang terms for this system the NEC refers to it as a high leg.
The high leg is unusable for a 208 volt circuit. For one thing a standard 1 pole CB is not suitable for a 208 volt load. In this application the high leg is there for using 3 phase loads.
As all have said this is a 3 phase service and the high voltage reading on the B phase means its a delta high leg. The high leg is provided for 3 phase power. Most likely an AC unit.
I disagree. It is certainly possible (in general) to use the high leg for a single phase straight 208 volt circuit. A single phase motor (most 230 volt rated motors get away on 208), single phase electric heater or a 208 volt HID lighting ballast.
Most standard breakers are not suitable for a high leg since they are slash rated (120/240). Any breaker would need to be straight 240 rated. For this panel you can special order a straight rated double pole breaker, or tri pole breaker (tri poles are straight rated automatically). Of note they do not sell a straight rated single pole 240 volt breaker in the US, so if you wanted a single pole on the high leg you would need a 480Y/277 volt panel board and use a 277 volt single pole breaker.
In this case however, the high leg is much smaller than the other two phase conductors, so its use is indeed limited, in fact more dedicated. Because of this, it should only be used for the AC unit.
