5 Wire 2 Phase?

This is a first for me.

It looked like a “standard” parallel service entrance, however, only one of the neutrals actually continued through the mast, to the meter base. So it was in fact, a 5 wire service, as indicated on the meter. But is it actually 2 phase? If so, what does that mean?

I’ve also included pictures of the dual Federal Pacific service panels.





A Mike Holt Forum page on 2 phase 5 wire

Strange stuff Jeff.

Thanks for the link Mike. . .


Do you have any good pictures of the transformer connections? The transformers will tell you what type of service it is.

I couldn’t see the transformer from the property. What would I expect to see from a transformer supplying this type of service?

Ever notice how hot dogs cooked using 2 phase just seem to taste better than hot dogs cooked using single phase or even 3 phase? :mrgreen:

You must be talking about regular hot dogs. Everyone knows when it comes to foot long hot dogs, 3 phase does a superior job of cooking them.

It helps to think “coil” when you hear the word “phase”. A common misconnection, even among electricians, is that the wires coming from a transformer are the phases. They are not. They are phase legs. A coil makes a phase.

Every coil has two legs extending from it. It may also have one or more taps. Single-phase has one coil, two-phase has two coils, three-phase has three coils, etc. The transformers and the connections tell you what the service type is.

A proper two-phase five-wire service will have all five conductors landed on a single disconnect. There can be multiple disconnects but all five conductors have to enter the building together into the same enclosure. From what I can see in your photo of the transformer connections, it appears to be a two-phase connection. However, your photos from the panels do not show a single entry point.

I developed a very effective classroom exercise that illustrates isolation transformer connections. Once you see this classroom demonstration, it all becomes very clear almost instantly. It is difficult for most people to visualize real transformer connections from schematic diagrams. I don’t have any photos of two-phase five-wire transformer connections but I do have a schematic.



Thanks for the explanation, although I’m not sure I understand the need for a single disconnect.

How does the disconnect affect the configuration?

The panels were side-by-side, each wired with 240 volts and bonded together after the meter pan. The single neutral was attached to the panel on the right, which was a split-bus with six throws. The left-side panel had no single disconnect.