ECN Forum Forums General Topics of the Trade General Discussion Area Customer Q

This isn't something that I get asked, but then we have only 240/415V and not the variety of systems you use.

I do sometimes get asked to explain 3-phase, though. Except for isolated single properties, all domestic distribution is 3-ph 4-w wye with homes tapped off one phase, so in rural areas with overhead lines I sometimes get the question: "Why are there four wires up there?" Some folks who work in commercial buidings and see the 415V stickers ask how 415 relates to 240V.

I've found that many people can understand the concept of a "back-to-back" arrangement like your domestic 120/240, but start mentioning the sq. root of 3 and they're lost.

In my area, the utility helps me with that question. They don't allow 3 phase to residences, they charge a premium for installing the extra xfmrs and the connection, and they charge a monthly premium for having it. That usually handles it. Two words- "costs more" does it.

I'm not sure what my local PoCo's response would be to a request for residential 3-phase. I don't THINK there's a specific policy against it, although I don't doubt the installation charge would be higher. With 1-ph 240V 100A now standard for new services, most folks have ample power for their needs.

About the only place normally to see 3-ph in a vaguely residential application is a large guest house. The IEE doesn't like the idea of the (eek!) "general public" getting close to 415V, so they specify that all recepts. in each room should be on the same phase.