Home>Discussions>ELECTRICAL & LIGHTING>Can someone explain the difference between phases and poles??
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NEC
Re: Can someone explain the difference between phases and poles??
ohmy wrote:

This is why old neighborhoods in the US have an old dumpster outside the house.

Ummm Yup!.............

JLMCDANIEL
Re: Can someone explain the difference between phases and poles??
ohmy wrote:

This is why old neighborhoods in the US have one transformer outside the house.

What????????

Jack

keith3267
Re: Can someone explain the difference between phases and poles??

Wow, I just read all 9 pages of this thread. I wish I had seen it sooner because the original poster and some of the original responders probably have lost interest in this thread.

I work for a distribution transformer manufacturer. We make single phase pole, single phase pad, three phase pose and three phase pad transformers for the coop market mainly but we do have some municipalities.

My main function is QA and training. My company sends me out to lineman classes on occasion to teach transformer fundamentals.

Single phase poles can have one or two bushings on top for the primary connection. One bushing pots are the most common. The two bushing pots are mainly for transformers that will be put in three phase banks with a primary delta connection.

The secondary of the transformer may be connected internally in phase with the primary or out of phase with the primary. The secondary bushings are labeled X1, X2 and X3, X2 is grounded and used as the return/neutral. Those connected in phase are called subtractive wound, those connected out of phase are additive wound. This is only important if three pots are being used in a three phase bank, they all have to be the same or the three secondary phases won't be 120 degrees apart.

Almost all utility systems today have a neutral wire. It not only provides a common ground reference for all the transformers on the grid, it provides a ground for all the telephones. Otherwise telephones, which are fed by 48vdc could float to a much higher and dangerous voltage.

Three phase transformers have three single phase coils inside them. The primary's can be connected in either a Wye or Delta configuration, same with the secondaries. The Y-Y (Wye primary, Wye secondary) is the most common, D-Y second most common. Delta secondaries are a real small part of our production and a D-D is so rare that we only see a couple a year.

The 480Y/277 is the most common secondary as this is what most large machines use. The 208Y/120 is second most common. We see some 480D secondaries but 240/120 delta secondaries are more common.

Delta's are not inherently more dangerous that Wye configurations. Both still use a fourth wire for ground. Either configuration that doesn't have a ground is equally dangerous. Yes there is an ungrounded three wire Wye configuration, but a ground wire is still provided for safety.

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