In chapter 9 there is a desription of a service to a structure as "2ph, 4 wire". I have been in the trade for 29 years and an instructor for 9. I have never seen this type of sevice before and is there aparticular application for it. It is feeding some "2ph motors. I used to believe that it was a misprint, hoever I checked previos nec codebooks and they are the same. Can You clarify this?
services
- Thread starter rlprice
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Re: services
I have seen diagrams of three-phase primary connections using two transformers to create a Two-Phase secondary. The primary is connected using a "T" or Scott configuration and the secondary has four phases, with one transformer secondary connected to phase L1 and L2 and the other transformer connected to the other two phases I will call L1(2) and L2(2). There is no common connection on the secondary of the two transformers or any established neutral. I think these configurations were for power equipment as no neutral was establised.
I have seen diagrams of three-phase primary connections using two transformers to create a Two-Phase secondary. The primary is connected using a "T" or Scott configuration and the secondary has four phases, with one transformer secondary connected to phase L1 and L2 and the other transformer connected to the other two phases I will call L1(2) and L2(2). There is no common connection on the secondary of the two transformers or any established neutral. I think these configurations were for power equipment as no neutral was establised.
Re: services
There are polyphase motors, Its been a long time since I worked on this project, we wired some exhaust motors, if I remember, it looks like a single phase, and you change rotation by switching the hot leads around, but like I said its been a looooooooooooooong time.
There are polyphase motors, Its been a long time since I worked on this project, we wired some exhaust motors, if I remember, it looks like a single phase, and you change rotation by switching the hot leads around, but like I said its been a looooooooooooooong time.
Re: services
I have seen two 2-phase configurations used on the north shore of Long Island. The Scott system is a 5 wire system and looks like a "+". It has four transformers or two center tap transformer and is grounded at the center points (see NEC 240.20(B)3). The second looks like a "T" with three transformers and grounded at the center of the top. I know these systems go back to the 1920's but I can not figure any advantages; cost or other wise. I don't know if they are still in use. The area was an old manufacturing area and has been mostly replaced with new buildings.
Jerry
I have seen two 2-phase configurations used on the north shore of Long Island. The Scott system is a 5 wire system and looks like a "+". It has four transformers or two center tap transformer and is grounded at the center points (see NEC 240.20(B)3). The second looks like a "T" with three transformers and grounded at the center of the top. I know these systems go back to the 1920's but I can not figure any advantages; cost or other wise. I don't know if they are still in use. The area was an old manufacturing area and has been mostly replaced with new buildings.
Jerry
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