The disconnects would need to be fused.
You could run a separate feed from the transformer to each disconnect as long as each met the 240.21(C) transformer secondary rules.
Design input - Revised
- Thread starter Alwayslearningelec
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You could run a separate feed from the transformer to each disconnect as long as each met the 240.21(C) transformer secondary rules.
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- New Jersey
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If I remember correctly the secondary conductors must terminate on an OCPD so the wireway is not an option.
Alwayslearningelec
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So you can run (3) separate feeders from a transformer?
Alwayslearningelec
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See my question #43.
Read Note 2 to 450.3(B) and 1st ppg of 240.21(C)
(short answer is yes)
Alwayslearningelec
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Thank you. I was just thinking about the lug setup I would need in the xfrmr to accomadate.
Alwayslearningelec
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I gave my breakdown/one line to someone in my office and he responded with below?
P=E x I x 1.73
45000= 208v x I x 1.73
45000/360=I=125 amp 3 ph for trailers with AC & Heat?
I don't follow his logic/calc exactly. I questioned what he meant by 3P for trailers.
P=E x I x 1.73
45000= 208v x I x 1.73
45000/360=I=125 amp 3 ph for trailers with AC & Heat?
I don't follow his logic/calc exactly. I questioned what he meant by 3P for trailers.
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- New Jersey
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- Journeyman Electrician
That is the output of a 3Ø, 45 kva transformer.
Alwayslearningelec
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Ok so with the new scheme of feeding 2P disconnects switches from a 3 phase xfrmr instead of feeding a 3P 4W panel, what would the make up of the cable/wires be from the secondary to the disconnects? 2 phase conductors or 3 phase conductors. Its weird because the xfrm is 3P but the disconnects are 2 pole.
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- New Jersey
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- Journeyman Electrician
The disconnects in those sizes are probably 3 pole but you'll only need to use two poles.
Alwayslearningelec
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Right so you can run a 2 hots from the secondary of a 3 phase transformer?
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- New Jersey
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- Journeyman Electrician
Yup you only need two so no need to run three.
Alwayslearningelec
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Thanks. So how what would that connection look like on a 3 phase xfrmr. Meaning what terminal would the 2 hots connect to?
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- Journeyman Electrician
Bullseye.
Alwayslearningelec
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Geniuses ...lol. Thank you. It was just a weird concept to me to have a 3P xfrm but coming off it with only 2 phase conductors.
winnie
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- Springfield, MA, USA
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- Electric motor research
Right, but keep in mind that you are using all three phases.
You have 3 separate loads, and each of these loads only uses 2 phase conductors.
But you distribute these 3 loads to use all 3 phases.
Jon
Alwayslearningelec
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If I was only able to source 3P disconnects could I use those and only use 2 poles?
- Location
- New Jersey
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- Journeyman Electrician
Yes that's pretty standard.
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