On your transformer chart, in the three phase area, you have 3a Wire, 4b Raceway, and 5. EGC while on the 208 volt side, you have 3b Wire, 4b Raceway and 5. Are these correct and if so where is the corresponding notes at the bottom as there is no 3a or 3b and 4a and 4b has to do with wire size and not raceway. Just a little confusing...

• Reply from: Mike Holt   January 26 2016, 9:02 am EST
  You are correct, I revised the single-phase table titles, but not the three-phase. We'll update right away.
  Reply to Mike Holt

I have become a Journeyman electrician in 1987. In 1999 I purchased one of Mike Holts books. I read it and it has helped me. In 2014 I reread it and took the Masters exam in the state of Michigan and passed. I have since been a fan of Mike Holt books and teachings. One problem that I still have is when calculating loads and applying all that I have learned and I come up with something different than the manufacturer has installed to their equipment that I am hooking up and responsible for.

example: I have a 12.5KVA Load at 230vac single phase. It goes to a Mag plate to hold dies in a CNC mill. Voltage available is 480vac. This Magnet is a continuous load. After my calculations the load comes in at 32.5amps @ 480vac. So I would size the conductors with a #8awg THHN on the primary of a 12.5KVA. This is what I believe to be correct for the primary. The Secondary current came out to be 67.92amps at 240vac. This would require a #4awg THHN. However, when I looked at the unit the manufacturer has placed a single phase #10awg 3 conductor Cable on the output to the mag unit. I will call Manufacturer soon however, I was hoping to get comments on others who have run into this problem.

• Reply from: Wyatt   January 24 2016, 8:32 pm EST
  Load: (single phase) 12.5 Kva @ 240v. 1/p = 52 A (for a 480-240v transformation.) 12.5 Kva @ 230v. 1/p = 54 A (for a 460-230v transformation.) I don't think 12.5 Kva is a "standard" rating for the transformer. The nearest sizes are 10 Kva and 15 Kva. Maybe you can get a "special" ?
  Reply to Wyatt

  • Reply from: Mike Holt   January 26 2016, 11:07 am EST
    I don't understand your comment, the table/chart doesn't include a 12.5 kVA transformer. Why did you make this comment?
    Reply to Mike Holt

  • Reply from: Wyatt   January 27 2016, 1:15 am EST
    This was in response to a reader question on this website.
    Reply to Wyatt

Hi Mike, Could the 15KVA, 208V 3 phase secondary be 60 amps (not 50 amps)to match standard panel sizes?

• Reply from: Mike Holt   January 24 2016, 12:06 pm EST
  Yep, can do and will do. I'll send out an updated table in the next few weeks.
  Reply to Mike Holt

  • Reply from: Jacob Mendelovici   January 24 2016, 12:53 pm EST
    Secondary 15 kVA Xfmr FLC = 15000 / (1.73 x 208) = 41.69A a) OCP for noncontinuous load = 42A; next std CB (up) = 50A b) OCP for continuous load = 41.69 x 1.25 = 52A; next std CB (up) = 60A. (OCP depends on continuous / noncontinuous load)
    Reply to Jacob Mendelovici

How come no 600 V ? It is a Code Recognised voltage (347/600).

• Reply from: Mike Holt   January 23 2016, 5:54 am EST
  What percentage of installations in the USA use this secondary voltage? I've never seen an installation in over 40 years. If you do see these, where, and what loads are served? What type of industry and where in the world?
  Reply to Mike Holt

  • Reply from: Jim Green   January 23 2016, 1:51 pm EST
    Mike:

    I saw one once in Northern Maine (Madawaska area) some 45+ years ago. I don't know who the utility was. Industrial loads.. very common in Canada.

    Respectfully,

    Jim Green
    Reply to Jim Green

    • Reply from: Mike Holt   January 23 2016, 6:29 pm EST
      Once 45 years ago is not sufficient for me to create a table for this, sorry, and thanks for the input.
      Reply to Mike Holt

This is not a comment need some info what circuits in a dwelling require arc fault breakers

• Reply from: Mike Holt   January 23 2016, 7:25 pm EST
  Comments not related to the newsletter need to be posted on the Code Forum at www.MikeHolt.com please.
  Reply to Mike Holt

Mike, When you released the former version of the motor tables, I called your attention to the fact that 240.6(A) tells that ?Additional standard ampere ratings for fuses shall be 1, 3, 6, 10 and 601?. Please note that in the updated tables, this was considered for the single-phase motors, but not for the 3-phase motors. Any reason for that? Jacob Mendelovici

• Reply from: Mike Holt   January 23 2016, 7:34 pm EST
  Sorry, will fix my friend!
  Reply to Mike Holt

thanks