Page 1 of 2 12 LastLast
Results 1 to 20 of 35
  1. #1
    3t3d is offline Titanium
    Join Date
    Nov 2004
    Location
    WI
    Posts
    3,885

    Default 100 amp wiring size.

    I have a building that I rent out parts of it.
    I have someone interested in one of the rooms, about 4200 square feet.

    There is an old circuit, that the former owner told me was a 100amp 480 volt service for a wood chipper. I looked at the wiring, and they are #4's

    The electrician for the new tenant tells me that they are too small, and will have to be upgraded to #3's.

    I don't think the equipment is really going to be pulling 100 amps....

    That's a Lot of copper!

    Any opinions?

  2. #2
    Dualkit is offline Diamond
    Join Date
    Apr 2005
    Location
    Beaverdam, Virginia
    Posts
    4,416

    Default

    If there are 3 or more inside conduit or a raceway 4s are only good for 85 amps. They would
    be good for 100 amps alone in free air, which would be usual.

  3. #3
    928gene928 is offline Aluminum
    Join Date
    Sep 2005
    Location
    Joliet, Illinois
    Posts
    178

    Default Wire Size

    You will need #2 wire for 100 amps.

  4. #4
    Rancher Bill is offline Aluminum
    Join Date
    Nov 2006
    Location
    Calgary, Alberta, Canada
    Posts
    211

    Default

    Here's a wire size calculator.

    Wire Size Calculator


    You need to know voltage, distance and amperage.

  5. #5
    3t3d is offline Titanium
    Join Date
    Nov 2004
    Location
    WI
    Posts
    3,885

    Default

    That wiring size "calculator" tells me I need #12 wires for a 100 amp service.... I'll bet!

    It is 80 feet from the panel to the load.
    480volts, 100 amps max. Copper wire.

  6. #6
    gunsmither is offline Aluminum
    Join Date
    Oct 2005
    Location
    Washington State
    Posts
    131

    Default #2 Aluminum, or #3 Copper

    #2 Aluminum, or #3 Copper I believe to be correct.

  7. #7
    wippin' boy is offline Diamond
    Join Date
    Sep 2005
    Location
    il.
    Posts
    5,434

    Default

    use the #4's for a 60 amp service
    then pull a set of #6's for the second 60 amp service
    120 amp potential total

  8. #8
    stef.'s Avatar
    stef. is offline Aluminum
    Join Date
    Apr 2006
    Location
    michigan
    Posts
    87

    Default Service size

    What are the specs. from the person that is interested in renting the 4200 ' sq. ft. unit. What voltage will he need. Will it be office or shop? Is there power to receptacles or lighting in that unit presently?

    Stef.

  9. #9
    Forrest Addy is online now Diamond
    Join Date
    Dec 2000
    Location
    Bremerton WA USA
    Posts
    9,218

    Default

    FIRST!!! Check local code. Some jurisdictions have more stringent requirements for conductor ampacity and other electrical minutia. Maybe not in Wisconsin but certaily in warm climates. Some jurisdictions require upgrading of the branch circuit or sometimes even the whole system if any parts is sub-code. Not always; it varies.

    Then consider conductor size and conduit size. Remember NEC and local code represents minimum standards. They're satisfactory in most situatations but not always suited to every application.

    Look up accaptable ampacity in the NEC and your local code for your application. #4 may be technically adequate for your immediate application for a 100 Amp service for equipment that's seldom run to capacity but when feeding a pump or a heater for example #4 may not be suitable. In electrical practice the overcurret protection is intened to protect the conductors it feeds not the power consuming equipment. OTH a 100 Amp service is defined by the breaker and the conductors it feeds have to meet code requirements for Ampacity, conduit fill, insulation, placement in construction, max ambient air temp, and other factors. While this is presented in tables, an informed judgement is still required.

    Procede well informed. My friends here in PM wish you well and would never knowingly mislead you but few of us (including me) are electrical professionals. You need good advice before making electrical mods. You want to pass your inspection first time around but without spending more money and time than you have to. So pay a consulting fee or buy a case of beer or a jug of hooch for a licensed local electrician to line out your project for you.

  10. #10
    Join Date
    Nov 2005
    Location
    Maryland
    Posts
    6,900

    Default

    Quote Originally Posted by Rancher Bill View Post
    Here's a wire size calculator.
    Minimum wire size is determined by the rating of the circuit interrupter (either a circuit breaker or a fuse). The primary reference for this information is the NEC (National Electrical Code), although local jurisdictions may have more stringent requirements.

    You can use larger wire than specified in the Code, but not smaller.

    And you can NEVER use parallel conductors to increase branch circuit capacity.

    - Leigh

  11. #11
    Polaraligned is offline Hot Rolled
    Join Date
    Jan 2007
    Location
    Northern, NJ
    Posts
    669

    Default

    Quote Originally Posted by 3t3d View Post

    The electrician for the new tenant tells me that they are too small, and will have to be upgraded to #3's.

    Any opinions?
    Tell the tenant to have his electrician upgrade the wire at his own expense.

  12. #12
    Ox's Avatar
    Ox
    Ox is offline Diamond
    Join Date
    Aug 2002
    Location
    West Unity, Ohio
    Posts
    17,618

    Default

    Cheapest fix would be to downgrade the service to a 60A 600V box.

    Or - OR ... you could throw some 75A fuses (breaker?) on your end! Cheaper yet prolly - and actually more to code.


    -----------------

    Sweating to the Oldies!
    Ox

  13. #13
    Mr. O is offline Cast Iron
    Join Date
    Feb 2007
    Location
    Mi. USA
    Posts
    300

    Default

    Quote Originally Posted by 3t3d View Post
    I have a building that I rent out parts of it.
    I have someone interested in one of the rooms, about 4200 square feet.

    There is an old circuit, that the former owner told me was a 100amp 480 volt service for a wood chipper. I looked at the wiring, and they are #4's

    The electrician for the new tenant tells me that they are too small, and will have to be upgraded to #3's.

    I don't think the equipment is really going to be pulling 100 amps....

    That's a Lot of copper!

    Any opinions?

    Since no-one has given a solid answer(it seems), go to www.selfhelpforums.com register and ask your question in the appropiate forum(electrical code, USA) an electrician will help you out.

  14. #14
    3t3d is offline Titanium
    Join Date
    Nov 2004
    Location
    WI
    Posts
    3,885

    Default

    The tenant is installing the wiring by his expwense.
    The panel feeding the room is a 250 amp 480 volt panel.

    There are already lighting and outlets.

    He has a printing line, the 100? amps is for one of the peices of equipment.
    About the only load on that panel, besides the lights (277 volt)

    It just seemed a little "hazy" about the fact that the previous tenants had a 100 amp load on those wires, and now he is forced to buy a lot of new copper.

    It affects the "salability" of the space.
    Ready to connect the wiring, or an expensive upgrade.

    Thanks for answers.
    His electrician is in charge of hooking it all up.

  15. #15
    Walter A's Avatar
    Walter A is offline Titanium
    Join Date
    Jul 2007
    Location
    Hampton, Virginia
    Posts
    2,212

    Default

    Either some of you guys are shooting from the hip or my industrial electrician that wired my entire plant with 480v is all wet.

    This is 480v 3 phase right? More volts = smaller wire? Why are there recommendations for #2 being posted?

    Am I missing something?

    Walter A.

  16. #16
    deltaenterprizes is offline Hot Rolled
    Join Date
    May 2006
    Location
    Longview,TX
    Posts
    983

    Default

    According to NEC Table 310.16 the allow ampacity of not more than 3 conductors in a raceway( conduit)THHN(90*C,194*F) 2AWG wire is130 amps,3 AWG is 110 amps , 4 AWG is 95 amps page 70-144 of the 2002 National Electrical Code the latest edition I have. The current edition can be viewed on line a the National Fire Protection website.

    The ampacity is determined by the quality of the insulation!

    The smaller the number the bigger the wire the more ampacity!

    According to NEC 310.4 ,page 70-134 2002 NEC, paralleled conductors in each phase ,neutral,or grounded circuit shall
    1 Be the same length
    2 Have the same conductor material
    3 Be the same sixe in circular mil area
    4 Have the same insulation type
    5 Be terminated in the same manner

  17. #17
    stef.'s Avatar
    stef. is offline Aluminum
    Join Date
    Apr 2006
    Location
    michigan
    Posts
    87

    Default Wire chart

    3T3D

    The machine you are wiring up has a tag which shows the voltage and amps needed to power up the machine. You can use the chart shown to size your wire.

    www.armstrongssupply.com/wire_chart.htm

  18. #18
    Ox's Avatar
    Ox
    Ox is offline Diamond
    Join Date
    Aug 2002
    Location
    West Unity, Ohio
    Posts
    17,618

    Default

    Amps is as Amps does.

    Volts means nothing in this equasion.


    (BTW - I didn't look at eny of the charts)

    I woodn't be afraid to run #4 all day long at 100A. It may run warm in 3/4"EMT, but 1" it should be fine. ???


    ----------

    Danger - High Voltage
    Ox

  19. #19
    Join Date
    Nov 2005
    Location
    Maryland
    Posts
    6,900

    Default

    Quote Originally Posted by Walter A View Post
    This is 480v 3 phase right? More volts = smaller wire? Why are there recommendations for #2 being posted?
    Hi Walter,

    Voltage has absolutely nothing to do with wire size (although it does affect insulation specs).

    The required wire gauge is determined by the current being drawn, and more specifically by the circuit protection device installed on the line.

    - Leigh

  20. #20
    Join Date
    Nov 2005
    Location
    Maryland
    Posts
    6,900

    Default

    Quote Originally Posted by deltaenterprizes View Post
    The ampacity is determined by the quality of the insulation!
    To be more specific, the ampacity is determined by the maximum permissible operating temperature of the insulation, i.e. the temperature above which the insulation melts or catches fire. This varies with the material, being a question of composition, not quality.

    Quote Originally Posted by deltaenterprizes View Post
    According to NEC 310.4 ,page 70-134 2002 NEC, paralleled conductors in each phase ,neutral,or grounded circuit shall...
    You missed the opening paragraph of that section (I have the same edition), which says:

    "310.4 Conductors in parallel. Aluminum, copper-clad aluminum, or copper conductors of size 1/0 AWG and larger..."

    This is simply recognition of the fact that it's extremely difficult to run huge conductors. You can't pull them or bend them with less than super-human strength. So parallel cable runs are permitted for large sizes. (nb. a 1/0 AWG conductor has a diameter of 0.325".)

    Also, the NFPA assumes that conductors of this size will be installed by professional electricians who have the tools, knowledge, and training to terminate the individual conductors properly.

    This NEC section does NOT permit parallel connection of conductors in the size range being discussed in this thread.

    - Leigh

Page 1 of 2 12 LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •