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Thread: 100 amp wiring size.
09-02-2008, 03:14 PM #1
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!
09-02-2008, 03:18 PM #2
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.
09-02-2008, 03:47 PM #3
You will need #2 wire for 100 amps.
09-02-2008, 04:09 PM #4
09-02-2008, 04:15 PM #5
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.
09-02-2008, 04:20 PM #6
#2 Aluminum, or #3 Copper
#2 Aluminum, or #3 Copper I believe to be correct.
09-02-2008, 04:36 PM #7
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
09-02-2008, 04:37 PM #8
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?
09-02-2008, 04:38 PM #9
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.
09-02-2008, 04:45 PM #10
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.
09-02-2008, 04:45 PM #11
09-02-2008, 05:10 PM #12
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!
09-02-2008, 05:40 PM #13
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.
09-02-2008, 06:23 PM #14
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.
09-02-2008, 06:34 PM #15
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?
09-02-2008, 06:57 PM #16
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
09-02-2008, 07:12 PM #17
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.
09-02-2008, 09:05 PM #18
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
09-02-2008, 09:06 PM #19
09-02-2008, 09:12 PM #20
"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.