Wiring 100 AMP panel from main 200 Amp panel with 100 amp breaker

Hi everyone
Right now I have 100 amp subpanel wired from 200 amp main panel with 6 gauge wire. I think there are 2 hot and one neutral but I may be wrong. Anyway my electrician told me to change that to 2 gauge wire. distance between two panels is about 80 foot so now my question is do I get three 80 foot copper wire? or is that wrong. my another question is do I need a ground on 100 amp subpanel. there is already ground on 200 amp subpanel.any suggestion will be appreciated{please pardon my English,its my second language}.Thank You all.

 

Welcome to the forums!

What size breaker/fuse are you feeding the sub panel with? (It does not need to be 100 amps) That will determine the size of the wire you need.
What are you planning to run off the sub panel?
Is this sub panel in an attached or detached building?
Is the feeder (wire between the two panels) in conduit or is it a cable? (You may not run individual wires that are not a cable, or in conduit.)

Yes, you need a ground.

 

Hi
Its a 100 AMP breaker
I am planning to use all amp I can get from this 100amp subpanel.
It is in attached building.
I am sorry I didn't understand conduit or cable part.
The three 6 gauze wire that are running right now are in steel pipes from 100 amp breaker to 100amp subpanel.

 

You can walk from one panel to the other without ever going outside?

You have individual conductors (the wires) in conduit (the steel pipe). How big is that pipe (inside diameter)?

#2 AWG copper is actually a bit small for a full 100 amps. Technically, you should have three #1 AWG conductors for the two hot wires and the neutral. And unless the conduit is threaded rigid conduit, you should add a #10 (I think) green insulated conductor for the ground.

In the subpanel, the neutrals must be isolated from any path to ground, including the panel box. The grounds must be bonded to each other and to the panel box.

 

Hi Nashkat1

I know it sounds strange but yes it is attached building,you don't have to go outside.

I was thinking can I run another 100 amp subpanel with 100 amp breaker from 200 amp main panel with 3 6awg wire{in short putting exactly another subpanel like I have right now}.would that be illegal? and then transfer some breakers from 1st 100 amp subpanel to 2nd 100 amp subpanel.

My guess is as there is 6 awg wire the most amp I could use would be anyway 60amp from one subpanel so I would be able to use total 120amp from 200 amp,right?

This would save me some serious money if I don't have to put 2awg or 1 awg wire b'cz getting 3 {2 awg} wire 80 foot is pricey.any other suggestion?

 

Yes, but you would have to protect the feed with a 60 amp breaker in the main panel as should be the existing 100 amp panel if connected with #6. Also the existing panel needs four wires not three and so will your new panel.

Bottom line, #6 feed is good for only 60 amps regardless of the size main breaker in the subpanel and therefore the breaker in the main panel that feeds it must be 60 amps or less. All subpanels must have two hots, one ground, one neutral. The ground bar normally must be bought separately and added to the subpanel. The neutral bar must have the bonding screw and/or strap removed.

 

Hi Ray

So should I change 100 amp breaker on 200 amp panel with 60amp? or it should be fine?

I know I have to put 60 amp breaker for 2nd 100amp panel,right?

I am just curious what difference does 100 amp breaker or 60 amp breaker makes if wire is 6 awg b'cz if I understand correctly 6awg wire won't be able to pull more than 60amp so above 60amp 100amp as well as 60 amp breaker will trip?

I don't have ground wire on 100 amp panel so what size wire should I use for ground?

Sometime it seems like I am in highschool learning new things everyday

 

Yes, if it is #6 wire*.

Yes.

The 60 amp breaker goes in the main panel and protects the #6 wire. The main breaker in the subpanel is not for protection. It is only used as a code required disconnect so can be any size 60 amps or greater. I get the feeling you are confusing the feeding breaker in the main panel with the main breaker in the subpanel.

#10 green for your grounding conductor assuming a 60 amp protected feed. Bare can not be used in conduit.

*On the existing subpanel you either change the breaker, easy job, or the wire as suggested by the electrician, not an easy job. A true 100 amp feed is probably over kill so I would suggest just changing the breaker.

 

A conductor will take as many amps as the loads demand. When that is more than the ampacity of the conductor, it will overheat and possibly start a fire. Conductors are protected by the size of the overcurrent protection device (the fuse or circuit breaker, typically) installed where they pick up the power. Nothing downline from that can protect them.

 

Hey Ray,

Thank you very much for the information.I am gonna go to lowes or home depot and start buying all the stuff that I need.

I am gonna replace 100 amp feeder breaker with 60 amp breaker.

I couldn't resist this so I have to ask this:

There was this one time when instead of 100amp feeder breaker there used to be 100 amp time delay fuse that blew up,so do you think that blew up b'cz it drawed more than 100 amp or did it blew b'cz it drew more than 60 amp?

If there are 6 awg wire with 60 amp feeder breaker that means anything more than 60 amp draw will trip the 60amp breaker right?

If there are 6 awg wire with 100 amp feeder breaker does that mean it allowes to draw more than 60 amp through 6 awg wire?(if it does than it might burn the wire or cause fire and that might be illegeal,right?)

 

Only thing I can add is that #3 THHN, in conduit, is good for 100 amps.

 

Hi Tolyn & nashkat1

#3 THHN ,does it has to be aluminum or copper?

now I understood why I need 60 amp breaker,thanks nashkat.

I checked at home depot and lowes but they didn't had #3 or #2 awg wire with THHN in one cable,they said I have to buy them individual

#6 awg 3 or 4 (not sure) wire were in cable and available for around $ 3.98/foot.

 

THHN is copper wire.
XHHW is aluminum.

IF you are going to use a cable, you would be required to use one that has #2 copper wires (which would be NM-b), or 1/0 aluminum wires in it (which would SE? cable) for 100 amps. This is because it is a cable and not individual wires installed in conduit.

You will likely need to go to an electrical supplier for that size cable.

 

Drew more then 100 amps or nearly 100 amps for a sustained period of time. Your lucky the wire didn't catch on fire.

Yes. That is the purpose of the breaker.

Yes, to all of the above.

That is correct it is not cable. Best practice you do not use cable in conduit except for short sleeves tp protect it if it is exposed to possible damage.

I suggest you buy the book Wiring Simplified Available in the electrical aisle of home center and on line sellers such as Amazon and read it cover.

 

Hey Tolyn

so I can use #3 awg individual(2 hot,1 neutral,1ground) wire in steel pipe(conduit) instead of using 2-2-2 wire that come in cable,right?

 

Hey Ray

Thank you very much for the information.seems like I dodged a bullet there,need to correct that as soon as possible.Thanks for the suggestion will make sure to buy that book.I will start working on it soon and will let you know how it turned out.

Thank you everyone,learned a lot here.

 

You will need three lengths of #3 AWG THHN for the two hots and the neutral.

Great. Probably the best single tool purchase someone starting out as a DIYer in this work can make, IMNSHO.

 

A continuous metallic conduit between the panels can be used as the 4th conductor for grounding.