100 amp Sub panel wiring

[skon1212]

I am contemplating putting a 100 amp sub panel in my attached garage as my main panel is filling up fast. The sub panel would have a circuit for a compressor, a circuit for a 110 welder, a circuit for garage outlets and a circuit for outdoor lighting ect.
The new panel would be on the inside of the garage on the same wall as the main panel which is on the outside of the wall. So the run to the new panel would be maybe 4 feet. I have looked at several wiring diagrams and many call for grounding rods for the sub panel. Do I need those? I thought the first picture may be the diagram to follow for my situation but I am not 100% sure.
ALSO, my main panel only has one bus bar that holds both the neutral and ground wires. Would I run the neutral and Ground wires from this bus bar to the new panel? I also attached a pic of my main panel so you can see what I am referring to. Thanks for any suggestions.

 

[Aceman]

I have looked at several wiring diagrams and many call for grounding rods for the sub panel. Do I need those?

No.

ALSO, my main panel only has one bus bar that holds both the neutral and ground wires. Would I run the neutral and Ground wires from this bus bar to the new panel?

Yes.

 

[skon1212]

No.




Yes.

So basically follow the wiring diagram in the first picture correct? Also would 1-1-1-3 Aluminum wire be overkill for about a 5 foot run to the subpanel?

I will need lugs to go to the bus bar though correct? I am sure the holes are too small.

 

[wyliesdiesels]

The main panel is the only panel that neutrals and grounds share the same bar.

Past that all subpanels need to have an isolated neutral bar.

The only exception is subpanels in detached structures wired before 2008 code cycle.

Subpanels in the same/attached structure dont need rods.

If u want 100a then the minimum size al wire u need is #1...

Yes that diagram is correct with an added note, that is missing, that the neutral bar needs to be isolated.

 

[pattenp]

So basically follow the wiring diagram in the first picture correct? Also would 1-1-1-3 Aluminum wire be overkill for about a 5 foot run to the subpanel?

I will need lugs to go to the bus bar though correct? I am sure the holes are too small.

1-1-1-3 Al SER is the wire to use for 100A to the subpanel without having to run conduit. I assume you know you can use a main lug panel for the subpanel and not a main breaker panel. As you said you'll need to buy a couple lugs for the neutral and perhaps the ground to fit the bar in the main panel.

 

[RichardC12]

You won’t be needing grounding rods for the subpanels.Make sure that you have good lightning when installing a subpanel you could use a battery operated light.They are several tutorials online where you can find detailed instructions on how to install sub panel,you could even get professional help.I had mine installed with the help of a home electrical repair service called the shock doctors.

 

[Angelfire]

1-1-1-3 Al SER is the wire to use for 100A to the subpanel without having to run conduit. I assume you know you can use a main lug panel for the subpanel and not a main breaker panel. As you said you'll need to buy a couple lugs for the neutral and perhaps the ground to fit the bar in the main panel.

I believe if the OP is running the SER in an insulated cavity (ie. wall), he will need to derate the ampacity using the 60 degree column which would limit him to 85A capacity, correct?

 

[wyliesdiesels]

I believe if the OP is running the SER in an insulated cavity (ie. wall), he will need to derate the ampacity using the 60 degree column which would limit him to 85A capacity, correct?

Depends on how much of the SER is actually in insulation.

 

[Angelfire]

Depends on how much of the SER is actually in insulation.

Where is that defined? I seem to have the number 24" on my head but don't see a reference to it in the NEC offhand. The reference I was going by is 338.10(B)(4)(a) which simply states it needs to be derated. Just trying to get my NEC mojo back as it's been a number of years since I've looked through the code and need to brush up for my homeowner permit exam. Cheers!

 

[wolfhawk73]

On the same subject, but not specifically...

Could you use a smaller amperage sub-panel since you're not really loading it up all that much? It might save you some green.

 

[pattenp]

Where is that defined? I seem to have the number 24" on my head but don't see a reference to it in the NEC offhand. The reference I was going by is 338.10(B)(4)(a) which simply states it needs to be derated. Just trying to get my NEC mojo back as it's been a number of years since I've looked through the code and need to brush up for my homeowner permit exam. Cheers!

You need to look at 310.15(A)(2) Exception. It basically says if the lower ampacity is less than 10% of the run for a max of 10' you can use the higher ampacity. So if you have 10' of SER no more than 1' can be buried in insulation.

 

[wyliesdiesels]

On the same subject, but not specifically...

Could you use a smaller amperage sub-panel since you're not really loading it up all that much? It might save you some green.

The subpanel needs to be rated for at least the same amperage as the feeding breaker.

 

[matt_i]

Its just my personal preference but I would put in some PVC conduit a couple of LBs and #2 Cu THHN, I think a #6 awg bare ground is acceptable.

One point of stickiness when landing either a #1 awg or #2 awg on the ground/neutral bar in the main panel is that the typical hole is only drilled for I think #4 awg. I had to use a screw to attach an additional larger sized lug to that same drilled bar for the #2 in my sub panel.

The reason i like Cu especially for short runs are that you can get all the colors (red, white black) at Home D (at least my local one) "by the foot" which is pretty reasonable for a 5 foot run, probably need 8-10 feet of wire per conductor. Also never any worry about voltage drop, the Cu is a better, more efficient conductor per unit weight. While it costs slightly more, its a "better engineering material" for the job its called to do.

 

[Aceman]

Also never any worry about voltage drop, the Cu is a better, more efficient conductor per unit weight. While it costs slightly more, its a "better engineering material" for the job its called to do.

I don't agree with any of that.

1. There is voltage drop no matter what kind of conductor you use. I can assure you I still upsize my copper branch circuits on a regular basis just for voltage drop concerns.

2. More efficient per weight?? I don't think so. According to Southwire's website, it looks to me like 1000' of 250 AL THHN weighs 311 lbs vs 3/0 THHN copper at 575 lbs. Either one can be used for a 200 amp feeder/circuit. We almost always use aluminum for long feeders just because they are easier to handle over copper.

http://www.southwire.com/products/ProductCatalog.htm

 

[gnxtc2]

We almost always use aluminum for long feeders just because they are easier to handle over copper.

http://www.southwire.com/products/ProductCatalog.htm

No..... the real truth is that it's cheaper.

3/0 Cu = approx $2.77 per foot
250MCM Al = approx $1.06 per foot

Depending on use, you can use 4/0 Al for 200A ( approx $0.80 per foot)

Billy T.
[email protected]