electrical subpanel question

[Bob Cooper]

Installing a 200Amp subpanel for the new shop -- fed from a 100Amp breaker in the main panel. It's a Square D QO panel. My electrician ran AL 2-2-2-4 feeder cable but i can't tell what type -- i know depending on the sheathing it may be rated to carry 100Amps or 70Amps.

Questions

1) can you tell from this picture what type of cable/sheathing this is?
2) in order to seperate the ground from the neutral do i need to install a seperate ground bar or is there a way to isolate these 4 existing bars (2 of each side) so that 1-2 can be used for ground and the others for neutral?
3) I want to make sure the ground/case screw is not installed but i don't see one nor though do i see where it would go...can you point it out? I'm 99% sure i'm OK but want to make sure.

[Scott T Smith]

Bob, re the current capacity, to determine what insulation you have check the outer jacket of the individual wires. There should be a manufactures code, wires size, and a temperature rating printed there, and you want to look for the temperature rating. #2 aluminum wire is rated as follows: 60 degreeC rating -= 75A, 75 degree C rating = 90 amp, 90 degree C rating = 100A.


As far as isolating the ground and neutral buss, there is typically a transfer bar between them and you remove a screw. Use an ohm meter to determine if they are connected, and if so look for the transfer bar and how it is attached. Usually you can find it once you start tracing between the two buss bars.

[Anthony Whitesell]

A) I REALLY hope you going to put some type of relief in the top of the box to keep the box from chaffing through the wire.

B) I'd have to check my box (a QO140M200) I believe the bonding screw was in the top hole of the third bus bar from the left, or the inner of the two on the right side.

[Guy Bratt]

Hi there You have 100 amp SE Service Entrance cable You need a connector in the panel. The two bars are connected and can't be seperated with out violating te UL listing. You go back to the borg where you got the panel and buy a ground bar. It will fit holes in the panel back. Do not install the green bonding screw throught the neutral bar into the panel back. That happens only at the main service. At this location the ground and neutral are seperate per NEC. Be Carefull.

[Anthony Whitesell]

I believe SEU cable only has three conductors, the photo is of 4. I believe the cable he has is correct.

It took me a moment to understand the second half of the last post, and now I recall how the grounding screw works. (I have also taken a look inside my panel) The four bars are all connected to neutral and you drive the screw home in order to connect the box tub to neutral. With the screw driven home, you can either use the PK23GTA style ground bars or connect the grounds directly to the neutral busses. As a sub panel, you remove the screw (which has been done) and you MUST install the PK23GTA ground bars in order to have a place to connect the ground wires.

The bonding screw would be in the top of the third bus bar from the left as I mentioned earlier, but it appears to have been removed. In addition, you'll notice a slotted screw to the left of the center hex screw (for the neutral). This lug is the ONLY used to attach the ground wire to IF this panel was being used as a main panel. As this is a sub-panel. The ground wire is connected to an "add-on" ground bar, which you will add to bottom of the photo just outside the left and right sides of the photo frame.

With the new Square D panels, I found the phillips and slotted screw patterns to be very weak and cam'ed out easily. The screws also had a square drive which worked perfectly. I don't know why the phillips and slotted patterns were so weak. I highly suggest the use of a square drive screwdriver, if you don't have one already.

[Bob Cooper]

OK...here's what i've done/learned since the first post...BTW i really do appreciate all your help.

The bar runs horizontally across the top that the neutral wire connects to is one solid piece so as several of you have mentioned i need to install a seperate ground bar. In order to install the ground bar in the pre-drilled holes i'll need to pull some make the ground a good 6" longer than my hots/neutral. I do have some slack so that shouldn't be an issue.

Regarding the wire type -- i peeled back a good bit of the sheathing but the writing on the hot conductor is barely readable. I think it says (and i'm sure this is wrong but it's probably close enough for you guys to tell me what it actually says) XAAW-2 600 Volts. I don't see any mention of temperature. Does this help?

Also i picked up a 2" male adapter and ring to insert in the cutout to keep the wire from rubbing on the case -- clearly a good practice but for my own education, is this a code issue as well?

[Guy Bratt]

Hi Bob Yes any cable entering a box or cabinet must have a connector. Also a support is required 12 inches from a box. support your feeder close to the cabinet also. Don't beat down your supports to the point where the cable jackets are pinched they should be able to move slightly.
To do a better job get some "No Ox" gel and put it on your aluminum connections before you tighten them down to prevent oxidation of the joints. Aluminum oxide does not conduct well.
For cable identification read the cable jacket.

Good luck be carefull. Guy

[Lee Schierer]

Installing a 200Amp subpanel for the new shop -- fed from a 100Amp breaker in the main panel. It's a Square D QO panel. My electrician ran AL 2-2-2-4 feeder cable but i can't tell what type -- i know depending on the sheathing it may be rated to carry 100Amps or 70Amps.

Why not ask your electrician what the rating of the wire he furnished is??? Did he also provide the breaker or did you? No offense, but based on the fact that did not know to install a clamp on the wire entering the box, you may not be as qualified as you think to complete this wiring job safely. Don't forget that most municipalities/power providers will require you to have an electrical inspection of the new panel and wiring before you energize it.

[Rollie Meyers]

The cable is SER, since the 2008 NEC SER cable is required to be sized at 60 degrees C like NM cable, which means for 100A you need 1/0 AL. Prior to the 2008 NEC #2 AL could be used for 90A, a common misconseption is #2 AL is OK for 100A, but a subpanel or a feed to a outbuilding do not meet the criteria allowing one to undersize the conductors...

[Roger Frazee]

The cable is SER, since the 2008 NEC SER cable is required to be sized at 60 degrees C like NM cable, which means for 100A you need 1/0 AL. Prior to the 2008 NEC #2 AL could be used for 90A, a common misconseption is #2 AL is OK for 100A, but a subpanel or a feed to a outbuilding do not meet the criteria allowing one to undersize the conductors

You need to read the 2011 code ... that is now changed. The se cable needs to be installed in thermal insulation before you must meet the 60C ampacity requirement. Otherwise terminal temperature ratings now apply in accordance with 110.14(c).

BTW you need a new electrician if he installed what you are showing in your pictures ...

[joe milana]

Just curious, does it make sense run a 200A sub panel off a 100A breaker? I have a main lug sub panel running off a 100A breaker in my main panel.

[Bob Cooper]

BTW this feeder cable was run about 3 years ago...i had talked to my electrician and he said he was pretty sure he ran #2 AL and that that would carry 100Amps but as this area is pretty mis-understood i do want to verify this. Also i'm planning on having him review all my work prior an inspection but i'd like to get this as correct as possible beforehand.

So based on Roger's last comment i'm not sure where this leaves us...this is terminating into Square D QO 200A Subpanel on one end and 100Amp breaker on the other and i'm not sure what temp these are rated at.

i'll send a new picture soon...the wiring has improved but suggestions are always welcome.

[Bob Cooper]

Joe...yes i did this for two reasons (1) i chose not to use a lug since i wanted to be able to turn everything off w/o having to go to the main panel (2) i chose 200A just so i would plenty of spaces...

[Anthony Whitesell]

BTW this feeder cable was run about 3 years ago...i had talked to my electrician and he said he was pretty sure he ran #2 AL and that that would carry 100Amps but as this area is pretty mis-understood i do want to verify this. Also i'm planning on having him review all my work prior an inspection but i'd like to get this as correct as possible beforehand.

So based on Roger's last comment i'm not sure where this leaves us...this is terminating into Square D QO 200A Subpanel on one end and 100Amp breaker on the other and i'm not sure what temp these are rated at.

i'll send a new picture soon...the wiring has improved but suggestions are always welcome.

The electricians, folks here, and others I spoke with said the source breaker is what the wire gauge is sized off of (or vice versa). I was thinking of using my old 100A main as a sub, but supplying it with a 60A breaker. I understood that the correct wire size would be 4g copper.