sub panel help.

[maniac0908]

Hey im new here so sorry for asking newb questions. I have a detached garage. It already has a sub panel. The main inside has 200amp coming in. From there i have 220v on a 60amp breaker go to the sub panel. The wire is 6 awg and goes into a 50amp 220v breaker which i guess feeds both sides of subpanel. In the garage is maybe 10 or 11 flouressent bulb fixtures and some outlets which will mainly be used for charging drill batteries and maybe other little things if needed. I am installing a lift which uses 220v 30amps and a compressor which uses the same. I will put them both on their own circuit. My main question is, will this setup be enough? Im ok with changing some breakers but if i have to run new wire to sub that will ****. Please help! Thanks. Here

 

[Syberia]

I doubt either the compressor or the lift will use a full 30 amps, is that the FLA or the recommended breaker size? I suspect this is the breaker size and the actual load of the motors is much less. If you don't run them both at the same time, you're sure to be fine, and even if you do, you're most likely fine.

 

[maniac0908]

The manual calls for 30amp breakers. Ok cool. I just thought that 2 30 amps running at the same time along with lights and stuff would blow a 60 amps fuse. Also, is it normal for the breaker on the main going to the sub be larger than the breaking on the subpanel coming from the main? Main is 60 and sub is 50.

 

[maniac0908]

Forgot to mention the garage opener. Dont know how much amps that thig uses.

 

[buildyourown]

If the appliance calls for a 30a breaker, it probably only ever pulls 25a, and that's at start up. A motor pulls a lot more when it starts than just running.
So, as long as you don't start everything at exactly the same time, you'll be fine. Compressor is the biggest.
This was mentioned in another thread, but if you are working alone, it's hard to use that much power.

 

[rburke65]

Retired electrician here.....I think you will be fine. Even if the lift and the compressor kick in at the same time, I don't think you will have an issue. You'll be ok.

 

[pattenp]

You can up the breaker in the sub-panel to a 60 if needed.

 

[maniac0908]

I think thats what ill do. Put a 60amp o the breaker as well. Is that a violation of code? I wonder why they had a 60 at main and 50 at sub.

 

[JACDes]

Wire sizing guidelines (rules of thumb)

14 ga = 15 amp max. breaker size.
12 ga = 20 amp
10 ga = 30 amp
8 ga = 50 amp
6 ga = 60 amp
4 ga = 80 amp
3 ga = 100 amp

it would appear the previous owner started out with the best intentions but cheaped out on the wiring to the sub-panel. The breaker at the main panel should match the main breaker at the sub-panel, but to keep from overloading the undersized wiring to the sub-panel the PO installed the correct smaller sized breaker at the sub-panel or used a 50 amp panel instead of 60.

If you need true 60 AMPs at the sub-panel the safest thing to do is replace the sub-panel wiring to the correct size and the sub-panel main breaker to the correct size. but be careful some mfg's you cannot replace the main breaker, you will have to replace the entire sub-panel instead.

IF your garage lighting circuit is maxed out, the most that it can draw is 20 amps which equates to 2,400 watts or ( 30 ) T12 4' strip lights @ 80 watts per fixture

I doubt you have that much lighting load.

 

[Aceman]

Wire sizing guidelines (rules of thumb)

14 ga = 15 amp max. breaker size.
12 ga = 20 amp
10 ga = 30 amp
8 ga = 50 amp
6 ga = 60 amp
4 ga = 80 amp
3 ga = 100 amp

These ampacities are NOT entirely accurate and should not be followed. It should also be mentioned there are different ratings for romex, mc cable, thhn, etc. One size of wire is NOT rated the same in all cable types. Then you add aluminum to the mix and it gets even more confusing. Will the wire be ran through insulation? That can change the ampacity too.

Someone looking for wire ampacity information would be better off to post their question specific to their situation rather than relying on a "rule of thumb" guide to size wire. Their have been countless instances of folks on this forum installing the wrong wire because they followed such a guide.

 

[JACDes]

sure ok...

Who the hell still uses aluminum wiring for branch wiring, is this this 1972?!

Only time I see alumin is for primaries... were not talking about primaries.

The aforementioned ampacities for branch wiring is for copper with THHN insulation, (all BIG box stores and supply houses sell THHN clad copper wire) installed in CONDUIT.
IT is a GUIDELINE.. not set in stone, HOWEVER the changes are so slight for Romex, BX, etc. that they are negligible.

Search online, this is not top secret information. Any basic wiring book will tell you the same thing.

I READ OPs post... did you? he should change the breaker in the main panel to 50 amp.. to match the sub-panel because the wiring to the sub panel is rated for 50 amp.
If he wants 60 amp at the sub-panel he should replace the feeder wired from the main panel.
simple actually.

IMHO I would redo it with 100 amp sub panel but that is just me.

 

[pattenp]

I think thats what ill do. Put a 60amp o the breaker as well. Is that a violation of code? I wonder why they had a 60 at main and 50 at sub.

You know what assuming does? So, I'm assuming your #6 feeder is copper. So at the least if it's NM-b cable it is 55 amps. You can up size to the next standard breaker size which is 60A. If the #6 is THHN in conduit then it's 65 amps, which means you can go with a 70 amp breaker at both ends. The conservative approach is to have 50A breaker for #6 NM and 60A breaker for #6 THHN.

 

[pattenp]

sure ok...

Who the hell uses aluminum wiring for branch wiring, is this this 1972?!

Only time I see alumin is for primaries... were not talking about primaries.

Aluminum wire is used a lot for a branch feeder to a sub-panel. May be where you live it's not common.

Oh.. and why did you highlight the #8 @ 50A in your chart when the OP said the wire is #6?


*

 

[JACDes]

because I mis-read it...

If he has #6 copper THHN in conduit then OP can safely change the sub-panel breaker
to 60 amp, if he needs a bit more power he could up it to 70, but I like to be conservative and have the additional safety factor.
Odds are you will trip a branch circuit breaker before ever tripping the main. really the main is convenient shut off.. a lot of people do a sub-panel with main lugs only.


My garage I did a 100 amp 12 cct sub-panel with #3 copper THHN in conduit.
3 power circuits, 1 lighting circuit, (3) 220V circuits (welder, compressor, & A/C)

2 spaces left over.

 

[maniac0908]

The wire is #6. Im trying to figure out what type. I know its copper. But cant read the label because its all worn off. The wire is insulated black with orange dot writting. It is ran underground in a tube. While my sub box can handle 100amps. I really dont want to redo that wire. It will be such a pain. I guess my next step is to try and figure out if my wire is thhn or nm-b. Is there a way to tell by just looking at it? Thanks everyone helping!

 

[Charles (in GA)]

If the wires are in a black jacket, that is NM. THHN wires are loose, not jacketed. NM is not supposed to be underground, conduit or not. Conduit underground is considered a wet location, always, and NM cannot be run in a wet location and stay within the code. You would need THWN which is usually THHN/THWN dual marked.

 

[Alchymist]

Wire sizing guidelines (rules of thumb)

14 ga = 15 amp max. breaker size.
12 ga = 20 amp
10 ga = 30 amp
8 ga = 50 amp
6 ga = 60 amp
4 ga = 80 amp
3 ga = 100 amp

it would appear the previous owner started out with the best intentions but cheaped out on the wiring to the sub-panel. The breaker at the main panel should match the main breaker at the sub-panel, but to keep from overloading the undersized wiring to the sub-panel the PO installed the correct smaller sized breaker at the sub-panel or used a 50 amp panel instead of 60.

If you need true 60 AMPs at the sub-panel the safest thing to do is replace the sub-panel wiring to the correct size and the sub-panel main breaker to the correct size. but be careful some mfg's you cannot replace the main breaker, you will have to replace the entire sub-panel instead.

IF your garage lighting circuit is maxed out, the most that it can draw is 20 amps which equates to 2,400 watts or ( 30 ) T12 4' strip lights @ 80 watts per fixture

I doubt you have that much lighting load.

Just to keep things straight - it matters not what the main breaker in the sub-panel is, its only function is a disconnect. The sub panel could be a 30 amp 2 circuit or a 100 amp 40 circuit - doesn't matter. Important thing is the wire size to the sub panel and the size of the breaker in the main panel feeding the sub panel.

 

[maniac0908]

Great.... so i dont even have the right cable in there. Let me double check it, and ill take pics so you guys can see. I hope i dont have to run new wire.....

 

[JACDes]

If the wire is in conduit it is not a big deal to pull new.

 

[pattenp]

Pictured is NM-b. Does it look like this?

 

[maniac0908]

Pictured is NM-b. Does it look like this?

I will take a pic when i get home and upload using tapatalk. Hopefully itll work. If i need to run new wire, do i just call ms utility to come mark where it is?

 

[pattenp]

Ms utility doesn't mark private owned wiring. If the wire is run within conduit you shouldn't have to dig it up, you just pull the old wire out and pull in the new wire behind. The ease all depends on the condition and size of the conduit you have.

 

[maniac0908]

Ok so its says 6 awg with a 10 awg ground nm-b. Sound right? It is run underground in a conduit. Since i cant afford new wire right now i think ill just change the breaker at the main to 60. I should be ok as long as i dont add more stuff. When i do decied to run the new wire. What kind and size should i use for 100amp? Can nm-b go umderground with a conduit? Or do i have to use thhn?

 

[Alchymist]

NM-B cannot be used underground. I'd pull it, and use it to pull in the correct wiring as you remove it. What size conduit do you have, length, and how many turns (fittings)?

 

[maniac0908]

Looks to be about a inch of pvc. About 200ft in lengt. Might be a little less. And about 5 turns

 

[pattenp]

If the conduit is 1" you're stuck. #6 is at the max you can do. You need new conduit to get 100A, about 1.5" to 2" depending on wire type. Also the distance plays a part as to the wire size needed.

 

[maniac0908]

Ok sorry. Just got home and measured. It is 2 inches. And there only about 100ft with 7 turns.

 

[pattenp]

There is to be no more than 360 degrees of bends between access/pull points. So if those 7 turns add up to more than 360 degrees of turns there needs to be a pull point some where in between.

 

[maniac0908]

Ok once i dig it up ill check all the turns. What size wire and what kind do you recommend?

 

[pattenp]

So what is the total distance from the main panel to the sub panel? I see 200ft and 100ft mentioned. I'm not sure that you need a full 100A.

 

[maniac0908]

So what is the total distance from the main panel to the sub panel? I see 200ft and 100ft mentioned. I'm not sure that you need a full 100A.

Its 100 ft. And id like to do 100amps to future proof it. I dont want to have to run another wire later down the road because i need 100amps.

 

[pattenp]

If you are set on the full 100A capacity you will need three #3 conductors with one #8 conductor for the ground in copper THHN/THWN, or three #1 conductors and one #6 conductor for the ground in aluminum THHN/THWN or XHHW. The aluminum will save you $$.

If you are willing to do 90A you can use aluminum 2-2-2-4 MHF, this comes as an assembled cable.

 

[maniac0908]

If you are set on the full 100A capacity you will need three #3 conductors with one #8 conductor for the ground in copper THHN/THWN, or three #1 conductors and one #6 conductor for the ground in aluminum THHN/THWN or XHHW. The aluminum will save you $$.

If you are willing to do 90A you can use aluminum 2-2-2-4 MHF, this comes as an assembled cable.

Ok cool. Thanks. I think im going to go with the xhhw aluminum. I read that it is more durable than thhn/thwn. I would go with the mhf but i cant find it sold by the foot. Home depot only has a 500ft roll.

 

[pattenp]

If looking at HD on line you'll see 500' roll. The HD and Lowes near me both sell the #2 MHF by the foot in the store. It cost about $1.50 - $1.60 a foot.

 

[maniac0908]

If looking at HD on line you'll see 500' roll. The HD and Lowes near me both sell the #2 MHF by the foot in the store. It cost about $1.50 - $1.60 a foot.

At 1.60 for 110ft it puts me at about 180. Online i can get the xhhw for $160. And ill be able to run 100amps.

 

[maniac0908]

Was just readig on aluminum wiring. Is it really a fire hazard? Id rather pay more if copper is better and safer.

 

[Norcal]

Was just readig on aluminum wiring. Is it really a fire hazard? Id rather pay more if copper is better and safer.

Copper is the conductor of choice, but properly installed aluminum alloy conductors are fine, aluminum is used almost exclusively by PoCo's & they are not going to use something that is going to give them a headache later.

 

[maniac0908]

If looking at HD on line you'll see 500' roll. The HD and Lowes near me both sell the #2 MHF by the foot in the store. It cost about $1.50 - $1.60 a foot.

Was just at home depot and lowes. Hd has 2-2-2-4 alluminum for 1.42 per ft and the guy says it can handle 100amps. Lowes has 2-2-2-2 for 1.34 per ft. Can those handle 100 amps?

 

[wyliesdiesels]

Was just at home depot and lowes. Hd has 2-2-2-4 alluminum for 1.42 per ft and the guy says it can handle 100amps. Lowes has 2-2-2-2 for 1.34 per ft. Can those handle 100 amps?

No not in your situation. #2 al is good for 100a when used as a feeder supplying the entire load of a dwelling...in your situation 90a is max!