3/4" Conduit - How many amps can be put through that?

[elm_street]

I have a detached garage that has a 3/4" PVC conduit running from the house underground to the garage that is about 15 feet away.

I'm wondering how much wire/how many amps I would be able to get to the garage. Will 3 12 gauge wires fit through that (for 3 20 amp circuits), or can one 3-8 wire go though that allowing me to have a 30-40 amp sub panel in the garage? Or am I limited to 2-3 14 gauge wires for 15 amp circuits.

The garage is 15x26 and I'm looking to get good lighting in it (probably 4-5 T8 fixtures plus 4-5 regular light sockets that I will probably put LED bulbs in) plus a couple exterior lights plus a garage door opener plus the flexibility to be able to run a table saw (probably around 2HP, at most 3HP) plus dust collection and maybe a small compressor (probably under 20 gallon and maybe a 1HP motor.

So will it be possible to get enough wire through a 3/4" conduit to supply the amps required to do what I'm hoping to do?

 

[LXCam]

You could do a 50amp subpanel with #8's.

 

[elm_street]

You could do a 50amp subpanel with #8's.

But will a 3-8 fit through a 3/4" conduit? There are two 90 degree bends to deal with and I'm wondering how hard it will be to get a #8 wire through those bends in a 3/4" conduit.

If it will then I'm pretty sure that will be more than enough power for what I want to do.

 

[OldNeons]

If you are concerned about fit, you could also pull individual conductors.

 

[LXCam]

But will a 3-8 fit through a 3/4" conduit? There are two 90 degree bends to deal with and I'm wondering how hard it will be to get a #8 wire through those bends in a 3/4" conduit.

If it will then I'm pretty sure that will be more than enough power for what I want to do.

Ya four #8 will fit and pull fine. I'm not sure if you're allowed to reduce the grounding conductor to a #10 in canada, but even if not you're in good shape.

 

[tfi racing]

Ya four #8 will fit and pull fine. I'm not sure if you're allowed to reduce the grounding conductor to a #10 in canada, but even if not you're in good shape.

Yep,should be fine,your max breaker size would be 40A which should be plenty for what you want to do.

 

[Charles (in GA)]

You are asking about pulling a single romex type cable thru the conduit, underground. This type of cable is not rated for a wet environment and in the US and I assume in Canada also, conduit underground is considered a wet location. What you need to pull are three separate #8 THHN/THWN wires (white, red, and black) and a #10 Green ground (if Canadian code allows the reduced ground like the NEC does). These four wires will be relatively easy to pull with wire lube. Practically impossible to pull jacketed cable like Romex thru conduit.

No matter what you think, you are most likely to find water standing in that conduit.

Charles

 

[MTW]

In order for you to use individual wires to feed your garage panel, the conduit will need to be continuous between both panels. 4 wires will be required, 3) #8 and 1) #10. The #8 for the two hots and neutral, and the # 10 for the ground. To comply with the NEC the neutral must have white insulation, and the #10 ground needs to be green. The wire type should be water resistant type such as THWN or XHHW. The garage panel will also require a ground rod and grounding electrode wire installed. Here are some charts from the NEC for wire fill in PVC conduit, and wire ampacity. The fill chart says you could install 4) # 6 but that could be very tough to do if your conduit isn't perfect and you let the wires get bunched and twisted while pulling them, better to stick with #8. for the wire ampacity chart you need to use the 60 deg C column for anything under 100A. So for you this means 40A. These rules and charts are for the US National Electric Code, Canada may be slightly different but is usually very similar.

 

[elm_street]

Thanks everyone. I will be having an electrician do the work, I was just wondering if it was going to be possible to get 40 amps to the garage through that conduit.

 

[Vladymere]

Run 4 8awg wires, green (ground), white (neutral), red and black or black or blue, etc (two hots). Use a 50 amp two pole breaker. Use THWN copper wire. Use Dawn dish detergent for the wire lube, it's cheaper then commercial wire lube. This can feed a sub panel in the adjacent structure.

Vlad

 

[Charles (in GA)]

Need to add that if you will have more than six breaker handles, you must have a disconnect. The disconnect can be inside in the panel (such as a backfed breaker), or it can be outside of the building. Your local codes may require it on the outside. The NEC requires that the disconnect be rated at 60 amps or more. Don't know about the Canadian code on this.

If you use a backfed breaker for the disconnect, you will also need a main breaker retaining kit for the panel. The part number of the kit will be found on the label that specifies the part numbers of optional ground bars, breakers, and also gives torques for screws in the panel, etc. This placard may be found inside the door on the front cover of the panel.

You also need a neutral bar that is isolated from the metal of the panel, and a ground bar that is properly grounded to the metal of the panel. Most of the lower amperage panels do not provide the ground bar, they just punch a bunch of holes in the back wall of the panel, and you can select the proper length ground bar of the same brand as the panel, and the screw holes will line up with the holes punched in the back wall of the panel, it will be attached with self tapping machine screws.

Charles

 

[wyliesdiesels]

In order for you to use individual wires to feed your garage panel, the conduit will need to be continuous between both panels. 4 wires will be required, 3) #8 and 1) #10. The #8 for the two hots and neutral, and the # 10 for the ground. To comply with the NEC the neutral must have white insulation, and the #10 ground needs to be green. The wire type should be water resistant type such as THWN or XHHW. The garage panel will also require a ground rod and grounding electrode wire installed. Here are some charts from the NEC for wire fill in PVC conduit, and wire ampacity. The fill chart says you could install 4) # 6 but that could be very tough to do if your conduit isn't perfect and you let the wires get bunched and twisted while pulling them, better to stick with #8. for the wire ampacity chart you need to use the 60 deg C column for anything under 100A. So for you this means 40A. These rules and charts are for the US National Electric Code, Canada may be slightly different but is usually very similar.....

That only applies if the rating of the termination point(lug, bus bar, etc) is unknown or 60* c. If the termination point is 75* c rated or dual rated (60*/70* C) then the 75* c ampacity can be used! See 2011 NEC 110.14 (C)(1)(a)(3)

 

[MTW]

That only applies if the rating of the termination point(lug, bus bar, etc) is unknown or 60* c. If the termination point is 75* c rated or dual rated (60*/70* C) then the 75* c ampacity can be used! See 2011 NEC 110.14 (C)(1)(a)(3)

Yes you are correct, it can be sized @ 75 C if both termination temperatures listings are known. But in this case they are not know, he never mentioned what type panels he has, just wanted to know amp capacity of 3/4" conduit. In that case I defaulted to the main part of the rule for 60 C for 100A and less.

Verbiage for those interested.

 

[ddawg16]

Speaking from personal experience....3 #8's THWN and a bare #10 ground is NOT easy to pull through a 3/4" PVC with 2 90's.....that is what I 'used' to have to my garage.....

Now it's 1" with #6's....still not easy....the OP will need plenty of KY.

 

[Highbeam]

I recently pulled 3-#8 and a#10 THWN through 1" conduit for a 50 amp circuit and it was easy peasy. That run had a 7 foot vertical rise and four 90 degree elbows. If it was easy peasy in 1" then it should be doable in 3/4" with less bends.

 

[elm_street]

The electrician says he will be pulling individual conductors of #8 wire, I'm not sure what size ground he will use. He is going to be able to get 40 amps to the garage. I'm not sure if he is going to pull 3 wires plus ground or just 2.

The wiring in the garage is 80% done now and the feed from the house and the panel in the garage should be done by the weekend.

 

[pattenp]

He should pull 3 #8 and 1 #10. If it's THHN/THWN in conduit from panel to panel then you can put a 50A breaker on it.

The electrician says he will be pulling individual conductors of #8 wire, I'm not sure what size ground he will use. He is going to be able to get 40 amps to the garage. I'm not sure if he is going to pull 3 wires plus ground or just 2.

The wiring in the garage is 80% done now and the feed from the house and the panel in the garage should be done by the weekend.

 

[brewchief]

We pulled 3 #6 and one #10 through about 80' of 3/4" with 2 90's and one little offset without much difficultly, I don't think we even bothered with lube.

 

[sstock]

In order for you to use individual wires to feed your garage panel, the conduit will need to be continuous between both panels. 4 wires will be required, 3) #8 and 1) #10. The #8 for the two hots and neutral, and the # 10 for the ground. To comply with the NEC the neutral must have white insulation, and the #10 ground needs to be green. The wire type should be water resistant type such as THWN or XHHW. The garage panel will also require a ground rod and grounding electrode wire installed. Here are some charts from the NEC for wire fill in PVC conduit, and wire ampacity. The fill chart says you could install 4) # 6 but that could be very tough to do if your conduit isn't perfect and you let the wires get bunched and twisted while pulling them, better to stick with #8. for the wire ampacity chart you need to use the 60 deg C column for anything under 100A. So for you this means 40A. These rules and charts are for the US National Electric Code, Canada may be slightly different but is usually very similar.

Extremely useful info here, thanks for sharing.