Conduit fill - Three #8awg plus one #10awg in 1/2 EMT?

[therobthompson]

I'd like to use an existing underground 1/2" EMT conduit to run a 50 amp sub panel. The 1/2" is rated for three #8awg wires. I'd like to also pull a #10awg ground wire along with the three #8's. This calculates to a 40.6% fill, barely exceeding the nominal 40%. Will it pull? Is it safe? Thanks

 

[Dennis Alwon]

Safety is not something we can determine.... It would not be compliant --If that emt is underground I wonder how rusty it is inside. It may be a hard pull.

 

[LarryFine]

EMT is not suitable for underground use, and 1/2" is definitely too small.
"

 

[Beaches EE]

You'll need 3/4 (PVC) for that and often 1" is used in these applications in case of future expansion.

 

[LarryFine]

If that emt is underground I wonder how rusty it is inside.

I wonder if it still exists.

 

[therobthompson]

I sure wish this existing underground conduit was pvc and at least 3/4, but alas 1/2 EMT is what I have to work with. My pull rope went through easily, tied to the old wires (three #12awg) when I pulled them out. So the conduit itself is viable. Just not sure how the extra 1/2% of fill will impact the new pull. 358.10 allows EMT for underground.

 

[LarryFine]

According to this, adding a #10 to three #8 in 1/2" EMT will take it over.

Raceway Fill Calculator

Your question is whether it will work despite being non-compliant.

How do you think we'll respond?

 

[Beaches EE]

Non-compliant is just that. I would not design or recommend an installation that does not meet code.

 

[don_resqcapt19]

If your calculations included an insulated EGC, you can probably meet the fill rule by using a bare EGC.

 

[therobthompson]

Thanks don-resqcapt! Indeed using bare #10 instead of THHN gets me to 38.3% fill

 

[Chamuit]

According to this, adding a #10 to three #8 in 1/2" EMT will take it over.

Raceway Fill Calculator

Your question is whether it will work despite being non-compliant.

How do you think we'll respond?

No

Do you know what a bugger it would be to pull?

 

[oldsparky52]

No

Do you know what a bugger it would be to pull?

Hopefully the OP will let us know.

 

[drcampbell]

... emt is underground I wonder how rusty it is inside. ...

That's going to depend on local conditions. Out in the desert, it might be fine. Close to the ocean, it might soon be nothing but a vestigial line of orange-ish soil.

But will it pull? That depends on a lot of factors, including the number of unseen underground turns. Do everything you can to make it easier -- remove all the kinks & braids, band the wires together periodically, use a funnel and have a helper maintain a constant tension & smooth feed during the pull.

 

[don_resqcapt19]

To make the smallest pulling head, measure the conductors at twice the required length, fold them in the middle, strip the insulation and attach the stripped part to the pulling rope.

 

[therobthompson]

Well it's going to take all the tricks I can learn and an artisanally crafted pulling head but I think it will work. I sent my endoscopic camera down the pipe today and the cuts/transitions are not as deburred as one would like, but the conduit looks pretty good, not terribly rusty as far as the camera went, even though the knot in my pull rope squeegeed water out of the conduit. I plan to: use pull string instead of the poly rope I had on hand, pre-lubricate the conduit, use a funnel to get tons of lube in there while pulling, and get a helper to pull so feed end is well tended even though this is only a 30' run.

 

[LarryFine]

With a 30' pull and water, I predict you won't need any lube. Just keep the wires in the same position.

 

[Another C10]

358.10 allows EMT for underground.

I'm pretty sure that code mentioned is for any Emt to be encased in concrete when underground or that it is wrapped in a corrosive proof rubber tape.
358.10 when in accordance with 358.10 (B) (1) (2) / (C) (D). Emt rusts and falls apart after several years if simply buried in dirt.

Why not run a # 12 Ground, I'm pretty sure you can size down 2 times on a branch system. Its just a relief valve for fault. Just a thought.

 

[petersonra]

I'm pretty sure that code mentioned is for any Emt to be encased in concrete when underground or that it is wrapped in a corrosive proof rubber tape.
358.10 when in accordance with 358.10 (B) (1) (2) / (C) (D). Emt rusts and falls apart after several years if simply buried in dirt.

Why not run a # 12 Ground, I'm pretty sure you can size down 2 times on a branch system. Its just a relief valve for fault. Just a thought.

Take a look at table 250.122

 

[Jon456]

If it's only 30 feet, why not dig it out and replace it with 1" PVC? Yes it's more work and will cost time & money. But how much time and money will you lose if the "not as deburred as one would like" conduit damages the insulation on your #8 conductors? It will cost even more if the fault shows up later and you have to come back to redo the entire job.

 

[kwired]

If it's only 30 feet, why not dig it out and replace it with 1" PVC? Yes it's more work and will cost time & money. But how much time and money will you lose if the "not as deburred as one would like" conduit damages the insulation on your #8 conductors? It will cost even more if the fault shows up later and you have to come back to redo the entire job.

Maybe under a slab or something?