EMT direct burial lugs on roof

[ESolar]

There have been several users that suggest using direct burial lugs (or replacing lugs on bushings) for grounding EMT sleeves (not raceways) on the roof. Can someone please elaborate with suggestions. None of the standard screw on bushings show direct burial. Are we talking about one of those used for pipes that clamps around the EMT? Or does one attempt to replace the lug on a standard EMT bushing (in which case one would have to be careful regarding the galvanic potential of the various metals). A reference to an actual solution (product) would be useful here.

 

[jaggedben]

You'd replace the lug on the bushing. A direct burial lay-in lug will be tin-plated copper with a stainless set screw, instead of a tin-plated aluminum lug with a possibly only zinc-plated set screw. You're really not worried about the galvanic interaction with the zinc bushing nearly as much as not having a copper wire on an aluminum lug. It's gonna corrode anyway, just not nearly as fast.

Ilsco makes a lug, there's probably others. The real trick is making sure the screws which attach the lug to the bushing remain the right length, which will depend on yiu bushings.

 

[ESolar]

Reply and another question

Reply and another question

What about the bushing itself - the part screwed on to the end of the EMT. One doesn't have to worry about it and its contact with the lug?

 

[jaggedben]

I'm speaking from experience. The tin-plated copper will corrode slower than the tin-plated aluminum when used with a copper wire.

As far as galvanic theory yes, there is an interaction between the copper and tin and zinc, but it must somehow be less problematic without the aluminum in between as well.

 

[ESolar]

Reply

Reply

In your experience those will work better - I don't doubt it based on the material type and the fact that they are rated for burial. However, it seems like one should not have to jury rig two pieces together that were not designed to be together in the first place (and there would be no listing for that combo, right?). There should be a ready to use product off the shelf for this purpose given that this is a common problem. I see more than one person asking about what to do in this case and complaining about the lack of a listed solution.

 

[jaggedben]

I've seen people use direct burial grounding clamps or the type used for water pipes. I think that's also legit, but I just find it ugly.

 

[Zee]

what JBEN said.

A standard aluminum lug that comes standard on a gr. bshng. will corrode terribly in a couple of years with a copper wire in it on roof top (presence of moisture).

ILSCO and BURNDY.

Should be:
direct burial rated (typically DB in part#..... and T for tin plated)
tin plated
copper body (inside)
stainless steel setscrew

then you gotta buy the right length and thread st. steel screws to replace the zinc plated standard ones on bushing with)
Usually 10-24 or 10-32 st. steel screw
Get slightly longer screws as the DB lugs are thicker than the factory aluminum stock ones.
You gotta get length right as otherwise screw goes thru gr bushing and into conduit......so i also stock little st. steel washers as spacers.

Buy a bunch for different makes and conduit sizes (1/2", 3/4" etc) of gr bushings.

I make em up ahead of time.
I send newbies to van to strip gr. bushings of stock lay in lugs and screws and replace with above hdwr to make em roof ready ahead of time.


https://webosolar.com/store/en/pv-g...onqlxxjXcIvhwrYOf_N0GHpPDHyTABL4aAm7YEALw_wcB

 

[Zee]

In your experience those will work better - I don't doubt it based on the material type and the fact that they are rated for burial. However, it seems like one should not have to jury rig two pieces together that were not designed to be together in the first place (and there would be no listing for that combo, right?). There should be a ready to use product off the shelf for this purpose given that this is a common problem. I see more than one person asking about what to do in this case and complaining about the lack of a listed solution.

"should be a ready to use product"
yeah i agree. but there isn't.

sounds like you could make money on this.

 

[Zee]

FWIW - I prefer the "crusty" grounding bushings. These are hot dipped galvanized and look like they can handle weather.
As opposed to the zinc plated ones.

The steel is different too!
I think the steel might be superior also.
Malleable iron vs die cast last time I checked......:?

anyways, way too much detail

 

[Cow]

This is what I use for outdoor or wet location conduit bonding or grounding:

http://ecat.burndy.com/Comergent/burndy/cat/611603

 

[jaggedben]

This is what I use for outdoor or wet location conduit bonding or grounding:

http://ecat.burndy.com/Comergent/burndy/cat/611603

Too big.

 

[jaggedben]

I guess we could consider using this type.

https://www.google.com/shopping/pro...?q=hub+ground+clamp+3/4+outdoor+copper+washer

But it would have to be the outdoor type with the brass washer, which I can't seem to find online.
Gotta consider the cost though, and I'm not keen to have my guys pull PV wire through them either.

 

[oldsparky52]

... for grounding EMT sleeves (not raceways) on the roof. Can someone please elaborate with suggestions.

I have 2 questions,

1) What code section requires these sleeves to be grounded?

2) Could a non metallic product be used as a sleeve?

 

[jaggedben]

I have 2 questions,

1) What code section requires these sleeves to be grounded?

250.110

2) Could a non metallic product be used as a sleeve?

Non-metallic methods aren't necessarily suitable for rooftop surface temperatures. See 352.12 (D). Or 350.12(2).

There's probably more latitude in the code for non-metallic methods than industry-standard methods give credit to, but that's at least one major reason solar installers don't do it. Also I think doesn't save any time and typically comes out uglier looking.

 

[oldsparky52]

250.110



Non-metallic methods aren't necessarily suitable for rooftop surface temperatures. See 352.12 (D). Or 350.12(2).

There's probably more latitude in the code for non-metallic methods than industry-standard methods give credit to, but that's at least one major reason solar installers don't do it. Also I think doesn't save any time and typically comes out uglier looking.

Thank you!