300.5(J) Expansion Joint

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dnem

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I was asked by the chief of my department to put this situation out and see what responses come back. One of our local utilities requires that conductors coming into a meterbase from an underground conduit run have large loops, that they call an "Edison heart". When a contractor doesn't include these in his installation, we leave a red tag that lists 300.5(J). We apply this to all installations that use an expansion joint and not just where required by this one electrical utility.

There is a contractor that believes that if he adds an expansion joint to his underground riser, as spoken about in the FPN, then he has complied with the requirement. He doesn't seem to understand the difference between a FPN and an exception.

What is commonly required in your area on conduit runs with an expansion joint ? What do you do to make sure that "cables shall be arranged so as to prevent damage to the enclosed conductors" ?

David
 
We apply this to all installations that use an expansion joint and not just where required by this one electrical utility.
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On other than underground service laterals, we install the expansion joint for expansion of the conduit, not the conductors. For an expanding PVC raceway above grade with an expansion joint, the conductors should not need an additional loop since they will not really be expanding.

On a service lateral, 300.5(J) is asking for a method to compensate for ground movement. Around here we're required to install an expansion joint for this purpose. We've never been asked to leave a loop within the meter enclosure but the fact that the conduit enters the bottom of the meter enclosure and terminates at the top does effectively leave extra conductor length within the meter enclosure.
 
I think, around here, things only settle an inch or two after final grade. Generally, if the conductors were installed almost touching the top of the can, then there will be plenty of conductor to give up an inch or two, IMO.
 
infinity said:
We apply this to all installations that use an expansion joint and not just where required by this one electrical utility.
Click to expand...


On other than underground service laterals, we install the expansion joint for expansion of the conduit, not the conductors. For an expanding PVC raceway above grade with an expansion joint, the conductors should not need an additional loop since they will not really be expanding.
Click to expand...

You're right .
I miss spoke [or mistyped].
I should have specified that we require the wire expansion loop only in 300.5(J) installations and not where expansion joints are used for thermal expansion and contraction of the raceway.

Thanks for the response. Sometimes it helps to hear how other areas of the country handle things.

David
 
How much is the verticle riser going to expand? Maybe 1/4" over 10' for a 100 degree hi/low? Its just the pipe moving a tad, not the copper.
 
tonyi said:
How much is the verticle riser going to expand? Maybe 1/4" over 10' for a 100 degree hi/low? Its just the pipe moving a tad, not the copper.
Click to expand...

Yes, small expansion or contraction for expansion joints installed to deal with thermal expansion and contraction. Table352.44(A) shows about a 2 inch length change on a 100 foot run with a 50 degree temp change. That's really not as much movement as I would have guessed.

300.5(J) is talking about a different situation. In Ohio we have soils that can settle quite a bit. One building will have almost no settlement and the next one will have alot. It depends on the soil type mixture, how much was excavated, how deep they excavated, if they added to the natural grade, if they compacted the soil as they backfilled, time of year, and how much rain we've had, and maybe some other stuff too that doesn't come to mind right now.

In the end we just enforce expansion wire loops on all installations where an expansion joint is used coming out of the ground. But we don't require expansion joints everywhere.

Maybe that's a good comparison question.

Where are expansion joints required ?

We require expansion joints in PVC in all runs emerging from underground except
1] On conduit trade size 1 inch or smaller
2] On risers supported by poles, stakes, or stands that are not attached to building structures
3] On risers attached to horizontal runs that are 40 inches or deeper from final grade
4] On risers not attached to a horizontal conduit run
5] On risers that come up thru a concrete slab

David
 
We generally require an expansion coupling on all pvc conduits emerging from ground. The are all subject to ground movement around here. That includes small sizes. We have a lot of contractors who do not use them on projects such as pools.

We do not require them on risers at poles. On an installation down 40" we would take into consideration if there were any digging or filling below conduit which may cause some ground movement. So sometimes yes, sometimes no.

We do require expansion couplings on all services, too. We do not require the "edison hearts" or "bowties", as there is typically enough "slack" to account for minor expansion or settling in ground.
 
300.5(J) is for GROUND movement. In our area (lower NY) the utility companies have some different requirements themselves.
This typically means that the lateral is installed in a raceway. So, the contractor has to install an expansion coupling. The ground movement in our area can be considerable during some winters and almost nonexistent in others.


George
You wrote there is little settlement... that is not what this section is about. I am sure that in Colorado that there is considerable ground movement due to the severe winters you can get there.
 
I think there are at least 2 reasons for ground movement. One is frost. David indicated that his department does not require expansion coupling on an installation down at least 40". I'd agree with that provided the earth below remained undisturbed.

If not, even an installation below the frost line would be subject to settling, the other reason for ground movement. In this case I'd require expansion coupling.

Several side questions.

1. Does everyone enforce the same expansion coupling requirement on RMC installs as opposed to PVC?

2. On most residential installs around here contractors pull USE (also called URD around here) direct burial "cable" ( Triplex, Sweetbriar, whatever) through schedule 40 pvc. Typically complete raceway from pole or handhole to meter enclosure. Does anyone use the "S loop" to avoid expansion coupling? Instead of a complete raceway, 90 could be left off with S-loop at least 18" below ground. I haven't seen it, but it leaves a lot more slack for movement than the bowties in meter socket. Might be better in some circumstances. Especially on jobs where I've seen water follow pipe into meter socket.
 
The weather is so nice here most of the year that we don't have to worry about expansion joints.

And if an earthquake hit's the pipe will expand all by it's self. :roll:
 
j_erickson said:
2. On most residential installs around here contractors pull USE (also called URD around here) direct burial "cable" ( Triplex, Sweetbriar, whatever) through schedule 40 pvc. Typically complete raceway from pole or handhole to meter enclosure. Does anyone use the "S loop" to avoid expansion coupling? Instead of a complete raceway, 90 could be left off with S-loop at least 18" below ground. I haven't seen it, but it leaves a lot more slack for movement than the bowties in meter socket. Might be better in some circumstances. Especially on jobs where I've seen water follow pipe into meter socket.
Click to expand...

We have contractors that use the ground loop instead of a 90 and an expansion joint. It seems to be a good option.

David
 
I run into many instals were they did not leave aloop in the mtr can.What happens is the wire breaks the mtr block (which is made out of plastic)and when you pull the meter you are left with a hot wire flooping around.
 
newt said:
I run into many instals were they did not leave aloop in the mtr can.What happens is the wire breaks the mtr block (which is made out of plastic)and when you pull the meter you are left with a hot wire flooping around.
Click to expand...
And if it flops into the side of the meter can, you get an explosion. Depending on the speed of the OC that the utility has on the service conductors feeding the meter, it can be a huge explosion.

David
 
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