Expansion Joints For Underground Fed Meter Cans

mdshunk

A few years ago, when the supply houses started carrying the PVC expansion joints on a regular basis for meter cans, I was right there using them. After some growing pains, such as figuring out where and where not to clamp the pipe, and learning that expansion joints have a "right side up", things were fine.

Now, lately, we're getting static from power company engineers, because even though there's a way for the pipe to slip as the ground settles, there's no slack in the conductors. Certainly, there's no place in the meter can to leave slack. The PoCo guys claim that some padmount transformer terminals have been bent from these slip joints allowing the conduit to slip and jerking the conductors up tight. They're afraid of a padmount secondary going phase to phase.

Is it better to have the slip joint in the conduit, or just let the whole meter can get yanked loose of the wall?

Maybe this isn't a code issue, but it was on my mind tonight.

JoeTedesco

See 300.5(J) and download:

http://www.nema.org/stds/expansionjo...c.cfm#download

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RobertWilber

There was an outfit at a trade show here last fall that was exhibiting a "slack box" slip-fitter assembly.
They were working on getting acceptance by local utilities.
It was really cool. Had a slip fitter on the riser, a sweep into the box, which allowed a three foot or so loop of cable, which fed the conduit when the trench collapsed.
I will try to find their name.

mdshunk

duplicate deleted

mdshunk

What I learned by reading the information Joe encouraged me to read was:

PVC expansion joints are intended to be used for thermal expansion of the PVC conduit only. They are not (and never were) intended to be used to compensate for trench settlement. When the PVC expands and contracts due to thermal forces only, the wire does not move. The conduit just expands and contracts. So, in short, using a PVC expansion joint to compensate for trench settlement is an "off label use" for these fittings, and they aren't specifically intended to be used in this manner. It seems it would be better to do without them, unless there is a place to leave slack in the wire (which there normally isn't).

In my area, the excavators often run the pipe from the padmount to the house. There is no way for the electrical contractor to assure proper soil compaction under the conduit sweep under these circumstances. I prefer virgin soil under the meter sweep. If this can't happen, then I prefer to have the soil in that area compacted. Compaction equipment is seldom available on a residential construction site, however. What's a man to do? Sounds like the "Slack Box" people might be onto something.

ATS

Our local pocos say to loop the urd just after the sweep. They claim it allows for the necessary movement. I've never had a problem with this, albeit I'm sure I haven't been doing it as long as some here.

mdshunk

Yeah, that works okay if you're only doing a sleeve to the meter can. We run a complete conduit system from the meter can to the padmount.

ATS

OOHH, I misunderstood the situation. Robert Wilber seems to have found a decent solution, but is it cost effective when you're competing against guys who will not consider this possible problem? Unless of course, the poco starts mandating some sort of mitigation.

JoeTedesco

See 300.5(J) and the FPN in the NEC for specific rule and explainatory material.

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mdshunk

Robert... I've been curious about this, and I've been trying to find one to look at. Apparently, nobody's making it yet? Just asking, not saying. They might have been showing it at the show you were at to get a manufacturer interested. I did find the patent for it, though. It was invented by a fella not too far from us. http://appft1.uspto.gov/netacgi/nph-...DN/20060005983

Sparky Joe

This is an issue for services especially where the power company doesn't bury below frost. My dad with Pacificorp had one of his metermen get burned pretty bad simply from pulling a meter from it's socket.

It seems settling or something was pulling down on the underground feed so that the blades of the meter were the only thing holding it all together. When the meterman pulled the meter -ka-pow- blow up city, don't know the extent of the injury but I don't imagine he was wearing a face sheild, NoMex is standard issue though.

Just a friendly tip to keep you all safe.

ATS

Thanks, that is good info.

RobertWilber

http://www.rizzcon.com/index.html

Carlon, among others, also makes a slip fitter setup, but it is the Rizzcon slack box that really solves the problem!