GRS or LFMC - Unique Situation

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charlie b

charlie b

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This is not an NEC question, for I know that the NEC would allow what I want to do. The relevant code is unique to the client. My question is one of physics, and of just generally what is the right thing to do.

Consider a 40 foot shipping crate that has been outfitted with beds, tables, and other living accommodations. These things are called ?containerized living units,? or simply CLUs. Consider stacking these things three high, with such stacks side-by-side to create something that looks vaguely like a housing building. Each CLU has a 60 amp, single phase panel.

Our contractor wants to serve each CLU with LFMC attached to a large plug. I agree. The client insists that their rules require the use of GRS and a hard-wired connection at each CLU.

Question: Given that a stack of three CLUs will likely experience some swaying in the high winds that are common to the area, is the use of hard pipe (GRS) even a safe alternative? Would not the motion of the upper CLU in relation to the lower ones cause a strain on the GRS, and perhaps even cause a support to break?
 
petersonra said:
What kind of plug is listed to be attached to LFMC?
Click to expand...

I would think the only thing that would work would be a male inlet for a pin & sleeve connector.

If there were only one stack of containers then, yes they would sway a bit in the wind. Would they simply be stacked or somehow fastened together? I would think if they sway that much you may have a bigger problem than the electrical connections.

Aren't these usually done in multiple stacks, therefore eliminating the sway?
 
The brand is a "Commando Plug." The type is common for refrigerated shipping containers. There will be three CLUs, one on top of the other, with some type of bolted connection. Adjacent stacks are not bolted to each other, so each stack can sway independently.
 
This answer isn't based on a highly technical evaluation of material strengths or anything, but...

If the adjacent stacks of CLUs are not fastened to each other in any way, they will be allowed to slip and shift against each other, which could very well damage GRC going from one CLU to the next. I'm not sure how likely that is to happen if they're only stacked 3 high, unless they're exposed to earthquakes or maybe really high winds. You'll probably have to consult with a Structural Engineer to find out exactly how much offset could occur between adjacent stacks of CLUs.

The more I think about this, the more it sounds like an extreme version of a seismic joint in a regular building. We don't run GRC across those -- we always require some type of flexible connection (usually FMC or LFMC). I can't imagine that there would be less flex/shift in these connections than there is in a conventional seismic joint.

I'm curious about the desire to connect these CLUs using a plug. Is there some plan to allow somebody to come in with a crane and move them around later? That's about the only reason I can think of to use plugs to connect the panels rather than hard-wiring them, regardless of whether you're running GRC or LFMC.
 
Conduit (likely GRS) would be run at grade level from distribution panels in a nearby "utility CLU" to a junction box on the lower level CLU. The issue has to do with going vertical from the junction box to the three CLUs' power panels. The site is east Africa, and high winds are common. I think a flexible connection is needed. The client has a published guidance document that they are interpreting as requiring GRS in this circumstance.
 
I've seen the cooper XD deflection couplings for runs that transverse small multiple shacks. They are referenced at the bottom of the previous link.

Not sure if it would be applicable, but looks promising.
 
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