The ‘Ol “12 Inch Spacing” Rule Again

Birken Vogt said:
But these are all POCO and other utility rules, not rules for anything customer owned.
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I was just speculating that perhaps that is where the idea originated, was from folks being vaguely aware that someone somewhere had a rule about it.

And the justification I hear all the time is about electrical lines sparking leaking gas lines, and that’s not even the reasoning for the utility company rules, it was about access, not safety.
 
Seven-Delta-FortyOne said:
I was just speculating that perhaps that is where the idea originated, was from folks being vaguely aware that someone somewhere had a rule about it.

And the justification I hear all the time is about electrical lines sparking leaking gas lines, and that’s not even the reasoning for the utility company rules, it was about access, not safety.
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Hear same thing about water lines: keep them away from electrical. Water + 'lectricity= bad 🙄
 
The plumbing code (UPC based anyways) does have some restrictions for water and sewer sharing the same trench, I'd bet that's where the myth started and spread.

Chapter 12, fuel gas piping, just says "Underground gas piping shall be installed with sufficient clearance from any other underground structure to avoid contact therewith, to allow maintenance, and to protect against damage from proximity to other structures. In addition, underground plastic piping shall be installed with sufficient clearance or shall be insulated from any source of heat so as to prevent the heat from impacting the serviceability of the pipe."
 
609.2 Trenches. Water pipes shall not be run or laid in the same trench as building sewer or drainage piping constructed of clay or materials that are not approved for use within a building unless both of the following conditions are met:
1. The bottom of the water pipe shall be not less than 12 inches (305 mm) above the top of the sewer or drain line.
2. The water pipe shall be placed on a solid shelf excavated at one side of the common trench with a clear horizontal distance of not less than 12 inches (305 mm) from the sewer or drain line.
Water pipes crossing sewer or drainage piping constructed of clay or materials that are not approved for use within a building shall be laid not less than 12 inches (305 mm) above the sewer or drain pipe.

720.0 Sewer and Water Pipes.
720.1 General. Building sewers or drainage piping of clay or materials that are not approved for use within a building shall not be run or laid in the same trench as the water pipes unless the following requirements are met:
1. The bottom of the water pipe, at points, shall be not less than 12 inches (305 mm) above the top of the sewer or drain line.
2. The water pipe shall be placed on a solid shelf excavated at one side of the common trench with a clear horizontal distance of not less than 12 inches (305 mm) from the sewer or drain line.
3. Water pipes crossing sewer or drainage piping constructed of clay or materials that are not approved for use within a building shall be laid not less than 12 inches (305 mm) above the sewer or drain pipe.
For the purpose of this section, "within a building" shall mean within the fixed limits of the building foundation.

Basically, if you use glued ABS or PVC, all good. If not, keep 'em separated.
 
Joe.B said:
609.2 Trenches.

720.0 Sewer and Water Pipes.
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The only reasonable way to read those sections is that "in the same trench" means "in proximity". Any literal reading yields ridiculous results where the construction order matters, rather than just the final geometric configuration.

Cheers, Wayne
 
It has been explained to me that once you dig a trench into undisturbed soil no reasonable amount of compaction will ever remove the presence of the trench. Storm water (and leaking sewage) will follow that trench. Back when clay pipes, followed by AC, were common it was best practice to dig a separate trench because bacterial testing showed that the soil immediately surrounding the sewer pipe was always contaminated. If the water supply was in the same trench then you couldn't service it without spreading that contamination.
 
Joe.B said:
It has been explained to me that once you dig a trench into undisturbed soil no reasonable amount of compaction will ever remove the presence of the trench.
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I'll believe that if we posit that compaction in the vicinity of the pipe needs to be limited to avoid damage to the pipe. So then I guess it would be reasonable to read "in the same trench" as meaning "unseparated by never-disturbed soil".

Cheers, Wayne
 
rc/retired said:
Schedule 40 minimum, IIRC

Ron
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Table 701.2 has three columns, "approved for use within a building" falls into the middle column labeled "above ground drain, waste, vent pipe and fittings" and lists eleven approved materials. ABS (Schedule 40) and PVC (Schedule 40) are included, but PVC (Sewer and Drain) and PVC PSM are not.
 
Joe.B said:
The plumbing code (UPC based anyways) does have some restrictions for water and sewer sharing the same trench, I'd bet that's where the myth started and spread.

Chapter 12, fuel gas piping, just says "Underground gas piping shall be installed with sufficient clearance from any other underground structure to avoid contact therewith, to allow maintenance, and to protect against damage from proximity to other structures. In addition, underground plastic piping shall be installed with sufficient clearance or shall be insulated from any source of heat so as to prevent the heat from impacting the serviceability of the pipe."
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Thanks for that reference.

What defines an "underground structure"?
 
I guess that depends on how you want to interpret:

[A] STRUCTURE. That which is built or constructed.

Neither the plumbing nor electrical code have a definition for "structure", so we default to the building code. I would argue that yes, other underground electrical conduit could be considered a structure. But then what do you consider to be "sufficient clearance"? In my experience good installations will have each material laid into a shared trench separated as much as possible.
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Us generator guys are usually coming in on retrofit (even on new builds they only think of generators near the end so might as well be a retrofit) and we use a guy with a tiny excavator who defaults to a 6 inch trench. When you put a 1.25" conduit plus a 3/4 plus a gas line of 1" or 1.25" all in the same trench they are going to bump, but if you expand to a 12" trench you are moving a lot more dirt to do the same job. Last time I did this my excavator seemed confused that I was going to put it all in 6" but the inspector did not look twice. There were a couple of other things on that job he did not look twice at and I had to get corrected by other subs after final.
 
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