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Propane line for Onan 30KW


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  #11  
Old 02-04-2017, 11:59:56 AM
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Default Re: Propane line for Onan 30KW

We are precluded from using plastic pipe although I would use it or copper in my own installation. We have to bond to the perimeter counterpoise installed around structures but there is no anode, (sacrificial or permanent) installed I'm aware of.
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  #12  
Old 02-04-2017, 12:32:56 PM
Birken Vogt Birken Vogt is offline
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Default Re: Propane line for Onan 30KW

When we installed metallic pipe or tank underground it had to be insulated from building/electrical ground, etc. by a dielectric union or else the anode is kind of worthless.

If the steel pipe is bonded to building ground then it (least noble metal) becomes the sacrificial anode by default to the whole structure if there is any failure in the coating.

At least that is my understanding although using plastic almost exclusively, I have never paid much attention to it really.

Do you know of or use any better method to coat joints, elbows, and tool marks than that darn tape that never seems to stretch tight correctly? I always thought something sprayed or dipped in tar would be much better. Old pipes were coated in about 5/16" of tar it seemed. More substantial than the current plastic coatings.

I wonder why they say no plastic. Do they enforce this on natural gas utilities also? Seems like they might tell them to go pound sand.
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Old 02-04-2017, 12:57:26 PM
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Default Re: Propane line for Onan 30KW

I don't know why the ban on plastic either but I can't vary from the designer's drawings to go by. I can upsize pipe, and sometimes routing, but that's about it. Everything is grounded in these installs. Lots, and lots of money expended in copper and grounding type conduit connectors. The tape, or wrap as it's called comes from a couple of different vendors and it is specific to the application and does work quite well. It is a self bonding/sealing product and we set the pipe onto roller stands and spin the pipe rather than do it solely by hand. The joints are heat sealed with this same tape and heating attachment which is an open "C" shape to get around top and bottom. the wrap literally melts together and becomes an effective seal. Water or electrolysis damage has never been a problem I've seen so far. We don't use clamps but rather "CadWeld" the connections to the counterpoise and each site does have a monitor well for measuring resistance but I don't do any monitoring.
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Old 02-04-2017, 12:58:56 PM
len k len k is online now
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Default Re: Propane line for Onan 30KW

Since house underground copper water pipes are bonded to utility grid and if your steel gas pipe is also bonded to that grid , there's your corrosion battery right there. Even if YOU don't have copper pipe your neighbor may. So would need some kind of anode. Here code says need to bond utility gas pipe to power ground, not sure what it has to say about propane tanks.


Seem to remember someone saying above 2 psi in HOUSE is not legal, too much fire risk if pipe breaks.
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Old 02-04-2017, 02:05:14 PM
Vanman Vanman is offline
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Default Re: Propane line for Onan 30KW

Here there is a dielectric fitting between the incoming utility natural gas supply and the meter, and thus the building piping system. At first glance it looks like they didn't have the correct fitting on the truck, and so installed a 3/4" - 1" elbow, then used a bushing back down to 3/4", but that bushing is actually plastic.

I've thought about putting a dielectric union on the water line where the copper comes up out of the ground at the house, specifically to stop current flow between my interior bonded copper pipes and my line going to the meter at the street, and the rest of the water company's piping.

Code doesn't seem to require bonding the gas lines here, though they are effectively bonded as soon as even one electrically grounded appliance is connected.

Years ago, worked on a stop light job on Pacific Coast Highway, RIGHT on the beach. Specs required Rigid conduit be used exlusively (galvanized steel, like water pipe). This was being laid in trenches dug in the salt water saturated sand. I'm sure all of those cables are now just direct burial, the conduit having long since rotted away around them lol.
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Old 02-04-2017, 02:57:08 PM
len k len k is online now
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Default Re: Propane line for Onan 30KW

Been told in a building code wants gas pipes bonded to utility ground. Rational is not have voltage difference between gas pipes and water pipes, in case someone is touching both at once. Voltage difference can come from bad wiring, fault or lightning. Seems dielectric at the meter could co-exist with that rule, but it would likely arc over during a lightning strike. Then seems you have to worry about melting the dielectric and having a gas leak at the point of arcing ( ignition source)
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Old 02-04-2017, 03:54:59 PM
Birken Vogt Birken Vogt is offline
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Default Re: Propane line for Onan 30KW

Certainly interior building gas pipes are made of metal and bonded to all other metal in the building but they are not immersed in anything.

When I worked in the gas industry the single dielectric union was placed where the gas pipe came up outside and made connection to the building. So the pipe outside was (hopefully) floating to prevent electrolysis, and certainly not part of a battery. There should be no arc in a lightning strike because the interior pipe would all be at the same potential as the rest of the building and flow out on the electrical grounding system. If there was a problem the dielectric union is outside where it can be seen and dealt with, not buried interior somewhere.

The building department did not seem to care what we did with outside pipe so we were pretty much left to follow what seemed like reasonable practice.

I like the idea of a heat fused wrap. If done properly the pipe in the ground should be no wetter than the pipe inside the building. I just find it hard to imagine any coating being maintained over the years.

There is no way to bond a buried propane tank to building ground and also follow the manufacturer's instructions for cathodic protection.
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Old 02-04-2017, 04:03:04 PM
Jim Marcozzi Jim Marcozzi is offline
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Default Re: Propane line for Onan 30KW

Can you run the flexible metal pipe inside of a piece of PEX so that it doesn't come in contact with the soil?
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Old 02-04-2017, 04:21:57 PM
Leon N. Leon N. is offline
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Default Re: Propane line for Onan 30KW

Len K not sure why you say there is a corrosion battery between the buried copper water pipe and the steel natural gas line. At this location, the incoming utility line neutral is grounded to the buried copper water pipe. The incoming steel natural gas line is NOT bonded directly to the utility neutral. However, I measured zero resistance between the kitchen gas stove frame and the 110 volt ground pin at a receptacle outlet.

Recently, the gas company came by and buried a sacrificial anode in the ground adjacent to the outdoor gas meter and connected it to the 40 psi steel gas pipe coming out of the ground to their gas meter. Around here they no longer use steel gas lines to the new homes. It is all plastic now. In fact in some areas around here, the gas mains in the street are being replaced with plastic piping.

If I thought of it, I would like to have asked them if there is a dielectric unioun somewhere in the steel gas line. I hope their anti corrosion anode will also protect my inch and one half BI gas piping to my generator shed.
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Old 02-04-2017, 04:53:59 PM
len k len k is online now
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Default Re: Propane line for Onan 30KW

Just saying the iron gas pipe, copper water pipe and earth form a galvanic cell.
IF there is any electrical connection between the 2 pipes for current to flow thru then galvanic corrosion of steel pipe will occur.

I have no idea if gas company routinely uses dielectric at meter. Easy enough to test with an ohm meter. I didn't notice a dielectric at our place, but it's all painted over. Steel underground pipe to street is plastic coated. Was told gas company spent about a day cutting a ~ 14 inch dia hole thru paving near the meter and installed an anode on their line.

I know sometimes instead of an anode for corrosion protection they use a DC power supply. But maybe that is more for long pipe line installations, so you still have enough protective voltage at end of the line WRT earth.

Interesting side note, if a dielectric is used at water meter I believe code requires a jumper across it. Defeats the purpose of dielectric there.

In another application I worry about rusting of some old steel sign poles that were grounded to building power ground several years ago. Same for iron water pipe to street. Luckily nearest building that might have underground copper pipe is across street and hopefully resistance of earth is high.

Last edited by len k; 02-04-2017 at 07:48:52 PM.
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